Ergonomic and adjustable respiratory mask assembly with vent cover

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to U.S. Provisional Applications of Moore et al., Serial Nos. 60/377,254, 60/397,195, and 60/402,509, the entireties of which are hereby incorporated into the present application by reference.

FIELD OF THE INVENTION

[0002] The invention relates to a nasal mask for use in the delivery of Non-invasive Positive Pressure Ventilation (NPPV) and for nasal continuous positive airway pressure (nasal CPAP) therapy of sleep disordered breathing (SDB) conditions such as obstructive sleep apnea (OSA).

BACKGROUND OF THE INVENTION

[0003] The application of nCPAP for treatment of OSA was taught by Sullivan in U.S. Pat. No. 4,944,310, incorporated herein by reference in its entirety. In nCPAP treatment of OSA, pressurized air or other breathable gas is provided to the entrance of a patient's airways at a pressure elevated above atmospheric pressure, typically in the range 4 to 20 cm H₂O to “splint” open the patient's upper airways and prevent apneas.

[0004] Apparatus to deliver nasal CPAP and NPPV therapy typically comprises a blower, an air delivery conduit and a patient interface. The blower may be programmed to deliver a range of different forms of therapy. In one form, a constant pressure of air or breathable gas is provided to the patient. It is also known for the level of treatment pressure to vary from breath to breath in accordance with patient need, that form of treatment being known as automatically adjusting nasal CPAP treatment as described in U.S. Pat. No. 5,245,995 (Sullivan and Lynch), incorporated herein by reference in its entirety. NPPV is another form of treatment for breathing disorders. In its most basic form, a relatively higher pressure of gas may be provided in the patient mask during the inspiratory phase of respiration and a relatively lower pressure or atmospheric pressure being provided in the patient mask during the expiratory phase of respiration. In other modes, the pressure can be made to vary in a complex manner throughout the respiratory cycle. For example, the pressure at the mask during inspiration or expiration can be varied through the period of treatment. See, for example, U.S. Pat. No. 5,704,345 and International Patent Publication Nos. WO98/12965 and WO99/61088, all of which are incorporated by reference herein in their entireties. In this specification, the term NPPV therapy will be used to describe all these forms of NPPV and nasal CPAP therapy.

[0005] The patient interface for NPPV therapy may take many forms, such as a nasal mask assembly, a nose and mouth mask assembly, nasal cushions or a nasal prongs or pillows assembly. A mask assembly typically includes a rigid shell, a soft face-contacting cushion, a forehead support and headgear for securing the mask to the head.

[0006] In one known mask assembly, the headgear includes a cap portion with four straps. In use, the cap portion engages the occipital portion of the patient. Furthermore, in use, the two lower straps extend between the cap portion and a nasal mask while the two upper straps extend between the cap portion and a forehead support. See, for example, U.S. Pat. No. 6,119,693 (Kwok, Matchett and Grant), incorporated herein by reference in its entirety.

[0007] Some patient interfaces include quick or convenient release mechanisms for enabling a patient and/or clinician to disengage from the blower, blower tube and/or the mask/headgear assembly. Quick or convenient release mechanisms are useful where NPPV therapy needs to be temporarily interrupted or where a system failure causes a cessation of gas flow to the patient interface. For example, as disclosed in U.S. patent application Ser. No. 09/482,718, incorporated herein by reference in its entirety, the headgear and mask can be removed from the patient by pulling a conveniently located cord to decouple hook and loop fasteners between engaging headstraps that are positioned, for example, at the rear of the headgear assembly. In another example, as disclosed in U.S. patent application Ser. No. 09/504,220, incorporated herein by reference in its entirety, the headgear/mask assembly can be removed from the patient by detaching a connector member for the headstrap, which connector member is connected directly to the frame of the mask. See also U.S. Pat. No. 3,990,727, which discloses a quick detachable coupler that appears to be employed by the SleepNet™ IQ™ mask.

[0008] Since the patient must be able to sleep while wearing the patient interface, it is desirable that it be comfortable. In addition, the patient interface should provide a good seal to prevent or reduce leaks, or to better control any leak that occurs and to maintain efficacy of treatment. Since the shape of people's noses, faces and heads vary widely, from a commercial perspective, it is important to be able to manufacture patient interfaces which can accommodate this range of facial shapes without having to carry excessive inventory through a large number of sizes. A number of patient interfaces have been designed with the goals of patient comfort, ease of use, adjustability and the ability to accommodate a wide range of patient face and head shapes in mind.

[0009] U.S. Pat. No. 5,243,971 (Sullivan and Bruderer) provides a patient interface (both nasal and full-face masks) that is suitable for use in NPPV therapy. The mask has a face contacting portion mounted to a shell which is sized and shaped to overfit the nose region of an intended wearer, and the face contacting portion is in the form of a distendable membrane which is molded from an elastic material. U.S. Pat. No. 5,243,971 is hereby incorporated by reference in its entirety.

[0010] U.S. Pat. Nos. 6,357,441 and 6,112,746 (Kwok and Styles) each describe a nasal cushion which comprises a substantially triangularly shaped frame from which extends a membrane. These patents are hereby incorporated by reference in their entirety.

[0011] Other nasal masks are disclosed in U.S. Pat. Nos. 5,724,965 and 6,119,694, incorporated by reference in their entirety. Each describes a nasal cushion that engages with the tip of the nose or that portion of the nose in the horizontal plane just above the upper lip of the patient. In PCT/US00/11329 (WO 00/69521), incorporated by reference in its entirety, a triangular-shaped nasal cushion includes a tapered profile that narrows towards the face of the patient. Some of these prior art masks/cushions has experienced significant challenges from the perspective of patient comfort, potential nasal vent occlusion, stability and/or sealing (especially at the nasal bridge and cheek regions).

[0012] A number of adjustable forehead supports have been developed with the aim of achieving a serviceable seal while increasing patient comfort and accommodating the greatest number of patients in the population. For example, U.S. Pat. No. 6,119,693 (Kwok, Matchett and Grant) describes an adjustable forehead support for a nasal mask or full-face mask. The forehead support may be adjusted for the different shapes and sizes of a facial profile. The angle of the seal relative to the face may be adjusted with this invention. U.S. Pat. No. 6,119,693 is hereby incorporated by cross-reference in their entirety. In International Patent Application PCT/AU00/00097 (WO 00/78384), a forehead support is disclosed that is adapted to be secured to a respiratory mask. International Patent Application PCT/AU00/00097 (WO 00/78384) is hereby incorporated by cross-reference in its entirety.

[0013] Accordingly, a need has developed in the art to provide a mask assembly that is capable of overcoming the drawbacks or limitations of the prior art.

BRIEF SUMMARY OF THE INVENTION

[0014] One aspect of the present invention is directed towards a comfortable patient interface for delivering NPPV therapy.

[0015] Another aspect of the invention is to provide a patient interface that will result in improved patient compliance with NPPV therapy.

[0016] It is another aspect of the present invention to create a cushion that is capable of sealing on a smaller area of the nose as compared to known masks, while retaining or exceeding the comfort level of the ResMed Mirage® and Ultra Mirage® cushions.

[0017] It is a further aspect of the present invention to reduce the perceived and/or actual size and/or weight of a nasal mask and provide a less intrusive mask for the user.

[0018] Another aspect of the present invention is to provide a mask assembly in which the mask and headgear have a reduced amount of connections that are provided in a convenient and intuitive location for quick attachment and/or detachment by the patient, while not being easily detached accidentally.

[0019] Another aspect of the invention is to provide a mask assembly in which it is not necessary to provide a forehead support or an adjustment mechanism for the forehead support, while maintaining stability of the mask in use.

[0020] Another aspect is to provide a nasal mask capable of fitting a wide range of patients, so as to decrease or minimize inventory requirements and the number of differently sized masks/cushions that are required for production.

[0021] Yet another aspect of the present invention is to provide a nasal mask that offers more comfort to the patient, e.g., by better avoiding the application of unwanted localized pressure points in the facial contacting regions especially to the sensitive nasal bridge region of the patient, while maintaining a good seal, with or without the assistance of positive pressure to form or maintain the seal. Another aspect of the present invention is to avoid contact with the upper nasal bridge region, while avoiding localized pressure points along the lower nasal bridge region where the bony portion transitions into a portion of the nose containing more cartilage.

[0022] Another aspect of the present invention is to avoid application of unwanted localized contact pressure or forces that may increase undesirably the impedance of airflow through the patient's nares/naris and nasal passages, especially through the nasal vent.

[0023] Still another aspect is to provide a headgear assembly which can provide added stability to the mask/cushion assembly. In embodiments, the headgear may be made of or include at least one layer which imparts a degree of stiffness to the headstraps to assist in the stabilization of the mask/cushion assembly, which may obviate the need for a forehead support and thereby decrease visual obstructions near the patient's eyes and better enhance or at least not hinder the patient's ability to don, wear or remove eye glasses with the mask system in use. At least a portion of the headstrap itself may be formed of a relatively more rigid material in comparison to relatively flexible headstraps, instead of providing a multiple layer structure. The headgear may include a relatively large, hand-manipulable clip member that can be quickly and easily attached and/or detached from the head strap and/or the mask frame. Alternatively, the headgear may be magnetically coupled with the mask frame.

[0024] Another aspect of the present invention is to provide a convenient or quick release mechanism which requires little effort or dexterity to operate.

[0025] Another aspect of the present invention is to provide a frame which includes and/or integrates a quick release mechanism so that the clip member of the head straps can be easily detached from the frame. The quick release mechanism may include at least one connector portion formed in one piece with the frame. A mating connector portion can be provided on a portion of the headgear. The mask system is attached to a source of pressurized air which is delivered via an air delivery conduit. The conduit may be directly attached to the mask with its lumen in fluid communication with the mask chamber in order to supply pressurized air to the entrance of the patient's airway. Preferably an intermediate piece connects the air delivery conduit to the mask. Preferably the intermediate piece is an elbow joint, which will be better described below. The frame may include an extended tube protruding from the outside surface of the mask, which can improve the seal between the elbow joint and the mask frame and also improve the stability of the connection between the mask frame and the elbow joint. The extended tube may include a flange for attachment to the elbow assembly. Preferably the elbow assembly may be easily manipulated to quickly and readily detach the elbow joint from the mask frame during a temporary interruption in patient treatment. The elbow assembly may include a vent to atmosphere. Preferably the vent is in fluid communication with the system air path via an exhaust passage which is separated from the incoming gas path, for example, by using a baffle provided within a portion of the elbow joint.

[0026] Another aspect of the invention is to provide a generally trapezoidal shaped mask cushion for a patient interface.

[0027] Another aspect of the invention provides a respiratory mask assembly for delivering breathable gas to a patient. The respiratory mask assembly according to one embodiment includes a frame having a front surface and a rear surface adapted in use to face the patient. An elbow assembly is swivelably coupled to the front surface of the frame, the elbow assembly including one or more vent openings. A removable vent cover is detachably connected to the elbow assembly such that the vent cover is positioned in covering relation with respect to the one or more vent openings. The vent cover includes a main body and at least one vent aperture for gas washout. The vent cover includes a ring-shaped base defining an aperture into which a portion of the elbow assembly is inserted.

[0028] Of course, portions of the described aspects of the present invention may form sub-aspects of the present invention. Also, various ones of the sub-aspects and/or aspects may be combined in various manners and also constitute additional aspects or sub-aspects of the present invention. These and other features and aspects of the present invention will be described in or be apparent from the detailed description below read in conjunction with the attached Figures, where like reference numerals indicate like components.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings facilitate an understanding of the various embodiments of this invention. In such drawings:

[0030]FIG. 1 is a perspective view of a nasal mask assembly according to one preferred embodiment of the present invention;

[0031]FIG. 1<i>b </i>shows a headgear assembly according to an embodiment of the invention;

[0032]FIG. 2 is a partial side view of the nasal mask assembly of FIG. 1;

[0033]FIG. 3 is a partial front view of the nasal mask assembly of FIG. 1;

[0034]FIG. 4 is a partial top plan view of the nasal mask assembly of FIG. 1;

[0035]FIG. 5 is a front perspective view of a frame component of the nasal mask assembly of FIG. 1;

[0036]FIG. 5<i>a </i>is a top view of the frame of FIG. 5;

[0037]FIG. 5<i>b </i>is a schematic view showing various forces acting on the nasal mask assembly which may affect a patient;

[0038]FIG. 5<i>c </i>is a rear perspective view of the frame of FIG. 5;

[0039]FIG. 6<i>a </i>is a top view of an elbow assembly and frame according to another embodiment of the present invention;

[0040]FIG. 6<i>b </i>is an exploded view of the embodiment of FIG. 6<i>a; </i>

[0041]FIG. 7 is a partial sectional view of the frame of FIG. 5;

[0042]FIG. 8 is a side view of a left side yoke of the nasal mask assembly of FIG. 1;

[0043]FIG. 8<i>a </i>is an enlarged view of a right side yoke according to another embodiment of the present invention;

[0044]FIG. 9<i>a </i>is a top view of a locking clip of the nasal mask assembly of FIG. 1;

[0045]FIG. 9<i>b </i>is a bottom view of the locking clip of FIG. 9<i>a; </i>

[0046]FIG. 10<i>a </i>is a side view of a clip and frame in a nearly fully connected condition, according to the present invention;

[0047]FIG. 10<i>b </i>is a bottom view of the clip of FIG. 10<i>a; </i>

[0048]FIG. 10<i>c </i>is a top view of the clip of FIG. 10<i>a; </i>

[0049]FIG. 10<i>d </i>is a perspective view of the clip of FIG. 10<i>a; </i>

[0050]FIGS. 10<i>e</i>-<b>10</b><i>g </i>illustrate the clip and yoke of the present invention in various connected positions;

[0051]FIG. 11 is a perspective view of a buckle of the nasal mask assembly of FIG. 1;

[0052]FIG. 12 is a bottom view of a cross-over strap of the nasal mask assembly of FIG. 1 in a relaxed state;

[0053]FIG. 13 is a bottom view of the cross-over strap of FIG. 12 in a crossed-over state;

[0054]FIG. 14 is a view of a cross-over buckle of the cross-over strap of FIG. 13;

[0055]FIG. 15 is a perspective view of a strap loop for use with the nasal mask assembly of FIG. 1;

[0056]FIG. 16<i>a </i>is a perspective view of the swivel elbow shown in FIG. 1;

[0057]FIG. 16<i>b </i>is a side view of a swivel elbow of the nasal mask assembly of FIG. 1;

[0058]FIG. 17 is a front view of the swivel elbow of FIGS. 16<i>a </i>and <b>16</b><i>b; </i>

[0059]FIG. 18 is a rear view of the swivel elbow of FIGS. 16<i>a </i>and <b>16</b><i>b; </i>

[0060]FIG. 18<i>b </i>is a side view of another embodiment of a swivel elbow;

[0061]FIG. 18<i>c </i>is a front view of the swivel elbow of FIG. 18<i>b; </i>

[0062]FIG. 18<i>d </i>is a rear view of the swivel elbow of FIG. 18<i>b; </i>

[0063]FIG. 18<i>e </i>is a cross-sectional view of the swivel elbow of FIG. 18<i>b; </i>

[0064]FIGS. 19<i>a</i>-<b>1</b>-<b>19</b><i>c</i>-<b>2</b> are sequential sectional views of the swivel elbow as shown in FIG. 18, illustrating connection with a flange extending from the front surface of the frame;

[0065]FIG. 20 is a perspective view of a vent cover of the nasal mask assembly of FIG. 1;

[0066]FIG. 21 is a rear view of the vent cover of FIG. 20;

[0067]FIG. 22 is a bottom view of the vent cover of FIG. 20;

[0068]FIG. 22<i>b </i>is a perspective view of another embodiment of a vent cover for connection with the swivel elbow of FIG. 18<i>b; </i>

[0069]FIG. 22<i>c </i>is a rear view of the vent cover of FIG. 22<i>b; </i>

[0070]FIG. 22<i>d </i>is a bottom view of the vent cover of FIG. 22<i>b; </i>

[0071]FIG. 22<i>e </i>is a side view of the vent cover of FIG. 22<i>b; </i>

[0072]FIG. 22<i>f </i>is a side view of illustrating the vent cover of FIG. 22<i>b </i>connected to the swivel elbow of FIG. 18<i>b; </i>

[0073]FIG. 23 is a perspective view of a connector tube of the nasal mask of FIG. 6<i>a; </i>

[0074]FIG. 24<i>a </i>is a face side view of a cushion of the nasal mask assembly of FIG. 1 showing Computer Aided Design (CAD) construction lines;

[0075]FIG. 24<i>b </i>is a frame side view of the cushion of FIG. 24<i>a </i>showing CAD construction lines;

[0076]FIGS. 24<i>c</i>-<b>24</b><i>f </i>illustrate various perspectives of the cushion shown in FIG. 24<i>a; </i>

[0077]FIG. 24<i>g </i>shows a mask cushion in accordance with an embodiment of the invention incorporating a septum notch;

[0078]FIG. 25<i>a </i>is a perspective view of the cushion shown in FIG. 1 showing CAD construction lines;

[0079]FIG. 25<i>b </i>is a face side view of the cushion of FIG. 25<i>a; </i>

[0080]FIG. 25<i>c </i>is a frame side view of the cushion of FIG. 25<i>a </i>showing CAD construction lines;

[0081]FIG. 25<i>d </i>is a cross-section taken along line <b>25</b><i>d</i>-<b>25</b><i>d </i>of FIG. 25<i>b </i>showing CAD construction lines;

[0082]FIG. 25<i>e </i>is a cross-section taken along line <b>25</b><i>e</i>-<b>25</b><i>e </i>of FIG. 25<i>b; </i>

[0083]FIG. 25<i>f </i>is a cross-section taken along line <b>25</b><i>f</i>-<b>25</b><i>f </i>of FIG. 25<i>b; </i>

[0084]FIG. 25<i>g </i>is a cross-section taken along line <b>25</b><i>g</i>-<b>25</b><i>g </i>of FIG. 25<i>b; </i>

[0085]FIG. 25<i>h </i>is a cross-section taken along line <b>25</b><i>h</i>-<b>25</b><i>h </i>of FIG. 25<i>b; </i>

[0086]FIG. 25<i>i </i>is an enlarged view of FIG. 25<i>d </i>showing typical (TYP) dimensions of an embodiment (R-radius);

[0087]FIG. 26 is a perspective view of an air tube of the nasal mask assembly of FIG. 1;

[0088]FIGS. 27<i>a</i>-<b>27</b><i>e </i>are partial sectional views of a frame and cushion of the nasal mask assembly of FIG. 1 showing a sequence of positions of assembly and disassembly of the frame and cushion;

[0089]FIG. 28 is a partial sectional view of an alternative embodiment of the frame and cushion of the nasal mask assembly of FIG. 1;

[0090]FIGS. 29<i>a</i>-<b>29</b><i>d </i>show alternative sealing configurations of the cushion of FIGS. 27<i>a</i>-<b>27</b><i>e. </i>

[0091]FIGS. 30 and 31 show various dimensions used to design a mask according to FIG. 1;

[0092]FIGS. 32<i>a</i>-<b>1</b>-<b>32</b><i>c</i>-<b>2</b> illustrate an additional embodiment of the present invention for engagement between the frame and cushion, the cushion showing CAD construction lines;

[0093]FIG. 32<i>d </i>is an enlarged cross-sectional view of the frame shown in FIGS. 32<i>a</i>-<b>1</b>-<b>32</b><i>c</i>-<b>2</b>;

[0094]FIG. 32<i>e </i>illustrates an additional embodiment of the present invention for engagement between the frame and cushion;

[0095]FIG. 33 is a perspective view of another embodiment of a frame of the nasal mask assembly;

[0096]FIG. 34 is a top view of another embodiment of the yokes of the headgear assembly of the nasal mask assembly;

[0097]FIG. 35 is an enlarged view of a right side yoke of the headgear assembly shown in FIG. 34;

[0098]FIG. 36 is a perspective view illustrating the frame of FIG. 33 magnetically coupled to the headgear assembly of FIGS. 34 and 35;

[0099]FIG. 37 is a schematic view illustrating the magnetic coupling of the frame of FIG. 33 and the headgear assembly of FIGS. 34 and 35;

[0100] FIGS. <b>38</b>A-<b>38</b>D show various perspectives of another embodiment of the cushion, the cushion showing CAD construction lines;

[0101] FIGS. <b>39</b>A-<b>39</b>D show various perspectives of another embodiment of the cushion, the cushion showing CAD construction lines;

[0102]FIG. 40 is a perspective view of another embodiment of a frame of the nasal mask assembly;

[0103]FIG. 41 is a bottom view of the frame shown in FIG. 40;

[0104]FIG. 42 is a top view of an embodiment of the cushion structured to be engaged with the frame shown in FIG. 40, the cushion showing CAD construction lines; and

[0105]FIG. 43 is a rear view of the cushion shown in FIG. 42, the cushion showing CAD construction lines.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0106] Two main embodiments are described in the figures. Although many of the features and/or parts of each embodiment are the same, there are several parts and/or elements that are different. For example, while FIG. 1 shows one embodiment of an elbow assembly <b>60</b> according to the present invention, FIGS. 6<i>a</i>-<b>6</b><i>b </i>show another arrangement of the elbow assembly <b>60</b>. Other differences between the embodiments will be described below. Moreover, several alternative approaches are also described with respect to various parts and/or elements, and those alternative approaches should be considered as additional preferred embodiments of the present invention.

[0107] As shown in FIGS. <b>1</b>-<b>4</b>, a nasal mask assembly <b>10</b> according to one preferred embodiment of the present invention includes a frame <b>20</b> and a cushion <b>40</b> that is preferably detachably connected to the frame <b>20</b>. Alternatively, the cushion <b>40</b> can be permanently attached to the frame <b>20</b> using, e.g., co-molding or over-molding techniques, glue and/or mechanical fastening means. A swivel elbow assembly <b>60</b> and a headgear assembly <b>80</b> can be attached to the frame <b>20</b>. FIG. 1 shows the nasal mask assembly <b>10</b> generally as it is intended to be mounted onto a human head. Of course, the depiction in FIG. 1 is slightly spaced away from the head, or “floating”, for ease of understanding. FIG. 1<i>b </i>shows the headgear assembly laid flat with the frame <b>20</b> removed therefrom. FIG. 2 illustrates the mask assembly <b>10</b> from the left side view, FIG. 3 illustrates a front view thereof, and FIG. 4 illustrates a top view thereof. In FIGS. <b>2</b>-<b>4</b>, the rear portion of the headgear assembly <b>80</b> has been removed for clarity.

[0108] Mask Frame

[0109] As shown in FIG. 5, frame <b>20</b> includes an elongated body <b>22</b> having a central bore <b>24</b> for connecting to the swivel elbow assembly <b>60</b>. FIG. <b>5</b><i>a </i>is a top view of the frame <b>20</b> in which the cushion <b>40</b>, the elbow assembly <b>60</b> and the headgear assembly <b>80</b> have been detached. The frame <b>20</b> includes a main body <b>20</b><i>a</i>, which is designed to accommodate the cushion <b>40</b>, and a pair of side frame members <b>20</b><i>b </i>that are preferably formed in one piece with the main body <b>20</b><i>a </i>of the frame <b>20</b>. FIG. 5<i>a </i>shows that both side frame members preferably have the same configuration. The main body <b>20</b><i>a </i>and the side frame members <b>20</b><i>b </i>have been designed to have a curvature that generally follows the facial contour of the patient's face on each side of the nose. In accordance with one embodiment of the invention, the curvature follows a smooth transition from the two side members having an inclusive angle of 120°. With the cushion <b>40</b> in place, the main body <b>20</b><i>a </i>is spaced away from the patient's face in the nose region to prevent contacting the patient's nose, while the side frame members <b>20</b><i>b </i>are generally parallel the cheek regions. A space is maintained between each side frame member <b>20</b><i>b </i>and the cheek of the patient since contact is not desired in this area. However, if desired, the side frame members <b>20</b><i>b </i>may be constructed to include a comfort feature such as pad structure that engages the cheek regions of the patient. Such a pad can have the advantage of assisting in supporting the cheeks when pressure is applied in treatment mode.

[0110] Based on the curved design of the frame <b>20</b>, and other features, the center of gravity CG<b>1</b> (FIG. 5<i>b</i>) of the mask assembly <b>10</b> can be formed closer to the face of the patient. As such, rotative torque or moment created in the vertical plane due, for example, to the weight of the mask assembly can be reduced. For example, if the patient is sitting in the upright position as shown in FIG. 5<i>b</i>, the weight of the mask assembly <b>10</b> can produce torque about an axis A (into the page) that is transverse to the patient's nose in the horizontal plane. That torque can produce forces tending to rotate the mask assembly <b>10</b> in the direction of arrow B about the axis A which is generally positioned along the upper lip region of the cushion. Such torque may result in patient discomfort along the upper lip region and/or reduced sealing around the lower bridge region of the nose and/or at the cheek region. Specifically, a center of gravity CG<b>1</b> located close to the face can produce less torque than a mask having a center of gravity CG<b>2</b> that is further away from the face. This is because the distance d<b>1</b>, d<b>2</b> between the center of gravity CG<b>1</b>, CG<b>2</b> and the face defines the lever arm used to measure torque (torque=force×lever arm distance). Accordingly, torque can be reduced if the force or the lever arm distance is reduced. Similar torques can be created if the patient is lying on his or her side as well. The torque is affected by the geometry of the elbow, including such features as its length and height in relation to the cushion. It is desirable to minimise the effective lever arm length of the assembly which depends amongst other things on the configuration of the elbow.

[0111] Other factors which contribute towards reducing the distance between the center of gravity of the mask assembly and the face include design of the cushion <b>40</b>, the design of the frame <b>20</b>, and the design of the elbow assembly <b>60</b>. Another source of torque, which may affect stability of the mask, is the connection of the elbow assembly <b>60</b> to the gas delivery tube. In effect, the gas delivery tube may impart a force on the elbow assembly <b>60</b>, which in turn may create a torque tending to shift the mask assembly with respect to the patient. The amount of torque applied to the patient due to the connection between the elbow assembly and the gas delivery tube can be reduced using the elbow assembly <b>60</b> discussed below in relation to FIGS. 16<i>a</i>-<b>19</b><i>c</i>-<b>2</b>. In short, the lever arm of the elbow assembly can be effectively reduced because the elbow assembly is designed to be connected directly to a gas delivery tube <b>310</b> (FIG. 26), without the need for an intermediate swivel connector member <b>300</b> (FIGS. 6<i>b </i>and <b>23</b>) between the elbow assembly and the gas delivery tube <b>310</b>, as is currently used in some prior art. Alternatively, a swivel may be incorporated within the tube. In this way, an additional degree of freedom of movement may be added without increasing the undesirable torque. Also, because the cushion <b>40</b> is designed to distribute pressure at least along the lip and cheek regions of the cushion <b>40</b>, the possibility or tendency to rotate in the vertical plane is further reduced. Moreover, each of the cheek regions of the cushion <b>40</b> defines a relatively large contact pressure receiving surface that is elongated in the vertical direction and widened in the horizontal direction. As such the cushion <b>40</b>, at least in the cheek regions, resist rotational movement in the vertical and/or horizontal planes, which helps maintain the cushion <b>40</b> in a consistent position on the patient. More details of the cushion <b>40</b> are described below in relation to FIGS. 24<i>a</i>-<b>25</b><i>i</i>. Referring to FIG. 5<i>c</i>, the frame <b>20</b> includes a channel <b>26</b> having a generally trapezoidal shape for connecting to the cushion <b>40</b>. The channel <b>26</b> includes an inner wall <b>28</b>, an outer wall <b>30</b> and a channel floor <b>32</b>. The channel <b>26</b> will be described in further detail below.

[0112]FIG. 6<i>a </i>shows a frame <b>20</b> and elbow assembly <b>60</b> that is slightly different than the frame <b>20</b> and elbow assembly <b>60</b> shown in FIGS. <b>1</b>-<b>5</b><i>c</i>. Although the main differences between the embodiments reside in the elbow assembly <b>60</b>, there are other differences between the frames <b>20</b>, cushions <b>40</b>, etc., as will be readily seen by comparing the various figures, or understood in conjunction with the description in various sections below. Like elements are indicated with like reference numbers.

[0113] In FIGS. 6<i>a </i>and <b>6</b><i>b</i>, the elbow assembly <b>60</b> is attached to the mask <b>20</b> using a C-clip <b>23</b> (FIG. 6<i>b</i>) that can be expanded and contracted to fit within a circumferal groove <b>25</b> provided on a portion of the elbow assembly <b>60</b> that protrudes into the frame <b>20</b> using a mechanism similar to that provided on ResMed's ULTRA MIRAGE® mask and as described in U.S. patent application Ser. No. 09/594,775 (Drew et al.). An exploded view of the cushion <b>40</b>, the frame <b>20</b>, the elbow assembly <b>60</b> and the gas delivery tube is shown in FIG. 6<i>b</i>. The C-clip <b>23</b> has a surface that engages the inside surface of the frame <b>20</b> to prevent unwanted disconnection between elbow assembly <b>60</b> from the frame <b>20</b>. The elbow assembly <b>60</b> may also include one or more vent openings <b>61</b> open to atmosphere, for example, for gas washout of exhaled carbon dioxide, among other things. The vent openings <b>61</b> are structured so that treatment pressure will be maintained within the nasal cavity. The vent openings <b>61</b> may be covered with a shell member <b>65</b> which is resiliently and removably clipped onto an outer surface of the elbow assembly <b>60</b>. The vent openings <b>61</b> in FIG. 6<i>a </i>are visible through the clear shell member <b>65</b>. Details of the shell member <b>65</b> and the C-clip are described in the ResMed's U.S. patent application Ser. Nos. 09/502,745, 09/594,775 or PCT Application No. PCT/AU00/00097 (WO 00/78384), all of which are incorporated herein by reference.

[0114] As shown in FIG. 6<i>a</i>, the inner wall <b>28</b> of channel <b>26</b> preferably extends away from the frame <b>20</b> to a distance that is greater than the distance that the outer wall <b>30</b> extends away from the frame <b>20</b>. FIGS. 5<i>c </i>and <b>32</b><i>d </i>also show that the inner wall <b>28</b> extends away from the frame <b>20</b> a distance that is greater than the distance over which the outer wall <b>30</b> extends away from the frame <b>20</b>. As shown in FIG. 32<i>d</i>, the thickness of the inner wall <b>28</b> is in the range of about 1-2 mm, preferably 1.4 mm, the thickness of the outer wall <b>30</b> is in the range of about 1-2 mm, preferably 1.4 mm, and the distance between the tops of the inner and outer walls <b>28</b>, <b>30</b> is in the range of 0.5-10 mm, preferably 2 mm. Further, as shown in FIG. 32<i>d</i>, the width of channel <b>26</b> between the upstanding surfaces of the inner and outer walls <b>28</b>, <b>30</b> that face each other is in the range of about 2-10 mm, preferably 5 mm.

[0115] By adopting this relative distance between inner wall <b>28</b> and outer wall <b>30</b>, the engagement of the cushion <b>40</b> to the frame <b>20</b> is facilitated. As the cushion and mask frame are moved together, the inner wall <b>28</b> provides a visual and/or tactile cue to cushion alignment and then will facilitate the continuance of the engagement process by guiding the edge of the side wall or central portion <b>215</b> (FIGS. 24<i>e </i>and <b>27</b><i>a</i>) of the cushion <b>40</b> into channel <b>26</b>, as will be more fully explained with reference to FIGS. 27<i>a</i>-<b>29</b><i>d </i>and <b>32</b><i>a</i>-<b>1</b>-<b>32</b><i>c</i>-<b>2</b>. The shape of the channel <b>26</b>, e.g., a generally trapezoid shape as seen in FIG. 5<i>c</i>, is selected so as to achieve guidance to correct cushion orientation relative to the channel <b>26</b> without the need for additional guide pieces as would be the case should the channel <b>26</b> have a more symmetrical shape such as an equilateral triangle, circle, square or rectangle. Nevertheless, the cushion channel <b>26</b> could adopt any of these shapes.

[0116] As seen in FIGS. 5<i>c </i>and <b>6</b><i>a</i>, the frame <b>20</b> includes a locking clip receiver assembly <b>34</b> positioned on each side of the frame <b>20</b> for connecting to a respective locking clip <b>82</b> (FIGS. 9<i>a </i>and <b>10</b><i>a</i>) of the headgear assembly <b>80</b>. Each locking clip receiver assembly <b>34</b> includes an engagement face <b>35</b> (FIG. 5<i>c</i>), a central support slot <b>36</b> and two locking slots <b>38</b> positioned on opposite sides of the central support slot <b>36</b>. The central support slots <b>36</b> and locking slots <b>38</b> have a generally rectangular cross-section. Each of the locking slots <b>38</b> includes a locking flange <b>39</b> (FIG. 7) positioned on an outer wall thereof for engagement with a respective locking tab <b>116</b> (FIGS. 9<i>a </i>and <b>9</b><i>b</i>) of one of the locking clips <b>82</b>, as described below. The channel <b>38</b> may be provided with a slot <b>71</b> (FIG. 10<i>a</i>) in the outer wall of the frame <b>20</b> in addition to or in replacement of the locking flange <b>39</b> (FIG. 7). The slots <b>71</b> on the bottom of the frame <b>20</b> can be seen in FIG. 5<i>a</i>, while FIG. 4 shows the slots <b>71</b> from the top of the frame <b>20</b>. The slots <b>71</b> need not extend through the side walls of the frame <b>20</b>.

[0117] Headgear Assembly

[0118]FIG. 1<i>b </i>shows headgear assembly <b>80</b> in accordance with an embodiment of the invention, without the frame <b>20</b> or cushion <b>40</b>. In FIG. 1<i>b</i>, the headgear assembly is shown laid flat.

[0119] The Straps and Yokes

[0120] Referring to FIGS. <b>1</b>-<b>4</b>, headgear assembly <b>80</b> includes a pair of front straps <b>84</b>, with the left and right front straps <b>84</b> preferably being mirror images of each other. Each front strap <b>84</b> is in the general form of a “Y” and has a front strap end <b>86</b>, a top strap end <b>88</b> and a rear strap end <b>90</b> all formed in one piece or otherwise interconnected together by mechanical fastening or the like. The straps are made from laminated fabric and foam. One commercially available material is “Breath-O-Prene”™ manufactured by Accumed Inc., USA. Fastening of the straps may be assisted by use of a hook and loop material such as VELCRO®, however, the straps need not include hook and loop fasteners since the straps are fastened to the frame <b>20</b> using locking clips <b>82</b>, as more fully described below. As shown in FIGS. <b>1</b>-<b>3</b> and <b>8</b>, a yoke <b>92</b> is attached to each front strap <b>84</b>. Each yoke <b>92</b> has the same general shape as the corresponding front strap <b>84</b> and has a front end <b>94</b>, a top end <b>96</b> and a rear end <b>98</b>. Each yoke <b>92</b> is constructed of a somewhat rigid material, e.g., plastic, and has a thickness in the range of 0.3-2.0 mm, preferably 1 mm. Examples of the plastic include nylon <b>11</b> or polypropylene. The yoke <b>92</b> is attached to the corresponding front strap <b>84</b> with adhesives, stitching, or other known attachment mechanisms. The strap and yoke arrangement can have different flexibilities in different directions, for example being stiff in a first direction (e.g., to resist the deformation due to the weight of the swivel elbow, associated conduits, etc.), but flexible in a direction generally orthogonal to the first direction. Upon donning the mask on the user's head, the relative stiffness of the yokes helps position the frame and cushion in the correct position on the user. Although having the same general shape as the front straps <b>84</b>, the top ends <b>96</b> and rear ends <b>98</b> in this embodiment do not extend as far as the top strap ends <b>88</b> and rear strap ends <b>90</b> of the front straps <b>84</b>. However, in another embodiment, the top end <b>96</b> may be extended along the entire length of the top strap <b>88</b> and be formed integrally or in one piece with a connector element <b>128</b> (FIG. 1). The yokes <b>92</b> are also narrower than the front straps so that when they are attached together, the softer material of the front straps <b>84</b> extends beyond the more rigid material of the yokes <b>92</b>, thereby preventing or at least reducing the opportunity for contact between the user and the more rigid material of the yokes <b>92</b> that could cause irritation or discomfort. While the straps and associated yokes are formed from a multilayer construction, e.g., two layers, the strap <b>84</b> and yoke <b>92</b> could be formed of a single material, so long as patient comfort and the appropriate rigidity/flexibility are maintained.

[0121] The yokes <b>92</b> add to the rigidity of the straps <b>84</b> in certain planes and directions, which assists in stabilizing the mask assembly <b>10</b> on the head of the patient during use. In other planes and directions, the yoke and strap assembly has a different rigidity. For example, the strap and yoke should be able to resist bending or curling towards or away from the patient's face. In general, the strap <b>84</b> and yoke <b>92</b> should be able to maintain their positions with respect to the head of the patient when the straps <b>84</b> and yokes <b>92</b> are connected to the frame <b>20</b>. Moreover, the mask frame <b>20</b> need not be provided with a forehead support assembly, which may further increase the comfort of the patient since the patient's field of view is less obstructed as compared to masks with forehead supports. Of course, forehead supports of the type described above may be provided if desired for additional stability or comfort. Also, the mask frame <b>20</b> need not be provided with a chin strap, although a chin strap may be provided if desired for additional stability or comfort. In addition, beyond removal of the forehead support, the shapes of the straps <b>84</b> and yokes <b>92</b> are selected to avoid interference with the patient's field of view. In particular when fitted, the front ends <b>94</b> of each yoke <b>92</b> are connected to the frame <b>20</b> below the patient's eyes, and preferably extend along a curved arc resting across the cheek regions. The top end <b>88</b> of each strap <b>84</b> and the top end <b>96</b> of each yoke extend away from the intersection of the Y along the temple region of the patient's head. The rear end <b>98</b> of the yoke <b>92</b> and the rear end <b>90</b> of the strap <b>84</b> are curved downwardly and around the ear of the patient for connection with the rear strap member <b>138</b>, as more fully described below. Due to the rigidity provided by the yokes <b>92</b>, the straps <b>84</b> are better able to maintain a predetermined shape. On the other hand, a certain degree of flexibility of the yoke <b>92</b> and strap <b>84</b> is provided such that variations in patient physiology can be accommodated to a certain degree. The thickness of the yoke can also vary across its profile to modify flexibility characteristics, for example, thicker regions may be stiffer.

[0122] As shown in FIG. 8, each yoke <b>92</b> has a mounting flange <b>100</b> positioned on the front end <b>94</b>. The mounting flange <b>100</b> has an aperture or keyhole <b>101</b> leading to a bore <b>103</b>, see FIG. 8<i>a</i>. Two semi-annular flanges <b>102</b> are separated from each other by slots <b>104</b>. A radial inner surface of the semi-annular flanges <b>102</b> forms the central bore <b>103</b>. The yoke <b>92</b> also has a spring tab <b>106</b> positioned rearward of the mounting flange <b>100</b> with a front portion of the spring tab connected to the yoke <b>92</b> and a rear portion separated from the yoke <b>92</b> by space <b>107</b> to be able to flex with respect to the yoke <b>92</b> when pressure is applied to the spring tab <b>106</b>. The spring tab <b>106</b> preferably has a plurality of raised teeth <b>108</b> positioned in an arc about an axis of the mounting flange <b>100</b>. The spring tab <b>106</b> also has a textured surface <b>110</b> (FIG. 8) or a raised positioning member <b>110</b><i>a </i>(FIG. 8<i>a</i>) at its free end to assist the user in locating, engaging and manipulating the spring tab <b>106</b>. FIG. 8<i>a </i>is an enlarged view of a right side yoke <b>92</b> and strap <b>84</b>, like that shown in FIG. 8, to better show details of yoke <b>92</b>, including the manner in which the yoke <b>92</b> is stitched to the head strap <b>84</b>. Other fixing mechanisms such as locking or friction may be used.

[0123] The Locking Clip

[0124] The locking clip <b>82</b> is adjustably attached to each mounting flange <b>100</b>. As shown in FIGS. 9<i>a </i>and <b>9</b><i>b</i>, each locking clip <b>82</b> includes a main body <b>112</b>. Two spring arms <b>114</b> are attached to opposite sides of the main body <b>112</b> and extend away from the main body in a generally parallel manner. A latch hook <b>116</b> is attached to a free end of each spring arm <b>114</b>.

[0125] As shown in FIG. 10<i>a</i>, the clip <b>82</b> can be inserted into releasable engagement with the locking clip engagement receiver <b>34</b> of the frame <b>20</b>. In FIG. 10<i>a</i>, only one clip <b>82</b> is shown and the clip <b>82</b> is not assembled to the yoke <b>92</b>. Each latch hook <b>116</b> is received within a respective channel <b>38</b> (FIG. 5<i>c</i>) of the frame. In FIG. 10<i>a</i>, the distal ends of the latch hooks <b>116</b> are shown in a position just before they outwardly flex into the respective recesses <b>71</b> of the channel <b>38</b>. FIG. 4 shows the distal ends of the latch hooks in the engaged position within the recesses <b>71</b>. Of course, the clip <b>82</b> or at least the latch hook <b>116</b> thereof could be formed in the frame <b>20</b>, and the channel <b>38</b> or at least the recess <b>71</b> could be formed on the strap and/or yoke.

[0126]FIGS. 4 and 10<i>a </i>also show that the outward surfaces of the locking clip <b>82</b> and the frame <b>20</b> preferably form a generally continuous surface, which is not interrupted when connected. Preferably, the locking clip <b>82</b> is as wide as the frame <b>20</b> at each end, which facilitates tactile location of the locking clip by the patient. The spring arms <b>114</b> are designed to flex within the plane of the locking clip main body, which further improves the ease by which the locking clips <b>82</b> are attached and detached. This positioning improves the ergonomics of the release mechanism. The patient's thumb and an opposing finger can be used to readily locate and operate the locking clips <b>82</b>. Also, because of their increased size, patients with minimal dexterity can operate the locking clips <b>82</b>. Further, the locking clips <b>82</b> are connected to the strap <b>84</b>/yoke <b>92</b> so that length adjustment between the locking clips <b>82</b> and the strap <b>84</b>/yoke <b>92</b> is not necessary.

[0127] The locking clip <b>82</b> includes a retaining flange <b>118</b> (FIG. 9<i>b</i>) extending transversely outward from the main body <b>112</b>. The retaining flange <b>118</b> has a central hub <b>119</b> extending along an axis of the retaining flange <b>118</b> and two retaining tabs <b>120</b> extending transversely from the central hub <b>119</b> on opposite sides of the central hub <b>119</b>. FIGS. 10<i>b</i>-<i>d </i>show more details of the locking clips <b>82</b> shown in FIG. 10<i>a</i>, which are similar to features shown in FIGS. 9<i>a </i>and <b>9</b><i>b</i>. While the locking clip <b>82</b> has been shown to be separate from the yoke <b>92</b>, it is understood that the clip and yoke <b>92</b> could be formed in one piece if relative movement and/or detachment between the two is not required. Conversely, the clip <b>82</b> and frame <b>20</b> can be formed as an integral unit, and the clip portion could be connected to the yoke.

[0128] The retaining flange <b>118</b> is sized and shaped such that the retaining tabs <b>120</b> can be aligned with the slots <b>104</b> and the retaining flange <b>118</b> axially inserted into the mounting flange <b>100</b> of the yoke <b>92</b>. The central hub <b>119</b> is sized to have a close tolerance with the central bore <b>103</b> so that the locking clip <b>82</b> and yoke <b>92</b> are rotationally supported with one another. Once the retaining flange <b>118</b> has been inserted into the mounting flange <b>100</b>, the locking clip <b>82</b> can be rotated with respect to the yoke <b>92</b> such that the retaining tabs <b>120</b> engage an inside surface of the flanges <b>102</b>, thereby axially locking the mounting clip <b>82</b> to the yoke <b>92</b>. FIGS. 10<i>e</i>-<i>g </i>show the locking clip <b>82</b> in various positions with respect to the yoke <b>92</b>. In FIG. 10<i>e</i>, the tabs <b>120</b> of the clip <b>82</b> have been inserted through the openings <b>104</b> of the yoke <b>92</b>, and the clip <b>82</b> has been rotated slightly along the direction of arrow A such that the upper surfaces of the tabs <b>120</b> snugly engage the inside surfaces of the semi-annular portions <b>102</b>. When the clip <b>82</b> is attached such that the flexing arms <b>114</b> are positioned approximately 90 degrees with respect to the front end <b>94</b> of the yoke <b>92</b>, the clip <b>82</b> can be removed from the yoke <b>92</b>. In this embodiment, there are two positions in which the removal can occur, and both of these positions are selected such that they would not occur when the mask is in normal use; otherwise the clips <b>82</b> could be inadvertently detached from the yokes <b>92</b>. FIGS. 10<i>f </i>and <b>10</b><i>g </i>show the clip <b>82</b> in different rotational orientations with respect to the yoke <b>92</b>.

[0129] As seen in FIGS. 9<i>b </i>and <b>10</b><i>b</i>, the locking clip also has a plurality of raised teeth <b>122</b> positioned in an arc about an axis of the retaining flange <b>118</b>. The teeth <b>122</b> are constructed and arranged so as to engage the teeth <b>108</b> on spring tab <b>106</b>. Once the spring tab <b>106</b> has been depressed to lower teeth <b>108</b>, the locking clip <b>82</b> can be rotated to a desired position with respect to the yoke <b>92</b>. The spring tab <b>106</b> can then be released so that teeth <b>108</b> engage teeth <b>122</b> in the desired position (within a pitch of the teeth) and rotationally lock the locking clip <b>82</b> with respect to the yoke <b>92</b>. In accordance with one embodiment, the teeth <b>108</b> and <b>122</b> can be configured so that when a predetermined torque is applied to the locking clip <b>82</b>, the teeth <b>122</b> will automatically force the teeth <b>108</b> and spring tab <b>106</b> downwardly to allow rotation of the locking lip <b>82</b> until the torque is removed and the teeth <b>108</b> re-engage the teeth <b>122</b>. The locking clip <b>82</b> can thus be rotationally adjusted with respect to the yoke <b>92</b> within an angle of approximately 50-100°, and preferably 75°, depending on the position of engagement between teeth <b>108</b> and teeth <b>122</b>. The angle of available rotational adjustment can be altered as desired by altering the number and positioning of teeth <b>108</b> and <b>122</b>. The adjustment angle range reflects the relative cushion positions required on the face. Rotational adjustment with a toothed system as described above allows easy adjustment by the patient and allows a broad range of positions to accommodate a wide range of patients' faces. For example, the patient may adjust both locking clips <b>82</b> to have the same angle with respect to the yokes <b>92</b>. Alternatively, the patient may adjust the locking clips <b>82</b> such that the locking clips <b>82</b> have different respective angles with respect to the yokes <b>92</b>. The toothed system allows the patient to easily set and reproduce the desired angle for each locking clip <b>82</b>. For example, the toothed system may allow relative movement between each locking clip and its respective yoke in, for example, five positions, which should accommodate most faces. Of course more or less than five positions could be used instead, depending on application. Moreover, once it is determined that a particular angle for each locking clip <b>82</b> with respect to the yokes <b>92</b> is desired, the mask system may include a nonadjustable clip arrangement which fixes the rotational position of the locking clips <b>82</b> with respect to the yokes <b>92</b>. The teeth are large enough for the patient to easily determine the relative positions of the locking clip with respect to the yokes.

[0130] Further, the spring tab <b>106</b> is configured and positioned such that the patient cannot inadvertently depress the spring tab <b>106</b>, e.g., by rolling over on the locking clip/yoke during sleeping, to cause the locking clip <b>82</b> to move relative to the yoke <b>92</b>. For example, as shown in FIGS. 10<i>e</i>-<b>10</b><i>g </i>and FIG. 36 (a different embodiment), the locking clip <b>82</b> extends further outwardly from the yoke <b>92</b> than the spring tab <b>106</b>. That is, the spring tab <b>106</b> is positioned lower than the outer edge of the locking clip <b>82</b>. Thus, the positioning of the locking clip <b>82</b> with respect to the spring tab <b>106</b> prevents inadvertent actuation of the spring tab <b>106</b>. Moreover, the spring tab <b>106</b> is connected to the yoke <b>92</b> such that the yoke <b>92</b> can flex toward and away from the spring tab <b>106</b> without disengaging the teeth <b>108</b> of the spring tab <b>106</b> from the teeth <b>122</b> of the locking clip <b>82</b>.

[0131] Alternative adjustment assemblies may be achieved by simple reversal of some or all of the sub-assemblies. For example, the central hub <b>119</b> might be located on the yoke <b>92</b> while its reciprocal yoke central bore <b>103</b> may be located on the locking clip <b>82</b>. In a similar way, each sub-assembly and its reciprocal may be reversed. Alternatively, the yoke <b>92</b> and locking clip <b>82</b> may be adjustably connected by way of a screw or clamping mechanism, e.g., a part that may be separate from the yoke and clip, which can be used to selectively connect the yoke <b>92</b> and clip <b>82</b> in a plurality of desired positions. In addition, the central bore <b>103</b> can be shaped in any manner that allows detachment and attachment between the yoke and the clip. Also, a system of replacement yokes that would allow a fixed angle with respect to the locking clip may be used.

[0132] The locking clip <b>82</b> also includes a central support tab <b>124</b> extending outward from the main body <b>112</b> between and generally parallel to spring arms <b>114</b>. The central support tab <b>124</b> is configured to have a close fit with the central support slot <b>36</b>, so that when the central support tab <b>124</b> is inserted into the central support slot <b>36</b>, little rotational, rocking or side to side movement is permitted between the locking clip <b>82</b> and the locking clip receiver assembly <b>34</b>. Central support tab <b>124</b> is longer than arms <b>114</b> to assist with alignment into the frame. The locking clip <b>82</b> also has an engagement face <b>125</b> that engages engagement face <b>35</b> (FIG. 5<i>c</i>) when the locking clip <b>82</b> is inserted into the locking clip receiver assembly <b>34</b> to provide additional support for the locking clip <b>82</b>. The latch hooks <b>116</b> and/or the central support tab <b>124</b> may have tapered widths and/or thicknesses to facilitate entry into slots <b>36</b>, <b>38</b>. Also, the latch hooks <b>116</b> and/or central support tab <b>124</b> may have rounded or contoured edges to facilitate entry into slots <b>36</b>, <b>38</b>. Further, the central support tab <b>124</b> may have a groove that engages a protrusion provided in the central support slot <b>36</b> to facilitate entry of the central support tab <b>124</b> into the central support slot <b>36</b>. Alternatively, the central support tab <b>124</b> may have a protrusion that engages a groove provided in the central support slot <b>36</b>.

[0133] When the locking clip <b>82</b> is inserted into the locking clip receiver assembly <b>34</b>, the spring arms <b>114</b> are forced toward one another as the latch hooks <b>116</b> are inserted into recesses <b>71</b> (FIG. 4) or ride up and over the locking flanges <b>39</b> (FIG. 7). Once the latch hooks <b>116</b> have cleared the locking flanges <b>39</b> or recesses <b>71</b>, the spring arms <b>114</b> can spring outward, providing a locking engagement between the latch hooks <b>116</b> and the locking flanges <b>39</b> and/or recesses <b>71</b>. Sufficient clearance is provided in locking slots <b>38</b> to allow the necessary movement of the latch hooks <b>116</b> to clear the locking flanges <b>39</b>.

[0134] In this manner, the respective left and right front strap assemblies, including front straps <b>84</b>, yokes <b>92</b> and locking clips <b>82</b>, can be attached to the frame <b>20</b> and the yokes <b>92</b> and front straps <b>84</b> rotationally adjusted with respect to the frame <b>20</b> within an angle of approximately 50-100°, and preferably 75°.

[0135] In a preferred embodiment, the locking clip <b>82</b> is a unitary plastic piece formed by injection molding. Examples of the plastic include nylon, acetal, polycarbonate, and polypropylene. In one embodiment, the retaining tabs <b>120</b> are formed during the molding process by mold projections that leave bores <b>126</b> extending through the main body <b>112</b> of the locking clip <b>82</b>, thereby separating under surfaces of the retaining tabs <b>120</b> from the main body <b>112</b>.

[0136] Magnetic Interconnection

[0137] FIGS. <b>33</b>-<b>37</b> illustrate an alternative embodiment for removably coupling the frame <b>420</b> and the headgear assembly <b>480</b>. Specifically, the frame <b>420</b> and the yokes <b>492</b> are structured such that the yokes <b>492</b> may be magnetically coupled to the frame <b>420</b>.

[0138] As shown in FIG. 33, the frame includes a main body <b>420</b><i>a </i>and a pair of side frame members <b>420</b><i>b</i>. Similar to the embodiment of frame <b>20</b>, the main body <b>420</b><i>a </i>is structured to be removably coupled with the cushion <b>40</b>. Each side frame member <b>420</b><i>b </i>includes a first connector portion <b>434</b> for connecting to a second connector portion <b>435</b> provided by the yoke <b>492</b> of the headgear assembly <b>480</b>. In the illustrated embodiment, the first connector portion <b>434</b> includes a retaining structure <b>418</b> that extends outwardly from the side frame member <b>420</b><i>b</i>. The retaining structure <b>418</b> is structured to retain a magnet <b>419</b>. In one embodiment, the magnet <b>419</b> is constructed of Neodymium and has a cylindrical shape with a diameter of 6.35 mm and a thickness of 6.35 mm. However, the retaining structure <b>418</b> may be structured to retain a magnet of any suitable size and shape. Further, the outer edges of the side frame members <b>420</b><i>b </i>each include a plurality of raised teeth <b>422</b> positioned in an arc.

[0139] As shown in FIGS. 34 and 35, the yokes <b>492</b> of the headgear assembly <b>480</b> each include structure that is similar to the yokes <b>92</b> of headgear assembly <b>80</b>. Specifically, the yokes <b>492</b> each include the second connector portion <b>435</b> having a mounting flange <b>400</b> positioned on the front end <b>494</b> thereof. The mounting flange <b>400</b> has an aperture or keyhole <b>401</b> leading to a bore <b>403</b>. Two semi-annular flanges <b>402</b> are separated from each other by slots <b>404</b>. A radial inner surface of the semi-annular flanges <b>402</b> forms the central bore <b>403</b>. The yoke <b>492</b> also has a spring tab <b>406</b> positioned rearward of the mounting flange <b>400</b> with a front portion of the spring tab <b>406</b> connected to the yoke <b>492</b> and a rear portion separated from the yoke <b>492</b> by space <b>407</b> to be able to flex with respect to the yoke <b>492</b> when pressure is applied to the spring tab <b>406</b>. The spring tab <b>406</b> preferably has a plurality of raised teeth <b>408</b> positioned in an arc about an axis of the mounting flange <b>400</b>. The spring tab <b>406</b> also has a raised positioning member <b>410</b> at its free end to assist the user in locating, engaging and manipulating the spring tab <b>406</b>.

[0140] In contrast to the yoke <b>92</b>, the yoke <b>492</b> includes a ferrous metal disk <b>412</b> that is secured within the bore <b>403</b>. In one embodiment, the metal disk <b>412</b> is a steel washer with a diameter of 14 mm and a thickness of 1 mm. However, the metal disk <b>412</b> may have any suitable size and shape that can be mounted within the bore <b>403</b> of yoke <b>492</b>. Further, a magnet of suitable size and shape may be used in place of the metal disk <b>412</b>.

[0141] As shown in FIGS. 36 and 37, the first connector portion <b>434</b> of the frame <b>420</b> is engaged with the second connector portion <b>435</b> of the yoke <b>492</b> such that the magnet <b>419</b> is magnetically coupled with the metal disk <b>412</b>. Specifically, the magnet <b>419</b> is axially inserted into the bore <b>403</b> so that the magnet <b>419</b> is positioned adjacent to or engaged with the metal disk <b>412</b> which allows the magnetic attraction between the magnet <b>419</b> and the metal disk <b>412</b> to axially retain the yoke <b>492</b> to the frame <b>420</b>. The strength of the magnetic attraction between the yokes <b>492</b> and the frame <b>420</b> may be increased by replacing the metal disk <b>412</b> with a magnet, as discussed above. The retaining structure <b>418</b> is sized to have a close tolerance with the bore <b>403</b> so that the frame <b>420</b> and yoke <b>492</b> are rotationally supported with one another.

[0142] Further, the teeth <b>422</b> on the frame <b>420</b> are constructed and arranged to engage the teeth <b>408</b> on the spring tab <b>406</b> when the frame <b>420</b> is magnetically coupled with the yoke <b>492</b>. Once the spring tab <b>406</b> has been depressed to lower teeth <b>408</b>, the yoke <b>492</b> can be rotated to a desired position with respect to the frame <b>420</b>. The spring tab <b>406</b> can then be released so that teeth <b>408</b> engage teeth <b>422</b> in the desired position (within a pitch of the teeth) and rotationally lock the frame <b>420</b> with respect to the yoke <b>492</b>. In accordance with one embodiment, the teeth <b>408</b> and <b>422</b> can be configured so that when a predetermined torque is applied to the yoke <b>492</b>, the teeth <b>422</b> will automatically force the teeth <b>408</b> and spring tab <b>406</b> downwardly to allow rotation of the yoke <b>492</b> until the torque is removed and the teeth <b>408</b> re-engage the teeth <b>422</b>. The yoke <b>492</b> can thus be rotationally adjusted with respect to the frame <b>420</b> within an angle of approximately 50-100°, and preferably 75°, depending on the position of engagement between teeth <b>408</b> and teeth <b>422</b>.

[0143] The magnet <b>419</b> in each side frame member <b>420</b><i>b </i>may be oriented such that an incorrect attachment (e.g., left side yoke <b>492</b> to right side frame member <b>420</b><i>b</i>) is indicated by magnetic repulsion. Specifically, the magnet <b>419</b> on one side frame member <b>420</b><i>b </i>is oriented so that it will only magnetically couple with one of the yokes <b>492</b> and the magnet <b>419</b> on the other side frame member <b>420</b><i>b </i>is oriented so that it will only magnetically couple with the other of the yokes <b>492</b>. Thus, sensory indication of correct attachment of the frame <b>420</b> to the headgear assembly <b>480</b> is achieved by magnetic attraction of correctly paired yokes <b>492</b> and side frame members <b>420</b><i>b</i>. This construction ensures that the headgear assembly <b>480</b> and frame <b>420</b> are assembled correctly. Further, this construction enables the frame <b>420</b> to be easily coupled with the headgear assembly <b>480</b>, even in the dark, as the magnet <b>419</b> will automatically locate itself in the correct position with respect to the metal disk <b>412</b>. The headgear assembly <b>480</b> may be easily detached from the frame <b>420</b> by applying a suitable disengagement force that is greater than the attractive magnetic force between the magnet <b>419</b> and the metal disk <b>412</b>.

[0144] Alternatively, the first connector portion <b>434</b> on the frame <b>420</b> may provide a ferrous metal member and the second connector portion <b>435</b> on the yoke <b>492</b> may provide a magnet.

[0145] Straps

[0146] Each front strap <b>84</b> includes a ladder-type buckle <b>128</b> attached to the top strap <b>88</b> to connect the top strap <b>88</b> with a top strap <b>140</b> of cross-over strap <b>138</b>. See FIGS. <b>1</b>-<b>3</b> and <b>11</b>. The buckle <b>128</b> can be attached to the top strap <b>88</b> with adhesives, stitching and/or other known manners, such as being manufactured integral with the strap. In the embodiment shown in FIG. 11, the buckle <b>128</b> includes a plurality of bores <b>130</b> evenly spaced around an attachment tab <b>132</b> in the form of a square to allow the buckle to be stitched to the top strap <b>88</b>. The buckle further includes a crossbar <b>134</b> and a crossbar <b>136</b>, around which the top strap <b>140</b> can be threaded, in a known manner, so that top strap <b>140</b> wraps around crossbar <b>136</b> and a free end of top strap <b>140</b> is positioned between crossbar <b>134</b> and a remainder of top strap <b>140</b>. Thus, when tension is applied between the buckle <b>128</b> and top strap <b>140</b>, the free end of top strap is frictionally held between crossbar <b>134</b> and the remainder of top strap <b>140</b> so that the connection between buckle <b>128</b> and top strap <b>140</b> is self holding under tension. A single cross bar buckle can also be used if used in combination with a strap loop to hold the strap in position. Of course, other connector members can be used instead of the buckle, as is known in the art.

[0147] As shown in FIG. 12, cross-over strap <b>138</b> has a generally elongated shape in a relaxed state with two top straps <b>140</b> extending upward from a cross-strap <b>142</b> having ends <b>144</b>. To place the cross-over strap <b>138</b> in a configuration for wearing, the two top straps <b>140</b> are threaded through a crossover buckle <b>146</b>, so that they are held in the cross-over position. See FIGS. 13 and 14. In this manner, the left top strap <b>140</b> of cross-over strap <b>138</b> crosses over to connect with the buckle <b>128</b> of right top strap <b>88</b> and the right top strap <b>140</b> of cross-over strap <b>138</b> crosses over to connect with the buckle <b>128</b> of left top strap <b>88</b>. This crossing over of the respective straps helps maintain the headgear assembly <b>80</b> and nasal mask assembly <b>10</b> in a desired adjusted position on the user. A strap loop <b>148</b> can be used to hold down free ends of the respective straps. See FIG. 15. In one form of the invention, the straps are supplied oversized and then cut to length to suit the person.

[0148] Similarly to buckles <b>128</b> and top straps <b>88</b>, buckles <b>150</b> (FIG. 1) can be attached to cross-strap ends <b>144</b> so that the cross-strap ends <b>144</b> can be connected to the respective rear strap ends <b>90</b> of front straps <b>84</b>.

[0149] Swivel Elbow Assembly

[0150] The swivel elbow assembly <b>60</b> of FIG. 6<i>a </i>may be the same as is currently used in ResMed Limited's ULTRA MIRAGE® mask, which employs an internal C-clip member, as described above. The elbow assembly <b>60</b> of FIG. 6<i>a </i>is intended to be used with a connector tube <b>300</b> (FIG. 23). The connector tube <b>300</b> is provided between the elbow assembly <b>60</b> and the gas delivery tube <b>310</b> (FIG. 26).

[0151] Alternatively, the swivel elbow assembly may be constructed in accordance with FIGS. <b>1</b>-<b>4</b> and <b>16</b>-<b>22</b>. Such a swivel elbow assembly <b>60</b> may include a swivel elbow <b>160</b> and a vent cover <b>180</b>. Swivel elbow <b>160</b> is rotationally connected to frame <b>20</b>.

[0152] In another alternative form of the invention, a further swivel is connected to the end of tube <b>310</b>, as shown in FIG. 6<i>b. </i>

[0153] As shown in FIGS. 16<i>a</i>-<b>19</b><i>c</i>-<b>2</b>, swivel elbow <b>160</b> includes an intake port <b>162</b> and an exhaust port <b>164</b>. The air tube <b>310</b> (FIG. 26) is preferably directly connected to a stem <b>166</b> of swivel elbow <b>160</b> (without connector tube <b>300</b>) to supply pressurized breathable air or gas from a pressurized supply through air tube <b>310</b>, intake port <b>162</b> and into cushion <b>40</b> for breathing by the patient.

[0154] The exhaust port <b>164</b> is separated from the intake port <b>162</b> using, for example, a baffle <b>161</b> provided within the interior portion of the elbow <b>160</b>. See FIGS. 18 and 19<i>a</i>-<b>1</b>. In the illustrated embodiment, the baffle <b>161</b> has a generally planar configuration. However, the baffle <b>161</b> may have a curved configuration or any other suitable configuration for separating the exhaust port <b>164</b> from the intake port <b>162</b>. The orientation of the intake and exhaust ports <b>162</b>, <b>164</b> was selected such that the incoming gas, indicated by the directional arrow in the intake port <b>162</b>, less directly impacts the flow of gas washout along the exhaust port <b>164</b>. Further, the gas entering the elbow <b>160</b> is less likely to flow directly into the exhaust port <b>164</b> since the baffle <b>161</b> forces the incoming air to take a tortuous path, e.g., turn around about 180 degrees, before being able to exit through the exhaust port <b>164</b>.

[0155] The elbow <b>160</b> includes an end portion <b>169</b> that is adapted to engage the aperture <b>24</b> provided in the frame <b>20</b>, to provide gas into the nasal cavity formed by the frame <b>20</b> and the cushion <b>40</b>. The baffle <b>161</b> terminates just inside the end portion <b>169</b> of the elbow. A flexible quick release mechanism includes a collar <b>173</b> and an apron <b>170</b>. The collar <b>173</b> includes a generally T-shaped member, as seen in FIG. 16<i>b</i>, that surrounds the end portion <b>169</b> of the elbow <b>160</b>. Preferably, the end portion <b>169</b> of the elbow <b>160</b> extends beyond the collar <b>173</b> to improve alignment when assembling into frame <b>20</b>. The collar <b>173</b> is spaced away from the end portion <b>169</b> in concentric relation so as to form a receiving space <b>183</b> between the collar <b>173</b> and the end portion <b>169</b>, as shown in FIG. 18. The apron <b>170</b> is preferably formed as an integral part of the elbow <b>160</b>, and is connected to the lower leg of the T-shaped collar <b>173</b>. Two grooves <b>167</b> are provided between the collar <b>173</b> and the apron <b>170</b>. A portion <b>167</b><i>a </i>of the groove <b>167</b> allows the lower leg of the T-shaped collar <b>173</b> to flex with respect to the apron <b>170</b>. A portion <b>167</b><i>b </i>of the groove allows the cross portion of the T-shaped collar <b>173</b> to flex outwardly and inwardly with respect to the end portion <b>169</b> of the elbow <b>160</b>.

[0156]FIGS. 19<i>a</i>-<b>1</b>-<b>19</b><i>c</i>-<b>2</b> show sequential views illustrating connection between the elbow <b>160</b> and the frame <b>20</b>. FIGS. 19<i>a</i>-<b>1</b>-<b>19</b><i>a</i>-<b>2</b> show a cross section of the elbow <b>160</b> just before connection with the mask frame <b>20</b>. FIGS. 19<i>b</i>-<b>1</b>-<b>19</b><i>b</i>-<b>2</b> show the elbow <b>160</b> and frame <b>20</b> in the nearly connected condition, and FIGS. 19<i>c</i>-<b>1</b>-<b>19</b><i>c</i>-<b>2</b> show the elbow and frame in the fully connected condition.

[0157] The frame <b>20</b> includes a flange <b>21</b> provided at a distal end of a wall <b>25</b> defining the aperture <b>24</b>. FIGS. 5 and 5<i>a </i>show the flange <b>21</b>, while the embodiment of FIG. 6<i>a </i>does not show or include such a flange since a different elbow assembly <b>160</b> is employed. As the flange <b>21</b> is inserted within the space <b>183</b>, it engages protrusions <b>181</b> formed in the inside surface of the collar <b>173</b>. In this embodiment, only two protrusions <b>181</b> are provided. The protrusions <b>181</b> are ramped or inclined such that engagement with the flange <b>21</b> causes outward flexure (FIGS. 19<i>b</i>-<b>1</b>-<b>19</b><i>b</i>-<b>2</b>) of each end of the cross portion of the T-shaped collar <b>173</b>, until the flange <b>21</b> aligns with and is received within the groove portion <b>167</b><i>b </i>(FIGS. 19<i>c</i>-<b>1</b>-<b>19</b><i>c</i>-<b>2</b>). In this state, with the elbow <b>160</b> secured to the frame <b>20</b>, the collar <b>173</b> returns to its unflexed state. Portions of the flange <b>21</b> rest against lugs <b>165</b> provided within the space <b>183</b>.

[0158] The engagement between the collar <b>173</b> and the flange <b>21</b> during the snap-action connection of the elbow <b>160</b> and the frame <b>20</b> results in an audible click or sound indication. This sound indication is advantageous to signal the user that the elbow <b>160</b> is securely attached to the frame <b>20</b>.

[0159] To release the elbow <b>160</b> from the frame <b>20</b>, portions <b>185</b> on each side of the collar <b>173</b> are flexed towards one another in order to raise the protrusions <b>181</b> radially outwardly to allow passage of the flange <b>21</b>. In this manner, the elbow <b>160</b> can be quickly and easily removed from the frame <b>20</b> without accessing the interior portion of the nasal cavity, as would be the case with an elbow connected using a C-clip (FIG. 6<i>b</i>). As shown in FIG. 16<i>b</i>, a preferred form of the elbow <b>160</b> includes textured protrusions <b>185</b> to assist users to locate the release points. The distance between the opposed textured portions <b>185</b>, i.e., the diameter of the collar <b>173</b>, is approximately 35-45 mm, and preferably 40 mm.

[0160] The elbow <b>160</b> also is adapted to connect directly to the gas delivery tube <b>310</b> (FIG. 26) without the connector <b>300</b> shown in FIG. 23. (See FIG. 1). FIG. 6<i>b </i>shows the connector <b>300</b> between the elbow and the gas delivery tube <b>310</b>. Removal of the connector <b>300</b> is advantageous because the length of the effective lever arm of the combined elbow and connector <b>300</b> (FIG. 6<i>b</i>) may increase the possibility that unwanted levels of torque are applied to the frame <b>20</b> or mask assembly <b>10</b> relative to the patient's head/face. By eliminating the need to use the connector <b>300</b>, the effective length of the level arm can be reduced, which results in less torque being applied to the mask assembly which results in increased stability. With increased stability, patient comfort is increased and compliance is increased.

[0161] In the connected state, the inside surface of the wall <b>25</b> of the frame <b>20</b> sealingly engages the outside surface of the end portion <b>169</b> of the conduit as shown in FIG. 19<i>a</i>-<b>19</b><i>c</i>-<b>2</b>. These surfaces engage one another for a distance of approximately 1-10 mm, preferably 6 mm, which helps to seal as well as to provide stability to the connection between the elbow <b>160</b> and the frame <b>20</b>. As seen in FIGS. 19<i>c</i>-<b>1</b>-<b>19</b><i>c</i>-<b>2</b>, a portion of the wall <b>25</b> extends inside the mask <b>20</b> to further increase the area of contact between the elbow <b>160</b> and the frame <b>20</b>. In the connected state, an end portion <b>173</b><i>a </i>of the collar <b>173</b> is flush with the outside surface <b>20</b><i>c </i>of the frame <b>20</b>, as shown in FIGS. 19<i>c</i>-<b>1</b>-<b>19</b><i>c</i>-<b>2</b>. The wall <b>25</b> includes a flange <b>25</b><i>a </i>(FIGS. 19<i>c</i>-<b>2</b>) to form a stop for the insertion of the end portions <b>169</b>, and to permit a controlled leak between the elbow <b>160</b> and frame <b>20</b>. In one embodiment, the leak between the elbow <b>160</b> and frame <b>20</b> is minimal. In another embodiment, a seal is provided between the elbow <b>160</b> and frame <b>20</b> to prevent a leak.

[0162] This system allows for the rapid and precise connection between the elbow <b>160</b> and the frame <b>20</b>. It also allows for simple disassembly. Moreover, the elbow <b>160</b> is configured to allow the patient to attach and detach the elbow <b>160</b> from the frame <b>20</b> with one hand. This is advantageous when cleaning the mask or if the patient should choose to interrupt treatment during a session, while intending to resume treatment a short time later. The elbow assembly <b>60</b> and frame <b>20</b> connection allows the patient to rapidly disconnect the elbow <b>160</b> from the blower's gas delivery tube while keeping the mask frame, cushion and headgear in place on the patient's head during a momentary treatment interruption. The aperture <b>24</b> is large enough to lower impedance, to thereby enable the patient to breathe comfortably since a sufficient amount of gas can be accommodated by the aperture <b>24</b>. Specifically, the aperture <b>24</b> has an area of at least 180 mm². In one embodiment, the aperture <b>24</b> has a diameter in the range of 20-30 mm, preferably 27 mm, and an area in the range of 200-600 mm², preferably in the range of 500-600 mm². As illustrated, the aperture has a generally circular shape. However, the aperture may have a non-circular shape. Further, the frame may have a plurality of apertures therethrough with the elbow coupled to the frame such that it surrounds the plurality of apertures. In this respect, a mask in accordance with an embodiment of the invention differs from prior art mask arrangements which included quick release mechanisms with narrower apertures. Such narrower apertured quick release mechanisms could lead to patient discomfort, for example anxiety or claustrophobia. Discomfort is exacerbated by increased CO₂re-breathing or increased flow impedance.

[0163] Vent Cover

[0164] Vent cover <b>180</b> includes a main body <b>182</b> having a lower bore <b>184</b>, curved portion <b>186</b> and top portion <b>188</b>. See FIGS. <b>20</b>-<b>22</b>. The main body <b>182</b> also includes at least one vent <b>190</b>, and in a preferred embodiment, a plurality of vents <b>190</b> extending from an interior of the vent cover to an exterior of the vent cover. Top portion <b>188</b> of vent cover <b>180</b> includes flange or aperture <b>192</b> for engaging latch <b>168</b> of swivel joint <b>160</b>. In the illustrated embodiment, the vent cover <b>180</b> includes an aperture <b>192</b>. The vent cover <b>180</b> is connected to the swivel joint <b>160</b> by placing the stem <b>166</b> of the swivel joint <b>160</b> through lower bore <b>184</b> of the vent cover <b>180</b>. The vent cover <b>180</b> is then moved toward the swivel joint <b>160</b> until the latch <b>168</b> extends through the aperture <b>192</b>, as shown in FIG. 1. This configuration allows for the vent cover <b>180</b> to remain in the vicinity of the elbow assembly <b>160</b> and/or mask assembly <b>10</b>, as it is captured by the elbow <b>160</b> or the gas delivery conduit. This is convenient in that should the vent cover <b>180</b> become dislodged during cleaning or by inadvertence, it will not drop and become lost, as it is retained by the mask assembly.

[0165] The curved portion <b>186</b> of the vent cover fits adjacent apron <b>170</b> of the swivel joint <b>160</b> to provide a generally air-tight seal between an interior of the vent cover <b>180</b> and the swivel joint <b>160</b>. In this manner, exhalation gases from an interior of the mask can flow through exhaust port <b>164</b> of swivel joint <b>160</b>, through the interior of the vent cover <b>180</b> and to the atmosphere through vents <b>190</b>. FIGS. 19<i>c</i>-<b>1</b> includes an arrow B that approximates the path exhaust gas follows when the vent cover is in position. This arrangement has an additional advantage in that the vent direction reduces or prevents irritation of a bed partner of the patient by gas flow from the mask. FIGS. <b>1</b>-<b>4</b> show the elbow <b>160</b> and vent cover <b>180</b> in the connected position. A spacer <b>163</b> is provided to ensure that the vent cover <b>180</b> is spaced sufficiently away from the exterior surface of the elbow <b>160</b>, which especially helps prevent the air gap from collapsing since the vent cover is preferably made of a resilient flexible material. Of course, the vent cover could be made of a plastic member somewhat like the cover used in the Ultra Mirage™, if desired. In addition, this vent arrangement can be replaced or supplemented using ResMed's vent assembly disclosed, for example, in U.S. patent application Ser. No. 09/021,541, incorporated herein by reference in its entirety.

[0166]FIGS. 18<i>b</i>-<b>18</b><i>e </i>illustrate another embodiment of the swivel elbow, indicated as <b>360</b>, that is adapted to be connected to the vent cover <b>380</b> illustrated in FIGS. 22<i>b</i>-<b>22</b><i>e</i>. As shown in FIGS. 18<i>b</i>, <b>18</b><i>c</i>, and <b>18</b><i>e</i>, the swivel elbow <b>360</b> includes a flange <b>361</b> provided at a distal end of a wall <b>362</b> surrounding the outlet of the exhaust port <b>364</b>. FIGS. 18<i>d </i>and <b>18</b><i>e </i>shows the intake port <b>365</b>, the exhaust port <b>364</b>, and a baffle <b>369</b> that separates the intake and outlet ports <b>365</b>, <b>364</b>. As illustrated in FIG. 18<i>e</i>, the baffle <b>369</b> has a curved configuration. Specifically, the baffle <b>369</b> curves generally downwardly as it extends from the inlet of the exhaust port <b>364</b> to the outlet of the exhaust port <b>369</b>. However, the baffle <b>369</b> may have a generally planar configuration similar to baffle <b>161</b> shown in FIG. 19<i>a</i>-<b>1</b>. Alternatively, the baffle may have any other suitable configuration to separate the intake and outlet ports <b>365</b>, <b>364</b>. As shown in FIGS. 22<i>b</i>-<b>22</b><i>e</i>, the vent cover <b>380</b> includes a main body <b>382</b> having a lower bore <b>384</b>, an intermediate portion <b>386</b> and top portion <b>388</b>. The main body <b>382</b> also includes a plurality of vent holes <b>390</b> extending from an interior of the vent cover to an exterior of the vent cover. The top portion <b>388</b> of the vent cover <b>380</b> includes a collar <b>392</b> for engaging the flange <b>361</b> of swivel elbow <b>360</b>. The vent cover <b>380</b> is connected to the swivel elbow <b>360</b> by placing the stem <b>366</b> of the swivel elbow <b>360</b> through lower bore <b>384</b> of the vent cover <b>380</b>. The vent cover <b>380</b> is then moved toward the swivel elbow <b>360</b> until the collar <b>392</b> latches onto the flange <b>361</b> of the swivel elbow <b>360</b>. The collar <b>392</b> is stretched to overcome the flange <b>361</b>, and firmly grips the flange <b>361</b> due to its resiliency and elasticity. In the illustrated embodiment, the collar <b>392</b> has a generally circular shape so that stress (“hoop stress”) applied to the flange <b>361</b> and wall <b>362</b> is evenly distributed. Similar to the embodiment of vent cover <b>180</b>, this configuration allows for the vent cover <b>380</b> to remain connected on in the vicinity of the swivel elbow <b>360</b> and/or mask assembly, as it is captured by the elbow <b>360</b> or the gas delivery conduit. The vent cover can be considered “self-holding” in that it can be held in place on the elbow to cover the exhaust passage without an additional securing mechanism. In addition, the vent cover is held onto the elbow via the ring-shaped lower bore <b>184</b> as the patient stretches the collar <b>392</b> over the flange <b>361</b>, which minimizes the chances for losing the vent cover if the first assembly attempt is not successful.

[0167]FIG. 22<i>f </i>shows the swivel elbow <b>360</b> and vent cover <b>380</b> in the connected position. As shown in FIGS. 18<i>c </i>and <b>18</b><i>e</i>, the swivel elbow <b>360</b> includes a wall <b>363</b> that ensures that the vent cover <b>380</b> is spaced sufficiently away from the exterior surface of the swivel elbow <b>360</b>, which especially helps prevent the air gap from collapsing since the vent cover <b>380</b> is preferably made of a resilient flexible material. The vent cover <b>380</b> includes a recess <b>389</b> (FIG. 22<i>c</i>) on an inner surface of the top portion <b>388</b> that engages the wall <b>363</b>.

[0168] Mask Cushion

[0169] The cushion is designed to rest on the face and apply pressure around its perimeter while minimizing and/or avoiding contact with pressure sensitive regions on the face. Some parts of the face require special attention to achieve a balance of pressure and seal. It is also desirable to provide a low profile mask to improve patient comfort level by improving stability, and to reduce the forces which may tend to pivot the mask relative to the patient's face. Properties are listed below with the measures taken to create a successful design.

[0170] The cushion has a face-contacting side and a non face-contacting side with a wall therebetween. The non-face contacting side of the cushion engages with the mask frame. In one form of the invention, the shape of the cushion on its face-contacting side, as per the view shown in FIG. 24<i>c</i>, is generally trapezoidal. In this aspect, the shape of the cushion on the face contrasts with prior art cushions having a generally triangular shape. An advantage of this trapezoidal shape is that it assists sealing at a point lower down the nose without impeding flow through the patient's or user's nasal vents (that is, in the region of the lateral nasal cartilage and just below the nasal bone on either side of the nose). Thus, the cushion is positioned on a lower portion of the nasal bridge region of the patient. Moreover, the cushion is configured and positioned such that contact pressure of the cushion on the nasal vents is minimized or eliminated. The shape of the cushion may be altered, e.g., a triangular or other non-trapezoidal shape could be used, keeping in mind that localized pressure points on the lower nasal bridge region and occlusion of the nasal vents should be avoided. Some prior art mask cushions push on the nasal vents which can increase the impedance of the nasal vents to airflow. In a preferred form of the cushion, both the face-contacting and non face-contacting sides of the cushion have the same general trapezoidal shape.

[0171] In one form of the invention, a combination of support structure and sealing structure is provided in the region of the face contacting side of the cushion. The support and sealing structures may be provided as part of the cushion, or alternatively using separate components. Where the support and sealing structures are provided as part of the cushion, the cushion may have a single-walled, double-walled or triple- or more walled construction. In a preferred form of cushion, the sealing structure is provided by a thin membrane, whereas the support structure is provided by a thicker frame.

[0172] The center and sides of the nasal bridge are particularly sensitive to contact pressure. Thus, it is important that the cushion seals as lightly as possible in this area. Instability of the cushion may cause an increased pressure in the nasal bridge region and thus presents an extra challenge in this area. The supporting element (e.g., frame <b>200</b> shown in FIG. 24<i>a</i>) can be designed to totally avoid contact with the adjacent portion of the overlying face-contracting element (e.g., membrane <b>205</b> shown in FIG. 24<i>a</i>), thereby allowing the membrane <b>205</b> alone to seal. While localized points of contact pressure should be avoided in the nasal bridge region, especially at the sensitive apex thereof that contacts the lower nasal bridge region, the seal must be maintained. The lower nasal bridge region is positioned generally where the bony region of the nasal bridge transitions to a portion of the nose containing more cartilage. In addition, the forces that are applied to the face should be substantially evenly distributed around the entire perimeter of the cushion <b>40</b>. An aspect of the invention is that the facial contact pressure is controllably distributed around the face. Of course, the forces applied to the lower nasal bridge region can be spread out along a relatively wider section of the membrane <b>205</b>, to avoid the localized forces, while the forces in the lip and cheek regions can be slightly more localized, e.g., spread out over less distance in the width direction, since forces can be more comfortably accommodated in the lip and, particularly, in the cheek regions. Moreover, the contact area or width between the membrane and the face in the lower nasal bridge region may be greater than the contact area or width between the membrane and the lip and cheek regions, while maintaining a relatively constant overall force distribution around the face of the patient, which improves comfort. Using this arrangement, the patient perceives that the pressure is evenly distributed over the contact region, even though the actual force over the contact region may not be evenly distributed.

[0173] Another advantage is that the angle of the cushion with respect to the patient can change without adversely affecting sealing efficiency. For example, the cushion may contact different patients at different angles based on the shape of the patient's face, and the angle of the cushion can move with respect to the face during movement when the patient is asleep.

[0174] The sealing element (e.g., membrane <b>205</b>) incorporates a large effective rolled over section (large radius) to allow some degree of movement or rotation of the mask relative to the patient's face and prevents the membrane distal edge from irritating the patient's face and/or nose. The sealing element (e.g., membrane) snugly seals against the nose by conforming around a lower portion of the nasal bridge at sides of the nose. A compromise must be reached between a secure seal and membrane tightness/stretching across the nose. The membrane cutout can be notched to enable maximum stretch distance without edge tightness. Stretch can also be achieved by materials, for example softer material and or thinner materials, for example, elastomer, silicone, polyurethane, thermoplastic elastomers, foamed elastomers and/or composites.

[0175] The sealing element (e.g., membrane) is preferably elastomeric having a thickness in the range of 0.1 and 2.0 mm, preferably 0.35 mm, to allow the membrane to stretch readily over the lower portion of the nasal bridge. The stretch of the membrane may be varied in different regions by varying its thickness, adding stiffening structure such as ribs, or using composites.

[0176] Facial wrinkling is most pronounced at the facial or nasal crease between the sides of the nose (also known as the naso labial sulcus) and the cheek and presents a challenge in effective sealing. The underlying cushion (e.g., frame <b>200</b> shown in FIG. 24<i>a</i>) sits as close to the sides of the nose as possible. In this way it seals in the flattest area possible. The curved area designed to sit in the facial crease should have as small a radius as is practical. The membrane <b>205</b> extends inwardly and/or downwardly further than the edge of the cushion (e.g. rim <b>225</b>) to allow rolling around the outer edge at the sides of the nose. This lessens the likelihood of irritation arising from rough edges and prevents the inner cushion rim <b>225</b> from being a source of irritation against the patient's face and/or nose.

[0177] Excess pressure across the top lip can be caused by both cushion design and by the vertical rotation of the mask under its own weight, or by undesirable force applied to the mask, for example, due to tubing drag or the weight of components attached to the mask. The design of the headgear, as described above, can help reduce the possibility of adding unwanted pressure to the lip region due to vertical rotation of the mask under its own weight. The lip region <b>42</b> may include a notch to accommodate the bottom of the septum of the patient, to enhance sealing and comfort, as shown in FIG. 24<i>g</i>. The septum notch <b>264</b> would be provided in region <b>265</b>, as shown in FIG. 24<i>c</i>. FIGS. 24<i>a </i>and <b>24</b><i>b </i>show front and rear views of the cushion <b>40</b>. In an alternative embodiment, a septum notch may also be provided on the underlying frame.

[0178] The cushion <b>40</b> preferably has a generally trapezoidal shape in this embodiment. However, the cushion <b>40</b> may have a non-trapezoidal shape such as a triangular shape. The cushion <b>40</b> includes a pair of cheek regions <b>41</b> to provide a seal in the crease between the cheeks and the sides of the nose, a lip region <b>42</b> provided to provide a seal below the nose and above the upper lip of the patient, and a nasal bridge region <b>43</b>. The nasal bridge region <b>43</b> spans across the lower portion of the bridge and sloping sides of the bridge that intersect with the nasal crease formed between the cheeks and the sides of the nose. The transition between the lip region <b>42</b> and each cheek region <b>41</b> is where the cushion <b>40</b> begins to turn around the bottom of the nose towards the side of the nose. The transition between the nasal bridge region <b>43</b> and each cheek region <b>41</b> is where each cheek region <b>41</b> diverges upwardly towards the bridge of the nose. In other words, the nasal bridge region <b>43</b> starts where the cheek region begins to angle upwardly. See FIG. 24<i>d. </i>

[0179] The nasal bridge region <b>43</b> is designed to contact the patient's nose, for example, as shown in FIG. 1, where it can be seen that the lower portion of the bridge is selected for contact. Note that FIG. 1 shows the cushion <b>40</b> spaced away from the frame. However, pictures in Appendix C of incorporated U.S. Provisional Application of Moore et al., Serial No. 60/402,509, show the nasal mask assembly attached to two model noses (A &amp; B), described further below. More specifically, the nose includes relatively bony sections at the upper portion of the bridge, and flexible cartilage at the tip of the nose. Reference may be had to Gray's Anatomy, Thirty-Eighth Edition (1995), Figures 6.133A, B, 6.135A and 11.3A, B, incorporated herein by reference for drawings showing these regions. It is desirable to avoid localized pressure points along the bony region of the nose, to increase comfort to the patient. Conversely, it is desirable to avoid mask contact with only the cartilage portion of the nose, because its flexibility may allow too much unwanted movement of the cushion in use, may occlude the nasal passages of the patient, and may not provide a stable fit. In addition, positioning on the tip of the nose may increase the distance between the center of gravity of the mask assembly of the face of the patient—an undesirable consequence.

[0180] Accordingly, the optimal region of sealing engagement between the cushion and the bridge is somewhere between the uppermost bony region and the lower cartilage region of the nose. Optimally, the region of contact is just above the cartilage on the bone. Generally, the cushion can sit on the bone along the center of the nose, but it needs to avoid areas of cartilage on the sides of the nose. The nasal length and other appropriate dimensions can be measured from the base of the nose and the transition, or it can be obtained from statistical information on human anatomy. Samples of typical dimensions which are considered include one or more of those found in FIGS. 30 and 31. However, the cushion may not contact the patient in the lower nasal bridge region (positioned generally where the bony region of the nasal bridge transitions to a portion of the nose containing more cartilage) in all cases due to differences in the facial contour for each individual patient.

[0181] The cushion <b>40</b> is designed to accommodate most of the patient population (e.g., 80% of the patient population) in one or more sizes, preferably one to three sizes. The distance between the base of the nose and the top of the bridge is longer than the distance between the base of the nose and the transition between bone and cartilage. The cushion <b>40</b> can be made compact and/or lightweight since it need not accommodate the entire length of the nose. This frees designers to optimize or improve other areas of the cushion <b>40</b> and increases the patient's field of view while wearing the mask. Certain facial dimensions have been identified for optimal mask design to maximize the portion of the population that can be accommodated. In one embodiment, a series of color coded cushions is used. The cushion may be color coded for type or size, for example.

[0182]FIGS. 24<i>a</i>-<i>g </i>show additional views of the cushion <b>40</b>. As shown in FIG. 24<i>e</i>, the cushion <b>40</b> includes a frame <b>200</b> and a membrane <b>205</b> attached to the frame. The frame <b>200</b> and membrane <b>205</b> are formed, for example, in a one-shot injection molding process as is known in the art, using, e.g., silicone such as SILASTIC™ with 40 durometer hardness. Of course, the frame <b>20</b> and the membrane <b>205</b> can be formed from two different pieces that are connected together and/or to the frame <b>20</b>. The frame <b>200</b> has an edge <b>210</b>, which may be attached to the channel <b>26</b> of the frame <b>20</b>, as described in relation to FIGS. 27<i>a</i>-<b>29</b><i>d</i>. The edge <b>210</b> of the frame <b>200</b> may be attached to the frame <b>200</b> with clips, straps, friction or interference, direct molding to the frame, adhesives and/or a tongue and groove arrangement, as is known in the art. The edge <b>210</b> and a central portion or sidewall <b>215</b> above the edge <b>210</b> has a thickness which is able to withstand buckling forces which can be applied when the cushion <b>40</b> is placed in engagement with the channel <b>26</b> of the frame. In one form the central portion <b>215</b> has a thickness of 2-10 mm, preferably 5 mm. The central portion <b>215</b> extends from the edge <b>210</b> to a transition line <b>220</b> where the thin membrane <b>205</b> joins with the underlying frame <b>200</b>, between the frame <b>200</b> and the membrane <b>205</b>. In the preferred embodiment, the height of the central portion <b>215</b> of the frame <b>200</b> is most in the cheek regions <b>41</b> and less in the lip and nasal bridge regions <b>42</b>, <b>43</b>.

[0183] Beyond the transition line <b>220</b>, the frame <b>200</b> includes a rim <b>225</b>. In a preferred form, the rim <b>225</b> has a curved shape that curves inwardly into the nasal cavity of the cushion <b>40</b>. In an alternative form, the rim may be provided by a solid piece having a generally round cross-section. The membrane <b>205</b> forms a seal forming portion <b>270</b> (FIG. 24<i>e</i>) which contacts the patient in the lower nasal bridge region, cheek and lip regions <b>41</b>-<b>43</b>. The rim <b>225</b> has a thickness that is preferably less than the central portion <b>215</b> of the frame <b>200</b>, but preferably greater than the membrane <b>205</b>. For example, the membrane <b>205</b> has a thickness in the range of between about 0.1-2.0 mm, and preferably 0.35 mm, while the rim <b>225</b> has a thickness of between about 0.5 and 2.0 mm, and preferably 1.35 mm. While it is preferable that the membrane <b>205</b> be thinner than the rim <b>225</b>, they could have the same thicknesses. The membrane <b>205</b> completely covers and surrounds the rim <b>225</b> of the frame <b>200</b>, as shown in FIG. 25. The inside surface of the membrane <b>205</b> is spaced from the outside surface of the rim <b>225</b> so as to form a compliant seal with the patient. By compliant seal, it is meant that the membrane <b>205</b> can accommodate small variations in the shape of a patient's facial/nasal features without undue force, and can account for small movement of the mask relative to the patient during use, while maintaining an effective seal. The membrane <b>205</b> is preferably spaced away from the rim <b>225</b> at least in the nasal bridge region <b>43</b>, especially at a region <b>43</b><i>a </i>near the apex of the nasal bridge region <b>43</b> (FIG. 24<i>c</i>). This is because that area of the patient is most sensitive to localized contact pressure. Stated differently, the membrane <b>205</b> is preferably the only portion of the cushion <b>40</b> that contacts the patient to apply a sealing force to the patient in the lower portion of the nasal bridge region <b>43</b>. The membrane <b>205</b> can better evenly distribute the force across the entire bridge of the nose, applying a lighter pressure, thereby improving comfort. Of course, the sealing force applied to the transition between the bony region and the cartilage region of the nose is not so great as to partially or wholly close the nasal vents.

[0184] The rim <b>225</b> in the nasal bridge region, especially at the apex thereof, is spaced a sufficient distance away from the membrane <b>205</b> to avoid localized pressure points or regions on the lower bridge region of the nose. Moreover, the rim <b>225</b> should be inwardly curved to evenly distribute forces which may cause the membrane <b>205</b> to contact the rim <b>225</b>. Such forces may be the result of over tightening the headgear <b>80</b> or instability due to patient movement. The cushion <b>40</b> is designed to avoid contact between the rim <b>25</b> and the membrane <b>205</b> in the lower nasal bridge region even if the headgear <b>80</b> is over-tightened. In that event, the rim <b>225</b> in the lower nasal bridge region (at least at the apex <b>43</b><i>a</i>) can be eliminated to save material and weight, so long as the structural integrity of the cushion <b>40</b> is not compromised. Moreover, the rim <b>225</b> need not be curved along the entire perimeter thereof, especially those portions that are designed not to contact the membrane <b>205</b> in use.

[0185] Spacing between the membrane <b>205</b> and the rim <b>225</b> in the cheek and lip regions <b>41</b>, <b>42</b> is not necessary, but will add comfort and enable the cushion <b>40</b> to fit a wider range of patients due to the compliant membrane <b>205</b>.

[0186] A cushion in accordance with the invention provides improved stability over prior art cushions. The footprint, or contact area has been maximized, particularly along the sides of the nose. The side contact regions of the cushion have been maximized. This provides two further advantages. First, since the side walls of a cushion in accordance with the invention are longer than some prior art cushions, it is possible to design a mask which seals above the nasal vents but below the upper portion of the nasal bridge. Second, by distributing the contact pressure over a larger footprint, or contact area, stability of the mask assembly is improved. As such, the cushion <b>40</b> is much less likely to rotate in the vertical plane, as compared to prior art masks which tend to rotate about an axis substantially over the lip region.

[0187]FIGS. 25<i>d</i>-<b>25</b><i>i </i>show cross sections of the cushion <b>40</b>. As shown in FIG. 25<i>d</i>, the distance between the rim and the membrane in the nasal bridge region <b>43</b> is in the range of about 5-14 mm, preferably 9 mm. As shown in FIG. 25<i>e</i>, the distance between the rim and the membrane is in the range of about 7-16 mm, preferably 11 mm. As shown in FIGS. 25<i>f</i>, <b>25</b><i>g</i>, <b>25</b><i>h</i>, and FIGS. 25<i>d </i>and <b>25</b><i>i </i>in the lip region, the distance is in the range of about 1-6 mm, preferably 4 mm.

[0188]FIGS. 25<i>d</i>-<b>25</b><i>i </i>also show various other dimensions in one preferred embodiment, such as the radii of curvature, the angles at which the membrane extends, etc. For example, at the apex of the nasal bridge region, in FIG. 25<i>d</i>, the radius of curvature of the membrane is in the range of about 5-14 mm, preferably 9 mm, with an angle of about 70-90 degrees, preferably 80 degrees. As shown in FIG. 25<i>e</i>, the radius of curvature is within the range of about 4-10 mm, preferably 7 mm, with an angle of about 50-70 degrees, preferably 60 degrees. Generally, the spacing in the nasal bridge region <b>43</b> should be more than the spacing in the cheek and lip regions <b>41</b>, <b>42</b>. Of course, a cushion with a combined membrane and rim could be provided as well, e.g., a one layer structure. Conversely, the support function of the rim <b>225</b> could be accomplished using two or more support rims to support the membrane <b>205</b>, or two or more membranes could be provided over a single rim. In another alternative, the support function of the rim and the sealing function of the membrane can be split into two different members, which may be made of different materials.

[0189]FIG. 24<i>e </i>shows that the membrane <b>205</b> includes a preformed, contoured notch <b>255</b> in the nasal bridge region <b>43</b> to match generally the typical contours of the lower portion of the bridge region of the patient. The frame <b>200</b> includes a notch <b>260</b> which is co-located in relation to the notch <b>255</b>. The shape of the notch <b>255</b> is generally U-shaped, while the shape of the notch <b>260</b> is generally wider than the notch <b>255</b>, and the notch <b>260</b> is generally U-shaped. As shown in FIG. 24<i>f</i>, the notch <b>255</b> has a depth d₁in the range of 12-27 mm.

[0190] As seen in FIGS. 24<i>a</i>-<i>c</i>, an inner edge <b>230</b> of the membrane <b>205</b> defines an aperture <b>235</b> of the membrane <b>205</b>. In this preferred form, the shape of the aperture <b>235</b> is generally trapezoidal and has a base width w of about 31-45 mm, sides with a length s of 20-22 mm, and a top portion t, generally parallel to the base portion with a length of about 5-10mm. See FIG. 24<i>c</i>. The included angle a is in the range of 45°-55°, and preferably 50°. The height h between the base portion and the top portion of the membrane <b>205</b> is in the range of 19-22 mm. Further, the overall height h_oof the cushion <b>40</b> is in the range of 45-55 mm, preferably 50-51 mm and the overall width w_oof the cushion <b>40</b> is in the range of 65-75 mm, preferably 69-71 mm. Also, as shown in FIG. 24<i>f</i>, the dimension d₂of the cushion is in the range of 29-31 mm and the dimension d₃of the cushion is in the range of 41-43 mm. In one embodiment of a cushion <b>40</b> that has a “standard size”, the membrane <b>205</b> of the cushion <b>40</b> has a width w in the range of 31-34 mm, preferably 33 mm, a height h in the range of 19-28 mm, preferably 22 mm, and the notch <b>255</b> has a depth d₁in the range of 19-23 mm, preferably 21.5 mm. In another embodiment of a cushion <b>40</b> that has a “deep” size, the membrane <b>205</b> of the cushion <b>40</b> has a width w in the range of 31-34 mm, preferably 33 mm, a height h in the range of 19-28 mm, preferably 22 mm, and the notch <b>255</b> has a depth d₁in the range of 22-27 mm, preferably 24 mm. In yet another embodiment of a cushion <b>40</b> that is wider and/or shallower in depth (“wide/shallow”), the membrane <b>205</b> of the cushion <b>40</b> has a width w in the range of 35-45 mm, preferably 41 mm, a height h in the range of 19-28 mm, preferably 22 mm, and the notch <b>255</b> has a depth d₁in the range of 12-20 mm, preferably 16 mm. It is to be understood that these dimensions refer to a particular embodiment of the invention, and a differently sized mask (for example, a “small” size versus a “large” size) while having the same shape would have different dimensions and nevertheless be within the scope of the invention. Further, while the “standard” size cushion, “deep” size cushion, and “wide/shallow” size cushion may be provided individually, these cushions may be provided together as a set of cushions. This set of three cushions provides a good fit in a wide range of patients without having an excessive inventory.

[0191] The sides s of the membrane <b>205</b> adjacent the aperture <b>235</b> include a curved portion <b>250</b> (FIG. 24<i>c</i>) between the nasal bridge <b>43</b> and lip regions <b>41</b>. The curved portion <b>250</b> appears as a bulged portion curving inwardly toward the aperture <b>235</b>. In FIG. 24<i>f</i>, the curved portion <b>250</b> appears outwardly bulged in relation to the adjacent surfaces. FIG. 24<i>e </i>also shows the depth of the notch <b>255</b> provided in the membrane <b>205</b> in the nasal bridge region, as seen from the top view. FIG. 24<i>d </i>provides yet another view of the curved portion <b>250</b>, and the shape of the membrane <b>205</b> in relation to the underlying shape of the rim <b>225</b>. The curved portion <b>250</b> helps provide a good seal along the sides of the nose in the crevice where the cheek meets the nose. For example, as seen in FIG. 24<i>c</i>, the portion <b>250</b> is spaced away from the edge of the rim <b>225</b> so that more allowance for sealing in the crease and along the sides of the nose is provided. The edge <b>240</b> of the rim <b>225</b> and the edge <b>230</b> of the membrane <b>205</b> in the cheek region <b>41</b> begin diverge away from one another at an angle, as seen in FIG. 24<i>c</i>. The spacing between the edges <b>230</b>, <b>240</b> of the membrane <b>205</b> and the rim <b>225</b> are smallest in the lip region <b>42</b>, and gradually increases in the cheek regions <b>41</b>, and is most in the curved portion <b>250</b> and nasal bridge region <b>43</b>, as shown in FIGS. 25<i>e</i>-<b>25</b><i>i. </i>

[0192] The inner edge <b>240</b> of the rim <b>225</b> which defines an aperture <b>245</b> is shown in FIG. 24<i>b</i>. The base width W of the aperture <b>245</b> is in the range of 38-45 mm. The length of each side S is in the range of 20-23 mm. The length of the top portion T is in the range of 15-20 mm. The height H between the base portion and the top portion of the is in the range of 32-36 mm. These dimensions, and all other dimensions provided herein, are preferred dimensions and could be changed depending on the particular application. While the shape of the aperture can also be characterized as generally trapezoidal, the trapezoid is not in the same proportions to the trapezoidal shape of the aperture <b>235</b> of the membrane <b>205</b>. The aperture <b>235</b> is smaller than the aperture <b>245</b>.

[0193] Further, the apertures <b>235</b> and <b>245</b> may have a triangular shape or other non-trapezoidal shape. Further, the overall shape of the cushion may be triangular or non-trapezoidal. The shapes of the apertures <b>235</b> and <b>245</b> and cushion may be similar to one another or may be different, e.g., the aperture <b>235</b> has a trapezoidal shape and the aperture <b>245</b> has a triangular shape.

[0194] The width of the membrane <b>205</b> as measured from the transition line <b>220</b> to the edge of the membrane <b>205</b> is greatest in the curved portion <b>250</b> and nasal bridge region <b>43</b>, less in the cheek regions <b>41</b>, and the least in the lip region <b>42</b>. The membrane <b>205</b> generally extends upwardly away from the transition line <b>220</b> in the nasal bridge, cheek and lip regions <b>41</b>-<b>43</b>. In the nasal bridge region <b>43</b>, the membrane <b>205</b> curves inwardly along a generally constant radius to terminate at the edge <b>230</b>. In the cheek regions <b>41</b>, the membrane <b>205</b> curves around the rim <b>225</b> and then inwardly away from the rim <b>225</b> at an angle generally toward the opposite bottom position of the frame <b>200</b>. In the lip region <b>41</b>, the rim <b>225</b> and the membrane have substantially the same shape. See FIGS. 25<i>d</i>-<b>25</b><i>i. </i>

[0195] Mask Frame and Cushion Connection System

[0196] The mask of the present invention may be fabricated in a manner where the mask frame and mask cushion are permanently attached to each other. For example, the mask frame and cushion may be formed from the same material in one piece where the elbow is attached as a separate piece. Alternatively, the mask frame and cushion may be formed as two pieces of the same or different material where the cushion and mask shell are attached in a permanent manner. The permanent attachment may be achieved through co-molding, adhesives, the use of clips or other mechanical means.

[0197] Alternatively, the mask frame and cushion may be attached by way of a method that allows for it to be detached and then re-attached repeatedly through the useful life of the mask, as will be described below. This allows for disassembly for effective cleaning and maintenance or even allows replacement if a part is worn out.

[0198] The mask shell and cushion connection system of the present invention allows for the manufacture of a combination mask frame and cushion that allows for the independent determination of forces for engagement of the cushion and disengagement of the cushion from the frame. Because of this ability, it is possible to fabricate a mask connection system where the engagement force is equal to the disengagement force, or where the engagement force is less than the disengagement force, or where the engagement force is greater than the disengagement force.

[0199] The connection system may be designed to achieve a disengagement force that is less than or greater than the force asserted upon the mask system at maximum treatment pressure.

[0200] Preferably the disengagement force (i.e. the force that will detach the cushion from the mask frame) will be greater than the force that would be asserted against the mask shell and cushion combination when the maximum treatment pressure is achieved in the mask chamber. By setting this lower limit for the disengagement force by reference to that force asserted against the frame and cushion combination, the likelihood of a mask disengaging during the application of treatment pressure is reduced.

[0201] While the minimum disengagement force is preferably determined by reference to the force asserted by treatment pressure, the maximum disengagement force ought to be no greater than the force that is capable of being comfortably exerted by a user when manually disengaging the mask to prevent inadvertent release and annoyance to the user. Preferably, the displacement force will be no greater than the force that may be comfortably exerted by a user.

[0202] The engagement force for the cushion (that is the force required to correctly connect the cushion to the mask shell) may be predetermined and achieved by adoption of the sealing and retaining mechanisms of the present invention.

[0203] Preferably the engagement force will be no greater than the force that may be comfortably exerted by the user. As the present invention has application in a mass-produced product range, preferably the maximum engagement force will be no greater than the force that may be exerted by the target user population. In a clinical setting that target population may be the clinical staff who will be fitting and applying the mask to patients. In a non-clinical setting that target population may be the population of end users. Preferably the target engagement force would be determined by considering the preferred engagement force that may be exerted by the target population when manipulating the mask shell and cushion in a conventional manner. Of course, these principles also apply to the disengagement force as well.

[0204] In one embodiment of the nasal mask assembly <b>10</b>, an improved mechanism is used for engaging, i.e., retaining and sealing, the cushion <b>40</b> to the frame <b>20</b>. See FIGS. 27<i>a</i>-<b>29</b><i>d</i>. With the retaining and sealing mechanism, the cushion <b>40</b> can be fitted to the mask frame <b>20</b> in one movement that retains the cushion <b>40</b> and forms a secure seal with the frame <b>20</b>. Outer wall <b>30</b> of channel <b>26</b> on frame <b>20</b> is provided with a plurality of undercuts <b>33</b> spaced around the outer wall <b>30</b>. The undercuts <b>33</b> can pass partially or completely through the outer wall <b>30</b>. A slight taper can be provided to the interior surfaces of inner wall <b>28</b> and outer wall <b>30</b> to ease assembly of the cushion <b>40</b> to the frame <b>20</b>. The cushion <b>40</b> includes a side wall <b>215</b>. As shown in FIG. 25<i>d</i>, the side wall <b>215</b> has a width b of about 5 mm. The side wall <b>215</b> includes a plurality of retention lips <b>44</b>, spaced around the side wall <b>215</b> to align with the undercuts <b>33</b>. Each retention lip <b>44</b> includes a leading edge <b>45</b>, tapered to ease insertion of the cushion <b>40</b> into the channel <b>26</b>, and a retention surface <b>431</b>, shaped to catch the undercut <b>33</b> and prevent separation of the cushion <b>40</b> from the frame <b>20</b> until a predetermined separation force is applied between the cushion <b>40</b> and the frame <b>20</b>. Preferably the predetermined separation force is designed to be greater than the force to insert the cushion <b>40</b> into the channel <b>26</b>. Distally positioned on the side wall <b>215</b> are upper and lower sealing lips <b>46</b> and <b>47</b> extending outward from the side wall <b>215</b> and running around a periphery of the side wall <b>42</b>. Opposite the sealing lips <b>46</b> and <b>47</b> are upper and lower sealing lips <b>49</b> and <b>48</b> extending inward from the side wall <b>215</b> and running around an inner periphery of the side wall <b>215</b>. Opposite the retention lips <b>44</b>, the inner surface of the side wall <b>215</b> has a relieved portion <b>50</b> thus creating a space between the wall of the cushion and the channel allowing the wall of the cushion <b>40</b> to distort into the relieved portion <b>50</b>, as shown in FIGS. 27<i>b </i>and <b>27</b><i>e</i>, making insertion of the cushion <b>40</b> easier. The relieved portion <b>50</b> can be positioned just opposite each retention lip <b>44</b> or the relieved portion <b>50</b> can extend all the way around an inner periphery of the side wall <b>215</b>.

[0205] Assembly of the cushion <b>40</b> to the frame <b>20</b> according to one embodiment of the invention will now be described. The cushion <b>40</b> is first generally aligned with the channel <b>26</b>. See FIG. 27<i>a</i>. The inner wall <b>28</b> is slightly higher than the outer wall <b>30</b> to assist in aligning the cushion <b>40</b> with respect to the channel <b>26</b> before the cushion <b>40</b> enters the channel <b>26</b>. The cushion <b>40</b> is then moved into the channel <b>26</b>. See FIG. 27<i>b</i>. The leading edge <b>45</b> of each retention lip <b>44</b> will engage a top portion of the outer wall <b>30</b> and begin to deform. The relieved portion <b>50</b> of the side wall <b>215</b> allows this deformation to happen without greatly increasing the force necessary to insert the cushion <b>40</b> into the frame <b>20</b>. The sealing lips <b>46</b>-<b>49</b> have contacted the respective surfaces of the inner and outer walls <b>28</b> and <b>30</b> of channel <b>26</b>. The cushion <b>40</b> is further inserted into the channel <b>26</b> until it bottoms against the channel floor <b>32</b>. See FIG. 27<i>c</i>. The sealing lips <b>46</b>-<b>49</b> are in full contact with the inner and outer walls <b>28</b> and <b>30</b>. Each retention lip <b>44</b> has entered the respective undercut <b>33</b> but there is still deformation of the side wall <b>215</b>, accommodated by the relieved portion <b>50</b>. The cushion <b>40</b> is then slightly withdrawn as compression of the elastomer (Silastic™) relaxes from the channel <b>26</b>, seating the retention surface <b>431</b> of each retention lip <b>44</b> against the respective undercut <b>33</b>, with the sealing lips <b>46</b>-<b>49</b> in continuous sealing position around the inner and outer walls <b>28</b> and <b>30</b>. See FIG. 27<i>d</i>. This withdrawal and seating provides a tactile signal to the user that the cushion <b>40</b> is properly seated in the channel <b>26</b>. If the undercuts <b>33</b> are made visible to the user in this position, a visual indicator of seating is also provided. Deformation of the side wall <b>215</b> has generally been removed at this point and the relieved portion <b>50</b> returned to its relaxed configuration. Further withdrawal of the cushion <b>40</b> from the channel <b>26</b>, to disassemble the cushion <b>40</b> from the frame <b>20</b> will deform the retention lip <b>44</b> downward. See FIG. 27<i>e</i>. This deformation of the side wall <b>215</b> will again be accommodated by the relieved portion <b>50</b>. The shape of retention lip <b>44</b> results in the preferred more secure removal force compared to assembly force by the user.

[0206] Furthermore, where the cushion sealing lips or retention lip or both are made of a material that expands over time such as with some chemical cleaning exposure (i.e. increases in size in at least one dimension) such a material being silicone, the extra size or volume resulting from spread of material may be accommodated within the channel <b>26</b>, say by the sealing lips or retention lip flexing. This aspect of the invention has advantages over the prior art in that the spread of cushion material ought not compromise the seal of the mask shell and cushion, thereby prolonging the useful life of the component made of the expandable material.

[0207] The prior art typically requires the cushion material to achieve a snug fit with the frame so as to prevent leakage of gas from the mask chamber via one or more paths between the frame and cushion. In addition some masks utilized an interior or exterior cushion clip to sandwich the cushion between the clip and the frame. Such cushion clips are found in Respironics' ComfortSelect mask, and in ResMed's Ultra Mirage™ mask, which is described in U.S. Pat. No. 6,412,487, incorporated herein by reference.

[0208] With the prior art, should the cushion be made of a material that spreads with time, there is a tendency for the material to increase in at least one plane to the extent that it becomes difficult to fit or disengage from the mask frame channel, or to otherwise make use of a cushion clip. Also, the seal to prevent gas escaping from the mask chamber is compromised due to gaps appearing between the cushion seal portion and the mask frame channel. The prior art limitations have been described with reference to a mask which has the sealing channel located in the frame and the sealing edge located on the cushion. However, similar limitations will apply where the location of these features are reversed, that is to say where the sealing channel is located on the cushion and the sealing edge is located on the mask shell as well as where the interface between the cushion and mask shell surface are in the form of flat surfaces.

[0209] As treatment pressure within the mask chamber is not being achieved during mask assembly, the selection of engagement pressure is not necessarily determined by reference to the force exerted during treatment. Rather, it is possible to fabricate the connection system of the present invention so as to achieve an engagement force that is less than the disengagement force—such a configuration, where the engagement force is less than the disengagement force is consistent with data that any given human population is typically capable of exerting a pulling force (i.e. where one or two hands move away from a starting point while gripping an object) than they are capable of exerting a pushing force (i.e. where one or two hands move towards a fixed point while gripping an object).

[0210] The embodiment described above can maintain the relationship of a disengagement force being greater than an engagement force notwithstanding that a dimension of a component may change over time—such as is the case where the cushion is made of a material that expands over time such as is the case with silicone.

[0211] The embodiments of the present invention also overcome the prior art limitation of loss of friction fit where at least one component such as the cushion is made of a material that tends to lose its frictional quality over time, such as with silicone which material tends to become ‘greasy’ due to chemical change and its own absorption of environmental pollutants, such as the patient's skin oil. Accordingly, the present invention addresses the prior art problem of a loss of engagement effect between the frame and cushion over time notwithstanding the loss of the friction between them.

[0212] While the present invention teaches away from the need for strap, clip or other additional retaining devices, such devices may be included in the fabrication so as to add further security of engagement between frame and cushion or to otherwise reduce the design tolerances required to achieve a disengagement force that is consistent with the upper limit considered appropriate for the target population while maintaining engagement during the maximum treatment pressure.

[0213] The cushion <b>40</b> includes at least one sealing lip which functions to prevent escape of gas from the mask chamber via the interface between frame and cushion. Preferably there are provided at least two seal lips each having relatively small contact points with the frame channel <b>26</b> as shall be described so as to minimize the friction occurring during assembly and disassembly of the cushion with the frame without compromising the seal.

[0214] If one seal lip were used, then its configuration to achieve adequate sealing may require it to assert greater friction once in position than would be the case where there were adopted two or more seal lips of the same material.

[0215] By control of this source of friction, it is possible to influence the engagement and disengagement forces, i.e., the forces required to engage and disengage the cushion and frame. The preferred aim being to have those forces remain with defined limits for the expected useful life of the cushion.

[0216] The relieved portion <b>50</b> of the side wall also accommodates deformation of the side wall <b>215</b> upon assembly and disassembly of the cushion <b>40</b> and frame <b>20</b>, thereby reducing the force necessary for assembly/disassembly. This is especially important where the cushion <b>40</b> is made from a pliable but generally slightly compressible material, such as silicone. Alternatively, the inner wall <b>28</b> can be provided with an undercut <b>29</b> opposite each undercut <b>33</b> to accommodate deformation of the side wall <b>215</b>. See FIG. 28. The undercut <b>29</b> (and/or relieved portion <b>50</b>) can be sized and configured as desired to best accommodate the expected side wall deformation. Different combinations of the sealing lips <b>46</b>-<b>49</b> can alternatively be used. See, for example, FIG. 29<i>a </i>(sealing lips <b>47</b> and <b>48</b>), FIG. 29<i>b </i>(sealing lips <b>46</b> and <b>49</b>), FIG. 29<i>c </i>(sealing lips <b>48</b> and <b>49</b>) and FIG. 29<i>d </i>(sealing lips <b>46</b> and <b>47</b>). Other configurations of sealing lips and retention lips can also be used. This configuration separates the sealing function of cushion to frame from the functions of cushion and frame engagement and retention, so that each may be independently controlled and optimised in device configuration and fabrication.

[0217]FIGS. 32<i>a</i>-<b>1</b>-<b>32</b><i>c</i>-<b>2</b> show sequential engagement between the frame <b>20</b> and the cushion, according to another embodiment of the present invention. In this embodiment, the side wall <b>215</b> has been changed, as well as the channel <b>26</b> which receives the side wall <b>215</b>. FIGS. 32<i>a</i>-<b>1</b>-<b>32</b><i>a</i>-<b>2</b> show the frame and cushion before engagement, FIGS. 32<i>b</i>-<b>1</b>-<b>32</b><i>b</i>-<b>2</b> show the frame and cushion during engagement and FIGS. 32<i>c</i>-<b>1</b>-<b>32</b><i>c</i>-<b>2</b> show the frame and cushion in full engagement.

[0218] In this embodiment, the side wall <b>215</b> preferably includes an integral lug <b>215</b><i>a </i>at a distal end of the side wall <b>215</b>. The side wall <b>215</b> includes an undercut <b>215</b><i>b </i>which allows the lug <b>215</b><i>a </i>to flex toward the side wall <b>215</b>. During insertion (FIGS. 32<i>b</i>-<b>1</b>-<b>32</b><i>b</i>-<b>2</b>), the lug <b>215</b><i>a </i>flexes into the undercut <b>215</b><i>b </i>until it is pushed beyond a protrusion <b>26</b><i>a </i>in the channel <b>26</b>. After passing the protrusion <b>26</b><i>a</i>, the lug <b>215</b><i>a </i>flexes into a space of the channel <b>26</b> below the protrusion <b>26</b><i>a</i>. Therefore, the tip of the lug is positioned to be resiliently locked in place with the cushion <b>40</b> fully and securely connected to the frame <b>20</b>. In the connected condition, the side wall <b>215</b> provides a secure seal with the frame <b>20</b> against escape of pressurized gas from the nasal cavity. Engagement between the tip of the lug <b>215</b><i>a </i>and the protrusion <b>26</b><i>a </i>provides a retaining force to maintain the cushion in engagement with the frame. To disengage, the patient pulls the side wall <b>215</b> out of the channel <b>26</b> with a force sufficient to cause the lug <b>215</b><i>a </i>to deform and overcome the protrusion <b>26</b><i>a</i>. Both engagement and disengagement require a force that is enough to overcome the frictional contact between the walls of the channel <b>26</b> and side wall <b>215</b>. As the angle of protrusion <b>26</b><i>a </i>is substantially away from the insertion direction, it acts in much the same way as a “barb” allowing the preferred lower insertion force compared to disassembly force of the cushion to mask frame.

[0219] In the illustrated embodiment, the lug <b>215</b><i>a </i>at the distal end of the side wall <b>215</b> extends generally inwardly towards the breathing cavity of the cushion. However, as shown in FIG. 32<i>e</i>, the lug <b>215</b><i>a </i>may extend generally outwardly from the breathing cavity of the cushion <b>40</b> and engage a protrusion <b>26</b><i>a </i>provided on the outer wall <b>30</b> of the frame <b>20</b>.

[0220] FIGS. <b>40</b>-<b>41</b> illustrate another embodiment of the frame <b>20</b> that is structured to facilitate the engagement between the frame <b>20</b> and the cushion <b>40</b>. Specifically, the main body <b>20</b><i>a </i>of the frame includes alignment symbols A₁, e.g., diamonds, lines, colors, arrows, etc., on the outer surface of the outer wall <b>30</b> thereof. FIG. 40 illustrates a single alignment symbol A₁provided on an upper portion of the outer wall <b>30</b> and FIG. 41 illustrates a pair of alignment symbols A₁provided on a lower portion of the outer wall <b>30</b>.

[0221] The cushion <b>40</b> includes alignment symbols A₂, e.g., diamonds, lines, colors, arrows, etc., on the outer surface thereof that are positioned to align with the alignment symbols A₁provided on the frame <b>20</b> when the cushion <b>40</b> and frame <b>20</b> are engaged with one another. FIGS. 38B, 39B, and <b>42</b> illustrate a single alignment symbol A₂provided on the outer surface of the cushion <b>40</b> in the nasal bridge region and FIG. 43 illustrates a pair of alignment symbols A₂provided on the outer surface of the cushion <b>40</b> in the lip region. When the cushion <b>40</b> and frame <b>20</b> are engaged with one another, the alignment symbol A₁on the upper portion of the frame <b>20</b> aligns with the alignment symbol A₂in the nasal bridge region of the cushion <b>40</b>. Similarly, the pair of alignment symbols A₁provided on the lower portion of the frame <b>20</b> align with the pair of alignment symbols A₂in the lip region of the cushion <b>40</b>. The alignment of the alignment symbols A₁, A₂on the frame <b>20</b> and cushion <b>40</b>, respectively, ensures that the frame <b>20</b> and cushion <b>40</b> are correctly aligned and oriented with respect to one another. That is, the patient can correctly engage the frame <b>20</b> and cushion <b>40</b> by ensuring that the alignment symbols A₁, A₂on the frame <b>20</b> and cushion <b>40</b> are correctly aligned with one another.

[0222] The alignment symbols A₁, A₂may have any suitable configuration, e.g., diamonds, lines, colors, arrows, etc. Also, any corresponding number of alignment symbols A₁, A₂may be provided on the frame <b>20</b> and cushion <b>40</b>. In the illustrated embodiment, the upper portion of the frame <b>20</b> and the nasal bridge region of the cushion <b>40</b> have a different number of alignment symbols A₁, A₂than the lower portion of the frame <b>20</b> and the lip region of the cushion <b>20</b>. However, the upper and lower portions of the frame <b>20</b> and the respective nasal bridge and lip regions of the cushion <b>40</b> may have the same number of alignment symbols A₁, A₂so long as the alignment symbols A₁, A₂are positioned to facilitate correctly engaging the frame <b>20</b> and the cushion <b>40</b> in the correct orientation. Further, the alignment symbols A₁, A₂may be positioned at any suitable location along the outer surfaces of the frame <b>20</b> and the cushion <b>40</b> to facilitate the engagement between the frame <b>20</b> and the cushion <b>40</b>.

[0223] As shown in FIG. 40, the frame <b>20</b> may include alignment symbols A₁, e.g., diamonds, lines, colors, arrows, etc., on the side frame members <b>20</b><i>b </i>which are structured to facilitate the engagement between the frame <b>20</b> and the headgear assembly <b>80</b>. Specifically, the locking clip <b>82</b> of the headgear assembly <b>80</b> may include alignment symbols, e.g., diamonds, lines, colors, arrows, etc., on the outer surface thereof that are positioned to align with the alignment symbols A₁provided on the frame <b>20</b> when the locking clip <b>82</b> and frame <b>20</b> are engaged with one another.

[0224] Other Aspects

[0225] A nasal cushion was designed taking into account the shape and size of the nose of the patient, along with the size and shape of the surrounding facial features, such as the upper lip, the cheeks, etc. See FIGS. <b>30</b>-<b>31</b>. While there is little statistical information regarding the sizes and shapes of those patients likely using or in need of some sort of NPPV treatment, Applicants have discovered that a select amount of criteria can be used to statistically model the cushion <b>40</b> to fit a vast majority of the patient population (e.g., 80% of the patient population). For example, the cushion <b>40</b> may be structured to accommodate 60-90% of patient population, regardless of age, sex, or race. However, the cushion <b>40</b> may be structured to accommodate up to 70% or up to 80% of patient population, for example. Using nasal width, nasal tip protrusion and nose height, Applicants have been able to design the cushion such that a large proportion of the population likely to be in need of nasal masks can be accommodated comfortably with the same sized cushions/masks. One or two additional cushions/masks can be designed to accommodate other parts of the population. Age, race and sex of the patient can be factors in computer modeling the cushion. Moreover, by designing a cushion in which contact with the upper portion of the nasal bridge portion is avoided, Applicants have been able to eliminate one of the factors which limits the designs of cushions in general.

[0226] As shown in FIGS. 30 and 31, the nasal width determines the width of the opening in the cushion <b>40</b>. Nasal tip protrusion describes minimum depth of cushion and mask frame combined. This is measured from the bottom of the septum. A mask with too much depth may result in excessive dead space within the nasal cavity that increases undesirable CO₂re-breathing and movement of the center of gravity of the mask assembly further away from the face decreasing stability. Nose height reflects the distance between both sets of width/depth dimensions.

[0227] In general, cushions are sized to fit one or more maximum dimensions. However, user testing is important in verifying clearance at the nasal vent. If too large, the cushion may interfere with the eye area. The cushion is designed to sit low on the nasal bridge; possible interference in this area is minimized. If the cushion is too small, e.g., if the cushion applies pressure along the soft part of the nose that may collapse, the nasal vent may be partially or fully occluded, causing breathing restriction, as can occur with some prior art masks such as the Respironics Simplicity mask. Nose width, height and tip protrusion can be arrived at by reference to anthropometric data tables.

[0228] In one embodiment of the mask system, the mask system is designed to include a frame and a plurality of cushions that are each connectable with the frame. Each cushion would be configured to accommodate a percentage of the patient population such that the plurality of cushions, preferably 1-3 cushions, would together accommodate up to 95-100% of the patient population.

[0229] Thus, the plurality of cushions would each have a similar frame contacting side but a different face contacting side. Each cushion would have at least one parameter on the face contacting side that is different from the remaining plurality of cushions. In one embodiment, each cushion may differ in the nasal bridge region. For example, the cushion <b>40</b><i>a </i>shown in FIGS. <b>38</b>A-<b>38</b>D has a deeper contoured notch <b>255</b><i>a </i>in the nasal bridge region than the contoured notch <b>255</b><i>b </i>in the nasal bridge region of the cushion <b>40</b><i>b </i>shown in FIGS. <b>39</b>A-<b>39</b>D. Specifically, the contoured notch <b>255</b><i>a </i>has a depth d in the range of 22-27 mm, preferably 24 mm and the contoured notch <b>255</b><i>b </i>has a depth d in the range of 19-23 mm, preferably 21.5 mm. As illustrated, the notch <b>255</b><i>a </i>has a smaller radius of curvature than the radius of curvature of notch <b>255</b><i>b</i>. In another embodiment, each cushion may differ in the width of the aperture of the membrane. The plurality of cushions may be color coded to help distinguish the different cushions from one another.

[0230] Appendix A of incorporated U.S. Provisional Application of Moore et al., Serial No. 60/402,509, includes various pictures of the mask system according to one preferred embodiment of the present invention. Appendix A also includes various pictures of the mask system according to other embodiments of the present invention. For example, an embodiment of the frame is provided that illustrates a frame having oxygen or pressure ports. See, e.g., FIG. 41. Further details of oxygen or pressure ports in a frame are included in U.S. patent application Ser. No. 09/504,234, the entirety of which is hereby incorporated by reference. Appendix A also includes instructional information for the mask system. Appendix B of incorporated U.S. Provisional Application of Moore et al., Serial No. 60/402,509, includes pictures of two prior art masks discussed in the present invention. Appendix C of incorporated U.S. Provisional Application of Moore et al., Serial No. 60/402,509, includes pictures of two testing models (A+B) with widely varying nose and facial features, and the mask assembly of the present invention as well as one prior art mask connected to each model. Appendix C also includes a series of pictures comparing one embodiment of the present invention to a prior art cushion used for the MIRAGE® mask. See, e.g., U.S. Pat. No. 6,112,746 to Kwok et al., incorporated herein by reference. Generally speaking, the mask assembly of the present invention generally conformed to both nose models even though the sizes and shapes were vastly different. The mask cushion <b>40</b> also was able to successfully accommodate the deformity on model B. The mask assembly of the prior art tended not to fit the shape of the nose models, especially the shape of the smaller nose model where significant gaps are seen. One prior art model (see U.S. Pat. No. 5,724,965) was relatively unstable and tended to rock on the cheeks of the models, especially the smaller nose model.

[0231] It is intended that the components, elements and features of the various above-described embodiments can be used together in any desired combination or permutation to create new mask embodiments. For example, while the invention has been described in relation to a nasal mask, the teachings are also applicable to oro-nasal and full-face masks as well.