A closed venous-cardiotomy reservoir with improved air handling

GOVERNMENT INTERESTS

0001This invention was in part made with government support under SBIR Grants # R44HL-55034 and R44-HL66810 awarded by the National Institute Health, National Heart, Lung, and Blood Institute. As such the government may have certain rights in the invention.

CROSS REFERENCE TO RELATED APPLICATIONS

0002This application claims the date of the provisional Patent Application Ser. No. <patcit id="pcit0001" dnum="US60538277B"><text>60/538,277 filed January 22,2004</text></patcit> and with Foreign Filing License Granted 02/13/2004 and entitled "A Soft. Shell Venous reservoir-Cardiotomy Reservoir with Improved Air Removal Capability" the disclosures of that application being incorporated herein by reference thereto.

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

0003The invention consists of an air purging system that removes gas bubbles from the venous blood during cardiopulmonary bypass. The air purging system, in combination with a compliant storage chamber having at least one pliable wall forms a venous reservoir that prevents gross air exiting the venous reservoir. In another embodiment, a cardiotomy reservoir is incorporated atop the storage chamber. Each device allows vacuum assisted venous drainage (VAVD). The combination of the three innovative features provides a collapsible "closed" venous reservoir unitized with cardiotomy reservoir having air removal features that match that of a hardshell venous-cardiotomy reservoir unit.

DESCRIPTION OF THE PRIOR ART

0004During cardiopulmonary bypass, blood flow from the venous side of the patient to a venous reservoir depends on the resistance of the fluid conduit between patient and reservoir and the pressure difference between patient and reservoir. When the reservoir is maintained at atmospheric pressure, that pressure difference is the height difference between patient and reservoir; the resulting flow is referred to as gravity drainage. Venous drainage by gravity alone provides inadequate return during procedures such as minimally invasive cardiac surgery and bypass via femoral cannulation. Usually it is the resistance of the venous cannula that limits the flow rate. Vacuum assisted venous drainage (VAVD) is a technique that overcomes flow limitations by applying suction to the venous reservoir thereby increasing the pressure difference between the venous cannulation site and venous reservoir. VAVD allows for a decrease in the inner diameter (ID) of the venous line, thereby reducing prime volume and enabling the use of a smaller internal diameter cannula, which translates to an easier insertion, better surgical view and a smaller surgical incision.

0005Clinically, venous bags are used because they provide significant safety features: if the bag accidentally empties, it collapses, thereby preventing gross air from being pumped to the patient, they have no, or very little, air-blood interface, and they require no antifoam agents that can embolize into the blood. Designs that allow VAVD with venous bags have been previously described by <patcit id="pcit0002" dnum="US6337049B"><text>Tamari's US-Patents 6,337,049</text></patcit> and <patcit id="pcit0003" dnum="US6773426B"><text>6,773,426</text></patcit>, and Cambron's Patent <patcit id="pcit0004" dnum="US6537495B"><text>6,537,495</text></patcit> titled "Vacuum-assisted Venous Drainage System with Rigid Housing and Flexible Reservoir". The present invention also allows the user the option of VAVD.

0006When air enters blood, the blood foams. Hard shell reservoirs have defoamers within the venous inlet chamber (e.g. see defoamer 6 in distribution chamber 22 of <figref idref="f0001">FIG. 1</figref> in Fini, <patcit id="pcit0005" dnum="US6287270B"><text>US Patent 6,287,270</text></patcit>, "Combined device comprising a venous blood reservoir and a cardiotomy reservoir in an extracorporeal circuit"). In the open, hard shell reservoir, air escapes by floating to the top of the reservoir where it is purged to atmosphere. In prior art venous bag reservoirs, air also floats to the top but it must be actively eliminated. This can be done manually with a syringe, or more frequently with a roller pump intermittently operating to remove air accumulating at the top of the bag. This is shown in <figref idref="f0001">FIG. 1</figref> where foam that accumulates at the top of collapsible venous reservoir 1103 is removed by suction pump 1114 that pumps that foam/air to cardiotomy reservoir 1115. With either method, a sudden large volume of air can overwhelm the air removal system and cause disastrous consequences, especially without a vigilant perfusionist. Further, sucking blood and foam through the small diameter of the tubes and stopcocks used at the top of current bags results in blood damage. Various solutions have been proposed. Tamari's Patent '049 and '426 eliminate air from a venous bag automatically by utilizing a floating ball valve, a hydrophobic membrane, or a level sensor. All three systems require suction to remove the air. Also, with current available membrane materials, the membrane has limited effective life.

0007Tamari's '049 and '426 patents also describe a blood chamber with a level sensor that activates a vacuum source to remove the air when the blood level in the chamber drops below that sensor. This design provides automated means to remove air from that chamber. Similar designs are proposed by Gremel (Pats # 6,302,860 and 6,524,267 both titled: "Venous filter for assisted venous return" and-assigned to Medtronic) and Stringer (<patcit id="pcit0006" dnum="US6773670B"><text>US Patent US 6,773,670</text></patcit>, titled "Blood filter having a sensor for active gas removal and methods of use"). All three automated air removal systems require a level sensor that detects air in the filter, suction to remove the air, and the associated electronics to assure that the suction is applied only when so indicated by the sensor. Doing otherwise removes blood from the reservoir or risking air entering the outlet of the reservoir. A more recent invention is described by <patcit id="pcit0007" dnum="US20040220509A"><text>Olsen et al in US Patent Application number 20040220509</text></patcit> entitled "Active air removal from an extracorporeal blood circuit". That design requires complicated electronics as displayed by FIGS 14 through 56 of that application. Further, all these systems handle foam by sucking it out as part of the air removal system, a procedure that over time can result in a large blood loss if that blood is not returned to the cardiotomy reservoir. The blood that is returned to the cardiotomy, is then exposed the aforementioned deleterious affects of the cardiotomy. It should be noted that one of the major objectives for "venous filters" with air removal capabilities is to enable the user to reduce the priming volume of the CPB circuit by removing the venous reservoir while still removing air and foam from the venous line prior to it entering the arterial pump. The present invention provides further reduced volume and improved air handling.

0008With prior art soft-shell venous reservoirs air may be trapped at the top of the liquid by the collapsed walls of the reservoir, see <figref idref="f0001">FIG. 1a and 1aa</figref> of Tamari's '049 patent. It is safer to have no air trapped in the bag. Tamari's '049 and '426 patents provide a vertical chimney that can eliminate air trapping; however, suction is still required to remove that air.

0009Active air removal required for venous bags also results in more difficult priming. Thus, once a bag is primed and the prime solution is recirculated, the air in the rest of the circuit is returned to the bag, again filling it with air. A better system would not allow air to return to the primed bag. This would reduce priming time and the possibility that air can remain in the bag.

0010State-of-the-art soft-shell venous reservoirs with a screen are poorly designed: a large portion of their screen contacts the internal walls of the bag rendering that portion of the screen ineffective and thereby increasing the resistance to blood flow across the screen. This is illustrated in <figref idref="f0001">FIG. 1a</figref>, a line drawing of a prior art bag made by Cobe, <figref idref="f0001">FIG. 1aa</figref>, a line drawing of a cross section along line 1a-1a' of the bag shown in <figref idref="f0001">FIG. 1a, and FIG. 1ab</figref>, an enlargement of the circled section of the bag shown in <figref idref="f0001">FIG. 1aa</figref>. As illustrated, at low volume most of the screen contacts the walls of the bag and is unavailable for blood flow. The contact area of the screen contacting the walls of the bag increases as the volume in the reservoir decreases. Two typical prior art venous bags exhibiting these problems are the ones described in United States Patent <patcit id="pcit0008" dnum="US5573526A"><text>5,573,526 issued to Hess</text></patcit>, titled "Soft shell reservoir", and in United States Patent <patcit id="pcit0009" dnum="US5720741A"><text>5,720,741 issued to Stewart, et al.</text></patcit>, titled "Venous reservoir bag assembly". The latter is depicted in the present application in <figref idref="f0001">FIG. 1a</figref> as PRIOR ART. One aspect of the present invention eliminates contact between the screen and the walls of the chamber housing it, thereby allowing the use of a screen with smaller area and/or smaller pores. Though Tamari's '049 and '426 patents illustrate designs that prevent the screen from contacting the wall of the reservoir, (e.g. <figref idref="f0006">FIGS. 7a and 7b</figref> of '049), those designs in combination with a venous reservoir require that controlled vacuum be applied to the top of the venous bag.

0011As the pore size of filter screen used to trap bubbles decreases so does the effective open area and resistance to flow. For example, the preferred screen used for state-of-the-art venous bag has a pore size of 105µ and an open area of 52% as compared to an open area of only 30% for a screen with a pore size of 37p. However, the use of smaller pore screen reduces the size and number of bubbles that cross screen 2c. A test comparing bubble counts at the outlet of the air purging chamber showed that when 130cc/min of air are pumped into a 6L/min blood flow entering the venous air purging chamber, the bubble count of 15µ size bubbles were 6 bubbles/min, 410 bubbles/min, and 763bubbles/min for screens having a pore size of 37u, 65 µ and 85µ respectively, The smaller pore size screen had significantly lower bubbles crossing despite its lower open area (31% for the 37µ, 38% for the 65µ and 46% for the 85µ pore size screens), open area being the open part of the screen as % of the total area of the screen. The larger effective screen area of the present invention allows using a smaller pore size screen and still maintaining a total open area that is equal to, or is even larger than, state-of-the-art bags thereby maintaining a blood velocity across the screen that equals to or is lower than that associated with current bags. A lower velocity translates to lower number of bubbles crossing the screen.

0012At low blood levels or if there is air in current soft shell reservoirs, the indication of blood level are inaccurate and the alarms, mostly designed for hard shell reservoirs, are not reliable. The present invention provides more reliable means to alarm at low blood levels.

0013The only venous reservoir that combines a flexible wall and a rigid wall to form a "closed" variable blood chamber is that described in <patcit id="pcit0010" dnum="US4424190A"><text>U.S. Patents No. 4,424,190</text></patcit> and <patcit id="pcit0011" dnum="US4959062A"><text>4,959,062</text></patcit>. Each of these devices has its outlet at the lowest point of the venous reservoir (see 24 in FIG. 24 of US Pat. '062, and 36 in <figref idref="f0002">FIG. 3</figref> of US Pat. '190). This choice makes it more difficult to assure that the pliable wall seals against its mating rigid wall when the reservoir empties. The '190 patent has a drawback: once that reservoir empties, its pliable wall is sucked in at its outlet and shuts off as it should. However, when the volume returns, the flexible wall remains stuck to the outlet and does not open until the reservoir is almost full. The '062 Patent's design alleviates that flaw however it introduced another problem: when the reservoir empties the rib prevents the flexible wall from completely sealing against the outlet port allowing air from the cardiotomy reservoir to be sucked in, an undesirable outcome. The present invention provides a design that allows the outlet to close completely when the reservoir empties and to easily open when less than 1/3 of the volume of a full reservoir returns.

0014Currently almost all hard shell venous reservoirs incorporate a cardiotomy reservoir; the user gets a single unit (e.g.<patcit id="pcit0012" dnum="US5411705A"><text> Thor, et al US Patent 5,411,705</text></patcit> "Combined cardiotomy and venous blood reservoir or in aforementioned Fini's '270 patent). The lower cost, shorter setup time and ease of air removal are the major reasons that more hard shell reservoir are used than collapsible venous reservoirs. The present invention provides the user with a collapsible venous reservoir and a cardiotomy reservoir as a single units that is easy to setup, and is clinically safer than the state-of-the-art unified hard shell venous-cardiotomy reservoir unit.

0015During CPB, "clean" blood includes blood withdrawn from a venting site (e.g. the aortic root cardioplegia cannula, left ventricle vent), blood with entrapped air withdrawn from the top of the collapsible venous reservoir, and blood purged from the top of the arterial filter (hereinafter will be referred to as clean blood). "Dirty" blood is blood that has spilled out of the vascular tree and is sucked from the surgical field, mostly blood accumulating in the pericardial sack (hereinafter will be referred to as dirty blood). Exposure to surgical debris has been shown to cause complement activation, release of proinflammatory cytokines, and endothelial activation. Thus, some users prefer to wash that dirty blood through a cell saver before returning it to the patient. Before clean blood is returned to the collapsible venous reservoir, entrapped air is removed. Before sucked, or aspirated, blood is returned to the collapsible venous reservoir, it is filtered to remove debris (e.g. fat particles, tissue, clots, etc.) as well as entrapped air. When using venous bags both the clean and dirty blood are processed by passing through a cardiotomy reservoir, a disadvantage because the clean blood is exposed to the inlet of the filter for the dirty blood with its aforementioned deleterious consequences. Adding the clean blood directly to the venous bag is not possible because the volume of air in the clean blood can be so high that it causes massive foam generation introducing a large blood to gas interface as well as overwhelm the air handling capability of the venous bag. There are no cardiotomies with capability to filter the clean blood separate form the dirty blood. Some state-of-the-art hard shell reservoirs allow clean blood to bypass the filter for the dirty blood by directing the clean blood into the venous blood inlet chamber. However, none provide means to purge the air out of the clean blood prior to it combining with the venous blood, resulting clinically undesirable generation of large volume of foam Only Fini's '270 patent partially address this by having a valve that lets the user use the dirty blood (flow to the venous chamber) or collected for the cell saver. Current bags utilize cardiotomy reservoirs where the stored blood can contact the silicone antifoam agent or the debris trapped by the cardiotomy filter resulting in increased inflammatory response and some washout of the silicone antifoam into the patient. The present invention addresses these drawbacks by separating the clean blood from the dirty blood as well as gives the user a choice to return the dirty blood to the bag or to a cell saver.

0016Cardiotomy reservoirs are also used to accommodate the overflow of blood volume that exceeds the capacity of the venous bag (the largest one can accommodate less then 2.0L). Larger blood volume capacity is frequently required during aortic or mitral valve replacement during which the excess volume rises into the cardiotomy reservoir resulting in clean venous blood contacting the aggressive filter and the filtrate (e.g. fat, bone chips etc.) trapped at the bottom of the filter of the cardiotomy reservoir that can result in undesirable outcomes. The blood level at which the clean blood contacts the antifoam loaded defoamer in the venous reservoir and the volume at which the blood contacts the aggressive cardiotomy reservoir filter is summarized in Table 1 for typical state-of-the-art hard shell reservoirs-cardiotomy reservoir units. In one form of the present invention, additional volume capacity is provided by a larger capacity of the closed venous blood chamber and/or by the "clean" chamber of the cardiotomy reservoir thereby limiting clean blood contact with the "dirty" chamber.

0017Minimizing the blood gas interface is a major design objective of devices used in the cardiopulmonary bypass circuit. The last two columns in Table 1 provide the surface area of air that the blood is exposed to when the reservoir contain 500 or 1000 ml of blood. As will be shown, the present invention has 7 to 30 time smaller area than state-of-the-art hard shell venous reservoirs. The values assume that there is no air in the venous blood or foam above the blood. <tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="5"><colspec colnum="1" colname="col1" colwidth="42mm" /><colspec colnum="2" colname="col2" colwidth="42mm" /><colspec colnum="3" colname="col3" colwidth="38mm" /><colspec colnum="4" colname="col4" colwidth="23mm" /><colspec colnum="5" colname="col5" colwidth="23mm" /><thead><row><entry namest="col1" nameend="col5" align="left" valign="top">Table 1. Nominal values for adult Prior Art hard shell reservoirs v. present invention.</entry></row><row rowsep="0"><entry morerows="1" rowsep="1" align="center" valign="middle"><b>Model</b></entry><entry morerows="1" rowsep="1" align="center" valign="top">Volume to contact HSVR* Defoamer</entry><entry morerows="1" rowsep="1" align="center" valign="top">Volume to contact CR**</entry><entry namest="col4" nameend="col5" align="center" valign="top">Blood-Air area at</entry></row><row><entry align="center" valign="top">500ml</entry><entry align="center" valign="top">1000ml</entry></row></thead><tbody><row><entry>Present Invention</entry><entry align="center">3,000ml</entry><entry align="center">3500 ml</entry><entry align="center">10cm²</entry><entry align="center">10cm²</entry></row><row><entry>Terumo Capiox 18SX</entry><entry align="center">3,000ml</entry><entry align="center">3,000 ml</entry><entry align="center">75cm²</entry><entry align="center">213cm²</entry></row><row><entry>Dideco Synthesis</entry><entry align="center">600ml</entry><entry align="center">1,400 ml</entry><entry align="center">155cm²</entry><entry align="center">213cm²</entry></row><row><entry>Dideco Avant 903</entry><entry align="center">600ml</entry><entry align="center">3,500 ml</entry><entry align="center">303cm²</entry><entry align="center">303cm²</entry></row><row><entry>Jostra VHK 4200</entry><entry align="center">300ml</entry><entry align="center">500 ml</entry><entry align="center">181cm²</entry><entry align="center">181cm²</entry></row><row><entry>Medtronic Affinity CVR NT</entry><entry align="center">1,000ml</entry><entry align="center">400 ml</entry><entry align="center">232cm²</entry><entry align="center">232cm²</entry></row><row><entry>Cobe VVR 4000i</entry><entry align="center">200ml</entry><entry align="center">800 ml</entry><entry align="center" /><entry align="center" /></row><row><entry namest="col1" nameend="col5" align="left">*HSVR ― Hard shell venous reservoir, **CR - Cardiotomy reservoir</entry></row></tbody></tgroup></table></tables>

0018Blood flow from the cardiotomy reservoir to a venous bag can be intermittent or continuous depending on the frequency the suckers are used and the volume aspirated from the field. The outlet port of the cardiotomy reservoir is universally 3/8" internal diameter as is the tube connecting the outlet of the cardiotomy reservoir to the inlet of the venous bag (see tube 153 in <figref idref="f0001">FIG. 1</figref>). Further, the outlet port faces straight vertically or horizontally. That combination results in the air in tube 153 to be trapped by the incoming blood above it, and dragged with that blood into the venous bag thereby adding air to the blood in the venous bag. A form of the present invention provides a fluid path between the cardiotomy reservoir and venous bag with decreased tendency of trapping air.

0019The aforementioned short falls of state-of-art venous reservoirs, whether bags or hard shell, are dealt with by the innovative designs of the present invention as more fully described below.

BRIEF SUMMARY OF THE INVENTION

0020The present invention in its simplest form consists of a very efficient low volume chamber that removes air from the venous line, hereinafter referred to as the air purging chamber. The air purging chamber consists of a vertical blood chamber having an inlet, an outlet and an air purge port. The inlet and outlet preferably separated by a screen that allows blood to cross from the inlet to the outlet but retains air bubbles in the inlet chamber. The screen also defines an inlet chamber and an outlet chamber. Gas (e.g. air) bubbles in the blood entering the bottom of the inlet chamber rise to the top of the blood column contained by the inlet chamber and are purged to atmosphere. The inlet chamber has an effective cross sectional area that is larger than the internal diameter of the inlet tube, thereby slowing the blood velocity to allow more favorable conditions (longer residence time, lower drag on bubbles) for gas bubbles to float upward where they are purged. The air purging chamber separates air bubbles from the venous blood and purges that air to atmosphere as is the case with the hard shell reservoir. This is achieved without the need for the suction or vacuum that is required to remove air from the prior art soft-shell venous reservoir. A defoamer, located at the top of the inlet chamber, collapses foam that forms by the air bubbles in the blood column. The blood in the inlet chamber flows across the screen into the outlet chamber and downward towards the outlet port located along the bottom of the outlet chamber. In one preferred embodiment, the top of the air purging chamber is designed to also accept vented blood without the need for that blood to pass through a cardiotomy reservoir. In another preferred embodiment, the outlet port of the air purging chamber is in fluid communication with the inlet of a compliant storage chamber or a venous bag. The former is enhanced by providing the user with VAVD capabilities. Both provide superior air removal capabilities, the safety benefits of prior art collapsible venous reservoirs while avoiding such disadvantages as air entrapment, required vigilance for air removal, poor level control, slower priming, and lack of a cardiotomy reservoir incorporated as a single unit.

0021From the brief description of the invention and the aforementioned drawbacks of current reservoirs, it is the objective of the present invention to provide an improved venous air purging chamber that provides bubbles entering its inlet a path to move unhindered upward and passively purged to atmosphere.

0022It is another of the present invention to provide an improved venous air purging chamber that provides defoaming capabilities.

0023It is another of the present invention to provide an improved venous air purging chamber that provides defoaming capabilities even at low filling volume while minimizing blood contact with the defoamer.

0024It is another of the present invention to provide an improved low volume venous air purging chamber with a large effective screen area available for blood flow that provides defoaming capabilities and can accept vented blood without the vented blood being exposed to a cardiotomy reservoir.

0025It is another of the present invention to provide an improved low volume venous air purging chamber with a large effective screen area available for blood flow that provides defoaming capabilities that further incorporates a top and bottom defoamer, wherein the bottom defoamer is at least 50% smaller by volume and at least 2 times longer than the top defoamer and it extends into the inlet chamber of the air purging chamber.

0026Another objective is to provide fluid communication between the outlet of the air purging chamber and the inlet to a compliant storage chamber that is formed as part of the rigid structure forming the air purging chamber.

0027Another objective is to provide blood in the compliant storage chamber that once primed remains air free.

0028Another objective is to provide a compliant storage chamber that shuts off prior to air entering it and reopens at a blood volume that is less than 1/3 of volume capacity.

0029Another objective is to provide a venous reservoir with a "tall" and relatively narrow liquid column wherein even at low blood volumes a large screen area for blood flow is still available.

0030Another objective is to provide the fluid path between the air purging chamber and compliant storage chamber with an adjustable resistance to liquid flow thereby allowing the user to adjust the height of the blood column in the air purging chamber and thereby the screen area available for blood flow.

0031A. further objective of the present invention is an improved venous blood reservoir, having at least one pliable wall, allowing the user to adjust the negative pressure applied to the pliable wall thereby allowing for VAVD.

0032Yet another objective of the present invention is an improved venous blood reservoir, having at least one pliable wall, allowing the user to adjust the negative pressure applied to the pliable wall thereby allowing for VAVD by connecting the vacuum source to a single air port, the single air port providing the same vacuum to the blood in the air purging chamber, the cardiotomy reservoir and the compliant storage chamber.

0033A further objective of the present invention is an improved venous blood reservoir designed to maintain its screen from contacting the walls of the air purging chamber thereby maintaining a low resistance to blood flow across the screen.

0034Another objective of the present invention is to provide an improved venous blood reservoir with at least one pliable wall having passive means to eliminate air.

0035Yet another objective of the present invention is to provide a single venous bag that can be used with either gravity drainage or with VAVD thus, reducing cost of inventory and simplifying the user's set up.

0036A further objective of the present invention is to provide a venous blood reservoir having at least one pliable wall and a cardiotomy reservoir combined as a single unit with an outlet that shuts off when the venous bag empties.

0037A further objective of the present invention is to provide a venous blood reservoir having at least one pliable wall and a cardiotomy reservoir combined as a single unit with the venous blood reservoir accommodating at least 2000ml without the clean blood contacting the cardiotomy reservoir filter.

0038A further objective of the present invention is to provide a venous blood reservoir having at least one pliable wall and a cardiotomy reservoir combined as a single unit with the cardiotomy consisting of a clean blood chamber and a dirty blood chamber, said chambers in fluid communication with each other, and a means to allow the user to open/close said fluid communication.

0039A further objective of the present invention is to provide a blood path between the outlet of a cardiotomy reservoir and a venous blood reservoir having at least one pliable wall that incorporates means that limit the volume of air that can be entrapped and pumped into the venous bag from the cardiotomy reservoir.

0040A further objective of the present invention is to provide a venous blood reservoir with improved air removal capabilities and passive air removal, having a blood volume capacity of at least 500 ml and a flow capacity of at least 2l/min, wherein the blood in the reservoir is exposed to no more than 2.0 in² of air when there is no air in the venous blood.

0041Another objective of the present invention is to provide the manufacturing flexibility to accommodate future clinical finding that could determine which is more beneficial to the patient: collapsing the foam to reduce blood-gas interface or reducing blood contact with the defoamer.

0042Other objectives, features and advantages of the present invention will become apparent by reference to the following detailed description, an illustrative description not to be taken as limiting the present invention, of the presently preferred embodiments thereof with reference to the accompanying drawings therein.

BRIEF DESCRIPTION OF THE DRAWINGS

0043<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">FIG. 1</figref> is a line drawing of the pertinent components of a typical cardiopulmonary bypass circuit showing the prior art soft shell venous reservoir and a single chamber cardiotomy reservoir.</li><li><figref idref="f0001">FIG. 1a</figref> is a line drawing illustrating that at a low blood level in a prior art venous bag the effective screen area is very small relative to total area of the screen in the bag and that suction is required to remove air entering the bag.</li><li><figref idref="f0001">FIG. 1aa</figref> is a line drawing of a cross section along line 1aa and 1aa' of prior art bag shown in <figref idref="f0001">FIG. 1a</figref> illustrating that at low blood volume most of the screen of this bag is unavailable for blood flow.</li><li><figref idref="f0001">FIG. 1ab</figref> is a line drawing of an enlargement of the circled section of the bag shown in <figref idref="f0001">FIG. 1aa</figref> showing that at low volume with the prior art bag most of the screen in unavailable for blood flow.</li><li><figref idref="f0001">FIG. 2</figref> is a line drawing of the pertinent components of a typical cardiopulmonary bypass circuit showing the soft shell venous reservoir integrated with the air purging chamber and a two chambered cardiotomy reservoir.</li><li><figref idref="f0002">FIG. 3a</figref> is a line drawing of the front view of one preferred embodiment of the present invention illustrating a venous air purging chamber that purges air without the user input:</li><li><figref idref="f0002">FIG. 3aa</figref> is a line drawing illustrating a mean to prevent blood from overfilling the air purging chamber using an enlarged and vertically extended air exhaust tube.</li><li><figref idref="f0002">FIG. 3b</figref> is a line drawing illustrating another view of the air purging chamber illustrated in <figref idref="f0002">FIG. 3a</figref> taken along line 3a-3a' of <figref idref="f0002">FIG. 3a</figref>.</li><li><figref idref="f0002">FIG. 3c</figref> is a line drawing of the front view of another preferred embodiment of the present invention illustrating a venous air purging chamber similar to that illustrated in <figref idref="f0002">FIG. 3a</figref> that also incorporates a defoaming chamber for vented (clean) blood.</li><li><figref idref="f0002">FIG. 3d</figref> is a line drawing illustrating another view of the air purging chamber illustrated in <figref idref="f0002">FIG. 3c</figref> taken along line 3d-3d' of <figref idref="f0002">FIG. 3c</figref>.</li><li><figref idref="f0003">FIG. 4a</figref> is a line drawing illustrating one preferred embodiment of the present invention where the air purging chamber shown in <figref idref="f0002">FIG. 3a</figref> is combined with a venous reservoir having at least one flexible wall and two chamber cardiotomy reservoir.</li><li><figref idref="f0004">FIG. 4b</figref> is a line drawing illustrating another cross sectional view of the air purging chamber combined with the venous and cardiotomy reservoirs illustrated in <figref idref="f0003">FIG. 4a</figref> taken along line 4b-4b' of <figref idref="f0003">FIG. 4a</figref>.</li><li><figref idref="f0004">FIG. 4c</figref> is a line drawing illustrating another cross sectional view of the air purging chamber combined with the venous and cardiotomy reservoirs illustrated in <figref idref="f0003">FIG. 4a</figref> taken along line 4c-4c' of <figref idref="f0003">FIG. 4a</figref>.</li><li><figref idref="f0005">FIG. 4d</figref> is a line drawing illustrating another cross sectional view of the air purging chamber combined with the venous and cardiotomy reservoirs illustrated in <figref idref="f0003">FIG. 4a</figref> taken along line 4d-4d' of <figref idref="f0003">FIG. 4a</figref>.</li><li><figref idref="f0006">FIG. 5a</figref> is a line drawing illustrating the blood level in the air purging chamber relative to the blood level in the venous reservoir at high flow and low volume conditions.</li><li><figref idref="f0006">FIG. 5b</figref> is a line drawing illustrating the blood level in the air purging chamber relative to the blood level in the venous reservoir at low flow and low volume conditions.</li><li><figref idref="f0006">FIG. 6</figref> is a line drawing illustrating the air purging chamber used with state-of-the-art venous bag and an innovative cardiotomy reservoir that limits air from being dragged along its exit tubing into the air purging chamber.</li><li><figref idref="f0006">FIG. 6a</figref> is a line drawing illustrating the exit tubing into the air purging chamber shown in <figref idref="f0006">FIG. 6</figref> and the direction of flow of blood and air bubbles.</li><li><figref idref="f0006">FIG. 6a</figref> is a line drawing illustrating a cardiotomy and a compliant chamber combined as a single unit by sharing a common rigid wall.</li></ul>

DETAILED DESCRIPTION OF THE INVENTION

0044Reference should now be made to the drawings wherein the same reference numerals are used throughout to designate the same or similar parts. It should be noted that the use of cardiopulmonary bypass, as shown in <figref idref="f0001">FIG. 1</figref>, is for descriptive purposes, and should not be taken as a limitation to the use of the devices described hereinafter. Further, the description of the inventions that follow are for illustrative purposes, other embodiments are possible, and therefore what follows is suggestive of the art but should not be construed as a limitation of the scope or .the spirit of the invention. Hereinafter, the term soft-shell venous reservoir, venous bag and bag are used interchangeably and refer to a blood chamber with at least one flexible wall.

0045<figref idref="f0001">FIG. 1</figref> is a schematic representation of a typical cardiopulmonary bypass circuit according to the prior art showing the location of the venous reservoir relative to the patient and the other components in the circuit Tubing 123, receiving venous blood from patient 1102, is coupled to venous reservoir 1103. The blood is drawn from venous reservoir 1103 via tube 135 by arterial pump 1104 and pumped through membrane oxygenator 1105 wherein oxygen is supplied to the blood and carbon dioxide is removed. The blood from the oxygenator flows via tubing 157 to arterial filter 1107 and then via tubing 172 and an arterial cannula (not shown) back to the patient. One main function of the venous reservoir is to eliminate air contained in the venous blood before it is pumped back to the patient. Air entering venous bag 1103 rises to the top of the reservoir from where it is pumped out by suction pump 1114 into cardiotomy reservoir 1115. Suction pump 1104 is usually one of 3 to five pumps composing a heart-lung machine, which is part of a hardware required for cardiopulmonary bypass. The defoamed blood is returned from cardiotomy reservoir 1115 back to venous bag 1103 via connecting tubing 153. As described in the Description of the Prior Art, blood flowing from cardiotomy reservoir to venous bag can entrain air that is then pumped into the venous bag, none desirable outcome.

0046The ineffective air handling ofprior art soft shell venous reservoirs is illustrated by line drawings given in <figref idref="f0001">FIGs 1a, 1aa and 1ab. FIG. 1a</figref> is a line drawing of state-of-the-art venous reservoir as typically represented by Cobe's venous reservoir (Model # VRB, Cobe Lakewood, CO and described in United States Patent <patcit id="pcit0013" dnum="US5352218A"><text>5,352,218, issued to Buckley, et al. October 4, 1994</text></patcit> titled "Venous reservoir bag assembly"). Though this bag has a large screen (defined by the dashed lines in <figref idref="f0001">FIG. 1a</figref>), at low volumes only a very small area of the screen (defined by the double headed arrow in <figref idref="f0001">FIG. 1ab</figref>) is available for blood entering the screen area to flow to the outlet port. This is further exasperated at low blood volume, the bag is not fully expanded at the screen area causing most of the screen, defined by the double arrow, to contact the collapsed walls and not available for blood flow. At low volumes and high flow, large bubbles 27 entering the Cobe bag are dragged across the screen and break up into smaller bubbles (27a) that are more difficult to remove due to their lower buoyancy. As described below in reference to <figref idref="f0006">FIGs 5a and 5b</figref>, this is not the case with the present invention.

0047<figref idref="f0001">FIG. 2</figref> is a schematic representation of a system according to present invention showing the relative location of the collapsible venous reservoir in a typical cardiopulmonary bypass circuit and the incorporation of the air purging system. The circuit shown in <figref idref="f0001">FIG. 2</figref> is identical to <figref idref="f0001">FIG. 1</figref>, except that in <figref idref="f0001">FIG. 2</figref>, venous bag 1103 of the present invention incorporates cardiotomy reservoir with chamber 1115a for "clean" blood and separate chamber 1115b for "dirty" blood as well as incorporating air purging chamber 1116. Incorporating the cardiotomy reservoir eliminates the need for tubing 136 between the top of the collapsible venous reservoir and cardiotomy reservoir 1115 and suction pump 1114 required for the prior art systems shown in <figref idref="f0001">FIG. 1</figref>.

0048<figref idref="f0002">FIGs. 3a and 3b</figref> are line drawings of a front view and top view, respectively, illustrating one preferred embodiment of air purging chamber 1116. In general, the air purging chamber is a disposable consisting of an inlet chamber and an outlet chamber having a common screened wall. Screen wall 2c forms the outside wall of inlet chamber 2 and the inside wall of outlet chamber 3. While there are various configurations that can be used to form the air purging chamber, one of the more efficient and simpler designs is illustrated by <figref idref="f0002">FIGS. 3a and 3b, and 3c and 3d.</figref> Blood enters inlet chamber 2 via inlet port 1. Inlet chamber 2 is a vertical cylinder defined by screened wall 2c and extending from its bottom level 2a to its top level 2b. The internal diameter of chamber 2 preferably is larger than the internal diameter of inlet port 1. lnlet port 1 extends, and expands in diameter into outlet chamber 3 formed by rigid walls 3c and is sealed to bottom 2a of inlet chamber 2 to form a continuous fluid path with inlet chamber 2. The screened walled cylinder forming inlet chamber 2 is housed in, and preferably is screen centrally located along its-axis within a second cylindrical structure formed by rigid vertical wall 3c forming outlet chamber 3. Venous blood that contains air bubbles 27 enters air purging chamber 1116 via inlet port 1 into inlet chamber 2. Bubble movement upward in chamber 2 is enhanced by the larger diameter of inlet chamber 2 relative to that of the inlet port. The large internal diameter reduces the blood velocity thereby reducing drag and allowing longer time for the bubbles to move upward. Lower velocity also lowers the tendency of larger bubbles to break into smaller ones; larger bubbles have higher buoyancy and less of a chance of crossing screen 2c into outlet chamber 3. With sufficient pressure across screen 2c, bubbles can cross into chamber 3 and travel to outlet 4 of chamber 3, a very undesirable outcome. The upward direction of blood flow at inlet 1 further enhances desirable upward movement of the bubbles. It should be noted that by extending the top most level 2b of screen 2c to level 3d of outlet chamber 3 limits the chance of air crossing into outlet chamber 3.

0049The effective area of screened wall 2c is defined as the area available for blood in inlet chamber 2 to flow across screen 2c into outlet chamber 3. For air purging chamber 1116 that area equals the product of the periphery of the screen wall 2c (i.e. 3.14 x diameter of chamber 2) and the height difference between blood level 3d in chamber 3 and bottom level 2a of chamber 2. Because none of the screen area in contact with the blood (wetted area) is blocked by the walls 3c of outlet chamber 3, as is the case with state of art venous bags discussed in reference to <figref idref="f0001">FIGs 1a, 1aa and 1ab</figref>, blood flows across that entire wetted area. A larger effective area translates to lower velocity across each pore in the screen which lowers the drag force that can push bubbles across that screen into outlet chamber 3. Once the blood enters outlet chamber 3, it flows downward in the annular space defined by cylindrical screen wall 2c and rigid wall 3c until it exits through outlet port 4C Outlet port 4 extends off of wall 3c at a vertical level that is preferably lower than bottom level 2a of screen 2c, a location that reduces the chance of bubbles crossing from inlet chamber 2 to the outlet port 4. Air entering inlet chamber 2 may cross to outlet chamber 3 along a non wetted screen area and then flow upward to air exhaust tube 3e.

0050The air purging chamber preferably incorporates defoamer 20 (preferably made of reticulated polyurethane foam having a pore size in the range of 5 to 50 ppi treated with antifoam agents such as silicone) that breaks up foam that forms as air travels up the blood column in inlet chamber 2. Defoamer 20 preferably is located at the top most section of inlet chamber 2, a location that limits its contact with the blood in chamber 2 but avails it to defoam blood foam that rises to the top of chamber 2. The defoamer may also incorporate open channel 20a that-provides unrestricted fluid communication between inlet chamber 2, the top of chamber 3, and air exhaust port 3e. Air is then exhausted via channel 3e in wall 3c to atmosphere. Thus, foam (very large bubbles) entering channel 20a is exposed to defoamer 20 where it breaks up and collapses. For cases where excess foam-is-generated or if defoamer 20 loses some of its defoaming capacity, then having outlet of channel 3e directed from exhausting to atmosphere to the inlet of a cardiotomy reservoir, as shown in reference to tube 137 in <figref idref="f0006">FIG. 6</figref> where further defoaming can be achieved. It can also be achieved as described in reference to defoamer 15cc illustrated in <figref idref="f0003">FIGs.4a</figref> and <figref idref="f0004">4b</figref>:

0051Since foam has a very a large blood-gas interface, it is advantageous to limit its life and collapse it sooner rather then later. To that end, an additional length of defoamer; 20b is used. Defoamer 20b preferably has a nominal width equaling to 10% to 50% of the inside periphery of inlet chamber 2, and extends from the bottom of defoamer 20, downward up to 75% of the length of inlet chamber 2. It may also have a smaller surface area than defoamer 20. These dimensions reduce the undesirable blood contact with the defoamer yet still collapse blood foam that has not reached defoamer 20 and thereby significantly reducing the blood to gas interface associated with foam. The variable defoaming capabilities achieved by varying the width to less than the perimeter of chamber 2 and extending the defoamer into the blood chamber accommodates future clinical finding that would determine which is more beneficial to the patient: collapsing the foam to reduce blood-gas interface or reducing blood contact with the defoamer.

0052The dimensions of air purging chamber 1116 are balanced between decreasing the velocity of the blood and increasing the screen area to enhance bubble removal (i.e. large internal diameter) and limiting the prime volume (i.e. smaller internal diameter). It should also have low resistance to flow. With that in mind, it has been determined that for an air purging chamber designed for adult patients, the optimum internal effective diameter of outlet chamber 3 is between 7/8" and 3" (having a horizontal cross sectional area of 4 to 46cm²) and inlet chamber 2 preferably has a nominal internal diameter that is 1/8" to 3/16" smaller between than that of the outlet chamber. Another definition of the effective diameter of the inlet chamber is such that it results in annular cross sectional area (area of the outlet chamber less that of the inlet chamber) of at a least 1cm². The effective diameter is the average diameter of the chamber, (e.g. for an ellipse it would be average of the major and minor diameters). The height of inlet chamber 2 is preferably greater than state-of-the-art venous bags, or between 7" and 22". The screen filter is preferably made of medical grade polyester having a pore size between 20µ and 150µ but most preferably having a pore size between 20µ and 40µ. Most preferably the outlet chamber has an internal diameter of 1 3/8" and a height of 16" and the screened inlet chamber has an internal diameter of 1.2" and a height that is equal or up to 2" shorter than that of the outlet chamber. The top of the screen preferably extends to the top of the outlet chamber and may be closed at its top, a design that limits the blood foam crossing the defoamer radially and spill into the outlet chamber. The aforementioned most preferred dimensions result in an annular cross sectional area of 0,35in², an area that is 50% larger than that of 0.5" internal diameter tubing assuring low resistance to flow relative to that of the adult venous line. The preferred cross sectional area of the annular space between the inlet and outlet chamber can also be defined as Defoamer 20 preferably has an OD equal to the internal diameter of chamber 2 and a length of 3/4" to 4". If the defoamer is to be supported by the screen, then the OD of defoamer 20 can be slightly larger than the internal diameter of inlet chamber 2. The inside diameter of open channel 20a is preferably between 1/8" and 1/2", a diameter that allows free air flow yet maximizes the volume of defoamer per unit length.

0053It should be pointed out that the most preferred dimensions provide a screen area of 17in², a smaller area than most other venous bags (e.g. the screen used in Cobe's bag is 31in²). Further, as the pore size of filter screen used to retain bubbles decreases, the effective open area decreases and the resistance to flow increases. The preferred screen used for state-of the-art venous bags have a pore size of 105µ with an open area of 52%. However, the use of smaller pore screen reduces the size and number of bubbles that cross screen 2c. A test comparing bubble counts at the outlet of the air purging chamber showed that when 130 cc/min of air are pumped into a 6 L/min blood flow entering the venous air purging chamber, the bubble counts of 15µ size bubbles were 6 bubbles/min, 410 bubbles/min, and 763 bubbles/min for screens having a pore size of 37µ, 65µ and 85µ respectively. The smaller pore size screen had significantly lower bubbles crossing despite its lower open area (31% for the 37µ, 38% for the 65µ\and 46% for the 85µ pore size screens). For the preferred internal diameter of 1.2" internal diameter for chamber 2, a screen with a pore size of 37µ having an open area of 31%, the open area per one inch height of screen is over 1.2in². Since the screen makes no contact with wall 3c of outlet chamber 3, its entire wetted area is available for blood flow. It is the larger effective screen area of the present invention that allows using a smaller pore size screen and still maintaining a total open area that is equal to, or is even larger than, state-of-the-art bags thereby maintaining a blood velocity across the screen that equals to or is lower than that associated with current bags. Lower velocity translated to lower number of bubbles crossing the screen. As with many devices handling blood outlet chamber 3 preferably is made of clear biocompatible thermoform plastic such as PETG, PVC or polycarbonate. The entire blood contacting surfaces of air purging chamber 1116, and if possible the defoamer too, is preferably passiviated by one of the many coats available such as the heparin coating by Carmeda.

0054The preferred dimensions and the design of venous air purging chamber provide a smaller diameter air remover than state-of-the-art venous or arterial filters and allow the user to operate at a lower blood volume in line with minicircuit technology while providing superior air handling that includes passive air elimination.

0055It should be understood that the aforementioned specifications are for illustrative purposes and that other combination of dimensions can also achieve desirable results. For example, the circular cross sections can be replaced with elliptical, star, or rectangular cross sections. The design of the air purging chamber is not limited to the designs shown in <figref idref="f0002">FIGs 3a and 3b</figref>. For example the air purging chamber can also be effective by incorporating some of the designs suggested for arterial filters (<i>e.g.</i><patcit id="pcit0014" dnum="US5484474A"><text>US Pat. 5,484,474</text></patcit> or <patcit id="pcit0015" dnum="US4743371A"><text>4,743,371</text></patcit>) or bubble traps (e.g. <patcit id="pcit0016" dnum="US6019824A"><text>US Pat. 6,019,824</text></patcit>).

0056It should be further understood that the aforementioned specifications are given for adult patients with expected blood flow between 4 and 7L/min. The specifications can be easily scaled down to accommodate lower flows and lower prime volumes associated with pediatric and infant patients. Scaling can utilize well know equation relating resistance to flow as a function of cross sectional areas, such as Poiseuille law dictating flow, Q, to be a function of diameter, d, to the fourth power, Q =<i>f</i>(d⁴) while still having the diameter of the inlet chamber sufficiently large to allow bubbles to float up freely up the blood column. For example, for infants on bypass using 1/4" internal diameter tubing is used as venous line 123 in <figref idref="f0001">FIG. 1</figref>, then the nominal internal diameter of inlet chamber of the air purging chamber can be 3/8" and the internal diameter of the outlet chamber can be 1/16" to 1/8" larger.

0057The air purging chamber can incorporate means assuring that when inflow is higher than outflow, that blood does not overfill the air purging chamber and spills out. One such means is level sensor 32b shown in <figref idref="f0002">FIG. 3a</figref>, Thus, when sensor 32b detects that the blood level in outlet chamber 3 is too high, it sends a signal to alarm the user and/or increases pump speed to accommodate the increased inflow from the patient and prevent blood overflowing chamber 3. The alarm signal can also actuate a tubing clamp on the venous line to reduce the blood flow from the patient into the air purging blood chamber till it matches the outflow generated by the arterial pump.

0058<figref idref="f0002">FIG. 3aa</figref> illustrates yet another and the simplest means to assure that blood does not overfill and spills from the air purging chamber. Here, air exhaust tube 132 extends vertically up so its open end is at or higher than the height of the patient. Thus, should outflow from the air purging chamber cease, venous blood would continue to flow into the air purging chamber but only till the blood level in-tube 132 reaches the level of the patient. Tube 132 preferably has an internal diameter of at least 3/8" but preferably is 1/2" or greater.

0059The air purging chamber can also incorporate blood level maintaining means for maintaining the blood level in chamber 3 above outlet port 4 thereby preventing gross air. (as opposed to microbubbles) from exiting the outlet blood chamber. As an example, sensor 32 on wall 3c operably connected to controller 33 is attached wall 3c of outlet chamber 3 in <figref idref="f0002">FIGs 3a, and 3aa</figref> and is used as a low level sensor that maintains blood level 3d at a safe level above outlet 4 of chamber 3. When detector 32 senses that the blood level dropped below a safe level, it sends a signal to control unit 33. Control unit 33 is capable of at least sounding an alarm, slowing down or shutting off the arterial pump, or clamping off outlet port 4 increasing inlet flow such that the blood level does not reach outlet port 4. Level detectors already incorporated in state-of-the-art heart-lung machines can be used for this purpose. Thus the combination of state-of-art control units and the innovative disposable air purging chamber, provides the user a system that effectively purges air out of the venous line passively and automatically while preventing air from exiting outlet 4 of air purging chamber 1116. It should be pointed out that the rigid wall of air purging chamber 1116 can be easily adapted to the state-of-the-art level detectors. This is in contrast to the difficulties encountered when trying to use these level detectors by placing the sensor on the pliable wall of current venous bags. As described above, the air purging chamber acts much like a hard shell reservoir except that its diameter and hold up volume are significantly lower.

0060The air purging chamber allows many new designs not possible with state of art devices. For example line drawings of <figref idref="f0002">FIGs. 3c and 3d</figref> illustrate an air purging reservoir incorporating means to accept vented ("clean") blood. Combining the vented blood directly with the venous blood in chamber 2 is prohibitive because the high volume of air in the vented blood would cause excess foaming. Incorporating a vent blood air purging chamber at the top of the air purging chamber assures that the large volume of air, so common to vented blood, is eliminate prior to the vented blood combining with the blood in inlet chamber 2. As shown, the top section of the air purging chamber is radially enlarged preferably to 1.5 to 2.5 times the diameter of chamber 3 so channel 20a can accommodate vent chamber 22. Vent chamber 22 is formed of screen wall 22c; much like chamber 2 is formed by screen wall 2c, and incorporates defoamer15 at the top section of chamber 22. Vent chamber 22 is housed in top enlarged section of outlet chamber 3 formed by cylindrical outside wall 3cc and screen 2cc as its inside wall. Defoamer 20 is contained and supported by screen 2cc. Vent chamber is centrally suspended at the top and preferably does not contact defoamer 20 forming channel 20a. Vented blood enters vent chamber 22 via inlet vent port 23 located atop the air purging chamber and forming fluid communication screen chamber 22, and outlet end 23a of inlet vent tubing 23 ends within chamber 22, preferably in contact with bottom 22a of screen 22c. Further, the bottom of screen 22c is sealed on a diagonal with its lowest point contacting fluid path 22b described below. It is important that bottom 23a of vent tube 23 should be at a higher level than the maximum blood level 2d of inlet chamber 2. This would assure that the large air volume in the vented blood does not bubble into the venous blood entering chamber 2. Foam associated with the vented blood entering vent chamber 22 is collapsed when contacting defoamer 15, defoamer 15 disposed within the inside periphery of vent chamber 22. The only fluid communication between port 23 and enlarged channel 20a is via screen 22. This limits the foam and bubbles from the vented blood from entering channel 20a. Defoamer 20 is supported by circular screen 2cc and defoamer 15 is supported by screen 22c. With the exception noted in the next paragraph, the lower section of air purging chamber 1116a is identical to that described for air purging chamber 1116 in reference to <figref idref="f0002">FIG. 3a</figref>. Inlet chamber 2 forms unobstructed fluid communication with enlarged channel 20a via thin walled connector 24. Thus, <i>screen 2c</i> is sealed to the smaller diameter bottom section of connector 24 and screen 2cc is sealed to the larger diameter top section of fitting 24.

0061Also shown in <figref idref="f0002">FIG. 3c</figref> is path 22b between bottom 22a of vent chamber 22 to venous blood in chamber 2. Path 22b reduced the velocity at which the deaerated vented blood enters the venous blood thereby reducing air bubbles entrapment and foam formation in the venous blood Path 22b can be for example polyurethane foam as used for defoamer 20 but without the antifoam agents. Air entering inlet chamber 2 crosses to outlet chamber 3 along a non wetted screen area and then flow upward to air exhaust tube 3e. Air entrapped in vented blood entering vent chamber 22, is forced across non wetted section of screen 22c and then exhaust via port 3e. It should be clear that defoamer 15 may also facilitate defoaming venous blood foam formed in chamber 2.

0062<figref idref="f0002">FIG. 3c</figref> of air purging chamber 1116a also illustrates that a design where bottom 3a of outlet chamber 3 and bottom 2a of inlet chamber 2 can essentially be at the same vertical eight This design reduces the dead space associated with that shown in <figref idref="f0002">FIG 3a</figref> where some blood can always be left in inlet tube 1 because its opening is higher than outlet port 4. In this configuration, outlet port 4 is expanded to as shown in section 4c about the area of screen 2c at bottom 3a of outlet chamber 3 to provide slower and more uniform velocity.

0063Another preferred means to prevent air from entering blood pump 1104 of <figref idref="f0001">FIG. 2</figref> is to combine air purging chamber 1116 with a compliant outlet chamber having an outlet port that closes before the blood level in the outlet chamber drops to the level of the outlet of outlet chamber 7. <figref idref="f0003">FIG. 4a</figref> is a line drawing illustrating a front view of a unit combining air purging chamber 1116 with compliant venous reservoir 1103 having at least one pliable wall. The unit shown also incorporates dual chamber cardiotomy reservoir (1115a and 1115b in <figref idref="f0001">FIG. 2</figref>).. A line drawing of a cross sectional view of the combined unit shown in <figref idref="f0003">FIG. 4a</figref> taken along line 4b-4b' illustrated in <figref idref="f0004">FIG 4b</figref>. A line drawing of a cross sectional view of the combined unit shown in <figref idref="f0003">FIG. 4a</figref> taken along line 4c-4c' illustrated in <figref idref="f0004">FIG 4c</figref>. A line drawing of a cross sectional view of the combined unit shown in <figref idref="f0003">FIG. 4a</figref> taken along line 4d-4d' illustrated in <figref idref="f0005">FIG 4d</figref>. Here inlet channel extends from the top of the combined unit downward to form a fluid communication with inlet chamber 2 of air purging chamber 1116. Air purging chamber 1116 is essentially the same as described in reference to <figref idref="f0002">FIGs. 3a and 3b</figref>. Outlet 4 of outlet chamber 3 extends as channel 4b to form fluid communication with inlet 5 of compliant storage chamber 7. Compliant storage chamber 7 is formed by rigid concaved backwall 8c and matching in shape concaved pliable diaphragm 25, seen in <figref idref="f0004">FIGs. 4c</figref> and <figref idref="f0005">4d</figref>. Diaphragm 25, which can be formed from a film such as PVC, polyurethane or EVA, nestles in concaved backwall 8c and is sealed along its outside periphery to the outside periphery of rigid wall 8c to form a variable volume blood chamber 7. Chamber 7 has an inlet port 5 and outlet port 6, both located along bottom 7a of blood chamber 7 as illustrated in <figref idref="f0003">FIGs 4a</figref> and <figref idref="f0005">4d</figref>. Blood is pumped out of blood chamber 7 via outlet 6 that forms fluid communication with arterial pump 1104, shown in <figref idref="f0001">FIG. 2</figref>, via typical perfusion tubing (e.g. tube 135 in <figref idref="f0001">FIG. 2</figref>). As blood fills blood chamber 7, pliable diaphragm'25 moves outward, expanding the volume of blood chamber 7 to accommodate the additional blood volume. The only air to be removed from chamber 7 is that associated with initial priming of chamber 7. Air in blood chamber 7 is removed through tube 37 having one open end at top 7b of chamber 7 and the other open end accessible where the user can pull the air out. A one way valve or a stopcock can be adapted to tube 37 to facilitate air removal without allowing air to renter chamber 7. Air movement upward in chamber 7 may be enhanced by at least one protrusion 8ca incorporated into backwall 8c. The protrusion serve the same purpose as described in reference to air removal tubes shown in-<figref idref="f0001">FIG. 1b</figref> of aforementioned Tamari's US Patent '426. In short, protrusion 8ca forms channels between its wall and flexible diaphragm 25 to allow air to move up and be purged via air purging port 37. Protrusions 8ca also provide greater strength and stiffness to backwall 8c, thereby allowing wall 8c to be thinner, reducing its weight and cost. As described below; once primed and air free, no air should enter blood chamber 7.

0064The preferred dimensions of compliant chamber 7 depend on its use. For adult patients, the blood volume capacity should be between 1 and 3 liters, but can be reduced to 200 to 500 ml when designed to be used in association with minicircuits. 1. A critical design feature of the combined air purging chamber 1116 and venous reservoir. 1103 is that the vertical location of outlet port 4 of the air purging chamber 1116 is below the vertical location of outlet 6 of compliant chamber 7 of venous reservoir 1103. This design assures when blood chamber 3 empties, the negative pressure due to the hydraulic height difference between outlet 4 of the air purging chamber and outlet 6 of blood chamber 7 sufficient to cause' pliable diaphragm 25 to collapse against the opening of outlet 6, closing that port and preventing further emptying of blood chamber 7. The stoppage of outflow from compliant chamber 7 isolates outlet chamber 3 from the negative pressure that pump 1104 shown in <figref idref="f0001">FIG. 2</figref> generates. Since, when the outlet port of compliant chamber is closed, then the hydraulic pressure at outlet 3a is less than or equal to the hydraulic pressure in compliant chamber 7, and therefore the flow from outlet chamber 3 to complaint chamber 7 stops also. Thus, a cessation of outflow from chamber 7 translates to a cessation of flow from blood chamber 3 to blood chamber 7 thereby preventing the complete emptying of the blood chamber 3 and air flowing from empty blood chamber 3 into blood chamber 7 of venous reservoir 1103. Thus, the aforementioned combination illustrated in <figref idref="f0003">FIG. 4a</figref> provides automatic and passive air purging capabilities, as does a hard shell venous reservoir and the clinically preferred close blood chamber as does a soft shell venous reservoir. It also prevents air from entering the compliant venous blood chamber. All other venous bag containing air, allow that air to be pumped to the patient when they empty. With the combined unit illustrated in <figref idref="f0003 f0004 f0005">FIGS. 4a through 4d</figref>, because no air can enter compliant chamber 7, no air can be pumped to the patient.

0065The lower section of compliant storage chamber 7, that between 7a and 7c in FlGs 4a and 4d having a height of "h", is shallower, more vertical in shape, and accommodates much less volume per height than the upper section, that between 7c and 7b, defined as "H-h" in <figref idref="f0005">FIG. 4d</figref> The shallower section provides a larger change in height per unit change in blood volume and therefore a better visualization of small volume changes in that section. The larger increase in blood height also results in a greater force to move compliant diaphragm 25 from a closed position to an open position thereby overcoming the shortfall of prior art venous reservoir as previously described for aforementioned <patcit id="pcit0017" dnum="US4424190A"><text>US Patent 4,424,190</text></patcit>. The desirable early opening of a closed outlet is further assisted by virtue of outlet port 6 located on lower rigid wall 8cb that is flat and-close to vertical (e.g. between 70° and 90° of the horizontal plane). The vertical shape allows diaphragm 25 more easily. to "peel" away from rigid wall 8cb shown in <figref idref="f0005">FIG. 4d</figref>. The depth of lower section is preferably between 1/4" and 1" and most preferably between 3/8" and 5/8". Height "h" of the lower section is preferably between 1" and 4" but can be higher if a low volume compliant storage chamber is desired to meet minicircuit requirements. To further assure that pliable diaphragm 25 does open without requiring a large volume increase in chamber 7, outlet 6 of chamber 7 is not located at the lowest fluid level of chamber 7, as is the case for prior art compliant venous reservoirs, but preferably at least 1 to 4 lengths of the diameter for outlet port 6.

0066It should be clear that when using the air purging chamber for minicircuit applications, the compliant chamber can be limited in volume by reducing the chamber to that defined by height "h", a height sufficient to allow diaphragm 25 to close outlet port 6 when air purging chamber empties. Once closed, when flow returns to inlet chamber 2 blood level 3b increases. If blood level 3b rises above level "h" of compliant-Chamber 7, then the hydraulic pressure due to level 3b will exert a force to open outlet 6. Height "h" needs to be sufficient for the structure of chamber 7 to assure effective closing of port 6 but not necessarily to reopen the port when flow resumes. This allows to further minimization of operating volume of compliant chamber 7 to that needed for the compliant chamber to serve as a shut off valve to assure that blood flow from air purging chamber to complaint chamber 7 stops prior to air exiting outlet port 4 of outlet chamber 3. The minimum operating volume of the compliant chamber is preferably between 50ml and 200.ml. Since blood level 3b can rise above the vertical height of "h" (the maximum height for compliant chamber 7 when used only as a shut off valve) it will provide a higher hydraulic pressure than tha1 afforded by "h". This higher pressure will result in a higher force available to reopen port 6 without the large volume associated with filling section "H-h" shown in <figref idref="f0005">FIG. 4d</figref>.

0067It has been shown that bubble counts at the outlet of a venous bags decrease as its blood level increases (<nplcit id="ncit0001" npl-type="s"><text>Tamari Y, et, al.: A New Top-Loading Venous Bag Provides Vacuum Assisted Venous Drainage. Perfusion 17:383-390, 2002</text></nplcit>). Thus, the higher blood level in the air purging chamber as compared to that in the compliant storage chamber is an inherent safety characteristic of the system that assures more favorable conditions for air removal. Further, With state of art venous bags, as the blood volume in the bag decreases, the screen area available for blood flow from the inlet to the outlet of the bag decreases. A decrease in the screen area results in an increase in blood velocity across each pore of the screen which can cause more bubbles at the inlet side of the screen to cross to the outlet side of the screen. With the present design, the screened section in the air purging chamber can extend below the bottom of compliant storage chamber 7, assuring that even at very low blood level in compliant storage chamber 7, the blood column in the air purging chamber is high enough to provide a large screen area to inhibit bubbles in the venous line from reaching the outlet of the compliant storage chamber. This is clearly shown in <figref idref="f0003">FIGs. 4a</figref>, <figref idref="f0006">5a, 5b and 6</figref> where bottom 2a of screen inlet chamber 2 is vertically lower than bottom 7a of blood chamber 7. Another advantage is that whenever blood flows from the air purging chamber to the compliant storage chamber, the height of the blood column in the air purging chamber is always higher than the blood level in the compliant storage chamber.

0068<figref idref="f0006">FIGs. 5a and 5b</figref> are line drawings illustrating the superiority of the present invention in handling air. In each, air purging chamber 1116 is combined with venous reservoir 1103 in a similar manner to the combined air purging chamber 1116 and venous reservoir 1103 as described in reference to <figref idref="f0003">FIGs. 4a</figref>, <figref idref="f0004">4c</figref> and <figref idref="f0005">4d</figref>. Cardiotomy chambers 1115a and 1115b shown in <figref idref="f0006">FIGS. 5a and 5b</figref> do not affect the discussion below. <figref idref="f0006">FIG. 5a</figref> illustrates a condition that is most challenging to any venous reservoir: eliminate incoming venous air at low blood volume and high blood flow. With the combined air purging chamber 1116 and venous reservoir 1103, air is handled in an efficient manner by assuring that a large screen area is available. This is achieved by three means. First, bottom 2a of screen 2c forming cylindrical inlet chamber 2 can be located below bottom 7a of blood chamber 7. The height difference between bottom 2a and bottom 7a provides additional screen area not possible with state of art venous bags. Second, the blood volume where air is eliminated (i.e. chamber 2) is present as a tall vertical blood column surrounded by screened wall 2c provides a larger uninhibited screen area than the shallow but wide blood level of the aforementioned state-of-art venous bags that exposes a much smaller effective screen area as described in reference to <figref idref="f0001">FIGs 1a, 1aa, and 1ab</figref>. Third, because there is some resistance to flow between outlet chamber 3, outlet port 4, interconnecting channel 4b and inlet port 5 of blood chamber 7, then under any flow conditions, blood level 3d is higher than blood level 7d in blood chamber 7 of venous reservoir 1103 (i.e, the pressure required to overcome the aforementioned resistance to flow).

0069Further, for any given design, the <i>difference</i> in height between blood level 3d in air purging chamber 1116 and blood level 7d in venous reservoir 1103 increases as blood flow increases as is illustrated by comparing low flow conditions illustrated in <figref idref="f0006">FIG. 5b</figref> to high flow conditions illustrated in <figref idref="f0006">FIG. 5a</figref>, This inherent property provides additional safety: at higher flows when a fixed area screen is more vulnerable to bubbles crossing the screen (higher velocity and drag), the present invention presents a larger screen area for blood flow. The larger area reduces the velocity across the screen thereby compensating for the increased velocity due to the higher flow.

0070The inherent difference between blood level 3d and blood level 7d presented by the present invention system can be manipulated for good use. For example, channel 4b could:incorporate an adjustable resistance that controls the height of level 3d relative to level 7d. Thus, at very low volumes, the resistance to flow between chamber 3 and chamber 7 can be increased to maintain blood level 3d high. Conversely, with a high blood volume in chamber 7 the resistance to flow between chamber 3 and chamber 7 can be decreased because blood level 3b is already high. Further, it is easy to incorporate an adjustable resistance, to the flow fluid path between the air purging chamber and compliant storage chamber 7, such as tubing clamp 4bb shown in <figref idref="f0006">FIG. 5a</figref>, thereby allowing the end user to adjust the height of the blood column in the air purging chamber to accommodate different flow and air volume in the incoming venous blood. It should be noted that simple fluid physics dictate that when blood flow ceases, blood level 3b in inlet chamber 2 equals blood level 7d in venous blood chamber 7. The effective air handling described above, is in direct contrast to prior art soft shell venous reservoirs as previously described in reference illustrated in <figref idref="f0001">FIGs 1a, 1aa and 1ab</figref>.

0071<figref idref="f0006">FIGs. 5a and 5b</figref> also illustrate that interconnecting channel 4b could form U-shape bottom 4a having a vertical level that is lower than the level of outlet 4. Lower level 4a provides a higher hydraulic pressure to close outlet 6 by pliable film 25 when blood level 3d drops below the level oj outlet port 6, as described in reference to <figref idref="f0003">FIG. 4a</figref> and <figref idref="f0004">4b</figref>. Further, if lowest level 4a is lower than outlet port 6 of blood chamber 7, then the vertical height of outlet 4 of outlet chamber 3 can be raised above outlet 6.

0072Yet another advantage of the combined unit described in reference to <figref idref="f0003 f0004 f0005">FIGS. 4a-4d</figref> is that it limits the venous <u>blood gas interface</u> to the cross sectional area of outlet chamber 3 at blood level 3d, an area that is significantly lower than state-of-the-art hard shell reservoirs. For example, at a blood level of 1,000ml, the area of the blood to gas interface of the air purging chamber having the most preferred dimensions is only 10cm² as compared to an area from 180cm² to 230cm² for state-of the-art hard shell venous reservoir, see Table 1. At a blood level of 500ml, the area of the blood to gas interface of the air purging chamber is still only 10cm² as compared to an area from 84cm² to 230cm² for the state-of the-art hard shell venous reservoir shown in Table 1. Even the air purging chamber having the largest preferred diameter of 1 3/4" the cross sectional area is only 15cm², or no more than 8% at 1000 ml and 18% at 500 ml blood volume of the area of currently used hard shell venous reservoir. This significant reduction in blood-gas interface results in significant reduction in blood damage and should translate to better clinical outcome.

0073<figref idref="f0003 f0004 f0005">FIGs. 4a-4d</figref> also illustrate another permutation possible with the present invention: a unitized air purging chamber 1116, compliant blood chamber 7 forming venous reservoir 1103 and a two-chamber ("clean" blood chamber 1115a and "dirty" blood chamber 1115b) cardiotomy reservoir. The two chambers cardiotomy reservoir shown is for illustrative purposes only. Essentially it is similar to many of the cardiotomy reservoirs in the market (e.g. see cardiotomy reservoir 4 shown in <figref idref="f0001">FIG. 1</figref> of aforementioned <patcit id="pcit0018" dnum="US6287270B"><text>US Patent 6,287,270</text></patcit>) except that it provides clean blood chamber 10a and dirty blood chamber 10b, separated by wall 16. Cardiotomy section for dirty blood 1115b has at least one inlet port 11a to accept sucker blood and direct that blood to cardiotomy filter 11 composed of defoamer and a screen and or felt 11 c to filter debris and air associated with suction blood. The filtered blood then accumulates in chamber 10b. The purpose of section 1115a is to separate the air from the vented blood and it does not need the aggressive filter, 11, required for dirty blood chamber 10b. Further, the blood filtered in this chamber is "clean", there is no need to store it, and it can be combined with venous blood without concerns for the inflammatory response associated with the dirty blood in chamber 10b. Thus, it needs only screen, 14c to reduce the bubble size, volume in the clean blood, and defoamer 15 to collapse foam formed by the air in the clean blood and chamber 10a can be much smaller, preferably no more than 20%, of chamber 10b. Sections 1115a and 1115b can be formed to provide mat disproportionate volume distribution while maintaining the combined volume of both chamber the same. As shown, inlet port 15a accepts vented (clean) and directs it to closed-chamber 14 having screen wall 14c. Air is separated from the blood by having the blood flow across the lower portion of screen 14c and the air along the top section of the screen. Foam is collapsed by defoamer 15 located along the top section of screened chamber 14. Essentially, the filter for the clean blood is similar to that described in reference to inlet chamber 2 shown in <figref idref="f0002">FIGs. 3a and 3b</figref> with the exception that the inlet for chamber 14 is at the top. Unless chamber 10a is almost full, only foam contacts Defoamer 15. Channel 19 is angled to reduce blood velocity as well as allow air bubbles to rise to the top of the moving column as explained in detail in reference to channel 153 shown in <figref idref="f0006">FIG. 6</figref>. The top entrance of channel 19 at the bottom of chamber 10a is widened, as indicated by 19b in <figref idref="f0003">FIGs. 4a</figref> and <figref idref="f0004">4b</figref>, a design that allows the air bubbles to separate from the flowing blood and that limits the air volume trapped as clean blood intermittently flows down channel 19. Channel 19 should have at least the top portion enlarged to an equivalent diameter greater than 3/8" and preferably at least 1/2". Blood velocity in channel 19 can also be reduced by structure 19c, that can be for example be a polyurethane foam as used for defoamer 20 but without an antifoam agent. Reducing the blood velocity in channel 19 reduces air bubbles entrapment and foam formation in channel 19. To reduce air from venous blood entering channel 19, lowest level 19a of channel 19 and lowest level 1a of inlet channel I are lower then level 119 where channel 19 and channel combine. The deaerated vented blood combines with the venous blood at bottom 19a of channel 19 and bottom 1a of inlet channel 1. Chambers 10a and 10b are in fluid communication along their common top wall via always open channel 16a and along their common floor via ports 17 and 18. Ports 17 and 18 are in fluid communication via tubing 13 that can be closed or opened with valve 13a to allow or prevent the dirty blood to flow to clean chamber 10a and then to combine with the venous blood in chamber 2. As shown in <figref idref="f0004">FIG. 4b</figref>, valve 13a is a sliding tubing clamp.

0074The combination of the two chambers that allow separating the clean blood from the dirty blood, the ability to store dirty blood and if needed combine it with the venous blood, having an aggressive filter for the dirty blood and an air remover for the clean blood, reducing the volumes of air that can be dragged as the vented blood flows down channel 24, provide a unique clinical advantage. It should be clear that the filter for the clean blood consisting of screen 14c and defoamer 15 can also be fitted in channel 20a formed by defoamer 20 located in the top section of inlet chamber 2 in a manner similar to that described in reference to vent chamber 22 shown in <figref idref="f0002">FIGS. 3c and 3d</figref>.

0075It should be understood that the of three units, air purging chamber, compliant chamber and cardiotomy chamber, it is also possible to combine just the cardiotomy and complaint chamber by having those two units share a common rigid wall as described in reference to <figref idref="f0003 f0004 f0005">FIGs. 4a-d</figref> but without the air purging chamber as shown by line drawing illustrated in <figref idref="f0006">FIG. 7</figref>. Since the unit illustrated in <figref idref="f0006">FIG. 7</figref> shares the same design for the clean 1115a and dirty 1115b blood chambers combination forming the cardiotomy reservoir, as shown in <figref idref="f0003 f0004 f0005">FIGs 4a-4d</figref>, only the deviations from the unit illustrated in <figref idref="f0003 f0004 f0005">FIGs 4a-4d</figref> are described. As shown in <figref idref="f0006">FIG. 7</figref>, The combination unit consists of a venous reservoir 7103 having at least one flexible wall and one rigid wall, said walls sealed along their outside periphery to form closed complaint chamber 707 much like that compliant chamber 7 as described in reference to <figref idref="f0003 f0004 f0005">FIGs. 4a-4d</figref>. Venous blood enters chamber 707 via inlet port 701 and exits via outlet port 706 both preferably located along bottom 707a of chamber 707. Air entrained in the venous blood is purged via air purging port 703 located along the top most point in chamber 707. To facilitate use, port 703 preferably extends up to the top of the cardiotomy reservoir. Port 703 preferably is large in diameter (e.g. between 3/8 and 1/2") to form a low resistance channel for air bubbles to move up a blood column in that channel. Unlike other compliant venous bags, chamber 707 may also have defoamer 720 located along the top 707b of compliant chamber 707. Defoamer 720 may also extend into air purging port 703 and air sensor 732 may also be added for the same purpose and function as previously described in reference to sensor 32 in FIGs. D 3aa. The addition of a defoamer to the top of compliant chamber 7 and or air purging port 703 is to reduce aggressively collapse foam thereby reduce the large blood-air interface associated with foam. This method also allows port 703 to attach to a regulated vacuum source to purge the air without the need to pump the foam out of chamber 707 and without the need to have the foam/blood exiting port 703 to contact the aggressive filter of a cardiotomy reservoir.

0076Outlet port 706 is located in the lower portion of chamber 707 and is designed with considerations previously described for outlet 6 shown in reference to <figref idref="f0003 f0004 f0005">FIGs. 4a-4d</figref> Thus, level 719 is vertically lower than outlet port 706. This assures that outlet port 706 closes prior to blood level 719d in channel 719 drops to lowest point 719a of channel 719. As described before in reference to port 6 closing, when the blood in chamber 707 empties, the negative pressure due to the hydraulic height difference between 719a of channel 719 and outlet 706 of blood chamber 707 is sufficient to the flexible wall of chamber 707 to collapse against the opening of outlet 6, closing that port and preventing further emptying of blood chamber 707 and preventing air from passing point 719a and into chamber 707.

0077The dual chamber cardiotomy reservoir atop the venous reservoir has is almost identical to that described in reference to clean 1115a and dirty 111b blood chambers shown in <figref idref="f0003 f0004 f0005">FIGs 4a-4d</figref>. It has one large chamber 710 divided by separating wall 716 into chamber 710a for clean-blood and chamber 710b for dirty blood. Wall 716 extends from the bottom to the top of chamber 710 leaving a fluid communication 716a between the top of chambers 710a and 710b. Since clean blood need not be stored out of closed compliant chamber 707, then the volume of chamber 710a need only be sufficient to accommodate the screened chamber 714 used to deaerate defoam the clean blood. Thus, most of the volume of chamber 10 can be assigned to chamber 710b, thereby maximizing the volume available for dirty blood at the expense of volume for the clean blood. Typically the volume of chamber 710a should be no more than 20%, of the volume of chamber 10b. Clean blood enters via port 715a the clean filter composed chamber 714 formed of screen wall 714c that is sealed at its bottom. Defoamer 715 positioned at the top section of chamber 714 collapses foam in chamber 714. Clean blood flows through screen 14c, with the screen reducing the bubble size and air volume in the exiting clean blood. Similarly, dirty blood enters via port 711a to the aggressive filter 711, that also includes a defoaming agents. The filtered dirty blood flows into chamber 710b where it can be stored or flow to chamber 710a via port 718 and 717. Ports 717 and 718 are in fluid communication via tubing 713 that can be closed or opened with valve 713a to allow or prevent the dirty blood to flow to clean chamber 710a and then to combine with the venous blood in chamber 2. Blood in chamber 710a flows down channel 719 and combines with-venous blood at inlet port 701. It is preferred that lowest vertical level 719a of channel 719 is lower than inlet port 701. This minimizes air from the venous blood rising into channel 719.

0078<figref idref="f0004">FIGs. 4c</figref> and <figref idref="f0005">4d</figref> also illustrate that compliant blood chamber 7 can be fitted with front plate 28 sealed along the outside periphery of wall 8c to form sealed air chamber 26 with flexible diaphragm 25 as one wall and front plate 28 as the other wall. Channel 12 forms a fluid communication between air chamber 26 at opening 12a and cardiotomy reservoir chamber 10 at opening 12b assuring that the air pressure in these two chambers is equal. Air port 21 in fluid communication with chamber 10 can be open to ambient atmosphere, or as shown in <figref idref="f0005">FIG. 4d</figref>, to vacuum regulator 29. The latter can be used for VAVD. Freely moving flexible diaphragm 25 assures that the blood pressure in compliant storage chamber 7 equals the air pressure in air chamber 26. Thus, when vacuum is applied to port 21, it is transmitted to air chamber 10, and then via channel 12, to air chamber 26 and then, via moving diaphragm 25, to the blood in chamber 7. This is much like that described in reference to FIGS. 10a, 10b and 10c of aforementioned Tamari's '049 patent, vacuum can be applied to flexible diaphragm 25 that allows vacuum assisted venous drainage (VAVD). The shape of front plate 28 preferably is similar in shape to the shape of diaphragm 25 thereby allowing diaphragm 25 to fully expand and maximize the volume chamber 7 can fill to with blood. The same vacuum is also applied to inlet chamber 2 and outlet chamber 3 of air purging chamber 1116 via channel 3e shown in <figref idref="f0003">FIG. 4a</figref> and <figref idref="f0006">5a and 5b.</figref> Thus, the unrestricted fluid communication between air chamber 26 and cardiotomy chamber 10 and between cardiotomy chamber and inlet chamber 2 and outlet chamber 3 of air purging chamber 1116 (or 1116a) allows a single air port in any of these chambers to be used to apply vacuum to the other chambers and maintain these other chambers at the same vacuum as the chamber with that single air port. In the example shown that port is port 21 atop chamber 10 of cardiotomy 1115b shown in <figref idref="f0003">FIGs. 4a</figref>, <figref idref="f0004">4b</figref> and <figref idref="f0005">4d</figref>.

0079It should be understood that the description for gravity drainage (i.e. no vacuum applied to any port), where air is purged to atmosphere, also applies to VAVD applications except "atmosphere" is changed to the vacuum applied.

0080As shown in <figref idref="f0003">FIGS. 4a</figref>, <figref idref="f0004">4b, and 4c</figref>, air purging chamber 1116, venous reservoir 1103, cardiotomy reservoir 1115, as well as channels 1, 3e, 4 and 12 interconnecting these chambers, are at least partially formed with common rigid plate 8, a design that reduces manufacturing costs and simplifies setup. Thus for example, rigid wall 8a forms at least a part of the wall forming inlet channel 1 of air purging chamber 1116; rigid wall 8b forms at least one part of the wall forming outlet chamber 3 of air purging chamber 1116; rigid wall 8c forms at least a part of the wall forming compliant storage chamber 7; rigid wall 8d forms channel 4b connecting outlet chamber 3 to compliant storage chamber 7; rigid wall 8e forms channel 19 connecting chamber 10 of cardiotomy 1115 to the bottom of inlet channel 1; rigid wall 8f forms at least one part of the wall forming chamber 10 of cardiotomy 1115. Common wall 8 may also form channel 3e connecting the top of inlet chamber 2 to the top chamber 10 of cardiotomy 1115, outlet port 6 of compliant storage chamber 7 as well as the numerous connectors atop cardiotomy reservoir 1115.

0081It should be clear that rigid wall 8 can have a matching clam shell like mirror image structure that fits to complete the walls required to form the aforementioned chambers and channels. Other designs include having outlet chamber 3 and cardiotomy chamber 10 with its divider 16, and concave section 8c injected molded and then fitted with top covers that incorporate ports such air port 21 or inlet port 1 shown in <figref idref="f0003">FIG. 4a</figref>.

0082<figref idref="f0006">FIG. 6</figref> is a line drawing illustrating a design where tubing is used as channel 4b connecting outlet 4 of the air purging chamber, previously described in reference to <figref idref="f0002">FIGs. 3a-3d</figref>, to compliant reservoir 7, and tubing 153 is used to connect the outlet of cardiotomy reservoir and to inlet I of air purging chamber 1116. Using tubing has two advantages: it simplifies the mold and it enables the user to clamp off the tubing when needed. It also illustrates that air purging chamber 1116 can be used with state of the art venous bags eliminating air from entering the bag to provide a greater safety.

0083<figref idref="f0006">FIG. 6</figref> also illustrates another mean to reduce air being dragged from cardiotomy 1115 to inlet chamber 2 via channel 153. This is accomplished by slanting tube 153 to allow air bubbles 27 that have entered tube 153 to rise to the radial top of channel 153 and then, as illustrated in <figref idref="f0006">FIG. 6a</figref> by the upward pointing arrow, move up channel 153 along its top most wall. Raised section 153b facilitates air bubble escape from channel 153 by preventing blood flow at that highest outlet point during intermittent blood flow. To further reduce air bubbles entrapment and facilitate air bubbles movement up channel 153, channel should have at least the top portion enlarged to an equivalent diameter greater than 3/8" and preferably at least 1/2".

0084To summarize, the invention provides a venous reservoir that: <ol id="ol0001" compact="compact" ol-style=""><li>1) Has superb air handling.</li><li>2) A closed reservoir that passively removes air.</li><li>3) Primes easier and faster than any other closed venous reservoir.</li><li>4) It is the only venous bag that incorporates a cardiotomy reservoir and allows VAVD.</li><li>5) It brings vented (clean) blood into the venous reservoir without contacting the cardiotomy.</li><li>6) It allows for VAVD for a closed reservoir.</li><li>7) It closes shut when empty and requires very little volume to reopen.</li><li>8) It can operate at low volume without the danger of pumping air.</li><li>9) Once primed, air cannot enter it. The new reservoir is therefore safer.</li><li>10) A low level alarm can be placed on it as easily as on any hard shell.</li></ol> It should be understood that a comprehensive description of each of the applications of the invention is beyond the scope of a patent application and therefore the aforementioned descriptions are given as illustrations and should not be used to limit the intent, spirit, or scope of the invention. With that in mind, I Claim: