Oxygenating unit for extracorporeal circulation devices

May 14, 1957 _G. _v. a. malmros etal 2,792,002

OXYGENATING UNIT FOR EXTRACORPOREAL CIRCULATION DEVICES

Filed April 9, 1952

Sheets-Sheet 1

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FIG.I

INVENTORS

GUSTAV V.A. MALMROS

DONALD K. REX

BY.

ATTORNEY

May 14, 1957 _G. v. a. malmros etal 2,792,002

OXYGENATING UNIT FOR EXTRACORPOREAL CIRCULATION DEVICES

<img file="US2792002A_D0002.tif" />

May 14, 1957 g. v. a. malmros etal 2,792,002

OXYGENATING UNIT FOR EXTRACORPOREAL CIRCULATION DEVICES

Filed April 9, 1952 5 Sheets-Sheet 3

<img file="US2792002A_D0003.tif" />

May 14, 1957

OXYGENATING

Filed April 9, 1952

G. V. A. MALMROS ETAL 2,792,002

UNIT FOR EXTRACORPOREAL CIRCULATION DEVICES

Sheets-Sheet 4

<img file="US2792002A_D0004.tif" />

May 14, 1957

G. V. A. MALMROS ETAL

2,792,002

OXYGENATING UNIT FOR EXTRACORPOREAL CIRCULATION DEVICES

Filed April 9, 1952

Sheets-Sheet 5

<img file="US2792002A_D0005.tif" />

CO

SUPPLY

INVENTORS

GUSTAV V.A.MALMROS

DONALD K. REX

ATTORNEY

United States Patent Office

2,792,002

Patented May 14, 19S7

2,792,002

OXYGENATING UNIT FOR EXTRACORPOREAL CIRCULATION DEVICES

Gustav V. A. Malmros, Binghamton, and Donald K. Rex, Endicott, N. Y., assignors, by mesne assignments, to The Jefferson Medical College of Philadelphia, Philadelphia, Pa., a non profit corporation of Pennsylvania

Application April 9,1952, Serial No. 281,373

Claims. (CI. 128—214)

This invention relates generally to extracorporeal circulation devices and particularly to venous blood oxygenating units adapted for use in extracorporeal circulation devices, of the general type described in United States Patent No. 2,659,368.

Generally, the introduction of oxygen into venous blood and the accompanying removal of waste products, such as carbon dioxide therefrom in a mechanical device adapted to provide a functional replacement for the lungs is a problem beset by many difficulties. In order to introduce adequate and predetermined amounts of oxygen into venous blood and to remove the waste products therefrom, it is necessary to provide a large surface area for oxygenating and waste product transfer purposes and to manipulate the blood thereon in such a manner as to form a continuous thin film of extensive surface area having sufficient turbulence of flow to provide high oxygenation and transfer efficiencies by exposing every volume of the blood to an oxygen-enriched atmosphere and yet utilize only a small volume of blood at any given instant passing through the oxygenating atmosphere at relatively high flow rates without any detrimental foaming or bubbling of the blood in its passage through the unit.

Coupled with the problem of efficient oxygenation of the venous blood is a closely related but yet separate problem of assuring the removal of waste products, largely carbon dioxide, from the blood. The transfer phenomenon is a function, at least in part, of relative vapor pressures. Consequently, in order to effect efficient transfer of the waste material, it is necessary to control the composition of the oxygenating atmosphere at least as to the carbon dioxide content thereof.

Another problem attendant the utilization of all oxygenating units in extracorporeal circulation devices is the insuring of attaining a continuous, uniform and thin film of blood over the oxygenating surfaces. Rivulet flow of blood over the oxygenating surfaces greatly reduces the blood surface area available for oxygenating purposes and consequently reduces the oxygenation and transfer efficiency to negligible amounts.

In all devices of this type there must, in addition, be a simplicity and durability of construction that permits easy and repeated assembly and disassembly operations without damage to critically contoured components which must also be designed to permit easy cleaning and sterilization.

The present invention satisfies these rigid and conflicting requirements and may be briefly described as a venous blood oxygenating unit wherein the oxygenating and waste product transfer surface is formed of a plurality of vertically disposed wire mesh screens having the necessary qualities of mechanical rigidity, high blood film turbulence, and low hold-up through utilization of a relatively small amount of blood for film formation, supported at their upper extremities on particularly contoured and proportioned mounting members, which are shaped and arranged to provide a self-regulating blooddistributing system to insure continuous and uniform blood film formation without detrimental foaming and bubbling and without damage to the suspended blood cells. The screens are maintained in a predetermined array and in spaced relationship by a supporting member disposed within the oxygenated blood reservoir, and the entire unit is contained within a covered jacket or casing that cooperates with the internally disposed members to control the blood flow rate and the characteristics thereof in avoidance of foaming and bubbling. The invention also includes a method of insuring formation of a continuous, uniform and thin film of blood in an oxygenenriched atmosphere to avoid rivulet blood flow and assure operation at high oxygenation and transfer efficiencies. The invention further includes means for controlling the composition of the oxygenating atmosphere in response to the condition of the oxygenated blood to assure efficient waste product transfer.

The primary object of the invention is the provision of an improved venous blood oxygenating unit for extracorporeal circulation devices.

Another object of this invention is the provision of an improved venous blood oxygenating and waste product transfer unit for extracorporeal circulation devices.

Another object of this invention is the provision of a method of forming and maintaining a continuous, uniform and thin film of blood on the oxygenating surfaces in a venous blood oxygenating unit.

Another object of the invention is the provision of an improved and self-regulating, venous blood, distributing system for venous blood' oxygenating units.

Another object of this invention is the provision of an improved venous blood oxygenating unit wherein small volumes of venous blood may be efficiently oxygenated at high flow rates without damage to the suspended blood cells and without destructive foaming or bubbling.

Another object of this invention is the provision of an oxygenating unit that is simple in construction, easily assembled and disassembled for sterilization and cleaning purposes, and yet of sufficient durability to permit rough usage and handling in repeated assembly and disassembly operations without damage to critically contoured components.

A further object of this invention is the provision of a control system to regulate the composition of the oxygenating atmosphere to assure efficient waste product transfer operations in. addition to efficient oxygenation operations.

A still further object of this invention is the provision of a control system to regulate the composition of the oxygenating atmosphere to- maintain the proper proportion of carbon dioxide in the blood.

Other objects and advantages of the invention will be pointed out in the following disclosure and claims and illustrated in the accompanying drawings which disclose, by way of example, the principle of the invention and the presently preferred embodiment of the oxygenating unit incorporating that principle.

Referring to the drawings:

Fig. 1 is an oblique view of the assembled oxygenating unit;

Fig. 2 is a front elevation, partially in section of the oxygenating unit illustrated in Fig. 1:

Fig. 3 is a sectional view on the line 3—3 of Fig. 2;

Fig. 4 is a side elevational view of the oxygenating unit illustrated in Fig. 1; and

Fig. 5 is a schematic representation of the means utilized to control the composition of the oxygenating atmosphere.

Referring to the drawings, there is provided a supporting structure including a generally U-shaped base plate 10 having mounted on the extended arms thereof two upright columns 12. Positioned at the top of the columns 12 and supported thereby is a generally U-shaped support

2,702,002 ing frame member 14 having extended arm portions 20. Supported at their extremities on the extended arms 20 of the generally U-shaped frame member 14 are a plurality of horizontally disposed elongated mounting members 16 disposed intermediate an outside front mounting member 24 and an outside rear member 22. The mounting members 16, 22 and 24 are preferably made of a corrosion-resistant alloy such as stainless steel which resists the corrosive action of the blood and permits repeated sterilization and cleaning procedures without surface deterioration. The mounting members are disposed in close parallel alignment and are secured in that relationship by a pair of horizontally disposed mounting screws 18 passing through suitably aligned apertures in the intermediate mounting members 16 and the outside mounting members 22 and 24 respectively.

The intermediate mounting members 16 are, in the body portion thereof disposed intermediate their supported extremities, contoured in cross-section to provide a long side 26 (see Fig. 3) downwardly terminating in an extended continuous knife-like edge 28; and a short side 30 downwardly terminating in an acute angle 32 of greater extent than the acute angle formed by said knifelike edge 28.

When positioned in operative relationship as illustrated in the drawings, the mounting members 16 are disposed with the long side 26 of one mounting member disposed in close proximity adjacent the short side 30 of the adjacent mounting member. The rear mounting member 22 is contoured so as to provide a short side 30 adapted to be disposed adjacent the long side 26 of the adjacent intermediate mounting member 16. In a similar manner, the front mounting member 24 is contoured to provide a long side 26 downwardly terminating in a dependent knife-like edge 28 adapted to be disposed adjacent the short side 30 of the adjacent intermediate mounting member 16.

The short sides of the intermediate mounting members 16 and the rear mounting member 22 have a recessed portion machined in the body portion thereof disposed intermediate their supported extremities and over a length determined by the length of said knife-like edge 28 so that when the mounting members 16, 22 and 24 are assembled in operative relationship as illustrated in the drawings, there will be a lateral spacing 34 between adjacent mounting members. This spacing between adjacent mounting members serves as a venous blood distributing system, and it has been determined that a spacing of from .006 to .007 inch will function adequately for venous blood regulating and distributing purposes.

Dependent from and secured to each of the knife-like edges 28 is a vertically disposed semi-rigid metallic wire mesh screen 36 preferably made of stainless steel or other corrosion-resistant alloy. The screens 36 are supported at their lower extremities by a slotted plastic supporting member 38 which, in addition to supporting the screens, maintains the screens in parallel array and in spaced relationship. The slotted plastic supporting member 38 is suspended from the intermediate mounting members 16 by means of the oxygen supply tube 42 and the gas exhaust tube 40 which are also preferably formed of stainless steel or other suitable corrosion-resistant alloy. The tube 42 is provided with a number of suitable apertures 41 along its length to permit the introduction of oxygen at spaced locations along the length of the screens 36. Tube 40 is utilized as a gas exhaust tube, to exhaust the waste products given up by the venous blood, and to this end is provided with an aperture disposed above the support member 38.

Enclosing the dependent screens 36 and slotted supporting member 38 is a casing or jacket 44 rigidly supported from the front and rear mounting members 24 and 22 respectively by a plurality of vertically disposed mounting screws 46 which pass through suitable apertures in the mounting members and engage a dependent lip on the exterior surface of said casing or jacket 44. The casing 44 is preferably constructed of a clear plastic such as Lucite or any other plastic of suitable characteristics to permit visual observation of the oxygenating screens and blood manipulations therein. Disposed within the casing 44 are evenly spaced high resistance heating wires 48 connected to an external plug 50 disposed adjacent the bottom of said casing 44. The heating wires serve to aid in the maintenance of uniform temperature conditions within the oxygenating unit in order to prevent a decrease in blood temperature during its passage therethrough and to prevent undesirable and detrimental condensation of moisture introduced with the oxygen. The utilization of dry oxygen in avoidance of this problem is generally undesirable as it readily absorbs moisture from the blood exposed thereto.

Positioned at the lower extremity of the front of the jacket 44 is a large aperture 52, and positioned at the bottom of the jacket 44 is a second and smaller aperture 54. The lower portion of the casing serves as an oxygenated blood reservoir and the supporting member 38 is positioned so as to be beneath the surface of the collected oxygenated blood during operation. The supporting member 38 is sized to fill most of the volume within the blood reservoir to the end that a change in blood level therein denotes a relatively small volume change for control purposes. The control system responsive to the blood level within the oxygenated blood reservoir is described in detail in United States Patent No. 2,705,493.

The enclosure of the screens and slit distributing system is completed by an arched cover member 56 secured to the upper surface of the mounting members 16, 22 and 24 by means of a plurality of vertically disposed mounting screws 58. The arched cover member 56 is arranged in leak-proof relationship with the upper surface of the mounting members by the use of a gasket 60 disposed between said cover 56 and the mounting members 16, 22 and 24. The cover member 56 contains a centrally disposed exhaust orifice 62 and also includes an offset venous blood inlet orifice 64 having a horizontal baffle plate 65 interiorly disposed therebeneath. The cover member 56 is also suitably perforated to permit the extension of the tubes 40 and 42 and the extension of the auxiliary waste gas exhaust tubes 66 and 68. The waste gas exhaust tubes 66 and 68 are supported in suitable apertures by the intermediate mounting members 16 and extend to varying depths within the casing 44 and thus permit in conjunction with tube 40 the scavenging of waste gases at varying depths within said casing and to aid in the maintenance of a uniform and even gas flow across the screens 36 disposed therein.

In order to obtain high oxygenation and waste product transfer efficiencies during operation of the above described device, it is necessary to insure the formation of a continuous uniform and thin film of blood of extensive surface area on both the surfaces of the oxygenating screens 36 in order to expose every volume of blood to the oxy gen-enriched atmosphere.

The initial step in the operation of the above described unit in order to insure the formation of said desired blood film is a process of preliminarily wetting the wire mesh screens 36. This preliminary wetting is necessary in order to avoid rivulent flow characteristics and to assure the formation of a reasonably uniform film of blood at the start of operations, which, once established, is maintained without undue difficulty by the self-regulating blood distributing system disclosed herein.

The preliminary wetting is readily accomplished by initially filling the jacket 44, by means of a rubber hose 70 connected to a revolving joint 72 inserted in the aperture 52 in the base of the jacket 44, with a physiological saline solution so as to completely cover and submerge the screens 36. During the saline solution filling operation, the centrally disposed orifice 62 is left open and the

2,792,002 blood drainage tube 73 connected to the blood drainage orifice 54 is maintained closed.

After the jacket 44 is filled with the physiological saline solution as described above, a suitable tube from the venous blood supply is attached to the venous blood inlet orifice 64 in the arched cover member 56. Venous blood is then introduced into the arched cover member 56 through Orifice 64 until the slits 34 are filled with blood and the mounting members 16 are covered thereby. During the introduction of venous blood as described above, the exhaust orifice 62 is maintained open to permit the escape of air. After collection of a suitable amount of blood in the arched cover member 56, as set forth above, the physiological saline solution is rapidly drained from the casing 44 by means of the rubber hose 70. During the draining operation sufficient venous blood is introduced via orifice 64 to maintain the slits 34 in a submerged condition. After completion of the draining of the saline solution, the member 72 is revolved to place the hose 70 in an upright position which halts the saline draining operation. At this time the tube 73 is opened and the oxygenated blood is drained from the jacket 44 therethrough.

Coincident with the opening of blood drainage tube 73, the rate of introduction of venous blood into the cover 56 is increased until there is only a small amount of air left in the portion of the cover member beneath the orifice 62 and above the venous blood contained therein. Orifice 62 is then capped and remains capped throughout further operations. The spaced mounting members Ϊ6 in conjunction with the slightly compressed air in cover member 56 with orifice 62 capped provide a self-regulating blood distributing system that acts to smooth out any pulsations in the delivered venous blood and maintain a uniform flow onto the screens 36.

The draining of the saline solution and the immediate replacement thereof with the venous blood which flows down through the slits and onto the still wet screens insures the formation of a continuous thin blood film and prevents the formation of a rivulent flow. After initial film formation, the arched cover member 56, with the orifice 62 capped, in conjunction with the spaced mounting members 16 functions as a self-regulating metering device that requires no adjustment to accommodate variations in the flow rate of the venous blood. The slits 34 direct the blood onto the top edge of each of the screens 36 in a uniform manner and the screens being wet with the residue of the saline solution permit the vertical descent of a Uniform, continuous thin film of blood thereon. The downward flow of venous blood continues and collects at the bottom of the jacket 44. The small amount of saline solution remaining on the screens 36 after draining thereof has a negligible effect in being mixed with the blood flowing down thereon.

The screens 36 as used herein have the advantage of exposing blood on both sides of the screens simultaneously, thus greatly increasing the area available for blood film formation. The screens 36 are chosen to provide the desirable characteristics of mechanical rigidity, high blood film turbulence, and low hold-up, and stainless steel screen material having six spaced vertical wires per inch and twenty-four spaced horizontal wires per inch has been found suitable for setting up a turbulent blood film flow on said screens to provide a high oxygenation and waste product transfer efficiency Without the occurrence of foaming or bubbling.

Oxygenation of the blood disposed in film formation on the screens 36 is readily accomplished by introducing oxygen into the jacket 44 through the apertured tube 42. As mentioned above, the plurality of apertures 41 in this tube introduces the oxygen into the jacket 44 at predeterminated levels and this in conjunction with the disposition of the exhaust tubes 40, 66 and 68 as described above assures a flow of gas perpendicular to the direction of blood flow and provides a uniform oxygen-enriched atmosphere.

As mentioned above, the transfer of the waste products, which in practice if found to be largely carbon dioxide, is a closely related problem to that of oxygenation of the blood, but yet is distinct therefrom for the mere provision of an oxygenating atmosphere does not assure efficient waste product transfer. The waste product transfer phenomenon is 'largely dependent upon relative vapor pressures and to this end there is provided a system to control the carbon dioxide content of the oxygenating atmosphere.

Referring to Fig. 5 there is included in the blood drainage tube 73 connected to the drainage orifice 54 a unit 76, containing pH electrodes of conventional construction for measuring the hydrogen ion concentration which is indicative of the carbon dioxide alkalosis or acidosis of the oxygenated blood. The unit 76 containing the pH electrodes is preferably connected to a conventional electrical recording instrument 78 to provide a permanent record of the hydrogen ion concentration. Connected to the electrical recording instrument 78 and responsive thereto is an electrically actuated valve assembly 80 of conventional construction associated with a source of carbon dioxide 82. The electrically actuated valve assembly 80 is preset so as to open and close at predetermined values of pH so as to control the addition of carbon dioxide to the oxygen supply line 42 for the oxygenating unit and thereby control the composition of the oxygenating atmosphere within predetermined limits. The control of the composition of the oxygenating atmosphere as described above assures the maintenance of the proper proportion of carbon dioxide in the blood.

In accordance with the provisions of the patent statutes, we have herein described the principle of operation of this invention, together with the elements which we now consider to constitute a workable embodiment thereof, but we desire to have it understood that the structure disclosed is only illustrative and the invention can be carried out by other means. Also, while it is designed to use the various features and elements in the combinations and relations described, some of these may be altered and modified without interfering with the more general results outlined.