Title:
PULSATILE BY-PASS BLOOD PUMP
United States Patent 3656873


Abstract:
A by-pass pump system especially adapted for use in assisting or temporarily replacing the circulatory function of the heart in which a pair of highly elastic collapsible containers are coupled to one another through a resilient flap valve. Each flexible chamber is positioned within an associated housing whose interior pressure is regulated to control the expansion and contraction of the flexible housings. Blood enters the first of said chambers causing the chamber to fill when the blood pressure is greater than the pressure of the surrounding housing. The one-way valve mechanism enables the blood filling the first flexible chamber to enter the second flexible chamber when the interior pressure of the second flexible chamber is lower than that of the first chamber. Conversely, if the pressure within the interior of the second resilient chamber is greater than that within the first flexible container, the one-way valve structure prevents reverse flow. Pneumatic means is coupled to the housing surrounding the second flexible container to cause the blood to be pumped through an outlet opening provided in the second flexible container in order to enter into the arterial system at a rate substantially equal to the normal pumping rate of the patient. A second one-way valve mechanism is provided in the aforesaid outlet opening to prevent reverse flow. The action of the flexible containers upon the blood is non-occlusive due to the pneumatic controls utilized, as well as the nature of the design of the chambers. The one-way valve mechanisms may alternatively be of a flap valve form or a form in which the closure portions of the valve are highly elastic to permit ready flow of the blood in a first direction while preventing flow in the reverse direction. In one preferred design the one-way valve structures cooperate with their associated valve mounts to provide positive reliable operation and simple straightforward removal and insertion.



Inventors:
SCHIFF PETER
Application Number:
05/087487
Publication Date:
04/18/1972
Filing Date:
11/06/1970
Assignee:
PETER SCHIFF
Primary Class:
Other Classes:
128/DIG.3, 417/540, 623/3.1
International Classes:
A61M1/10; (IPC1-7): F04B43/06; F04B45/00; A61F1/00; A61B19/00
Field of Search:
417/474,475,395,540 3
View Patent Images:
US Patent References:



Primary Examiner:
Croyle, Carlton R.
Assistant Examiner:
Gluck, Richard E.
Claims:
The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows

1. Means for converting a low pressure fluid flow to a high pressure pulsatile flow comprising:

2. The device of claim 1 wherein said one-way valve means includes means adapted to permit fluid flow from said first to said second flexible container while preventing fluid flow in the reverse direction.

3. The device of claim 1 further comprising:

4. The device of claim 1 wherein said valve means is comprised of a pair of flap members diagonally aligned within said first conduit means to form a V-shaped configuration when closed whereby said flaps are curved near their free ends to cause engagement therebetween only in the marginal region of said flap free ends in the presence of reverse fluid flow.

5. The device of claim 1 wherein said valve means is comprised of a plurality of arcuate shaped flap members diagonally aligned within said first conduit means to form a dome-shaped configuration when closed, whereby said flaps are provided with V-shaped flanges along their free ends to cause engagement therebetween only in the marginal region of said flap flanges in the presence of reverse fluid flow.

6. The device of claim 1 wherein said flexible conduits are each formed from a pair of thin sheets of a flexible material whose marginal engaging portions are joined by a suitable adhesive means to air-tightly seal said containers as well as defining their perimeters.

7. Means for converting a low pressure fluid flow to a high pressure pulsatile flow comprising:

8. The device of claim 7 wherein said flexible membranes are formed of a flexible non-stretching material.

9. The device of claim 7 wherein the interior surface of the first chamber forming a portion of said first fluid receiving compartment has a substantially tapered configuration;

10. The device of claim 7 wherein said one-way valve means includes means adapted to permit fluid flow from said first to said second chamber fluid receiving compartment flexible container while preventing fluid flow in the reverse direction.

11. The device of claim 7 further comprising:

12. The device of claim 7 wherein said valve means is comprised of a plurality of arcuate shaped flap members diagonally aligned within said first conduit means to form a dome-shaped configuration when closed, whereby said flaps are provided with V-shaped flanges along their free ends to cause engagement therebetween only in the marginal region of said flap flanges in the presence of reverse fluid flow.

13. The device of claim 9 wherein the outlet port of said first chamber fluid receiving compartment is positioned at the apex of said tapered interior surface;

14. The device of claim 1 including means responsive to the nearly total collapse of said first flexible container for deactivating said actuator means.

15. The device of claim 7 wherein said means for maintaining the pressure in the non-fluid receiving compartment of said first container includes means for regulating the pressure level in said first container in inverse proportion to the amount of blood in said first container.

16. The device of claim 15 wherein said regulating means further comprises an adjustable clamp provided in the inlet part of said first fluid receiving container.

17. The device of claim 16 further comprising plunger means having a first end resting upon the membrane of said container and a second end extending outwardly from the non-fluid receiving compartment of said first container whereby the length of said second end extending beyond said first chamber is employed to determine the adjustment of said adjustable clamp.

18. The device of claim 15 wherein said pressure regulating means is further comprised of plunger means having a first end resting on the membrane of said first container and a second end extending outwardly from said first container;

Description:
The present invention relates to pumping systems and more particularly to a novel non-occlusive pumping system for use as a substitute or assistive non-occlusive blood pumping means.

BACKGROUND

During open-heart surgery or in applications where it is desired to assist the circulatory function of a failing heart, blood is removed from the body of a patient at a low pressure level and is pumped into the arterial system at a higher pressure. Quite often, portions of the normal circulatory system are by-passed in this manner to permit surgery to be performed upon the affected parts or organs such as, for example, the heart itself. Until recently, the pumping function was achieved primarily through the use of a roller pump. The characteristic of a roller pump is such as to progressively compress an elongated length of tubing, which acts as a conduit for blood flow, through the use of several rollers rollingly and compressingly engaging the tubing in a successive fashion so as to force the blood through the tube and thereby either replace or supplement the natural heart function. Conventional roller pumps have several disadvantages as compared to the natural heart. Among these are the fact that the roller pump is occlusive and thereby compresses and severely damages blood cells by compressing the cells between the two surfaces of the tubing due to the compressive action of the rollers upon the tubing. Furthermore, the roller pump is a positive displacement pump having no controlled output pressure limits or input suctions limits situations where the tubing delivering blood to the roller pump may become blocked for any reason. As a result, the tubing may burst or develop an excessive vacuum condition causing nitrogen to be extracted from the blood to an extent where the survival of the patient becomes endangered. Continuous outflow of blood from a conventional roller pump is undesirable since such operation fails to emulate the pulsatile nature of the natural heart.

It is therefore most important to provide a pumping system which most closely emulates the operation of the natural heart and which should therefore be characterized by providing: continuous innerflow of blood to the pump and a high pressure pulsatile outflow; means for limiting pressure at the outflow to a safe level even in the presence of obstructions in the outflow; means for adjustably controlling vacuum and pressure levels at the inflow end of the pump so as to accommodate the requirements of a particular application or patient; means for providing non-occlusive pumping action and a design which enables the system to be rapidly synchronized to operate in synchronism with the operation of a normal heart through the use of a design having low mechanical inertia in order to greatly enhance pump response time.

The present invention is comprised of a pair of highly resilient containers each mounted within an associated pressure controlled housing. The flexible containers are joined through a common connection having a one-way valve mechanism which permits fluid flow in a first direction while preventing any reverse fluid flow. The flexible container at the input end of the pump is permitted to fill at a rate dependent upon the pressure differential existing across the flexible walls of the container. Transfer of the incoming flow from the input side container to the output side container is a function of the pressure gradient across the one-way valve mechanism.

The output side flexible container is provided with an outlet port containing a second one-way valve mechanism to permit fluid flow only in the output direction while preventing any reverse flow. Pulsatile pumping means are coupled to an inlet port of the housing containing the flexible container of the output side to deliver any pulsatile high pressure output flow to the patient's arterial system. The walls forming each of the flexible containers are quite thin and highly resilient to provide for quick response to pressure differentials across the flexible walls and to provide positive non-occlusive pumping action.

In a preferred embodiment, the one-way valve mechanisms and their associated valve mounting means are designed so as to enhance the seating of the valve during normal operation while at the same time providing for simple rapid removal and/or replacement of the valve assembly.

It is therefore one object of the present invention to provide a novel non-occlusive pumping system for use in either assisting or by-passing normal heart function.

Another object of the present invention is to provide a novel non-occlusive pumping system comprised of at least two flexible chambers and pressure operated enclosures therefore which, together with connecting one-way valve mechanisms cooperate to emulate the operating characteristics of the natural heart.

Another object of the present invention is to provide a novel one-way valve design for use in by-pass pumping systems of the non-occlusive type.

These as well as other objects of the present invention will become apparent when reading the accompanying description and drawings in which:

FIG. 1 is a block diagram showing a total by-pass system.

FIG. 2 is a sectional view showing a by-pass pump designed in accordance with the principles of the present invention.

FIG. 3 is a sectional view showing one of the flap valve mechanisms of FIG. 2 in greater detail.

FIG. 4 is an exploded perspective view showing one physical form of the pump of FIG. 2.

FIG. 5 is a sectional elevational view of another preferred embodiment of the present invention.

FIGS. 6a and 6b are sectional and top plan views respectively, showing one of the valves of FIG. 5 in greater detail.

FIG. 7 is a sectional view showing the details of the liners used in FIGS. 2 and 5.

FIGS. 8 and 9 are sectional views of further embodiments of FIG. 5.

FIG. 1 illustrates a total by-pass system incorporating a blood pump. As shown therein, blood is taken from the venous system of a patient 1 and passes through an oxygenator 8 provided to oxygenate the blood as a substitute for function normally performed by the patient's lungs due to the fact that the lungs in both the right and left side of the heart have been by-passed. The oxygenator removes carbon dioxide and replenishes the blood with oxygen. A pulsatile blood pump 11 receives blood from oxygenator 8 and increases blood pressure from a pressure level equivalent to several millimeters of mercury which is a level normally found in the venous system of a patient, to a mean pressure of 100 millimeters of mercury which is a pressure normally found in the arterial system of a human. The output blood flow is then passed through a heat exchanger unit 4 provided to lower the patient's blood temperature level for surgery and also adjustable to increase blood temperature upon the termination of surgery. Unit 4 also serves to add heat dissipated by the blood due to the long extracorporeal path which the blood follows in moving through the total by-pass system. The low temperature during surgery reduces the oxygen consumption of the patient and therefore permits the patient to safely survice a substantially long time interval during which the mechanical by-pass system provides its supportive functions. The blood, after passing through heat exchanger 4, is returned to the arterial system of the patient.

Desirable by-pass pump characteristics, which can clearly be seen to closely emulate the properties of a natural heart can be summarized as follows:

1. The pump should provide a continuous venous inflow and a high pressure pulsatile arterial outflow.

2. The pump should provide safe limiting pressures at the outflow end even in the presence of obstructions which may occur at the outflow.

3. The pump should provide a means for readily adjusting and controlling vacuum and pressure levels at the inflow side to enable the pump to function at a variety of filing modes to suit the requirements of various oxygenators and by-pass systems. Examples are gravity filling, filling at a controlled vacuum, and filling at a controlled inlet pressure as is required by some membrane oxygenators of recent design.

4. The pump should provide non-occlusive blood flow since any contact between two occlusive surfaces may cause excessive blood cell damage due to abrasion and/or due to the non-compatible nature of present synthetic materials with blood.

5. The pump must exhibit a low blood damage or hemolysis factor which may be accomplished through a design incorporating low blood turbulance, selection of proper materials and a non-occlusive construction.

6. The driving mechanism must be capable of being synchronized to the operation of the natural heart with sufficient rapidity to provide proper phase relationships to the heart which requires a design of low mechanical inertia and small delay so as to prevent pump response from being either too slow or too late. This design characteristic generally restricts the pump driving means to hydraulic or pneumatic operation as opposed to mechanically driven devices.

The design objectives may be accomplished by the pulsatile by-pass pump shown in schematic fashion in the cross-sectional view of FIG. 2.

The pump assembly of FIG. 2 is comprised of an "atrium" chamber 17 and a "ventricle" chamber 30 which are similar in design and function to corresponding portions of a natural heart. The venous return line 14 which may be coupled to the patient through any suitable manner (or through any oxygenator 8, as shown in FIG. 1) is coupled into the interior of atrium 17 through an inlet port 17a. Incoming blood passes through atrium 17 and a common conduit 22 containing one-way flap valve 21 so as to enter ventricle 30 through its inlet port 30a. The blood leaves the ventricle 30 through outlet port 30b and conduit 28 which contains one-way flap valve 26. Ventricular conduit 28 may be connected to the arterial system of the patient (or heat exchanger unit 4, as shown in FIG. 1).

The valve mechanisms 20 and 26 are so arranged to respectively permit free flow in the directions from inlet conduit 14 to outlet conduit 28 while preventing reverse flow therethrough.

Atrium 17 and ventricle 30 are preferably comprised of a pair of substantially flat sheets of a material which is elastic and compatible with the blood so as not to have any effect upon the characteristics or composition of the blood as a result of the physical contact therebetween. The highly resilient elastic sheets are preferably cemented to one another along their marginal surfaces so as to air-tightly join the sheets to one another and thereby define the atrium and ventrical enclosures 17 and 30, respectively, as well as the associated connections therebetween.

Ventricle 30 is positioned within a rigid chamber 13 having an opening 31 for connection to pneumatic actuator 27. The application of a slight vacuum into the interior of chamber 13 to pneumatic actuator 27 serves to separate the two cooperating portions of sheets 24 and 25 which form ventricle 30, to provide a suction within the interior of the ventricle. As a result, blood is drawn from atrium 17 through one-way valve 21 into ventricle 30. One-way valve 26 is closed as a result of the suction developed within ventricle 30 and the high pressure level in conduit 28 on the output side of the system. The pneumatic actuator is then operated to periodically pressurize the interior of chamber 13 causing the flexible membrane portion of sheets 24 and 25 to transmit this pressure condition to the blood contained within ventricle 30. Due to the action of one-way valves 21 and 26, the blood is constrained to flow through outlet port 30b and one-way valve 26 as soon as the pressure within ventricle 30 is greater than the pressure within the outlet end of conduit 28. Valve 21 is closed during this phase since the pressure at its left-hand side is less than the pressure at its right-hand side. In this manner, ventricle 30 is operated to repetitively fill and empty to simulate a pumping pulsatile operation.

Atrium 17 performs the dual functions of acting as a buffer between the pulsatile operation of ventricle 30 and the continuous venous return flow condition at inlet conduit 14 as well as controlling the vacuum of pressure within conduit 14 to adjustably selected values. Since the portions of elastic sheets 24 and 25 perform a limp bladder, the atrium operates as a reservoir which stores the blood draining into it through the venous return line 14. Upon demand of ventricle 30, blood is drained from atrium 17 through the connecting conduit 22 and one-way valve 21 into ventricle 30. The suction or negative pressure condition within ventricle 30 during its filling stage is transferred to atrium 17 when the atrium is drained of blood and is no longer capable of supplying adequate blood as a result of insufficient blow flow entering atrium 17. This suction within atrium 17 causes the opposing sheet portions forming atrium 17 to collapse upon one another and thereby effectively isolate the filling phase suction imparted upon atrium 17 by ventricle 30 from reaching input line 14. As more blood becomes available and enters input line 14, its slightly positive pressure causes a separation of the membrane portions forming atrium 17 to reinitiate blood flow from atrium 17 into ventricle 30.

Isolation of the pulsatile suction or negative pressure developed by ventricle 30 due to collapse of atrium 17 in the presence of insufficient blood flow occurs as a result of the pressure differential across the interior and exterior surfaces of the portions of sheets 24 and 25 forming atrium 17. By placing atrium 17 within closed chamber 12, the pressure or suction within the interior of chamber 12 may be controlled through the connection of the pressure of vacuum generating source 19 to opening 18. Thus, expansion or contraction of the atrium 17 may occur at pressures other than atmospheric, if desired. Since atrium 17 is a flexible and elastic structure, any pressures or suction across its walls will be directly transferred to the enclosed fluid and to input line 14 at any time during which the atrium is not at its completely full or completely empty state. Therefore, the pressure or suction within closed chamber 12 is normally selected to be that level which appears to be at the input venous return line 14 during normal operation and this input pressure or suction can be effectively controlled to accommodate the particular by-pass or partial support function for which it is provided.

FIG. 3 shows a detailed sectional view of a suitable valve design which may be employed in the system of FIG. 2. As shown in FIG. 3, fluid flow through conduit 22 is from left to right relative to FIG. 3, with the left-hand end of conduit 22 being connected to atrium 17 and the right-hand or downstream end thereof being connected to ventricle 30. Fluid flow through the valve structure occurs whenever the pressure on its left-hand side is greater than the pressure on its right-hand side and further wherein the pressure differential is of a sufficient magnitude to overcome the restriction imposed by the two valve flap portions 34 and 36. The flaps 34 and 36 are each formed of an elastic material capable of resuming its normal configuration (shown in solid line fashion in FIG. 3) until the appropriate pressure differential exists across the valve structure whereby the valve flaps 34 and 36 are forced apart to permit flow from left to right. When the pressure differential is reversed, flaps 34 and 36 are forced into engagement with one another so as to isolate the left and right-hand portions of conduit 22.

One important characteristic of the valve design shown in FIG. 3 is that the valve design does not obstruct the central flow pattern of blood flowing therethrough so as to minimize turbulance and pressure loss across the valve. Furthermore, the surfaces that come into engagement upon valve closure is limited to the marginal tip portions of flaps 34 and 36. Due to their flexible nature, the flaps tend to distribute the reverse fluid pressure evenly along the contact surface so as to significantly reduce the surface contact therebetween and thereby minimize resultant damage to blood cells passing therethrough. This structure compares favorably with valve designs in which one or both surfaces thereof are comprised of valve seats formed of a rigid inelastic material.

FIG. 4 shows an exploded perspective view which illustrates the physical form of the pump assembly. A pair of complementary transparent (preferably plastic) covers 40 and 44 for each design to receive the liner assembly 42 comprised of a pair of liner sheets previously joined together by any suitable manner to form the resultant assembly 42. The liner assembly is preferably formed from two elastic membranes which are configured so as to define atrium 17, conduit 22 (which contains valve 21), ventricle 30 and conduit or chamber 32 (containing valve assembly 26). The covers 40 and 44 are each provided with complementary shaped cavities for receiving each of the components of the pump assembly, which recesses and/or cavities have been designated by like primed numerals. The cover halves 40 and 44, when joined together further define the closed chambers 12 and 13 shown in schematic fashion in FIG. 2. Although FIG. 4 shows the connecting conduits 18 and 31 as being provided in cover member 44, it should be understood that any other arrangement may be utilized. Cover member 44 is provided with a plurality of spaced threaded fasteners 47 adapted to align with associated openings 48 provided in cover member 40. At least the extreme end portions of threaded members 47 are arranged to extend beyond the upper edge of cover member 40 so as to threadedly engage suitable tapped members such as, for example, thumb screws (not shown for purposes of simplicity). In a like manner, the membrane assembly 42 is provided with a similar arrangement of openings 49 for receiving the threaded fastening members 47. The pump, when fully assembled is further provided with a support stand 46 suitably joined to cover member 44 so as to hold the assembly at a predetermined inclined angle. This arrangement causes gravity to aid in the collection of blood in both the atrium and ventricle compartments 17 and 30 to thereby expedite blood flow. Liner structure 42 may be utilized as a disposable item and thereby is readily replaceable.

As an obvious alternative, in the arrangement shown in FIG. 4, the assembly 42 may be a single sheet which cooperates with cover member 40 to form the atrium 17, ventricle 30 and associated connecting conduits whereby the recesses provided in cover member 44 may be utilized to serve as the enclosed chambers 12 and 13. In such a case, suitable sealing means may be provided in the immediate region of the inlet and outlet openings of each of the flexible chambers to isolate the differing pressure conditions between the chambers.

The sheets forming atrium 17 may come into contact during those times in which the chamber is empty and the pressure surrounding the chamber is greater than the internal pressure. Since the pressure within closed chamber 12 is static, abrasive damage to the blood is minimum even under those condition. However, the pulsatile actuating forces imparted to ventricle 30 may result in occlusive pumping, which is undesirable. This shortcoming may be remedied by providing photocell means and cooperating detector means each arranged above and below the cooperating sheets to detect the absence of fluid within the chambers and thereby automatically terminate operation of the pneumatic actuator 27 to prevent the exertion of occlusive pressure upon the blood when the chamber is nearly empty. In the case where only a single flexible sheet is utilized to form the above mentioned chambers, only a single light source and photocell detector combination need be provided to control the deenergization of the actuator 27.

FIG. 5 shows another alternative embodiment of the present invention which provides superior non-occlusive operation as compared with the embodiments of FIG. 4 and which is comprised of atrium chamber 62, a ventricle chamber 63, an inflow or venous return 50 and an outflow connection 65.

Valve assembly 55 serves to connect atrium chamber 62, ventricle chamber 63, while valve assembly 66 controls the outflow from ventricle 63. The ventricle chamber 63 is defined by flexible membrane 57 and the interior contour of housing 54. Membrane 57 also serves as the barrier member for separating the ventricle chamber 63 from the chamber 61 which is defined by membrane 57 and the interior contour of housing member 52. Connection 31 serves as a means for coupling the pulsatile pneumatic actuator to hollow chamber 61 and thereby exert pulsatile pressure upon the ventricle chamber 63.

In like fashion, membrane 59 serves as the means for isolating atrium chamber 62 from hollow chamber 60 which is defined by the interior contour of housing member 56 and membrane 59. Connection 18 serves as the means for connecting an adjustable pressure of vacuum source to chamber 60. Housing members 52, 54 and 56 may be machined molded or otherwise formed preferably from a transparent material. Membranes 57 and 59 are preferably formed of a flexible non-stretching material such as polyurethane or dacron reinforced silicon rubber. Liners of this design, while thin and quite flexible, do not stretch. Housing portion 54 is constructed so that atrium chamber 62 and ventricle chamber 63 each have a slightly larger radius than the curved liners when they are in their fully expanded state so as to provide non-occlusive pumping action. Liners 57 and 59 also provide the seals between chambers 60-62 and 61-63 eliminating the need for additional gaskets which would otherwise be required for sealing against the possibility of air or fluid leaks. The three housing sections and membranes are preferably held together by threaded members and cooperating thumb screws (not shown) which may be substantially similar in nature to those shown in FIG. 4. The design of the housing sections make the liners and valves readily accessible for cleaning, removal and/or displacement. Liners and valve assemblies are preferably of the disposable type.

Atrium chamber 62 provides continuous venous return flow despite the pulsatile operation of ventricle chamber 63, as well as regulating venous return vacuum or pressures at desired levels. The latter function is obtained by sealing input line 50 from ventricle 63 as atrium 62 is emptied. This is carried out by liner 59 which when moved to its uppermost position cooperates with the circular shaped protruding rim 64 to provide a temporary and yet effective seal therebetween so as to isolate the low pressure state of ventricle chamber 63 from the higher pressure state of the venous return flow line 50. When sufficient blood flow is again made available in excess of the pressures in chamber 60, the antrium chamber is again free to be filled and the temporary seal formed between liner 59 and rim 64 is removed.

The valve design of the pump assembly of FIG. 5 is rather unique and is shown in detail in FIGS. 6a and 6b. The valve is formed of a flexible resilient material such as, for example, silicone rubber. The valve is provided with an annular seating rim 85 which is partially fitted within a retaining flange 90, cut or otherwise formed in the appropriate housing portion 54 of the pump body. The lower seating surface 89 provided in housing portion 54 is diagonally aligned relative to the direction of flow so that the force exerted by reverse flow urges the valve more firmly into the mounting recess in such a manner that the diagonally aligned surface portion 89 causes the downward force exerted upon the valve assembly to urge the seating flange of the valve assembly outwardly and upwardly against the undercut portion 90 of the recess. In other words, the angle of the seating surface 89 prevents the valve body from being displaced or otherwise moved from its normal position when high reverse pressures are exerted upon the valve. During normal fluid flow, the three flaps of the valve whose mating edges are defined by slits 87a, 87b and 87c are easily urged apart to permit fluid flow in the normal normal (upward, in the case of FIG. 5) direction. The slightly outward force component present during the opening of the valve flaps serves to urge the annular flange 85 outward and retain the valve firmly seated within its associated recess so as to prevent high flow rates from urging the valve assembly from its seated position.

The flaps are each provided with substantially V-shaped lips 84 which mate with adjoining lips to provide good sealing in the case of reverse fluid flow (i.e., in the downward direction relative to FIG. 5). The advantages of the valve assembly shown and described hereinabove are such that no obstruction in the central flow pattern occurs, the valve surfaces are formed of a plastic material to minimize blood damages and to be highly compatible with the blood, as well as providing for simple and rapid removal and/or insertion of the valves without the need for any special tools. In the case of ventricle outflow valve 66, the seating flange provides the additional function of sealing against the possibility of leakage between housing portion 54 and outflow conduit 65. Fitting 65 may be attached to the pump body portion 54 by any suitable fastening means (not shown) for purposes of simplicity.

It is important to provide liners in the embodiments of FIGS. 2, 4 and 5 that, while flexible, do not stretch and thereby make the pump occlusive and which furthermore provide adequate protection against breakage. In order to incorporate these characteristics into the pump, I have devised a dual liner. For example, considering each liner half 24 and 25 of the embodiment of FIG. 2, or either of the liners 57 and 59 in FIG. 5, these liners are preferably designed in accordance with the principles shown in FIG. 7 wherein a pair of plastic liners 71 and 72, preferably formed of polyurethane, are bonded together along their marginal edges by means of silicone rubber as shown at 73 and 74. In the case of the embodiment shown in FIG. 5, for example, the silicone rubber is further employed to bond the liners 59 and 57 to the housing portions and these sections of silicone rubber are shown as 75,75 and 76,76, respectively. Bonding in this manner facilitates handling and assembly of the liners and further provides a good seal between the air and blood cavities provided within the pump assembly of FIG. 5.

A small amount of water in the form of droplets 77 is provided and these water droplets are sealed between the liners 71 and 72 to aid in lubrication of the liners as well as preventing undue wearing of the liners due to abrasive contact therebetween which would otherwise occur in the absence of the water droplets. The droplets 77 further enhance the flexibility of the liners 71 and 72 since a portion of the water droplets are absorbed by the material. Two thin liners respond more rapidly than one heavy liner in that the stresses in the liner material are reduced, resulting in a greatly improved flex life.

Another modification in the embodiment of FIG. 5 concerns the operation of the atrium 62. Continuous venous return flow is an important factor. Continuity of flow can occur only if the atrium chamber is partially filled, so that the venous return blood can flow into the atrium at all times instead of only part of the time and in a pulsatile fashion. To obtain the desired operation, an adjustable clamp 57 is placed in line 50. By adjusting threaded member 57a, return flow may be accordingly regulated.

As an alternative method, the air pressure in the atrium may be increased to reduce the venous flow. In order to simplify the adjustment of the adjustable clamp, a small plunger is positioned in the air chamber 60 which cooperates with the atrium 62, whereby the plunger moves either up or down as shown by arrow 95 to indicate when the atrium is full and more atrium pressure is therefore necessary or to indicate when the clamp must be further closed. To facilitate observation of the plunger, the apparatus shown in FIG. 8 may be set upside down relative to the orientation of FIG. 5 so that the atrium chamber is positioned above the ventricle chamber. The operation of the pump, however, remains the same. As shown in FIG. 8, the housing portion 56 is provided with a narrow opening 56a for reciprocally mounting plunger 96 which is provided with a widened portion 96a resting upon liner 59. Scale graduations 56b may be provided along the length of the plunger 96 to indicate the blood level within the atrium. The reservoir of blood within atrium 62 enables a constant atrium pressure to be maintained despite volume changes within the atrium.

A still further modification of the embodiment of FIG. 8 is shown in FIG. 9, wherein the plunger 96', shown therein, is provided with a relief valve opening 96b which communicates with an opening 96c at the opposite end thereof. Whenever the atrium is filled with blood, plunger 96' is pushed upwardly whereby opening 96c is sealed by a surrounding sleeve 98 positioned within opening 56a. This causes pressure to build up in the chamber due to the provision of a small capacity air pressure pump 99 coupled to conduit 18. As the atrium chamber empties, plunger 96' moves vertically downward so as to unseal opening 96d, providing a relief passage through to opening 96c, enabling the pressure to be vented from chamber 60 into the atmosphere whereby operation of plunger 96' automatically regulates the venous return blood flow.

It can be seen from the foregoing description that the present invention provides a novel by-pass pumping system for use as an assistive blood pump or as a temporary substitute for the natural heart and whose design is such as to closely emulate the normal heart functions and characteristics to provide highly reliable and effective operation in such applications.

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specific disclosure herein, but only by the appending claims.