WO1994027657A1

WO1994027657A1 - Artificial heart pump

Info

Publication number: WO1994027657A1
Application number: PCT/US1994/005839
Authority: WO
Inventors: David E. Mohrman; Thomas J. Van Hale
Original assignee: Mohrman David E; Hale Thomas J Van
Priority date: 1993-05-28
Filing date: 1994-05-24
Publication date: 1994-12-08
Also published as: AU7044394A

Abstract

An artificial heart pump includes first and second opposing leaves (22, 24) having side edges joined in face-to-face relation. First and second housing portions (26, 28) surround outer surfaces of each of the first and second leaves (22, 24). Pressurized fluid is admitted into chambers (32, 33) between the leaves (22, 24) and the housing portions (26, 28) to urge the leaves (22, 24) toward one another to cause a pumping action.

Description

ARTIFICIAL HEART PUMP

I. BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to an apparatus for pumping fluids. More particularly, this invention pertains to pumps and closure valves for fluids. More particularly, this invention pertains to an artificial heart pump and a valve for use with an artificial heart pump.

2. Description of the Prior Art

In the prior art, pumps and valves for controlling and actuating the flow of blood are well known. The pumps may be utilized external to the body (for example in dialysis) or may be implantable to either assist the human heart or used in place of the human heart. An artificial heart pump, particularly one to be implanted, must be designed to withstand a substantial amount of pumping action. For example in pumping blood, the blood typically is pumped at about five liters per minute against a pressure of 100 milliliters Hg. That flow rate and pressure rate are the resting cardiac performance of a normal adult human. The pumping action in the human heart is a pulsing operation which ejects blood about 25 percent of the time. Thus, peak instantaneous flows of 20 liters per minute through various cross sections of a blood pump should be expected. Also, the design of the heart pump must be such to permit the device to operate over substantial cycles.

In addition to meeting the fluid dynamic requirements of a heart pump, such a pump should avoid damage to blood cells. Blood is a complex fluid consisting of cells (red blood cells and white blood cells) suspended in a fluid solution called plasma. The cells occupy about 45 percent of the volume of the blood. Red cells are flexible discs about eight microns in diameter. White cells are more round in shape and may be up to 15 microns in diameter. Blood plasma has a viscosity of about 1.5 times that of pure water. During the pumping action of blood, the red and white blood cells may be damaged by mechanical crushing between components in the pump, damaged through turbulent flow patterns within the pump or damaged through excessive shear stresses in laminar flow regions within the pump.

It is an object of the present invention to design a blood pump which will meet the pumping requirements to replace a human heart while minimizing damage to blood cells.

II. SUMMARY OF THE INVENTION According to a preferred embodiment of the present invention, an artificial heart pump is disclosed. The pump includes first and second leafs which are disposed in opposing relation. A housing surrounds the leaves and divides the leaves into an inlet section, a pumping section and an outlet section. The spaces between the housing and the leaves define chambers into which fluids may be injected. Injection of fluid into the chambers forces the leaves together to act either as a seal or to provide pumping action.

III. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a cross sectional longitudinal view of an heart pump according to the present invention;

Fig. 2 is a view taken along line 2-2 of Fig.

1; Fig. 3 is a view taken along line 3-3 of Fig. i; Fig. 3A is an enlarged view of a portion of Fig 3;

Fig. 4 is a view taken along line 4-4 of Fig.

1; Fig. 5 is a view taken along line 5-5 of Fig. i;

Fig. 6 is a view taken along line 6-6 of Fig. i; Fig. 6A is an enlarged view of a portion of Fig 6;

Fig. 7 is an enlarged view, taken in perspective, of valve surfaces approaching one another;

Fig. 8 is a cross sectional view showing valve surfaces abutting one another; Fig. 9 is a perspective view of a valve surface according to an alternative embodiment of the present invention.

IV. DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the several drawing figures in which identical elements are numbered identically throughout, a description of the preferred embodiment will not be provided. The description of the preferred embodiment will be used with reference to a heart pump and valve for use in replacement of the human heart. However, it will be appreciated by those skilled in the art that the present heart pumps and valves could be used to assist an existing heart or it could be used external (for example, in a dialysis machine).

A heart pump assembly is shown generally at 10. The assembly includes an inlet section 12, an inlet valve section 14, a pump section 16, an outlet valve section 18 and an outlet section 20. The apparatus 10 includes upper and lower leaves 22,24 (the terms "upper" and "lower" being used with reference to the views of Figs. 2-6). Each of leaves 22,24 will be more fully described. In the drawings, thickness of the leaves 22,24 are shown exaggerated for purpose of illustration. The assembly further includes a housing consisting of an upper housing section 26 and a lower housing section 28. As shown best in Fig. 2, each of the leaves

22,24 include side edges 22a,24a and 22b,24b. Extending between edges 22a,22b is the main body 22c of leaf 22. Similarly, extending between side edges 24a,24b is the main body 24c of leaf 24. Each of upper housing 26 and lower housing 28 include side flanges 26a,26b and 28a,28b. Extending through side flanges 26a,26b is the main body portion 26c of upper housing 26. Extending between side flanges 28a and 28b is the main body portion 28c of lawn housing 28.

As shown in Figs. 2-6, the leaves 22,24 are joined in opposing relation with edge 22a abutting edge 24a and with edge 22b abutting edge 24b in face-to-face relation. The upper housing 26 surrounds the outer surface of leaf 22 and the lower housing 28 surrounds the outer surface of leaf 24. Edges 22a,24a are captured between flanges 26a,28a. Similarly, side edges 22b,24b are captured between flanges 26b,28b. The flanges 26a,28a are joined through any suitable means such as thermal fusion. Similarly, flanges 26,28b are joined. As a result, side edges 22a,24a are permanently compressed opposing one another as are side edges 22b,24b.

Both the inlet section 12 and the outlet section 20 are substantially identical. As shown in Fig. 2, each are circular in cross section with the surfaces 26c,28c cooperating to define a circular volume 30 through which blood may flow. At the circular ends, an artery of a patient may be sutured to the housings 26,28 at the outlet with a vein similarly sutured at the inlet to provide a continuous flow therebetween. Since the housing is circular in the region of the outlet and the inlet as shown in Fig. 2, the pressure of blood within the chamber 30 urges the leaves 22,24 against the circular inner surface of the housing 26,28.

Each of the inlet valves 14 and outlet valve 18 are identical and a description of the outlet valve with reference to Fig. 3 will suffice as a description of the inlet valve. In the view shown, the inlet valve 14 is shown in the closed position as best shown in Fig. 6. The outlet valve is shown in the open position as will be more fully described with reference to Fig. 3.

With reference to Figs. 3A and 6A, the reader will note that the body portions 26c and 28c of the housing are not circular. Instead, each are segments of a circular arc opposing one another to form a double-arc tube. Opposing inner surfaces of the leaf bodies 22c,24c define a volume 30' in the inlet and outlet. As a result when pressurized fluid is admitted into the chamber 30', the pressurized fluid urges the leaf bodies 22c,24c against the arcuate surfaces 26c,28c to the shape shown in Fig. 3. Opposing outer surfaces of leaf pprtion 22c and housing portion 26c define a chamber 32 best shown in Figs. 6 and 6A. Similarly, opposing outer surfaces of leaf 24 and housing 28 define a chamber 33. The ends of the chambers 32,33 are sealed by thickened portions 22d, 24d, 22d', 24d' of upper and lower leaves 22,24 as best shown in Fig. 1.

A fluid first port 34 communicates with chamber 32. A second fluid port 36 communicates with chamber 33 in the inlet valve. In the region of the outlet valve, an inlet port 38 is provided and an inlet port 40 is provided.

Injection of a fluid from an external source into ports 34,36 (illustrated by arrows A) causes leaves 22,24 to be urged away from walls 26,28 into close contact as best shown in Figs. 6 6A. With the close contact of leaves 22,24, as shown in Fig. 6, the leaves block flow through the valve. Upon evacuation of the fluid (or simple venting of the fluid, illustrated by arrows B) from chambers 32,33, the pressure of the blood within the chamber 30' urges the leaves 22,24 to assume the shape of the housing as shown in Fig. 3.

The pump section 16 includes a double-arc cross section as shown in Fig. 5. However, the reader will note that the radius of curvature of the arc portion housings 26,28 in the pump section is smaller than the radius of curvature in the valve sections resulting in an enlarged chamber within the pump section.

Ports 42,44 communicate with chambers 32,33 in the pump section to admit a pressurized fluid into the chambers 32,33 to urge the leaves 22,24 toward one another. Venting through the ports 42,44 permits the leaves 22,24 to move away from one another. The pump section 16 has chambers 32,33 sealed by the thickened portions 22d', 24d', 22d", 24d" of the leaves 22,24. Shown best in Fig. 1, the housings 26,28 cooperate to define enlarged diameter portions 100, 200, 300, 400. The thickened portions 22d, 24d, 22d', 24d', 22d", 24d'', 22d'" and 24d" ' are received within the enlarged diameter portions 100, 200, 300, 400 to securely capture the leaves as well as seal off the inlet valve section 12, the pumping section 16, and the outlet valve 18. Also, due to the thickened portions, as leaves 22,24 are closed in the inlet and outlet valve sections, the thickened portions stretch to define a smoothly contoured transition as the valves open and close (illustrated in the inlet section 14 in Fig. 1).

In a preferred embodiment, the leaves 22,24 are formed of a smooth substance which avoids damage and physiological reaction to blood. A preferred material is a silicon elastomer such as that sold under the trademark Silastic of Dow Corning Company. The housing portions 26,28 are formed of a rigid plastic material. As best shown with reference to the inlet valve section 14 in Fig. 1, a cantilevered portion 22e,24e is provided for leaves 22,24 to give a smooth transition and added strength from the thickened portions 22d,24d. Although not numbered for purposes of illustration, such transitions are provided for each of thickened portions 22d', 24d', 22d", 24d", 22d'", 24d" ' .

The thickening of the leaves 22,24 is greater at the entrance (22d,24d) than at the exit of the valve (22d',24d') because greater pressure differences exist across the leaf at the entrance than at the exit. The adjacent thickened and fixed areas act to transmit forces to the rigid shell 26,28.

The inlet and outlet ends 12,20 provide a smooth transition from the circular cross-section (Fig. 2) to the double circular arc flow path found in regions 14, 16 and 18.

The double circular arc cross-section minimizes stresses and strains on the internal leaves 22,24 during pump operation. For example, at the location of joinder of the ends 22a, 24a, 22b, 24b, the amount of flexing of the leaves is minimized as opposed to having a completely circular cross section in those areas. Also, the cross- sectional dimensions shown limit turbulent flow and excessive shear stress in the blood being pumped. Indeed, my calculations indicate that the shear stresses and flow in the blood being pumped is less than or equal to those existing in the normal human cardiovascular system. In operation, the inlet valve is closed by injecting fluid under pressure through ports 34,36. Ports 38, 40, 42 and 44 are vented. Fluid is then admitted under pressure to ports 42,44 causing the leaf 22,24 in pump section 16 to urge together and pump blood through the outlet 20. Upon completion of the pumping stroke, pressurized fluid is admitted to ports 38,40. The fluid closes the outlet valve 18. Ports 34, 36, 42, 44 are vented. Pressure in the cardiovascular system opens the inlet valve 14 permitting fluid to enter into the pumping section 16 and fill the pumping section 16 by urging the leaves 22,24 against the walls of the housing 26,28 in the pumping section 16. At this point, pressurized fluid is again admitted to ports 34,36 to close the inlet valve 14. Ports 38,40 are vented and pressurized fluid is admitted to ports 42,44 to urge the blood through the outlet valve 18 and the cycle repeats. With reference to Figs. 7 and 8, leaf portions for both the outlet valve and inlet valve are shown. The opposing surface 23 of the upper leaf portions 22c is flat. The opposing surface 25 of the bottom leaf portions 24c is provided with an undulated pattern consisting of a plurality of valleys 60 and ridges 62. Upon closure of the valve, the ridges 62 abut the upper surface 23 and the valleys 60 are spaced from the upper surface 23 (see Fig. 8). The ridges 62 run generally transverse to the direction of flow (arrow C) of blood through the valve.

As shown in Fig. 8, upon closure of the valve membranes, the ridges 62 and valleys 60 cooperate with the smooth upper surface 23 to define a plurality of enclosed troughs 64. The troughs 64 are sized to receive and retain human blood cells such as a white blood cell 65 or a red blood cell 66.

In a preferred embodiment, the width, W, of the troughs 64 is about .002 inch. The depth, D, of the valley is about .001 inch. This structure prevents mechanical damage to blood cells during valve closure. When the leaflets are touching, the troughs 64 provide a space in which trapped blood cells may reside without being crushed. Since leakage over any given ridge 62 is possible, the length of the valve section is provided such that a substantial plurality of troughs 64 will be provided in each outlet valve 18 and inlet valve section 14. During closure of the valve, as the ridges 62 approach the flat upper surface 23, the shear velocities increase to ensure blood cells move to and reside within the troughs 64.

Fig. 9 shows an alternative embodiment. In Fig. 9, cross-ridges 67 are added to leaf 24c for surface 25' to present a waffle-like appearance. Instead of longitudinal troughs 64 (Fig. 8), the surface 25' has longitudinal cross-ridges 67 and transverse ridges 62' to define a plurality of discrete pockets 64' to receive blood cells.

The grooved valve described above has numerous uses beyond those shown in the preferred embodiment. Any pump, valve or other device for pumping blood may benefit from the teachings of the the invention where the device includes surfaces which move into contact and which could otherwise damage blood cells.

From the foregoing detailed description of the present invention, it has been shown how the objects of the invention have been attained in a preferred embodiment. However, modifications and equivalents of the disclosed concepts, such as those which readily occur to one skilled in the art, are intended to be included within the scope of the present invention.

Claims

WHAT IS CLAIMED IS:

1. A device for controlling blood flow, said device comprising: at least first and second opposing surfaces relatively movable between first and second positions, in said first positions, said first and second surfaces are disposed in spaced apart relation permitting blood flow between said surfaces; in said second positions, said surfaces are urged against one another to block blood flow between said surfaces; at least one of said first and second opposing surfaces being an undulated surface of first ridges and valleys opposing the other of said first and second opposing surfaces.

2. A device according to claim 2 wherein said first ridges and valleys extend generally transverse to a direction of said blood flow.

3. A device according to claim 2 wherein said ridges and valleys are sized for said ridges to be urged against said other surface in fluid-sealing contact with said valleys spaced from said other surface when said first and second surfaces are in said second position and with said valleys and said other surface cooperating to define a plurality of sealed troughs.

4. A device according to claim 3 wherein said ridges and valleys are sized for said troughs to be sized to receive blood cells.

5. A device according to claim 4 wherein said valleys have a depth of about .001 inch.

6. A device according to claim 5 wherein said valleys have a width of about .002 inch.

7. A device according to claim 3 comprising a plurality of second ridges extending generally transverse to said first ridges and dividing said troughs into a plurality of pockets.

8. A device according to claim 1 wherein said first surface and said second surface are opposing surfaces of a first leaf and a second leaf, respectively, each of said leaves extending between side edges; means for urging and holding said side surfaces in face-to-face fluid-sealing contact when said surfaces are in either of said first and second positions.

9. A device according to claim 8 comprising a housing surrounding at least one of said leaves and opposing a back surface thereof with said back surface and housing cooperating to define an enclosed chamber, means for selectively injecting and evacuating a fluid from said chamber, injection of said fluid into said chamber urging said surfaces from said first position to said second position and evacuation of said fluid from said chamber urges said surfaces from said second position to said first position.

10. A device according to claim 9 comprising applying a vacuum to said chamber upon evacuation of said fluid to assist a movement of said surfaces from said first to said second chamber.

11. A device according to claim 9 wherein said housing surrounds both of said leaves to form first and second chambers opposite back surfaces of said first and second leaves, respectively, with means for injecting and evacuating said fluid into each of said first and second chambers.

12. A device according to claim 11 wherein said housing include a first and second housing portion, said first housing portion is provided with an arcuate surface opposing an arcuate surface of said second housing portion for said first and second housing portions to cooperate to define a non-circular double arc geometry in cross section.

13. A device according to claim 12 wherein said leaves are urged upon pressure of fluid flow between said leaves to assume said shape of said first and second housings.

14. An artificial blood pump comprising: a first flexible membrane and a second flexible membrane; means for sealing longitudinal edges of said first and second membranes; a first housing surrounding an outer surface of said second membrane and a second housing surrounding an outer surface of said first membrane to define a chamber between said first membrane and said first housing and a second chamber between said second membrane and said second housing; means for sealing axial ends of said first and second chambers; means for admitting and evacuating a fluid from each of said first and second chambers with said membranes urged toward one another upon admission of said fluid to said chambers.

15. A blood pump according to claim 14 wherein said first and second housings have concave arcuate inner surfaces cooperating to define a double arc bounded volume between said first and second housing portions.

16. A heart pump according to claim 14 wherein said housing is divided into an inlet valve portion, a pump portion and an outlet valve portion with said chambers between said portions being axially sealed and with means for selectively admitting and evacuating a pressurized fluid into each of said chambers in each of said portions.

17. A heart pump according to claim 14 wherein said means for sealing includes a thickened area of said membrane including a portion of said thickened area secured to said housing and a portion of said thickened area extending from said housing.