US3550162A - Blood pump control system - Google Patents

Description

Dec. 29,1970 F. N. HUFFMAN ETAL 3,550,162

BLOOD PUMP CONTROL SYSTEM Filed Feb. 6, 1969 3 Sheets-Sheet 1 FROM VENTRICLE TO AORTA INVENTORS FRED N. HUFFMAN THOMAS C. ROBINSON SOTIRIS S. KITRILAKIS ATTORNEYS Dec. 29, 1970 HUFFMAN ETAL BLOOD PUMP CONTROL SYSTEM 3 Sheets-Sheet 2 Filed Feb. 6, 1969 BLOOD PUMP HPR III I] l'l' ll'l Ill I'l'll'llli l W. W m L f m w llllllllilJ m m m I L M B n w m I I i H l0: 4 1 m i w; m R I. W

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INVENTORS ROBINSON BY SOTIRIS, S. KITRILAKIS p/vm r14! II.- ATTORNEYS .Dec. 29, 1970 F. N. HUFFMAN ETAL 3,550,162

BLOOD PUMP CONTROL SYSTEM Filed Feb. 6 1969 3 Sheets-Sheet 3 F|G.4 47 FIG.5

INVENTORS FRED N. HUFFMAN THOMAS $1. ROBINSON SOT-IRIS S. KITRILAKIS ATTORNEYS q- BY United States Patent 3,550,162 BLOOD PUMP CONTROL SYSTEM Fred N. Huffman, Sudbury, Thomas C. Robinson, West Newton, and Sotiris S. Kitrilakis, Newtonville, Mass,

assignors to Thermo Electron Corporation, Waltham,

Mass, a corporation of Delaware Filed Feb. 6, 1969, Ser. No. 797,183 Int. Cl. A6193 1/24; F0411 17/00 US. Cl. 3--1 8 Claims ABSTRACT OF THE DISCLOSURE An implantable control system for an implanted blood pump connected between ventricle and aorta to supplement the natural heart, comprising means responsive to ventricular pressure for supplying pumping fluid under pressure to the blood pump at the end of the natural systole to force blood into the aorta, and means responsive to the volume of blood ejected into the pump by the ventricle during each systolic contraction to control the amount of pumping fluid supplied to the pump.

Our invention relates to prosthetic devices, and particularly to a novel blood pump control system for a heart assist blood pump.

Various devices have been proposed and developed for supplementing the function of a damaged or diseased heart. A most promising approach is the use of an implanted left ventricle assist pump connected in series between the left ventricle and the aorta of the host. One such pump that has been developed comprises a bladder, for receiving blood from the ventricle, within a housing adapted to receive pumping fluid. A pair of check valves are located, one at the intake and one at the outlet of the bladder, and the pumping action of the ventricle may be supplemented by appropriately controlling the pressure of the pumping fluid admitted to the housing.

Highly developed surgical techniques make the implantation of a left ventricle assist pump a practical procedure in many instances. The problem, however, is to exercise the appropriate control over the pumping fluid without interfering with the delicate physiological balance and rhythm of the natural circulatory system.

The natural system senses the blood pumping rate needed at any time in dependence on the demands on the host. Both the timing of the natural systole and diastole, and the volume of blood moved by the ventricle during its systolic contraction, are variables in the natural circulatory process.

It has been proposed to actuate a left ventricle assist pump of the type described by transcut-aneous pneumatic connections to an external air supply under the control of electrical signals produced by electrodes externally connected to the host. Those signals are the physiological motor signals used in controlling the natural circulatory system. However, while that approach is direct and workable, such a system obviously greatly restricts the potential mobility of the host. It would be highly desirable to be able to implant the total circulatory assist system in the body, so that the patient could potentially regain full mobility and maintain an adequate circulatory function for a period of years without additional surgical procedures. It is the object of our invention to facilitate the control of an implanted heart assist pump with a totally implanted control system.

Briefly, the above and other objects of our invention are attained by a novel blood pump control system comprising a variable volume pump for delivering hydraulic fluid to the pumping chamber of a heart assist pump,

Patented Dec. 29, 1970 ice with the use of energy supplied from a power supply in the form of hydraulic fluid under pressure. The blood pump control system returns the hydraulic fluid to the power supply at lower pressure in a closed pumping cycle. As the bladder of the blood pump is filled during the systolic phase of the ventricle, a portion of a fixed volume intermediate charge of hydraulic fluid in the blood pump is returned to the variable volume hydraulic pump under the relatively low ventricular pressure. Towards the end of this natural systole, ventricular pressure drops. Means are provided for sensing that pressure drop to drive the portion of the fixed charge of hydraulic fluid taken into the variable volume hydraulic pump back into the blood pump to express the blood into the aorta under a pressure lower than, but proportional to, that in the pressure supply line. When the volume of the hydraulic fluid delivered to the blood pump equals the volume of blood supplied to the ventricle, a volume sensing device functions to disconnect the high pressure fluid and discharge it to the low pressure line, whereupon the system awaits the next natural systole. By that arrangement, the assist system functions, both in volume delivered and in stroke timing, as directed by the natural circulatory system.

The apparatus of our invention, and its mode of operation, will best be understood in light of the following detailed description, together with the accompanying drawings, of a preferred embodiment thereof.

In the drawings:

FIG. 1 is a schematic elevational view, with parts shown in cross-section and parts broken away, of a blood pump control system in accordance with our invention shown connected to a left ventricle assist pump;

FIG. 2 is a schematic cross-sectional view, taken substantially along the lines 2-2 in FIG. 1, showing a typical cross-section through the blood pump;

FIG. 3 is a schematic piping diagram showing the relationship between the blood pump control unit of our invention, the blood pump, and the blood pump power supply; and

FIGS. 4, 5, 6, and 7 are a series of schematic diagrams of the apparatus of FIG. 1, illustrating the positions of the parts in various typical points in a cycle of operation.

Referring to FIG. 1, the blood pump control unit of our invention is generally designated 1. The control unit 1 comprises a housing generally designated 3, of metal such as stainless steel or the like, devided and connected together in any convenient way, not shown, to facilitate assembly, and including the moving parts and passages which together function to control the supply of pumping energy to the blood pump.

The blood pump is generally designated 5, and is interconnected with the blood pump control unit by a flexible tube 7 of any suitable conventional synthetic resin or the like. The exterior surfaces of all parts to be described may be partly coated with substance that promotes tissue ingrowth as with Dacron cloth or velour or the like in a manner known in the art per se.

The blood pump 5 comprises an outer housing 9 of aluminum or the like, covered as just described and provided with an outlet passage 11 adapted to be grafted to the aorta of the host by a suitable conventional graft connection 13. An inlet passage '15 is adapted to be secured to the left ventricle by means of a suture ring 17. The pump is provided with an inlet check valve 19 and an outlet check valve 21 adapted to function in a conventional manner to control the flow of blood to and from the pump in a conventional manner known in the art.

Within the housing 9 is a thin flexible bladder 23, preferably of polyurethane having a wall thickness on the order of magnitude of 0.03 inch. That material is desirable because it is highly durable, flexible, and chemically inert in the environment in which it will be used, and it can be made relatively thin while retaining a safe margin of strength. It is desirably thin, because, as will appear, it is preferably used as a heat exchange surface to exchange heat between the hydraulic fluid from the control unit 1 and the blood stream. Preferably, the interior surface of the bladder 23 is coated to promote tissue ingrowth to form an outologous pseudoendothelium surface.

The flexible hydraulic connecting tube 7 is connected between a suitable outlet fitting 27 formed in the housing 9 and a corresponding fitting 29 on the blood pump control unit 1. The fitting 29 is formed at the outlet of a cylinder 31 in which an expansible chamber 32 is formed by a piston 33 connected to the end wall of the cylinder 31 by means of an expansible metal or rubber bellows or diaphragm 34.

Extending upwardly from and formed integrally with the piston 33 is a smaller piston 35 slidable in a cylinder 37. The ratio of the areas of the pistons 35 and 33 is such that high pressure fluid, at approximately 80 p.s.i.a., supplied to the pump control unit in a manner to appear, will be converted to approximately 18 p.s.i.a. in the expansible chamber 32 to simulate the systolic pressure that would be produced in the circulatory system by a normally functioning heart.

Filling the expansible chamber 32, the connecting line 7, and the space between the housing 9 and the diaphragm 23 of the blood pump 5 is a fixed volume charge of intermediate energy exchange fluid. This fluid is preferably an isotonic aqueous saline solution, to minimize shock in the event of any leakage into the bloodstream. The constant volume of this fluid charge is proportioned and exchanged between the blood pump and the blood pump control unit in a manner to be described.

High pressure hydraulic fluid is supplied to the blood pump control unit 1 through a flexible line 39, and lower pressure exhaust fluid at approximately 15 p.s.i.a is returned to the fluid pressure source through a flexible line 41. The high pressure line 39 is connected to the unit 1 by a means of a suitable fitting shown at 43, and the low pressure line is connected to a suitable fitting formed in the housing 3.

A composite spool valve generally designated 47 is slideably mounted in a cylindrical bore 49, for movement between the position shown and a position in which the lower end of the spool valve 47 engages a stop ledge 51. The top of the spool valve 47 communicates with the piston 35 through a conduit 53, diverging into two passages 54 and 55 for purposes to be described.

In the upper position of the spool valve shown, the high pressure line 39 communicates with the upper portion of the piston 35 through a passage 56, the channel around a reduced portion 57 formed on the spool valve 47, and a passage 59. At the same time, the line 39 is in communication with a passage 61, the latter being closed by the lower portion of the piston 35 in the position shown in FIG. 1.

In the position shown in FIG. 1, the space above the spool valve 47 is in communication with the exhaust line 41 over the passage 53, the passage 54, a reduced portion 63 formed on the piston 35, a passage 65, and a restricted orifice 67 in parallel with a spring loaded relief valve 69.

The bottom portion of the spool valve 47 is in continuous communication with the exhaust line 41 over a passage 71. The space in the cylinder 31 around the expansible chamber formed by the bellows 34 and the piston 33 communicates with the exhaust line 41 over a passage 73.

In the lower position of the spool valve 47, to be described in more detail in connection with FIGS. 6 and 7, the upper portion of the piston 35 communicates with the exhaust line 4 1 through a passage 75, a reduced portion 77 formed on the spool valve 47, a passage 79, and

- through the restricted orifice 67 in parallel with the relief valve 69. The spool valve 67 is resiliently urged to the position shown in FIG. 1 by a spring 81.

Preferably, the pumping fluid in the cylinder 31 and surrounding the sealed expansible chamber formed by the piston 33 and the bellows 34, the high pressure fluid in the line 39, and the low pressure fluid in the line 41, are all a part of the same closed system of hydraulic fluid that is preferably water. Moving parts such as the spool valve 47 and the piston 35 are preferably provided with graphite bearings, not shown, and some leakage is permitted so that the water serves as the lubricant for the moving parts.

Referring to FIG. 3, we have there shown the blood pump control unit 1 quite schematically in its relationship with the blood pump 5 and the power supply, generally designated 101. While within the broader aspects of our invention, any suitable power supply may be employed, it is preferred to use as the power supply that apparatus shown and described in more detail in copending application Ser. No. 797,094, filed on the same date as the present application by Thomas C. Robinson for Dual Fluid Circulatory Support System, and assigned to the assignee of our application.

As schematically shown in FIG. 3, the power supply 181 comprises an expansible low pressure reservoir 103 connected to the low pressure return line 41. The reservoir 103 expands to the volume dictated by the amount of fluid in the low pressure portion of the system at any given time. The amount of fluid in the low pressure reservoir will fluctuate as dictated by the demands upon the assist system by the host, and will also be regulated in accordance with the demand on the engine to maintain system stability, in a manner that will appear below.

The pressure in the low pressure reservoir 103 is established at a predetermined value of, for example, 15 p.s.i.a., by means of a conduit 105 connected to the output of a sump pump 107 and by the compliance which equalizes internal and approximately external pressures. The output side of the sump pump 107 is also connected through a conduit 109 to the intake of a hydraulic pump 111 that serves to supply working fluid over a conduit 113 to an expansible high pressure reservoir 115. The reservoir 115 is maintained at a pressure of, for example, 80 p.s.i.a. The high pressure reservoir 1 15 supplies fluid to the conduit 39 for purposes to be described. A relief valve 117 is connected across the hydraulic pump 111 to dump fluid from the high pressure reservoir into the low pressure reservoir should the pressure in the high pressure reservoir exceed the desired value.

Fluid from the high pressure reservoir 115 is also supplied to a boiler 119 by means of a feed pump .121. The output pressure of the feed pump 12 1 may be, for example, 400 p.s.i.a. Excess pressure at the outlet of the feed pump 121 is prevented by a relief valve 123 connected across the pump 121.

The boiler 119 is supplied with heat by a thermal energy storage system, not shown, which is more fully described in the above cited copending application of Thomas C. Robinson. Basically, this thermal energy storage apparatus preferably comprises a shielded source of radioactive energy within a constant temperature bath comprising a eutectic mixture of lithium chloride and lithium fluoride which has a melting point of about 930 F. The thermal energy storage material supplies heat at constant temperature to the boiler 119, to raise the temperature of the working fluid to about 900 F. at a pressure of approximately 800 p.s.i.a. The high pressure working fluid from the boiler is supplied to a steam engine schematically shown at 125, preferably of the type shown and described in the above cited application of Thomas C. Robinson. However, any suitable miniature heat engine can be employed.

Exhaust fluid from the engine 125 is supplied over a line 127 to a condenser 129 located within the high pressure reservoir 115 to be cooled by the hydraulic fluid in the high pressure reservoir. Exit liquid from the condenser 129 is returned to the input of the sump pump 107 at a low pressure of, for example, 2.9 p.s.i.a.

As will appear, the blood pump control unit 1 will demand more or less high pressure fluid through the line 39, in dependence on the demands of the host for a larger blood supply, as when exercising, or a smaller blood supply, as when at rest.

The engine 125 preferably drives a flywheel 131, and also preferably drives the hydraulic pump 111, the sump pump 107 and the feedwater pump 121. The sump pump and feedwater pump carry essentially the same flow, namely that requiredto maintain the operation of the engine. The flow rate through the hydraulic pump 111 is approximately five thousand times as great as the flow through those pumps.

The work done by the hydraulic pump 111 will necessarily depend on the pressure in the high pressure reservoir 115, which varies because of varying demands by the host, as noted above. The engine 125 is arranged to do a constant amount of work per stroke, because the boiler temperature and pressure are constant. Thus, the engine will adjust its speed to the demand by varying the speed of the flywheel 131, dividing the energy produced per stroke between the flywheel and the hydraulic pump 111. When the host demands more pumping fluid, and therefore reduces the pressure in the high pressure reservoir 115, the engine will speed up to increase the speed of the pump 111, causing the pressure in the reservoir 115 to be increased. When the pressure in the reservoir 115 rises, the larger amount of energy demanded by the pump 111 will cause the flywheel to slow down, thus lowering the pressure in the reservoir 115. The engine 125 thus acts as a load responsive coupling between the heat suply to the boiler 119 and the mechanical energy supplied to the blood pump control unit 1 over the line 39.

So far as the blood-pump control unit 1 is concerned, the power supply 101 merely acts as a source of fluid under pressure in the line '39 and a sink of fluid at lower pressure connected to the line 41. A further characteristie that should be noted is that because heat is transferred to the hydraulic fluid in the reservoir 115 by the condenser 129, the temperature in the line 39 is above the temperature in the return line 41. The difference in heat is accounted for by heat transfer in the blood pump, as will appear.

Referring again to FIGS. 1 and 2, the operation of the apparatus of our invention will next be described on the assumption that high pressure fluid is available in the conduit 39, the low pressure line 41 is connected to the power supply of FIG. 3, and the parts have just reached the position shown in FIG. 1.

In that position, the bladder 23 will have been filled with blood in an amount equal to that supplied by the last systolic contraction of the ventricle plus a residual amount allowed to prevent contact of the opposite walls of the bladder 23, as seen in FIG. 2. The reason for preventing the walls of the bladder from coming into contact is to prevent damage to blood cells that might be occasioned thereby.

With the parts in the position shown in FIG. 1, the piston 35 will be in communication with the high pressure fluid in the line 39 as described above, and the piston 33 will be driven down to express fluid in the expansible chamber 32 into the outer chamber of the blood pump 5. That will cause contraction of the bladder 23 as shown in FIG. 2, the closing of the inlet valve 19, and a opening of the outlet valve 21 to express blood to the aorta. In the position shown in FIG. 1, the upper end of the spool valve 47 will be in communication with the exhaust line 41. Thus, the spool valve will be held in the position shown by the spring 81.

As the piston 35 descends, the next significant event will be the closing of the passage 54 by the top part of the piston 35, as depicted in FIG. 4. That will occur before the passage 55 is opened. Thus during the portion of the piston stroke in which both of the passages 54 and 55 are closed, the fluid above the spool valve 47 will be trapped and will lock the spool valve in the position shown.

Referring next to FIG. 5, as the piston 35 approaches and reaches the bottom of its stroke, the reduced portion 63 on the poston 35 will connect the ports 55 and 61, and thereby admit high pressure fluid from the passage 56 into the passage 53 leading to the upper part of the cylinder 49, driving the spool valve 47 downwardly to the position show in FIG. 5. The space above the piston 35 will now be connected to the exhaust line 41 through the passage 75, the reduced portion 77 on the spool valve 47, and the passage 79, and thence through the restricted orifice 67 in parallel with the relief valve 69. The spool valve 47 will be held in the position shown in FIG. 5 as long as the passage 55 is open.

The apparatus will wait in the state just described until the next systolic contraction of the nautral heart. When that occurs, blood will be expressed ino the conduit 15 in FIG. 1 from the left ventricle, causing the bladder 23 to distend and expressing fluid up into the expansible chamber 32 to raise the piston under ventricular pressure. Fluid in the cylinder 37 will be expressed by the piston 35 out through the orifice 67, relieved by the valve 69 at a pressure selected to prevent overtaxing the ventricle when reflected back through the piston 33.

As the piston 35 rises to the position shown in FIG. 6, the passage 55 will be closed by the lower portion of the piston 35. The valve 47 will remain locked in the position shown by the trapped high pressure fluid above it.

The next significant event will occur after the piston has moved to a position such as that shown in FIG. 7 in which the passage 54 is again connected to the passage 65. When that occurs, the top of the spool valve 47 and the top of the piston 35 will be essentially at the same pressure established by the drop through the orifice 67 and limited by the check valve 69 to a predetermined maximum pressure as described above.

During the natural systole, the pressure communicated to the expansible chamber 32 will be communicated to the piston 35 as a pressure sutficient to hold the spool valve 47 down as shown in FIG. 7. Toward the end of the natural systole, the ventricular pressure will drop, and this pressure drop will be sensed by the system as a pressure drop in the cylinder 49 over the spool valve 47, allowing the spring 81 to expand and drive the piston back to the position shown in FIG. 1. The next pumping cycle will then begin and will proceed as described above.

It will be apparent that the lower position of the piston 33 reached at the bottom of its stroke is fixed by the position at which the passage 55 is opened. How ever, the top position of the piston 33 is determined in dependence on the volume of blood expressed by the left ventricle during the systole and before the pressure drop that occurs as described above. Thus, the amount of pumping fluid taken into the expansible chamber 32 is determined at each stroke by the volume of blood supplied by the ventricle, and the volume expressed by the blood pump during the next pumping stroke will be that same volume. In other words, the timing of the blood pump is determined by the timing of the natural systole, and the volume of blood expressed at each stroke is also determined by the natural system in dependence on the demands of the host.

As noted above, the fluid in the line 39 carries excess heat extracted from the working fluid in the condenser 129, FIG. 3. That heat is discharged to the bloodstream in a manner next to be described.

The fixed volume charge of isotonic pumping fluid in the blood pump 5, the line 7, and the expansible chamber 32 exchanges heat with the fluid in the hydraulic lines 39 and 41 through the metal walls of the piston 33 and the bellows 34. The fixed fluid charge is transferred back and forth between the expansible chamber 32 and the blood pump, and exchanges heat with the blood through the diaphragm 23. The excess heat in the power supply system is thereby discharged without causing any physiologically significant increase in blood temperature. The heat that is added to the blood is dissipated by the normal physiological processes of perspiration, conduction, convection and respiration.

While we have described our invention with respect to the details of a preferred embodiment thereof, many changes and variations will occur to those skilled in the art upon reading our description, and such can obviously be made without departing from the scope of our invention.

Having thus described our invention, what we claim is:

1. A control system for an implantable fluid actuated blood pump having a fitting for admitting actuating fluid, comprising means forming a fluid conduit adapted to be connected at a first end to said fitting, a fluid barrier movable in said conduit and dividing said conduit into an outlet chamber adjacent said first end and an inlet chamber adjacent a second end of said conduit, valve means movable between a first position and a second position, means controlled by said valve means in its first position for connecting said inlet chamber to a source of fluid under pressure, means controlled by said valve in its second position for venting said inlet chamber, means responsive to a predetermined pressure in said outlet chamber for moving said valve means to its first position, and means responsive to a predetermined volume of said outlet chamber for moving said valve means to its second position.

2. In combination, a blood pump comprising a housing and inlet and outlet tubes connected to said housing for connection to a blood circulation system, a flexible expansible bladder in said housing and connected between said tubes and forming an expansible blood chamber in said housing, a cylinder connected to said hous ing, a piston reciprocable in said cylinder to exchange fluid in said cylinder with fluid in said housing and outside of said bladder and thereby vary the volume inside said bladder, means forming a manifold comprising an operating chamber communicating with said piston, a fluid supply passage, and a fluid return passage, valve means mounted in said manifold for movement between a first position in which said supply passage is connected to said operating chamber and a second position in which said return passage is connected to said operating chamber, means responsive to a predetermined pressure in said hOusing for moving said valve means to its first position, and means responsive to the position of said piston in said cylinder for moving said valve means to its second position when the piston reaches a predetermined position.

3. In combination, a blood pump comprising a housing provided with a blood inlet tube and a blood outlet tube, a thin flexible expansible bladder in said housing and connected between said inlet tube and said outlet tube to form an expansible blood receiving chamber, check valve means in said tubes for producing a unidirectional flow of blood through said tubes when said bladder is expanded and compressed, an expansible fluid chamber outside of and connected to said housing to exchange fluid with the space in said housing outside of said bladder, whereby compression of said fluid chamber will express fluid into said housing and compress said bladder and expansion of said bladder will express fluid into said chamber, and a control unit for manipulating said expansible fluid chamber, said control unit comprising a first fluid conduit adapted to be connected to a source of fluid under pressure, a second fluid conduit adapted to be connected to a fluid sink at lower pressure than said source pressure, fluid motor means connected to said expansible fluid chamber and responsive to applied fluid pressure to adjust the volume of said expansible fluid chamber, control valve means movable to a first position in which said first fluid conduit is connected to said fluid motor means to compress said expansible fluid chamber and to a second position to permit ventricular pressure in said blood pump to expand said expansible fluid pressure, means controlled by the volume of said expansible fluid chamber for moving said control valve means to its second position when said volume reaches a predetermined minimum, means for producing a reference pressure signal, means operatively connected to said bladder for producing a blood pressure signal, and comparator mean controlled by said pressure signals for moving said valve means to its first position when said blood pressure signal is less than said reference pressure signal.

4. A control unit for a fluid actuated bladder type blood assist pump, said pump comprising an expansible bladder adapted to be compressed to expel blood and expanded to receive blood, said control unit comprising a cylinder having a head at one end adapted to be connected to said pump, a piston reciprocable in said cylinder to exchange pumping fluid in said cylinder with said pump and thereby manipulate said bladder, and control means for said piston comprising pressure responsive means controlled by the pressure of blood in said bladder for applying a first force to said piston to drive it toward said head when the blood pressure drops at the end of a natural systole, and volume sensing means controlled by the position of the piston in the cylinder for applying a second force to said piston when said piston reaches a predetermined distance from said head, said second force being below the force exerted on the piston and transmitted to the piston through the bladder during a natural systole.

5. The apparatus of claim 4, in which said pressure responsive means comprises valve means movable between a first position and a second position, means controlled by said valve means in its first position for applying fluid under a first pressure to said piston over an area suflicient to produce said first force, means for producing a reference pressure signal, means for producing a blood pressure signal in accordance with the pressure in said bladder, and means controlled by said signals for moving said valve means to its first position when said blood pressure signal is less than said reference pressure signal, and in which said volume Sensing means comprises means connected to said piston to move said valve means to its second position when said piston is said predetermined distance from said head.

6. A blood pump control unit for a heart assist circulatory support system comprising power supply means for producing from a supply of hydraulic pumping fluid at a first pressure a supply of hydraulic fluid at a second higher pressure, and a blood pump comprising a thin resilient expansible bladder sealed in a housing between openings adapted to be connected in a blood circulation system, said openings being provided with check valves to produce a pulsing unidirectional flow of blood through said bladder when hydraulic fluid is forced in and out of said housing outside of said bladder, said blood pump control unit comprising fluid exchange means connected between said housing and said power supply by a supply line containing pumping fluid at said first pressure and a return line containing fluid at said second pressure, said fluid exchange means comprising an inlet chamber, a communicating passage between said inlet chamber and said outlet chamber, and piston means movable in said communicating passage to vary the volume of said inlet chamber with respect to the volume of said outlet chamber, said outlet chamber being connected to said housing to exchange hydraulic fluid with said pump, means responsive to a drop in pressure in said bladder for connecting said supply line to said inlet chamber to admit a slug of fluid to said inlet chamber, thereby moving said piston means to drive fluid into said pump to compress said bladder, and means responsive to the volume of said outlet chamber for connecting said inlet chamber to said return line and disconnecting said supply line when said outlet chamber reaches a predetermined minimum volume.

7. A blood pump control unit for a heart assist circulatory support system comprising an implantable blood pump comprising a housing, a thin resilient bladder mounted in said housing and having a pair of openings adapted to be connected in a mammalian circulatory system, a power supply comprising a source of fluid at a predetermined high pressure and a fluid sink at a predetermined low pressure, said blood pump control unit comprising fluid motor means connected to said housing by a fluid exchange passage and connected to said Power supply by a supply line of fluid at said high pressure and a return line of fluid at said low pressure, said fluid motor means comprising means energized by the difference between said supply and return lines and responsive to a first signal to supply pumping fluid at one pressure to said housing to compress said bladder, said motor means fur ther comprising means responsive to a second signal to return fluid at said low pressure to said return line when said bladder expands and returns fluid through said fluid exchange passage during a natural systole, and control means for said motor means, said control means comprising means for sensing the blood pressure in said bladder to produce said first signal at the end of a natural systole, and means responsive to the volume of fluid returned through said exchange passage for producing said second signal when the same volume has been supplied to said housing after said first signal is produced.

8. A blood pump control unit, comprising means forming a supply passage adapted to be connected to a source of fluid under pressure, means forming a return passage adapted to be connected to a fluid sink at a lower pres sure than said source, a fluid exchange passage adapted to be connected to the actuating chamber of a fluid actuated blood pump on one side of a resilient expansible bladder separating the actuating chamber from an expansible blood chamber, a fluid barrier movable in said passage, volume sensing means responsive to the position of said barrier for connecting said return passage to said fluid exchange passage on the side of said barrier opposite said blood pump when the volume in said passage between said barrier and said pump reaches a predetermined minimum, a reference source of fluid under a reference pressure, pressure sensing means operatively connected to said reference source and said bladder and responsive to the difference between the pressure in said bladder and said reference pressure for connecting said supply passage to said fluid exchange passage on the side of said barrier opposite said blood pump in response to a pressure in said bladder below said reference pressure.

References Cited UNITED STATES PATENTS 4/1968 Harvey 3lX 3/1969 Wolfe 31 OTHER REFERENCES DALTON L. TRULUCK, Primary Examiner R. L. FRINKS, Assistant Examiner U.S. Cl. X.R.

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