US3514218A - Single acting follower heart assist device - Google Patents

Description

y 1970 c. A. MAHER, JR 3,514,218

SINGLE ACTING FOLLOWER HEART ASSIST DEVICE Filed Dec. 24, 1968 INVENTOR.

CHARLES A. MAHER,Jr. BY

4 M /M W United States Patent 3,514,218 SINGLE ACTING FOLLOWER HEART ASSIST DEVICE Charles A. Maher, In, Wakefield, Mass., assignor, by mesne assignments, to the United States of America as represented by the United States Atomic Energy Commission Filed Dec. 24, 1968, Ser. 'No. 786,559 Int. Cl. F04!) 17/00 US. Cl. 417-43 5 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The invention described herein was made in the course of, or under a contract with the United States Atomic Energy Commission.

In recent years rapid progress has been made in the development of assist and replacement devices for use in connection with damaged or weak human hearts. However, the heart is more than merely a blood pump as its operation must conform to a variety of physiological conditions which fluctuate continuously. As a result, up to the present time, there have been many problems yet to be overcome before a completely adequate heart replacement or assist device could be perfected. For example, any such device must meet high standards of reliability, have the ability to meet varying blood requirernents, and produce a pulsating flow to which the human body apparently requires or at least finds important.-

As already noted, devices of the type herein referred to generally are classified as either replacement or heart assist pumps. The former type has the advantage of being able to replace completely a heart which is incapable of any continued use, but at the same time suffers the drawbacks of very high power requirements, complex control systems, and complications arising out of pump failure. On the other hand, an assist device has reduced power requirements and can rely on the heart for control function and aid at the time of peak demand or pump failure. An important drawback of the heart assist device is the problem of providing for synchronized function with that of the natural heart.

SUMMARY OF THE INVENTION The present invention provides for an assist device for use with a heart capable of automatically operating in synchronism with the latter under a variety of expected operating conditions.

3,5 14,2 1 8 Patented May 26, 1 970 In accordance with this invention, the assist device is in series with the left ventricle of the heart and the aorta, performing the function of the left ventricle and permitting the latter to operate at a reduced pressure level. As is understood in the art, the left ventricle provides flow through the systemic circulatory system which carries most of the pumping demand on the heart. The single acting follower device, as the preferred embodiment of this invention is described, permits the heart to function at unimpeded rate and flow conditions and reproduces physiologically systemic flow and pressure conditions at the discharge. The device utilizes hydraulic fluid from a regulated pressure source to pulse the blood passing through to the system at the same time the left ventricle is pulsing. Flow into the blood system from the device is matched with flow into it from the left ventricle so that pressure and flow conditions in the blood system are physiological.

It is thus a principal object of this invention to provide a heart assist device of improved design and function.

Other objects and advantages of this invention will become readily apparent from the following description of a preferred embodiment of this invention taken with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The figure shows in section a partially schematized view in section of a preferred embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the figure, single acting follower heart assist device 10 comprises an inlet tube 12, a vessel or main body 14, an outlet tube 16, and a control unit 18. Tubes 12, 16 and main body 14 are constructed from a suitable inert flexible or pliable material such as polyurethane. Inlet tube 12 would be connected by known surgical techniques to the outlet of the left ventricle (not shown) while outlet tube 14 would be similarly connected to the aorta (not shown). Blood flow would be in direction shown by arrows A and B and it is evident that device 10 is in a series flow relationship with the heart. Control unit 18 is connected to main body 14 by way of a conduit or hose 22 and other linkage to be later described.

Main body 14 is divided into upper and lower chambers 24 and 26, respectively, by a pair of walls 28 and 32 in which is mounted as illustrated a power piston 34 from which extends a connecting rod 36 through the outer wall of body 14 into control unit 18 shown. Check valves 38, 42 and 44 restricted in movement by retainers 38a, 42a, and 44a, respectively, are located in inlet and outlet tubes 12 and 16, and between chambers 24 and 26, respectively. From the description above, it is seen that when piston 34 is reciprocated up and down fluid will be pumped from chamber 24 and 26 through check valve 44, with upper chamber 24 being refilled through check valve 38, and lower chamber 26 being emptied through check valve 42.

Control unit 18 consists of a housing 46 in which is formed a cylinder 48 in which a control piston 52 is slidable and biased upwardly by a spring 54. Piston 52 is mounted on rod 36 which extends through the former and has a pin shaft 56 through its upper end thereof.

Also within housing 46 is a double piston hydraulic spool valve 58 mounted slidably within a cylinder 62 which communicates with a supply port 64, an exhaust port 66, and a feed port 68 leading into the chamber formed above piston 52 in cylinder 48. A supply manifold 73 maintains inlet port 64 with a continuous supply of a suitable high pressure hydraulic fluid.

A rod 72 with a guide pin 74 at the end thereof extends from piston valve 58 for a purpose to be later described. Movement of spool valve 58 either permits the hydraulic fluid from port 64 to pressurize the space above piston 52 or permits the fluid to exhaust from the aforementioned space out through exhaust port 66, as is understood in the art.

A receiver bellows 76 mounted in control unit 18 communicates with a sensor 'bollows 78 mounted in upper chamber 24 of body 14 by way of tube 22 already mentioned. Within bellows 76 and 78, and tube 22 is a suitable liquid so that collapsing of bellows 78 due to an increase in pressure in upper chamber 24 will cause an expansion of bellows 76 in control unit 18. A decrease of pressure in chamber 24 will cause the opposite effect. Bellows 76 has a rod 82 with a pin 84 extending therefrom. Rods 36, 72 and 82 are interconnected by a floating link 86 which is pivoted at pin 84, and engaged by the use of slots with pins 74 and 56.

In the operation of heart assist device 10, inlet tube 12 and outlet tube would be connected to the left ventricle outlet and the aorta, respectively, as already noted. De- =vice can be either connected externally for use during relatively short periods such as operations or emergency, or implanted as part of a totally implanted system. Supply manifold 73 would be connected to receive a suitable hydraulic fluid under pressure from a separate source which can be either implanted or externally located. Exhaust port 66 would be connected by a pipe (not shown) to return at reduced pressure the hydraulic fluid back to the source where it would be pressurized as understood in the art.

The figure shows device 10 in position just prior to a left ventricle pulse. When the left ventricle pulses, blood flows through tube 12 and check valve 38, which opens, into upper chamber 24. Sensor bellows 78 compresses slightly under the increased pressure which causes the expansion of receiving bellows 76. This causes floating link or connecting element 86 to pivot about pin 56 which causes spool valve 58 to be raised permitting a pressure buildup in the space above piston 52 from supply port 64. As the pressure rises a force imbalance will result, causing piston 52 and hence piston 34 to start to move down. As the blood flow into upper chamber 24 continues, sensing bellows 78 will continue to signal the opening of valve 58. This permits piston 52 to continue moving at a rate directly related to the supply of blood from the left ventricle.

As pistons 52 and 34 start their downward movement, the blood already in lower chamber 26 will become pressurized holding check valve 44 closed. When the pressure in lower chamber 26 builds to a value just above that in the system downstream of check valve 42, the latter will open and blood from lower chamber 26 will flow out through check valve 42. Thus, as upper chamber 24 is being filled, lower chamber 26 is being discharged at a matching flow rate. As pistons 34 and 52 move against any increase in systemic resistance, a steady state force balance is maintained by a corresponding increase in pressure within the space above piston 52 achieved by an increased spool valve 58 opening. This higher pressure now acting on the effective area of piston 52 will match the force produced by the difference in pressures in chambers 24 and 26 less the bias due to the spring 54 acting on the effective areas of piston 34 in contact with them.

When the flow into upper chamber 24 stops, at the time the left ventricle has completed its pulse thereby accommodating the exact volume of blood delivered, the piston movement will stop and the pressure will drop in chambers 24 and 26. Check valves 38 and 42 will also close. Sensor bellows 78 'will expand and thus collapse bellows 76, causing hydraulic valve 58 to move down, closing off the opening above piston 52 from inlet port 64 and opening it to exhaust port 66. The energy stored in spring 54 during the movement of piston 52 will now create an unbalanced force condition. This will cause pistons 52 and 34 to rise, forcing blood to 'be transferred from upper chamber 24 to lower chamber 26 through check valve 44. When this transfer is completed device 10 is ready for the next left ventricle pulse.

It will be seen that the heart assist device just described not only relieves much of the work on the left ventricle of the heart, but is always synchronized with the heart pulses of the left ventricle and will accommodate changing volumes pulsed from the heart. Also, it is apparent that in being synchronized with the heart, exact physiological conditions in the system are followed. Another important feature of this invention is that the left ventricle working pressure level can be adjusted simply by changing the supply pressure of the hydraulic fluid, and also can be set or changed by adjusting the load characteristics of the bellows 76 and 78. In the event of failure of device 10 in any position, the heart will merely function properly at normal systemic loads, an important consideration in all heart assist apparatus.

It is thus seen that there has been provided an improved heart assist device capable of either implanted or external application. While only a preferred embodiment has been described it is understood that the scope of this invention is defined only by the appended claims.

What is claimed is:

1. Heart assist apparatus comprising:

(a) a flexible walled vessel divided into a pair of first and second chambers separated by movable wall means and having a check valve permitting flow from said first chamber into said second chamber;

(b) inlet check valve means permitting flow into said first chamber;

(c) outlet check valve means permitting flow out of said second chamber; and

(d) control means responsive to flow of liquid into said first chamber to move said movable wall to expand said first chamber and collapse said second chamber to close said check valve and pump liquid out of said second chamber through said outlet valve means and responsive to termination of flow into said first chamber to move said movable wall means to expand said second chamber and collapse said first chamber, blood flowing from said first chamber through said check valve into said second chamber.

2. The apparatus of claim 1 in which said control means includes a power piston mounted in said movable wall means exposed on opposite sides to pressures within said first and second chambers, respectively, connecting means extending from said piston, and hydraulically actuated means for actuating said connecting means in accordance with changes in pressure within said first chamber.

3. The apparatus of claim 2 in which said hydraulically actuated means includes pressure sensing means in said first chamber, a control unit containing a pressure receiving means for receiving pressure information from said pressure sensing means, hydraulic valve means for controllably delivering fluid pressure and relieving fluid pressure, a cylinder containing a control piston connected to said connecting means, said control piston biased in one direction and receiving fluid pressure acting in the opposite direction to the biasing force, and linkage means between said pressure receiving means, hydraulic valve 5 6 means, and said control piston to move said hydraulic References Cited valve means in accordance with changes in pressure re- UNITED STATES PATENTS ccivecl by said pressure receiving means and changes in posieion of said conirol piston.

4-. The apparatus of claim 3 in which said pressure sensing means and receiving means are each a bellows interconnected to form a sealed fluid system such that ROBERT WALKER Primary Exammer collapse of said sensing bellows causes expansion of the US Cl XR receiving bellows.

5. The apparatus of claim 4- in Which biasing for said 10 6, 244, 18 control piston is a spring.

3,101,058 8/1963 Carr et a1. 103-21 XR 3,298,320 1/1967 Latham 103-152

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