Abstract:
Apparatus for mechanically assisting circulation of the blood in the human body comprises a pumping chamber outside the cardiovascular system of a patient but communicating with said system through only one connection, and means for blocking the backflow of blood from the pumping chamber into the cardiovascular system. The blocking means may be one or more variable flow resistant devices or valves which are suitably located inside the cardiovascular system and controlled to operate in synchronism with the heart beat.

Description:
This is a continuation-in-part of copending application Ser. No. 436,226 filed Jan. 24, 1974 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to apparatus for mechanically assisting circulation of the blood in the human body. The apparatus comprises a pumping chamber in association with a variable flow resistant device or valve directly in the cardiovascular system. According to the invention the apparatus is so positioned in the cardiovascular system that a fully effective pump is formed with the help of the valve functions of the cardiovascular system itself. 
     Various devices for mechanically assisting circulation of the blood in the human body have been developed in the course of the last twenty years. A primary feature of all these devices is that the diseased heart remains in the body and that its functions are taken over by the assisting device either in toto or more usually only in part (Wolner E.:-Die mechanische Kreislaufunterstutzung in Experiment und Klinik. Weiner klinische Wochenschrift, 84, No. 26, 1972). 
     From a functional point of view two types of apparatus can be distinguished, namely parallel and series (by-pass and series pass) pumps. The former are parallel to a part of the heart (right or left chamber), the latter are in series therewith. If the whole of the heart is short-circuited (total by-pass) then it is necessary at the same time to reoxygenate the blood because the pulmonary circulation is by-passed. Short period total by-pass has been practiced for many years in cardiac surgery. All these pumps have two openings for the blood stream, viz. an entry and an exit. Some move the blood through valves, others by direct displacement (pinch pumps, roller pumps) in a desired direction. The alternative principle of counterpulsation provides mechanical circulatory relief. Since the heart has a period of rest after each period of work, it is possible during the work period, i.e., during blood ejection (systole) to relieve the pressure in the cardiovascular system, and to introduce energy into the system, i.e., raise the pressure during the period of rest (diastole). This relieves the heart during systole, whereas the required pressure for circulation is mechanically generated during diastole. The particular advantage of counterpulsation is less the relief afforded to the heart than the possibility of properly filling the coronary vessels during diastole. Disregarding short period temporary employment of the total by-pass, i.e., of the heart-lung machine, it can be generally said that circulating pumps are not at present in clinical use, but that the principle of counterpulsation is being employed to an increasing extent. 
     A major reason for this development is the difficulty of application of the pump because two connections (anastomoses) with the cardiovascular system are needed, whereas in counterpulsation only one of such connection is necessary. 
     The disadvantage of counterpulsation is the described limited degree of relief afforded to the heart because the pressure in the circulating system may not be arbitrarily reduced during systole. The object of the present invention is to overcome this disadvantage. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus for mechanically assisting circulation of the blood in the human body. The apparatus comprises a pumping chamber arranged outside the cardiovascular system of a patient which communicates with the system through only one connection, and means adapted to be positioned in the cardiovascular system to control the pumping chamber in synchronism with the heart beat. 
     A Dacron graft through the right second intercostal space connects the ascending aorta to the subcutaneously implanted elipsoidal-shaped artificial ventricle. A spherical polyurethane balloon is positioned in the aorta distal to the Dacron graft via the femoral artery. The ventricle and balloon are pneumatically driven synchronously with the EKG. In natural systole the balloon is inflated, occluding the aorta, and the artificial ventricle sucks the entire stroke volume. In natural diastole, the balloon deflates and the artificial ventricle ejects the blood to the aorta. With this system the systolic pressure wave is turned 180° to the natural. The system has high hemodynamic efficiency: the left ventricular systolic pressure is unloaded by 90%, the pump maintains a normal systemic pressure, and the coronary artery flow is increased 5%. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described by way of example and with reference to the accompanying drawings, in which: 
     FIG. 1 is a diagram illustrating the working principle of an apparatus according to the invention; 
     FIG. 2 is a schematic representation of curves measured in an electrical circuit simulating the employment of the apparatus according to the invention in a cardiovascular system; 
     FIG. 3 illustrates the apparatus of FIG. 1 in greater detail; 
     FIG. 4 illustrates schematically the control system for the apparatus of the present invention; and 
     FIG. 5 illustrates a further embodiment of the present invention. 
    
    
     DESCRIPTION OF THE INVENTION 
     Referring first to FIG. 1, the reference A denotes a heart with its several connecting arteries and veins, B the ascending branch of the aorta, C the arterial branch vessels to the upper part of the body and D the descending branch of the aorta. A mechanical pumping chamber 17 comprises a strong envelope 40 and a movable pumping diaphragm 34 which divides the pumping chamber into upper and lower compartments. The pumping chamber 17 has two connections. The upper compartment of the pumping chamber is cyclically connected to a source of gas pressure and suction (controlled by the heart beat itself) by a pneumatic connection 16. The lower compartment of the pumping chamber is provided with a bottom entry 41 which directly communicates via a connection 25 with the ascending branch B of the aorta. The pressure and suction pulses are transmitted by the movable pumping diaphragm 34 to the lower blood-filled compartment of the pumping chamber and by virtue of the effect of the vacuum this compartment fills with blood during systole. During diastole the pressure in the upper compartment forces the blood out of the lower compartment. This operation constitutes the working phrase of the pumping chamber. 
     The functioning of this arrangement is based on the principle of couterpulsation. The apparatus has the particular advantage of being extremely effective because it is located so close to the heart and the pump lumen can be made as large as may be desired. 
     The pumping action is generated by the cyclic inflation and evacuation of a controlling balloon 22. The systemic circulation is separated from the ventricular exit by the controlling balloon 22 during systole, the balloon performing the function of a variable resistance to the flow of blood. This enables the blood from the heart to enter the pumping chamber 17 practically without back pressure. The controlling balloon could be replaced by a valve which prevent back flow from the aorta. During diastole the controlling balloon collapses and the blood is discharged from the pumping chamber into the arteries. It will be apparent that in this arrangement the semi-lunar valve L (arotic valve) is utilized in the pumping action. 
     FIG. 3 illustrates is greater detail the apparatus of FIG. 1. A Dacron ring 24 is sutured to the ascending main artery 23 and the connection 25 is made with the Dacron ring 24 by means of a tobacco pouch seam 26. A guide tube 20 extends through the connection 25 and towards the ascending main artery. A smaller tube 21 passes through the guide tube 20 to the control balloon 22 located in the artery. The smaller tube 21 serves as a pneumatic connection to the control balloon 22 to inflate and deflate the control balloon alternately to control the flow of blood through the artery. The guide tube 20 also provides means for inserting and withdrawing the control balloon 22 as required. 
     FIG. 4 diagrammatically illustrates the control system for synchronously operating the system. An EKG amplifier 1 is responsive to the pumping action of the heart 11. A trigger 2 is connected to the EKG amplifier 1 and operates two delaying elements 3 and 4 which in turn control amplifiers 5 and 6 respectively. The amplifiers 5 and 6 operate electromagnetic valves 7 and 8 controlling the flow of gas from supply 9. Valve 7 controls diaphragm pump 17 while valve 8 controls the balloon 22 located in the aorta 23 of the circulation system 12 of the patient 10. 
     The mechanical assist pump may be monitored by a pressure-measuring device connected at 18 and an electromagnetic flow meter 19 (see FIG. 3). 
     FIG. 2 illustrates curves obtained in an electrical circulation model simulating the apparatus according to the present invention. In this figure: 
     A -- the time pulses at one-second intervals of the recording, 
     B -- the EKG simulated by the model, 
     C -- the blood flow at the heart exit, 
     D -- the pressure cycle in the central circulating system, and 
     E -- the pressure cycle in the intermediate section between the heart exit and the variable resistance, i.e., the controlling balloon 22. 
     The system pressure is thus displaced in phase 180° as is the case in counterpulsation. During systole the pressure in the intermediate section is very low and principally depends upon the suction in the pumping chamber. 
     The apparatus is preferably applied by simultaneously introducing the controlling balloon 22 together with the connecting conduit 25 including the guide tube 20. For inactivating the system, the controlling balloon 22 needs merely be withdrawn into the connecting conduit 25, and the pumping chamber 17 as well as the balloon 22 is then pressurized. It will be appreciated that parameters such as the pressure in the circulating system can be measured via the guide tube 20. The apparatus can be removed by completely withdrawing the controlling balloon 22 and pinching off the connecting conduit 25. A pre-formed fracture or tear-off line may be incorporated in the connecting conduit 25 so that eventually only a very small piece of the connecting conduit 25 remains permanently in the body. 
     FIG. 5 illustrates a further embodiment of the invention wherein the control balloon 22 is replaced by a hydraulically or electromagnetically operated slide valve. In the conduit or pipe connection 25 there is an additional shiftable sliding pipe 27 which at its lower end is open on one side. Consequently, only the right opening of the pipe connection 25 is closed when the slide valve is closed. The left opening facing the heart always remains open. This corresponds to the action of the inflated control balloon 22. 
     An annular piston 28 is welded to the sliding pipe 27 and reciprocally moves in cylinder 29. Thus, the sliding pipe 27 may be operated hydraulically. Liquid under pressure is fed into the cylinder by way of pipe 30 causing the sliding pipe 27 to be pushed downwardly. The connecting pipe 31 extends downwardly through the cylinder 29 and a hole in the annular piston 28 so that upon fluid pressure being fed in through connecting pipe 31 the piston is caused to rise and the valve is opened. The connecting pipe 31 by passing through the annular piston 28 prevents the sliding pipe 27 from rotating. 
     In accordance with the invention, pressure is alternately applied to the two connecting pipes 30 and 31 respectively, synchronized with the heart beat. The control mechanism is the same as that illustrated in FIG. 4 and described above. 
     There is no special seal required between the annular piston 28 and the wall of the cylinder 29. Preferably, the piston is operated by an isotonic salt solution. To avoid thrombosis of the sliding valve it must be rinsed continuously with the salt solution, and consequently some leakage between the annular piston 28 and the wall of the cylinder 29 is required. 
     FIG. 5 also illustrates a convenient means for securing the wall of blood vessel 23 about the pipe connection 25. An annular inflatable member 33 is placed around the exterior surface of the pipe connection 25 with the wall of the blood vessel between the interior surface of the annular inflatable member 33 and the exterior surface of the pipe connection 25. A metal annular member 32 is positioned about the inflatable member 33 before the inflatable member 33 is inflated, thereby securing the wall of the blood vessel 23 without injury to the wall of the blood vessel. 
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed are therefore to be considered in all respects as illustrative and not restrictive.