US3452738A - Heart pump apparatus - Google Patents

Description

United States Patent 3,452,738 HEART PUMP APPARATUS Robert T. Jones, Lexington, Mass., assignor to Avco Corporation, Cincinnati, Ohio, a corporation of Delaware Filed July 20, 1966, Ser. No. 566,527 Int. Cl. A61b 19/00; A61m 1/00 US. Cl. 1281 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates to heart pump apparatus and more particularly to circulatory assist systems wherein a blood pumping unit is pneumatically driven by an actuator unit.

The advent of open heart surgery has presented to the medical profession the opportunity of repairing damaged or diseased hearts of individuals and where appropriate, using circulatory assist systems in individuals who Without such correction and/or systems face premature death. Many devices are involved in this type of surgery. For example, one circulatory assist system may comprise an auxiliar ventricle or valveless blood pump connected across the arch of the aorta and driven by fluid pressure in response to electronic signals (QRS wave) provided by the heart itself. By operating the blood pump or auxiliary ventricle in proper phase, the systolic pressure in the left heart can be reduced and the systemic circulation can be maintained with a substantially reduced work load on the heart muscle. In addition, the operation of the auxiliary ventricle has the effect of shifting the phase of the normal systolic pressure so that this pressure appears in the aorta at a time when the left ventricle is relaxed. Assuming competence of the normal aortic valve, one then has an increased perfusion pressure available to the coronary arteries. It is believed that such an increase in coronary perfusion, together with a reduction in the effort required from the heart, should be effective in a number of cases of cardiac insufiiciency.

As may be seen from the above, one important component of circulatory assist systems is a pump that either assumes the hearts role of pumping blood or which reduces the work load of the heart muscle, By using heart pump equipment for extended periods of time, it is contemplated that the equipment may be utilized for regional perfusions in therapeutic treatment of the heart. Still other use of the equipment will be to provide circulation of blood through an artificial organ such as an external artificial kidney. In connection with this function of the apparatus, it should be noted that many research institutions at this time are concentrating their research activities on providing artificial counterparts of other organs and whenever such application requires circulation, the present invention may be utilized.

Implantable prior art pulsatile pumps usually consist of a flexible bulb or ventricle squeezed by pressurized fluids from a pumping or actuating unit and is coupled to one or more blood vessels such as arteries or veins, Generally, arterial graft sections connect the bulb to the circulatory system. These arterial graft sections are generally of the woven Teflon-type or Dacrontype employed in the insertion of arterial grafts and the AVAILABLE COPY replacement of damaged sections of an artery. Edwards seamless arterial graft manufactured by the United States Catheter and Instrument Company have been found to be satisfactory.

In most, if not all, circulatory assist systems, it is necessary that the flexible bulb be synchronized with the patients heart. A typical pneumatically driven and electrically controlled circulatory assist system is disclosed in US. Patent No. 3,099,260. Other systems are disclosed in patent application No. 355,273 filed Mar. 27, 1964, now abandoned and patent application No. 531,281 filed Mar. 2, 1966, to which reference is made and which are assigned to the same assignee as this application.

In the use of circulatory assist systems, it is desirable if not necessary to be able to, for example, safely shut down the system if a component fails, to be able to visually display the work being performed by the pumping unit, or to be able to visually indicate at any one time through what portion of its cycle the pumping unit is passing. Accordingly, a feature of the present invention is the provision of means in a circulatory assist system for providing an electrical output signal representative of the operation of the blood pumping unit.

Another feature of the present invention is the provision of apparatus in a circulatory assist system for actuating the blood pumping unit and providing an electrical signal representative of the operation of the blood pumping unit.

A further feature of the present invention is the provision of an actuating unit having a pressure actuated dia phragm which not only controls the blood pumping unit but actuates a transducer adapted to provide an output signal representative of the position of the diaphragm and, hence, the condition of the blood pumping unit.

The novel features that are considered characteristic of the present invention are set forth in the appended claims; the invention itself, however, both as to its organization and method of operation together with additional objects and advantages thereof, will best be understood from the description of a specific embodiment when read in conjunction with the accompanying drawings, in which:

FIGURE 1 is a block diagram of a circulatory assist system in accordance with the present invention;

FIGURE 2 is a diagrammatic representation of the actuating unit and the transducer controlled thereby;

FIGURE 3 is a block diagram showing one way in which the invention may be used to actuate a fail-safe circuit;

FIGURE 4 is a block diagram showing another way in which the invention may be used to display the work diagram of the blood pumping unit; and

FIGURE 5. is a block diagram showing still another way in which the invention may be used to visually indicate the condition of the blood pumping unit.

Directing attention now to FIGURE 1, there is shown a schematic illustration of heart pumping or circulatory assist apparatus intended to provide intercorporeal me chanical assistance and incorporating the present invention. As shown in FIGURE 1, in a typical system a suitable pressurized source of gas 11 feeds into a low pressure regulator 12. Large oxygen bottles which are readily available and are a satisfactory source of oxygen are generally pressurized to a pressure of several thousand pounds and generally have a pressure regulator which, while not particularly sensitive, is satisfactory to provide a reduction in pressure approaching that required for the actuation of the blood pumping unit. A satisfactory pressure for the pumping unit has been found to be approximately 3 pounds per square inch; hence, pressure regulator 12, while of conventional design, should permit small adjustments in the pressure range of about 10 to 3 pounds per square inch. The output of: the low pressure regulator 12 BEST AVAlLABLE C is fed to a three-way solenoid actuated valve 13. The valve 13, which is normally vented to the atmosphere, is adapted to be operated by a synchronizing circuit 14 and allows compressed gas to be supplied to an actuating unit 15. Thus, only when the valve 13 is actuated by the synchronizing circuit 14 does the valve 13 supply compressed gas to the actuating unit 15 which in turn con-' trols the action of the pumping unit 16.

Broadly, the action of both the actuating unit and the pumping unit must be capable of being synchronized with the patients heart. The actuating unit and hence the pumping unit must be capable of being phased with the patients heart while the duration of the systole and diastole strokes should be adjustable. The synchronizing circuit 14 performs the function of pro erly synchronizing the operation of the solenoid in valve 13 for admitting the pressurized gas into the actuating unit 15 in accordance with the demands of the patient. Typically, the Synchronizing circuit is actuated by the patients electrocardiogram or the R-wave taken directly from his heart. By way of example, the output of an EKG unit may be fed into an amplifier and synchronizer pulse circuit that is adapted to amplify the sync pulse or electrical signal used for synchronizing purposes. The am lifier and synchronizing pulse shaper if provided may be designed not only to limit the magnitude of the synch pulse but also to shape it. Since the actuating unit is designed to be synchronized with the Rwave of the sync pulse, all other portions of the wave may be either reduced or removed, thereby leaving only the R-wave. Since the hydraulic events in the patients heart are not simultaneous with the EKG unit or the R-wave and, furthermore, since the hydraulic events in the patients circulatory system are delayed behind the systolic pulse of the heart by varying amounts depending on the distance of the artery or vein from the left ventricle of the heart, it is desirable to provide means for phasing the systolic pulse of the pumping unit with the systolic pulse of the heart in order to accommodate these time delays and provide the desired time delay. For this purpose, a systole delay network triggered by the R-way may be provided to create a sync pulse delayed behind the R-Wave by a controlled amount to enable the systolic pulse of the pumping unit to be delayed behind the systolic pulse of the patients heart by an appropriate time interval. By providing this time delay interval, the pumping unit may be adjusted so that the pressure reflections from the systolic pulse of the pumping unit will be properly phased with the pressure reflections from the systolic pulse of the patients heart and in such a way as to physiologically aid the patients heart.

The sync pulse produced by the aforementioned systolic delay network may be utilized to actuate a trigger circuit which may include a systole duration control circuit which is provided for controlling the duration of the tripped condition of the trigger circuit. The output of the trigger circuit may be fed directly into an amplifier, the function of which is to create a signal for firing a thyratron switching circuit or the like which controls the operation of the three-way solenoid valve 13. For a further discussion of suitable synchronizing circuits for different applications, reference is made to the aforementioned US. Patent No. 3,099,260, and patent application Ser. No. 355,273.

Directing attention now to the actuating unit 15 diagrammatically represented in FIGURE 2, it may be the type disclosed in the aforementioned patent but is pref erably of the type comprising as shown in FIGURE 2 a low inertial diaphragm 21 separating the unit into an input compartment 22 and an output compartment 23, the pressurized gas from valve 13 being admitted into the input compartment 22 and the gas in the output compartment 23 being in communication with the pumping unit 16 through pressure line 32, a percutaneous connector 25 and pressure line 33. The actuating unit preferably is provided with stops such as, for example, stops 25-26, one of which should be adjustable, to prevent the diaphragm from providing a volumetric displacement greater than a preselected amount and in any event not greater than about 60 cc. which is in the range of the average volumetric displacement of the left ventricle of the human heart. Further, the actuating unit should have a low resistance to maintain the load on the heart as low as possible since the heart must move the diaphragm 21 unless the input compartment is coupled at the appropriate time to an appropriate back pressure through valve 13 during diastole.

Mounted or afiixed to the actuating unit 15 is a transducer 27 (see FIGURE 1) actuated by the movement of the diaphragm 21 in the actuating unit 15. This may be accomplished in conventional fashion, for example, as shown in FIGURE 2 by providing a mechanical connection such as a rod 28 between the transducer 27 and the aforementioned diaphragm 21 in the actuating unit 15. While the particular type of transducer used is not critical, it should preferably provide a direct current signal, the magnitude and polarity of which is representative of the movement of the diaphragm. Thus, if the diaphragm 21 is moving, the output signal of the transducer 27 will be a varying but unidirectional signal, if the diaphragm stops in any particular place, the output signal will be a direct current voltage, when the diaphragm reaches one end of its travel, the output signal will be of a maximum value of given polarity, and when the diaphragm reaches the other end of its travel, the output signal will again be of a maximum value but of opposite polarity.

A typical pumping unit comprises a rigid case containing a collapsible bulb, the outer surface of which is in communication with a pressurized gas (the output compartment of the pumping unit 15) and the inner surface of which is in communication with the circulatory system of a body. A typical extracorporeal ventricle is disclosed in the aforementioned US. Patent No. 3,099,260, and a typical intercorporeal ventricle is disclosed in the aforementioned patent application Ser. No. 355,273.

By way of example, as diagrammatically represented in FIGURE 2, the rod 28 actuated by the diaphragm 21 may be movable into and out of a coil 29 to vary the output frequency of an oscillator (not shown) which is rectified to provide either a constant direct current signal or a varying direct current signal, depending on the movement of the diaphragm.

Since the zero position of a low inertia diaphragm can move or be made to move because, for example, of a slow leak, changes in pressure, diffusion of the gas through the bulb and/or tubing and the like, an adjustable centering valve 31 (see FIGURE 1) coupling the input compartment 22 and the outer compartment 23 of the pumping unit is provided for centering and/ or recentering of the diaphragm. Centering valve 31 may comprise a conventional manually or automatically adjustable needle valve to provide the desired flow rate between input compartment 22 and output compartment 23 when a difference of pressure exists between them. Such an arrangement or its equivalent is essential to insure that a given volumetric displacement in the actuating unit 15 is reflected in the pumping unit 16.

Returning now to FIGURE 1, for the moment, attention is directed to the fact that three-way valve 13 is vented to atmosphere through diastolic back-pressure producing means 30. Means 30 may comprise, for example, a volume large with respect to the volumetric displacement of actuating unit 15 and an adjustable needle valve or the like (not shown) to permit controlled venting of actuating unit 15 and thereby provide a back pressure substantially equal to the diastolic pressure of the patient. The provision of a diastolic back pressure is essential to insure that output signal of transducer 27 is representative of diastole in the patient. It has been found that if diastolic back-pressure producing means 30 is not provided not only will back flow of blood into the pumping unit 15 occur, but during diastole the diaphragm 21 now actuated by the diastolic pressure in the circulatory system will be permitted to move at a rate not representative BEST AVAILABLE co of pressure in the circulatory system during diastole. This has the added disadvantage of resulting in undue wear on the bulb by permitting it to strike the case at the end of its diastolic stroke.

All of the foregoing components with, of course, the exception of the percutaneous connector and pumping unit may be located in a bedside control panel. Tube 32 connects the pneumatic portion of the system to the patient in which is implanted the percutaneous connector 25 and the pumping unit 16. Tube 33 which is disposed interior of the body connects the percutaneous connector to the pumping unit.

FIGURES 3, 4, and 5 illustrate various ways in which the invention may be used or incorporated in useful circuits. Directing attention now to FIGURE 3, there is shown fail-safe circuit means 40 actuated by the output signal from transducer 27. The fail-safe circuit means 40 controls a solenoid valve 41. Thus, if the actuating unit or some other critical component fails, for example, this may cause the fail-safe circuit 40 to actuate valve 41 and vent the pumping unit 16 to atmosphere, thereby preventing the pumping unit from restricting or possibly preventing the flow of blood from the heart. For a more complete discussion of the fail-safe circuit 40 and its associated components, reference is made to the aforementioned patent application No. 531,281.

FIGURE 4 illustrates the use of the output signal from transducer 27 in combination with a signal proportional to pressure in the pumping unit to permit the visual display of the Work diagram of the pumping unit on an oscilloscope 42. In this case, the output signal from transducer 27 may be supplied to the vertical deflection plates of oscilloscope 42 and the output signal from intra-arterial pressure measuring means 43 may be supplied to the horizontal deflection plates of oscilloscope 42. For a more complete discussion of suitable intra-arterial pressure measuring means, reference is made to patent application Ser. No. 566,659, filed July 20, 1966 in the name of John D. Laird and assigned to the same assignee as this application.

FIGURE 5 illustrates the use of the output signal of transducer 27 to actuate lights which are indicative of, for example, the systolic (pressure) phase and the diastolic (filling) phase of the pumping unit. As shown in FIGURE 5, the output signal of transducer 27 may be supplied to a conventional emitter follower 44, the output of which is amplified by a conventional amplifier 45. The output of amplifier. 45 actuates a conventional Schmitt circuit 46 which causes current to be supplied to light 47 when the output signal of transducer 27 is at its most positive point and indicative, for example, that the bulb in the pumping unit is at the end of its pressure stroke, i.e., is fully compressed. Similarly, second amplifier 48 which is coupled to the output of emitter follower 44 actuates a second Schmitt circuit 49 similar to Schmitt circuit 46. Schmitt circuit 49 actuates light 50 when the output signal of transducer 27 is at its most negative point and, hence, when the bulb in the pumping unit is fully expanded.

While there is shown and described herein certain specific structure embodying the invention, it will be manitest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein shown and described except insofar as indicated by the scope of the appended claims.

What is claimed is:

1. In a system for assisting blood flow within a living body comprising a source of pneumatic pressure, threeway valve means coupled to said source of pressure, means for synchronizing the operation of said valve means with the pumping action of the heart, and a pneumatically actuated blood pumping unit, the combination comprising:

(a) an actuating unit pneumatically coupled to said pumping unit to produce a systolic and diastolic stroke in said pumping unit, said actuating unit including a movable diaphragm sealably separating an inlet compartment coupled to said source of pressure through said three-way valve means and an out let compartment coupled to said pumping unit;

(b) valve means connecting said inlet and outlet compartments for equalizing the pressure in said compartments; and

(c) transducer means mechanically actuated by said actuating unit for producing an output signal representative of said systolic and diastolic strokes.

2. The combination as defined in claim 1 wherein said valve means is insensitive to rapid changes in pressure in said inlet compartment.

3. The combination as defined in claim 2 and additionally including back-pressure means coupled to said inlet compartment for providing a back pressure on said diaphragm after systole.

4. The combination as defined in claim 3 wherein said back-pressure means is in direct pneumatic communication with said diaphragm only after systole and permits pressure in said inlet compartment to decrease at a predetermined rate.

5. The combination as defined in claim 1 wherein the output signal of said transducer means is a signal the magnitude of which is representative of the magnitude of movement of said diaphragm and the polarity of which is representative of the direction of movement of said diaphragm.

6. The combination as defined in claim 5 and additionally including:

(a) an electrical coil forming part of an electrical circuit; and

(b) a rod actuated by said diaphragm and movable within said coil to vary the inductance thereof in ac- .cordance with movement of said diaphragm.

References Cited UNITED STATES PATENTS 3,099,260 7/1963 Birtwell 128-1 3,266,487 8/1966 Watkins et a1. 128-1 OTHER REFERENCES Hiller et al.: Amer. Soc. Art. Inter. Org., vol. VIII, 1962, pp. -130.

Chesnut et al.: I.E.E.E. Trans. Bio-Med Engr., July/ October 1965, vol. BME-12, Nos. 3 and 4, pp. 173-186.

DALTON L. TRULUCK, Primary Examiner.

U.S. Cl. X.R. 31

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