US3456444A

US3456444A - Actuating unit for circulatory assist systems

Info

Publication number: US3456444A
Application number: US568248A
Authority: US
Inventors: Michael L Rishton
Original assignee: Avco Corp
Current assignee: KONTROL CARDIOVASCULAR Inc
Priority date: 1966-07-27
Filing date: 1966-07-27
Publication date: 1969-07-22
Anticipated expiration: 1986-07-22

Description

July 22, 1969 M. L. RISHTON 3,456,

ACTUATING UNIT FOR CIRCULATORY ASSIST SYSTEMS WMKW ' ATTOR NEYS July 22, 1969 M. L. RISHTON 3,456,444

ACTUATING UNIT FOR CIRCULATORY ASSIST SYSTEMS Filed July 27, 1966 3 Sheets-Sheet 5 MICHAEL L.- HTON 1N TOR.

ATTORNEYS United States Patent 3,456,444 ACTUATING UNIT FOR CIRCULATORY ASSIST SYSTEMS Michael L. Rishton, Reading, Mass, assignor to Avco Corporation, Cincinnati, Ohio, a corporation of Delaware Filed July 27, 1966, Ser. No. 568,248 Int. Cl. Fb 7/02; F04b 9/10 US. Cl. 6062.5 11 Claims ABSTRACT OF THE DISCLOSURE An actuating unit for driving a blood pump in circulatory assist systems having a low inertial diaphragm, a small and adjustable axial displacement of which provides the necessary volumetric displacement for any given system. Means for maintaining a minimum pressure in the outlet compartment may also be included.

This invention relates to circulatory assist systems and more particularly to actuating units for driving blood pumps in circulatory assist systems.

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 auxiliary 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 insufficiency.

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 blood pumps usually consist of a flexible bulb or ventricle squeezed by pressurized fluids from an 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 Dacron-type employed in the insertion of arterial grafts and the 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 control the blood pump through an actuating unit that is pneumatically operated to eject an operating fluid to drive the blood pump to meet the requirements of a patients circulatory system. The actuating unit embodied in the present invention satisfies all of the requirements for an actuating unit set forth above that has been proved successful in carrying out the difiicult task of driving a blood pump under various types of conditions.

Accordingly, it is an object of the present invention to provide an actuating unit for driving a blood pump.

Another object of the present invention is to provide an actuating unit that is simple in construction and operation and that is not susceptible to breakdown.

A further object of the present invention is to provide an automatically operated actuating unit for operating a heart pump wherein the actuator is adapted to control a hydraulic pulse for deforming a pump unit or ventricle to move an equal volume of blood through the pumping unit.

A still further object of the invention is to provide an actuating unit in a circulatory assist system that automatically provides a minimum predetermined pressure on the blood pump side of the actuating unit.

Still another object of the invention is to provide an actuating unit that has a stroke volume that is controllable and calibrated.

A still further object of the invention is to provide an actuating unit in a circulatory assist system wherein a minimum pressure on the blood pump side of the actuating unit may be automatically and mechanically maintained during and as a result of operation of the actuating 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 typical circulatory assist system;

FIGURE 2 is a sectional side view of an actuating unit in accordance with the invention;

FIGURE 3 is an end view taken on line 33 of FIG- URE 2; and

FIGURE 4 is an end view taken on line 4-4 of FIG- URE 2.

Directing attention now to FIGURE 1, there is shown a schematic illustration of heart pumping or circulatory assist apparatus intended to provide intercorporeal mechanical assistance. As shown in FIGURE 1, in a typical system a suitable pressurized source of gas 10 feeds a low pressure regulator 11. 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 presure 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 11, while of conventional design, should permit small adjustments in the pressure range of about to 3 pounds per square inch. The output of the low pressure regulator 11 is fed to a three-way solenoid actuated valve 12. The valve 12, which is normally vented to the atmosphere through diastolic back-presure produing means 13, 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 12 is actuated by the synchronizing circuit 14 does the valve 12 supply compressed gas to the actuating unit 15 which in turn controls 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 patents heart. The actuating unit and sence the pumping unit must be capable of being phased with the patents heart while the duration of the systolic and diastolic strokes should be adjustable. The synchronizing circuit 14 performs the function of properly synchronizing the operation of the solenoid in valve 12 for admitting the pressurized gas into an actuating unit 15 in accordance with the demands of the patient. Typically, the synchro nizing 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 amplifiy the sync pulse or electrical signal used for synchronizing purposes. The amplifier and synchronizing pulse shaper if provided may be designed not only to limit the magnitude of the sync pulse but also to shape it. Since the actuating unit is designed to be synchronized with the R-wave 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-wave may be provided to create a sync pulse delayed behind the R-wave by a controlled amount to enable the systolic or diastolic pulse as the case may be 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 12. For a further discussion of circulatory assist systems and 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 as more fully described hereinafter, it is preferably of the type comprising a low inertial diaphragm separating the unit into an input compartment and an output compartment, the presurized gas from valve 12 being admitted into the input compartment and the gas in the output compartment being in communication with the pumping unit 16 through, for example, pressure line 32, a percutaneous connector 25 and pressure line 33. The stroke of the actuating unit is adjustable to provide a variable greater than about 60 cc. which is in the range of the average volumetric displacement of the left ventricle of the human heart is not necesary. 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 unless the input compartment is coupled at the appropriate time to an appropriate back-pressure through valve 12 during its diastolic stroke.

Mounted or afiixed to the actuating unit 15 is a transducer 27 actuated by the movement of the diahragm in the actuating unit 15. This may be accomplished in conventional fashion, for example, by providing a mechanical connection such as a rod between the transducer 27 and the aforementioned diaphragm 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 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. For a further discussion of transducer 27 and its associated circuitry, reference is made to the aforementioned patent application No. 531,281 and patent application No. 566,527 filed July 20, 1966 in the name of Robert T. Jones and assigned to the same assignee as this application.

A typical pumping unit comprises a rigid container 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 the 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.

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.

Having now described a typical circulatory system, attention is directed to FIGURE 2 which is a sectional side view of apparatus in accordance with the invention.

Directing attention now to FIGURES 2, 3, and 4, there is shown an actuating unit 15 in accordance with a preferred embodiment of the invention. As shown in FIG- URE 2, the acutating unit is comprised of upper and

lower flange members

41 and 42 defining a hollow cylindrical chamber 43, the radial dimension of which is substantially greater than its axial dimension to produce maximum volumetric displacement for minimum axial movement of the piston. An axial displacement of about one-eigth of an inch to produce a volumetric displacement of about 60 cc. has been found satisfactory. A piston generally designated by the numeral 44 is disposed in chamber 43 and comprised of a flexible diaphragm 45 preferably composed of a suitable rubber-like material, such as medical Silastic, gripped between a lower reinforcing member 46 formed of, for example, linen phenolic and an upper reinforcing member 47 formed of, for example, aluminum. The metal reinforcing member 47 is provided with an axial boss 48 to receive rod 49 and is adapted for engagement with a metal stop member 51 fixedly attached to a cylindrical spool 52. Spool 52 is slidably carried in a spool housing 53 which is fixedly attached to the upper flange member 41.

Flange members

41 and 42 are beveled and provided with respectively continuous smooth surfaces at 54 and 55 at their points of contact with the diaphragm to keep wear on the diaphragm at these points to a minimum. Accordingly, all edges of the aforementioned flanges and reinforcing members which contact or can come into contact with the diaphragm should be rounded olf as shown. The outer periphery of the diaphragm 45 is gripped between

flanges

41 and 42 and in addition to providing a pressure tight seal at this point, also separates the chamber 43 into an inlet compartment 56 and an outlet compartment 57. Inlet port 61 permits inlet compartment 56 to be coupled to a suitable source of pressure and outlet port 62 permits the outlet compartment 57 to be coupled to the pumping unit (see FIGURE 1) as and for the purposes set forth hereinabove.

Flanges

41 and 42, reinforcing members 46 and 47, stop member 51 and spool 52, and upper flange 41 and spool housing 53 may be assembled and held in their respective positions as by screws 63 or the like as shown in FIGURE 1. The manner in which the various components of the actuating unit are assembled as well as the material of which they are composed is not critical. While the parts subjected to wear, impact forces and the like are preferably made of metal, other parts may be made of a suitable clear plastic material to permit visual inspection of the interior of the actuating unit.

Directing attention now to the piston, it will be noted that reinforcing members 46 and 47 each have a diameter which is Slightly less than that of chamber 43 and in combination with diaphragm 45 functions as a piston. O-rings 64 in conventional manner provide sliding seals at the critical locations (more fully described hereinafter) to prevent leakage.

Directing attention now to stop member 51 and spool 52, it will be seen that the position of the stop member 51 may be adjusted axially within chamber 43 as by rotating threaded knob 67. Knob 67 is attached as by screws 63 to the distal end of spool 52 and adapted for threaded engagement with the distal end of spool housing 53. Accordingly, rotation of knob 67 will vary the volumetric displacement provided by piston 44 from a maximum value to a small value and if desired, substantially zero.

Inasmuch as some leakage will be present or at least it must be assumed that some leakage will be present in the outlet compartment and pumping unit as by leaky joints, diffusion of oxygen through the bulb in the pumping unit and the like as well as within the actuating unit itself, it has been found that some means is necessary to maintain a substantially constant minimum pressure within the outlet compartment 57. This minimum pressure is preferably approximately equal to the diastolic pressure in the circulatory system of the patient with which the actuating unit is to be used. Accordingly, in accordance with the invention, the outlet compartment 57 is periodically placed in communication with a loading pressure from any suitable source (not shown) by a second inlet port 71 in spool housing 53, upper annular groove 72 and upper passage 73 in spool 52, valve means generally designated by the numeral 74, lower passage 75 and lower annular groove 76 in spool 52, and passage 77 in the

flanges

41 and 42.

The particular location of the annular grooves 72 and 76 is not important but for the embodiment shown and described herein, they must be cylindrical and have a width sufficient to permit spool 52 to be adjusted to its maximum upper and lower positions without cutting off the outlet compartment 57 from the loading pressure supplied through inlet port 71. O-rmgs 64 prevent leakage from the loading pressure portion of the actuating unit.

Value 74 is comprised of a flexible rolling diaphragm 81 such as, for example, a Bellofram diaphragm the periphery of which is disposed and sealably gripped between knob 67 and spool 52. The center portion of the rolling diaphragm 81 is bonded to end cap 82 which with diaphragm 81 sealably covers pasage 73. End cap 82 is provided with axial projection 83 extending down into the axial passage 84 in spool 52 and which is adapted for engagement with rod 49 just prior, for example, to the time when reinforcing plate 47 is brought into abutting engagement with stop 51, e.g., the actuating unit has substantially completed its diastolic stroke and the bulb in the pumping unit is substantially filled with blood.

Bushings

85 and 86 formed of Teflon, for example, maintain rod 49 in spaced relationship with passage 84.

Screw 91 and spring 92 axially carried by knob 67 permit adjustment of the force or pressure required to unseat the end cap 82 and thereby provide communication between passages 73 and 75. In use, screw 91 is preferably adjusted to require a small pressure of, for example, 5 mm. by rod 49 to unseat cap 82. Knob 67 is provided with a recess 93 which is in communication with passage 75, and, hence, the outlet compartment 57 through opening 94 in the rolling diaphragm 81. As will now be evident, if the diastolic pressure of a patient is, for example, 40 mm. and the loading pressure is set at a slightly higher value of, for example, 45 mm., it will now be evident that the rolling diaphragm 81 is subjected to a pressure dilferential tending to unseat cap 82 of only 5 mm. and that a comparably small pressure is all that is required of rod 49 to unseat cap 82. O-ring 95 prevents leakage past screw 91.

If desired, a marker 96 may be provided on knob 67 and in conjunction with a calibrated indicator ring 97, used to permit simple and accurate adjustment of the volumetric displacement provided by piston 44.

Attached to lower flange member 42 as 'by bonding is a hollow cylindrical sleeve 98 for removably receiving transducer 27 (see FIGURE 1). O-ring 99 provide a pressure tight seal between sleeve 98 and transducer 27 which is actuated by guide rod 100 fixedly attached to reinforcing member 46.

Having described a preferred embodiment of the invention, what is claimed is:

1. In an actuating unit for periodically ejecting an operating fluid into a pneumatically actuated blood pumping unit to produce a systolic and diastolic stroke in a system for assisting blood flow within a living body, the combination comprising:

(a) an inlet compartment having a first inlet port for receiving a first pressurized fluid;

(b) an outlet compartment having a second inlet port for receiving a second pressurized fluid and a first outlet port for supplying a pressurized fluid to said pumping unit;

(c) piston means sealab'ly separating said inlet and outlet compartments and movable in response to pressure in said compartments;

(d) pressure correcting means for adjustably maintaining a minimum pressure in said outlet compartment when operatively coupled to said blood pumping unit, said pressure correcting means including valve means for providing communication between a source of said second pressurized fluid and said second inlet port in said outlet compartment, said valve means comprising a movable member movable to provide an open position and a closed position, said open position coupling said second inlet port to said source of pressure; and

(e) rod means operatively connected to said piston means for actuating said movable member to said open position and said closed position.

2. The combination as defined in claim 1 wherein said pressure correcting means includes a second outlet port in communication with one side of said movable member means and said second inlet port in said outlet compart ment and a third inlet port in communication with the other side of said movable member means when it is in its said closed position, and loading means for continuously urging said movable means toward its closed position whereby a pressure small compared to said minimum pressure and exerted by said rod means will move said movable member means to its said open position.

3. The combination as defined in claim 2 wherein said second outlet port is in continuous communication with said one side of said movable member means; said loading means is adjustable to vary the force it exerts on said movable member means; and additionally including means for adjustably limiting the distance through which said piston means can move.

4. In an actuating unit for periodically ejecting an operating fluid into a pneumatically actuated blood pumping unit -to produce a systolic and diastolic stroke in a system for assisting blood flow within a living body, the combination comprising:

(a) an inlet compartment adapted to receive a first pressurized fluid;

(b) an outlet compartment adapted to supply pres surized fluid to said pumping unit, the radial dimensions of said compartments being substantially greater than their axial dimension whereby a small axial displacement of said diaphragm center portion produces a large volumetric displacement;

(c) piston means sealably separating said inlet and outlet compartment and movable in response to pressure in said compartments; and

(d) pressure correcting means for maintaining a predetermined minimum pressure in said outlet compartment, said means being actuated by said piston means during the diastolic stroke to place said outlet compartment in communication with said predetermined pressure.

5. The combination as defined in claim 4 wherein said pressure correcting means includes valve means having a normally closed position, said valve means is actuated to its open position by said piston means; and additionally including means for adjustably loading said valve means whereby the pressure required by said piston means to actuate said valve means to its open position may be reduced to about zero.

6. The combination as defined in claim 5 and additionally including volume control means for varying the maximum volumetric displacement of said piston member, and said valve means is carried in said volume control means.

7. In an actuating unit for periodically ejecting an operating fluid into a pneumatically actuated blood pumping unit to produce a systolic and diastolic stroke in a system for assisting blood flow within a living body, the combination comprising:

(a) case means defining a hollow cylindrical chamber having an axial opening and a first pressure inlet port adjacent one end and a first pressure outlet port adjacent its other end;

(b) a piston member movably disposed within said chamber intermediate said ports and sealably separating said chamber into an inlet compartment and an outlet compartment;

(c) a cylindrical spool housing open at both ends, concentric with said axial opening, and carried by said case means, said spool housing having a second pressure inlet port;

(d) a spool member slidably disposed in said spool housing, said spool member having one end adapted for engagement with said piston member and additionally having an axial passage open at both ends, said spool member having a first passage continuously in communication with said second inlet port and a second passage in continuous communication with said outlet compartment;

(e) valve means having an open position and normally closed position disposed at the end of said spool housing remote from said piston member and intermediate said first and second passages, said first and second passages being in communication only when said valve means is in its open position;

(f) a rod member carried by said piston member and extending into the axial passage of said spool member for actuating said valve means;

(g) volume control means for varying the position of said spool member in said spool housing; and

(h) means carried by said volume controlling means for varying the pressure required by said rod member to actuate said valve means to its open position.

8. In an actuating unit for periodically ejecting an operating fluid into a pneumatically actuated blood pumping unit to produce a systolic and diastolic stroke in a system for assisting blood flow within a living body, the combination comprising:

(b) piston means comprising a low inertial unfolded diaphragm extending across said chamber intermediate said port and sealably separating said chamber into an inlet compartment and an outlet compartment, said diaphragm comprising a stiff center portion and an elastic outer portion, the radial dimensions of said compartments being substantially greater than their axial dimension whereby a small axial displacement of said diaphragm center portion produces a large volumetric displacement;

(c) a cylindrical spool housing open at both ends, concentric with said axial opening, and carried by said case means;

((1) a spool member slidably disposed in said spool housing, said spool member having one end adapted for engagement with said piston means; and

(e) volume control means for varying the position of said spool member in said spool housing.

9. The combination as defined in claim 8 wherein an axial displacement of about one-eighth inch of said diaphragm center portion produces a volumetric displacement of about 60 cubic centimeters.

10. The combination as defined in claim 8 wherein said spool member has an axial passage open at its end adjacent said piston means, and a rod carried by said piston means and movably extending into said passage.

11. The combination as defined in claim 10 wherein said volume control means includes threaded means for adjustab'ly varying the position of said spool member whereby engagegent of said piston means and said one end of said spool member results in selectable variation of the volumetric displacement of said piston means.

References Cited UNITED STATES PATENTS 2,444,5 86 7/ 1948 Wuensch. 2,915,016 12/1959 Weaver et a]. 2,975,599 3/1961 Bennett. 3,099,260 7/1963 Birtwell l281 3,240,152 3/1966 Bower. 3,266,487 8/1966 Watkins et al. 1281 MARTIN P. SCHWADRON, Primary Examiner ROBERT R. BUNEVICH, Assistant Examiner US. Cl. X.R. 103-44; 128-1 2 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 444 Dated y 9 9 Inventor(s) Michael L. Rishton It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

r- Column 3, line 19, for "sence" read---hence---; Column 4, line 7, after "variable" read---volumetric displacement. A displacement substantially---; Column 6, line 3, for "Value read---Valve---; Column 6, line 13, for "e. g. read--i. e. Column 6, line 41, for "O-ring" read---O-rings---; Column 8, line 3, after "and" read---a---; Column 8, line 55, for "engagegent" read- -engagement- SIGNED AN'D SEALED JUL14B70 (SEAL) Attest:

mm: 1:. sum, an.

Edward M. Fletcher, II-

, Commissioner of Patents Atbesting Officer