US 3376863 A
Description (OCR text may contain errors)
April 9, 1968 T. KOLOBOW Em. 3,376,863
BIVENTRICULAR CARDIAC ASSISTER Filed Feb. 9, 1966 INVENTORS THEODOR KOLOBOW ROBERT L. BOWMAN M ATTORNEY United States Patent O 3,376,863 BIVENTRICULAR CARDIAC ASSISTER Theodor Kolobow, Rockville, and Robert L. Bowman,
Bethesda, Md., assignors to the United States of America as represented by the Secretary of the Department of Health, Education, and Welfare Filed Feb. 9, 1966, Ser. No. 526,211 Claims. (Cl. 128-64) The present invention relates to a biventricular assistor and, more particularly, to a biventricular assistor for functionally assisting the pumping of the heart by acting on all four heart chambers.
Sudden cessation of cardiac output secondary to ventricular fibrillation is an immediate life threatening event, and if left unattended, necessarily culminates in death. A lesser emergency exists when cardiac output gradually begins to fall due to some trauma to the myocardium itself, such as acute or chronic coronary insufliciency which itself often leads to a drop in blood pressure reducing myocardial perfusion with oxygenated blood. This vicious cycle, continuously diminishing cardiac output, finally ends in death.
Methods of augment failing cardiac output have included artificial heart-lung devices, as Well as various devices which simulate cardiac message and rely on an intact pericardium. Besides such known devices to assist the natural heart, other prosthetic devices which replace the heart entirely have been devised; similarly heart transplants have also been attempted.
Certain of the prior devices have been provided for applying pressure in a rhythmic manner to the outside of the chest and thereby cause massaging of the heart. In addition, it has been previously contemplated that artificial contraction of an impaired natural intact heart is feasible with a system utilizing a prosthesis tailor tted to and surrounding the heart. However, all the previously contemplated mechanical systems for effecting artificial contraction of an impaired heart, particularly while intact, have not been satisfactory for one reason or another, e.g. control, retention and function are unsatisfactory, and it is still generally necessary for the surgeon to massage the impaired heart by hand.
Mechanical devices to induce open chest cardiac massage have usually relied on an intact pericardium. However, the mammal pericardium is of insufficient strength to withstand frequent insuiation with balloons, gases or otherwise and it has been found that the previous mechanical devices provide assistance of but a few hours duration. In addition, balloons or air insutliation of the pericardial sac are hazardous because both atriums and both ventricles are simultaneously subject to identical or elevated pressures and this results in elevated right and left atrial pressures with its resultant great dangers.
Prosthetic devices intended to replace the heart entirely formed of plastic and/or metal have had two extremely serious problems, i.e. problems with valves and the unnatural clotting of the blood while in contact with the metal or plastic. These problems have so far proved insoluble.
The present invention, on the other band, embodies a device to provide for a rhythmic contraction of lthe ventricles until a primary regular cardiac rhythm can be established, at which time it continues to assist the ventricles synchronously with the heart beat until the ventricular force is able to sustain adequate circulation on its own. In addition, the device of the present invention will function as a prosthetic intrathoracic heart if the ventricular force of the heart itself is not able to sustain adequate circulation on its own.
Devices in accordance with the present invention have the advantage over the entirely prosthetic heart in that the normal endocardium, as well as the normal cardiac valves, are functionally retained and this eliminates the 3,376,863 Patented Apr. 9, 1968 major problem of artificial prosthetic hearts, i.e. clotting and problems with valves.
The present invention has been described in some detail in the Transactions of the American Society of Artificial Internal Organs, volume XI, submitted Apr. 9, 1965.
It is therefore an object of the present invention to etfect artificial contraction of the heart in an improved manner.
It is another object of the present invention to obviate the deliciencies of the prior art, such as indicated above.
f It is another object of the present invention to provide an improved cardiac assistor which is adapted to surround the ventricle portions of the heart and function effectively to provide articial contraction.
It is another object of the present invention to provide a biventricular cardiac assistor for enveloping the heart to provide better control, retention and function.
These and other objects and the nature and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the drawing wherein:
FIG. l is a generally vertical section view through a device in accordance with one embodiment of the present invention;
FIG. 2 is a vertical section View of another and preferred device in accordance with the present invention; and
FIG. 3 is a perspective view of the device of FIG. 2.
Muscle exerts force by contracting and shortening. In the heart this results in the contraction of a ventricle chamber from a large diastolic volume to a smaller volume in systole with concomitant ejection of blood. In the present invention, a similar property of elastomers, i.e. the ability of elastomers, which have been prestretched to snap back into their original size and shape, has been used to provide a change from diastolic volume to systole volume and vice versa.
A cardiac assistor in accordance with the present invention is shown generally in FIG. l at 10 and includes an elastomeric layer or heavy rubber ventricle 12 having lips 14. The lips 14 are snapped about a rigid generally conical shell 16. A leak-proof annular cavity 18 is defined between the elastomeric layer 12 and the rigid shell 16. This annular chamber 18 provides for the alternate application and withdrawal of fluid pressure to effect the heart massage by liexing the elastomeric layer 12. A venting port 20 is provided in the rigid shell 16 to provide egress to the chamber 18 and permit the application of Huid pressure thereto.
The fluid pressure provided is preferably in the form of a vacuum and this causes the elastomeric layer to ilex towards the rigid shell 16. Upon release of the vacuum the elastomeric layer 12 then snaps back to its natural position and in so doing applies massaging pressure to the heart. Depending upon the thickness and the selection of the particular material from which elastomeric layer 12 is fabricated, a suction of 100 mm. Hg would cause the elastomeric layer 12 to bulge from its rest position shown to a new position shown in phantom at b. Venting of the vacuum to atmosphere would then cause the elastomeric layer to return to its state of rest. Similarly, the application of 200, 300 or 400 mm. of Hg of suction would cause the walls of the layer 12 to bulge from its state of rest to the positions c, d and e. If the vacuum is reduced from 400 mm. Hg to mm. Hg, for example, then the elastomeric layer 12 will move from position e to position b.
In operation, controlled gradual suction and controlled gradual release of suction at rates of up to several cycles per second provides a gentle and smooth pumping action with a force not exceeding central aortic pressure. Cardiac assistor devices have been produced in accordance with the present invention with a capacity of up to 16 liters/min.
In the device of FIG. 1, a bulge 22 is provided in the rigid shell 16. The bulge 22 permits the application of greater suction, e.g.. between 400 and 500 mm. Hg, while insuring that the further suction has only a small and controlled pumping effect as compared to suction between 100 and 200 mm. Hg. The small volumetric effect permitted by the bulge 22 is schematically illustrated in FIG. 1 by the additional lines in phantom f and g. For any given construction embodying a particular material and thickness of the elastomeric layer 12, the pumping pressure or effect of the assistor can be easily determined experimentally and plotted, if desired, as a function of the suction gradients.
To obviate the need for a custom fit assistor 10 for each heart and to improve the control of the assistor 10, a thin elastomeric liner 24 is provided within the elastomeric layer 12. The space between the elastomeric layer 12 and the elastomeric line 24 is filled with a suitable gelatinous fluid 26. The cardiac assistor 10 is also provided with a thin elastomeric cover for the outside of the rigid shell 16.
The rigid shell 16 may be formed of a number of materials such as highly resistant stainless steel, reinforced inert thermosetting plastics such as glass reinforced polyesters or epoxies, or naturally rigid inert plastics such as polycarbonate resin (Lexan, manufactured by General Electric). At any rate, the shell 16 should be rigid and should be inert to body tissue and free from contamination. The elastomeric material forming the layer 12, the liner 24 and the cover 28 is preferably formed of natural rubber; however, any elastic material, such as artificial rubbers and silicone rubber, may be used so long as the elastic material is inert to body tissue and not contaminated. With regard to the gelatinous uid 26, it is preferred that a jelly-like material be used such as gelatin or a lyophilic gel; other materials such as viscous oils of various types or mixtures of silicone oils with silicone elastomers may also be used. In fact, non-viscous liquids may also be used, ybut these do not generally provide the degree of support desired and their use is not preferred.
The assistor 100 of FIG. 2 is similar in many respects to the assistor 10 of FIG. 1. Thus, the assistor 100 comprises an elastomeric layer 112, a rigid shell 116, an annular cavity 11S therebetween, a suction and venting port 120 in the shell 116 permitting egress to the annular cavity 118, an elastomeric liner 124, a gelatinous fluid 126 between the liner 124 and the layer 112, and an elastomeric cover 128 for the shell 116.
In the assistor 100, a suitable port means 130 is provided to feed and withdraw gelatinous iiuid 126 to the space between the elastomeric liner 124 and the elastomeric layer 112 in order to adjust the size of the assistor. The port 130 may also be used to vary the level of suction at which it' is desired to operate the assistor. Thus, more gelatinous uid may be injected to compensate for the increased dead space it is desired to operate at between the levels of 300 and 200 mm. Hg (lines d and c in FIG. l). The required priming volume of blood, therefore, thus remains the same.
An important feature of the assistor 100 is the fabrication of the elastomeric layer 112 to a shape (and size, if possible) to that of the natural heart ventricles in systole. When using natural rubber for the elastomeric layer 112, it has been found that a wall thickness of about 60 mils is adequate to provide the necessary and desirable durability and strength. The elastomeric layer 112 need not be of uniform thickness throughout, although such a uniform thickness will simplify design and construction. Certain areas of the elastomeric layer 112 may be constructed of a considerably greater thickness than the remainder in which case the thicker areas will stretch later than the thinner areas after reaching the higher degrees of vacuum. In this manner the relative excursion and timing of both the expansion and the contraction phase of the elastomeric layer 112 can be controllcd, in which case the layer 112 will act as an artificial heart muscle.
Since the layer 112 is formed tol the shape of the heart in cystole, the rigid shell 116 is formed to closely approximate the contours of the ventricles of the heart in diastole. As a result of this shape, introduction of vacuum and venting of same through the port 120 permits the rubber ventricle 112 to move to and from in the space provided rather than to lballoon out at random.
Because the ventricle size varies from mammal to mammal and even among different mammals of the same species, it is difficult to predict an exact size of any common elastomeric ventricle layer, such as elastomeric layer 112. Therefore, and as described above, the elastomeric liner 1124 and the gelatinous fluid 126 is provided to accommodate a reasonable range of smaller ventricles than the particular heart that the particular assistor was originally designed for.
While the assistor 10 of FIG. l is provided with a more or less closed structure at the vertex 15 thereof where the elastomeric cover 28, the elastomeric liner 24, and the elastomeric layer 12 all join together, the assistor 160 is provided with a vent 132 extending from the vcrtex `115. Because the major excursion of the heart in systole occurs in its circumference, the vent 132 is provided to suck the ventricle into the assistor for its initial placement and this may be accomplished by merely applying vacuum through the vent 132. Conversely, com pressed gas may be applied through the vent 132 to make the heart pop out of the assistor when it is desired to remove the assistor.
The assistor is also provided with a flexible collar 1134 which extends about the inner periphery of rigid shell about the opening at the base thereof. The iiexible collar 134 is a accid structure that fits perfectly snug into the atrioventricular groove. It is formedl Iby an extended portion of both the elastomeric liner 124 and the gelatinous uid 126 therein. Its purpose is to provide a flaccid seal between the assistor and the ventricles, so that any motion of the rub-ber ventricles will promptly be reected in a corresponding motion of the ventricles of the heart. In addition, the flexible collar 134 assists in the sucking of blood into both natural ventricles, thereby mimicking a trial function of a normal heart. Functionally, the assistor 100 is therefore not only a biventricular assistor, but is actually a cardiac assistor since all four heart chambers are functionally assisted. Shouldblood ow into both atria be inadequate or totally obstructed, no undue suction Will be exerted on the ventricles because external air or other fluid will then enter between the jelly collar and the true ventricle, thus breaking the suction.
Alternate suction and venting through the port is preferably controlled by a vacuum-motor powered valve (not shown). The switching rate, venting, suction, and timing of the systole in relation to the diastole can be accomplished by manipulating proper control valves (also not shown). The provision of such valves Will be clear to those in the eld. No electrical power or control devices are needed lif assistive power is provided to a fibrillating heart.
The assistor of the present invention is able to provide is stored therein and is subsequently released by the4 stretched rubberlayer. Starlings law on the heart need not be violated during biventricular assistance, provided right atrial pressure can be monitored so as to adjust the assistors rate or degree of energizing it. The biventricular assistor acts functionally as a bi-atrial assistor as well as due to expansion of the ventricles to the diastole stage, and concomitant suction of blood from atria into ventricles. Because of this, the contracting atria contribute to optimal ventricular lling. Even in the normally beating but failing heart, normal atrial contraction becomes redundant as soon as the assistor is placed onto the ventricles.
In applying an assistor in accordance with the present invention, it is necessary to at least partially remove the pericardium. In such a case, it is desirable to simulate a synthetic pericardial lining and this is, in part, the function of the elastomeric liner 124 and the gelatinous :Huid 126.
An assistor in accordance with the present invention is particularly useful for acute cardiac emergencies where defibrillation in an .open chest cannot be readily accomplished, :but may be accomplished subsequently. It is equally applicable in a deti-brillated, but obviously failing heart or in a frankly failing heart where the circulation `cannot be maintained otherwise. In addition, the device has great potential in use as a prosthetic intrathoracic heart since the major problems of conventional prosthetic intrathoracic hearts involve clotting and valvular di- 4culties which are overcome by the present invention.
As compared to assistors of the prior art that do not contact circulating blood, the present invention offers several distinct advantages. First, it exerts its force only where needed, i.e. the failing ventricles. Second, pressure is never exerted on the atria at any time. Third, the assistor provides an atrial function by creating an atria ventricular pressure gradient to facilitate ventricle lling. Fourth, it snaps onto both ventricles instantaneously, and pops off when rdesired in a similar manner. No positioning of the assistor is necessary as it seeks the correct position on its own.
It will be obvious to those skilled in the art that various changes may be made without departing from the scope of the invention. Thus, for example, in place of the elastomeric liner l124 and the gelatinous fluid 126, a single relatively thick layer of a jelly-like material such as a silicone elastomer (Sylgard, manufactured by Dow Corning) or foam rubber or plastic bonded rmly to the underlying elastomeric layer 112 may be utilized. In such a case, the inner surface of the thick silicone layer will yfunction as the liner 124 and the remainder will function as the gelatinous fluid 126. Therefore, the invention is not limited to what is shown in the drawings and described in the specification but only as indicated in the appended claims.
What is claimed is:
1. A biventricular cardiac assistor comprising:
a rigid, generally conical shell having a vertex, an opening at the base opposite said vertex, an inner surface and .an outer surface and defining a cavity generally complementary in shape to the ventricle portion of the heart;
an elastomeric layer adjacent the inner surface of said rigid shell and deiining `an annular cavity therebetween;
means to withdraw and apply fluid pressure to said annular cavity between said rigid shell and said elastomeric layer, the withdrawal and application of fluid pressure being to eifect massage of the heart;
a thin elastomeric liner within said elastomeric layer;
a gelatinous uid disposed between said elastomeric layer and said elastomeric liner.
2. An assistor in accordance with claim 1 wherein said rigid shell is formed to a shape generally similar to the heart in diastole and said elastomeric layer is formed to a shape generally similar to the heart in systole, said heart massage being effected by applying vacuum through said means to apply iluid pressure to elastically enlarge said elastomeric layer and then withdrawing said vacuum to permit said elastomeric layer to return to its normal size.
3. An assistor in accordance with claim 1 further comprising a thin elastomeric cover for the outer surface of said rigid shell.
4. An assistor in accordance with claim 3 wherein said elastomeric cover, said elastomeric layer and said elastomeric liner are joined at the vertex of said shell to form a closed structure.
5. An assistor in accordance with claim 3 wherein said elastomeric cover, said elastomeric layer and said elastomeric liner are joined at the vertex of said shell, said assistor further comprising a vent at said vertex to suck the heart ventricle into said assistor for initial placement.
6. An assistor in accordance with claim 1 further comprising means to feed and withdraw gelatinous Huid to the space between said elastomeric liner and said elastomeric layer to adjust the size of said assistor.
7. An assistor in accordance with claim 1 wherein said elastomeric layer deiines lips adjacent the edges 0f said rigid shell, said lips snapping over the edges of said rigid shell and anchoring said elastomeric layer in place.
8. An assistor in accordance with claim 1 further comprising a exible collar extending about the inner periphery of said rigid shell at the opening at the base thereof, said flexible `collar being formed of an extension of said thin elastomeric liner and said gelatinous uid there 1n.
9. An assistor in accordance with claim 1 wherein said rigid shell is formed of a material selected from the group consisting of stainless steel, reinforced inert plastic and naturally rigid inert plastic; said elastomeric material is selected from the group consisting of natural rubber, silicone rubber and inert artificial rubbers; and said gelatinous fluid is selected from the group consisting of gelatin, viscous oils, silicone oils, mixtures of silicone oils and silicone elastomers, and lyophilic gels.
10. An assistor in accordance with claim 1 wherein said elastomeric layer is of non-uniform thickness, the thicker portions of said layer stretching later than the thinner portions during said withdrawal of iluid pressure.
References Cited UNITED STATES PATENTS 2,826,193 3/ 1958 Vineberg 128-64 3,233,607 2/ 1966 Bolie 128-64 3,279,464 10/ 1966 Kline 12S-64 L. W. TRAPP, Primary Examiner.