Mechanical drive for blood pump

Abstract

The invention presents a highly efficient blood pump to be used as a replacement for a ventricle of the human heart to restore people disabled by heart disease. The mechanical drive of the present invention is designed to operate in conjunction with a thermoelectric converter power source. The mechanical drive system essentially converts the output of a rotary motor into pulsatile motion so that the power demand from the thermoelectric converter remains essentially constant while the blood pump output is pulsed.

Description

BACKGROUND OF THE INVENTION

At the present time, there is a need for artificial blood pumps to take over all or part of the blood pumping function of the natural heart in some heart patients on a permanent basis. Attempts to use currently available equipment have resulted in extension of the patients life by at most weeks and more often days or hours. One of the important requirements for successful partial or total longterm heart replacement is that the replacement system, including the blood pump, be totally implantable. Totally implantable means that there are no penetrations through the body's protective converings, such as to external power supplies or controls, to provide a conduit for infection.

Another important requirement for such a blood pump is that it provide a pulsatile flow of pressure level and pulse rate acceptable to the rest of the body. In addition, such a pump must be sufficiently small, light, and vibration-free to be installed within the body without undue stress on other body components. It should also cause minimal damage to the blood pumped.

In any body implantable system, a miniaturized power source is necessary. Most, if not all, miniature power sources, whether electromechanical or thermo-mechanical, provide power through shafts rotating at speeds considerably above heart rate. Such power sources are effectively high speed, constant power output devices, in contrast to the relatively low frequency, pulsatile output required of a satisfactory blood pump. Therefore, another requirement of the pump drive is that it accept a relatively high speed, constant power input and efficiently convert that in order to provide a low frequency pulsatile blood output.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a mechanical drive for a blood pump which translates input rotary motion to reduced speed pulsatile motion compatible with bodily needs.

While the blood pump of this invention is capable of attachment to an external power source, it has features which make it particularly suited to be a part of the totally implanted system. This is accomplished by incorporating the desirable principles of control and hemodynamics of the Kwan-Gett blood pump, a pneumatically driven blood pump, in a mechanically driven pump. For a reference describing the Kwan-Gett principle see Kwan-Gett, C. S., et al., "Total Replacement Artificial Heart and Driving System with Inherent Regulation of Cardiac Output," Trans. Amer. Soc. Artif. Int. Organs, 15:245, 1969. The Kwan-Gett pump is unsuited for full implantation because the expanded gas volume at the end of the pneumatic stroke is too large to conveniently retain within the body. In addition, gas leakage will be a problem for relatively long implantation periods. Further, pneumatic drives are less efficient than mechanical drives and will therefore require larger power supplies for equivalent blood pumping capability.

Incorporation of the Kwan-Gett control principle is important to the total implantability of the mechanical blood pump drive proposed. The Kwan-Gett principle includes driving the blood pump at a constant beat rate. The bladder which expells the blood is driven only during the expelling period (systole). During the filling period, (diastole), the extent of filling of the bladder is set by the body through its control over venous pressure and flow rate. That is, the blood pump expels whatever blood is returned to it up to the maximum capacity of the expulsion bladder. The blood pump maintains system balance using a speed sensor and control as the sole artificial control components.

The bladder configuration of the Kwan-Gett pump is also retained in the blood pump of the present invention since it has demonstrated good hemodynamics in animal experiments.

The purpose of the blood pump and drive embodiment of the present invention is to replace, functionally, a ventricle of the natural heart. This may be accomplished by connecting the blood pump into the blood system in parallel with the natural ventricle. The pump is to be implanted in the chest cavity and will circulate blood at rates required at, for instance, the left side of the heart to support body activities. It maintains sufficient pressure in the aorta (main left side artery) at all times so that the left ventricle discharge valve of the natural heart never opens. Thus, the left ventricle, which does 87 percent of all the heart's work, is relieved of all effort. The device of the present invention can be used as a total right ventricle replacement as well. In this capacity, the pump will be installed in parallel with the right ventricle. Total heart replacement can be effected by using two such ventricles in by-passing modes.

DESCRIPTION OF THE DRAWINGS

FIG. 1 presents a view of the blood pump and its mechanical drive.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The blood pump and its driving mechanism are shown in FIG. 1. The flexible shaft 11 from a power source converter enters the pump assembly and drives a flywheel 12 through a set of right angle bevel gears 13. The flywheel which has a diameter slightly less than the maximum inner diameter of the pump as shown is a key element in this concept. It is the means by which the relatively constant power output of the power source is stored efficiently to meet the wide variation of power necessary to produce pulsatile blood flow. From the flywheel the power is transmitted through a compound planetary gear speed reducer generally shown at 14 to reduce the rotational speed of the system as required to achieve the desired pump beat rate. The sun gear 15 of the speed reducer is integral with the flywheel, the ring gear 16 is held stationary in the substantially hemispherical pump housing 18 and the compound planetary gears 28 and 29 are mounted on a spider 17 attached to a sleeve 30 which rotates on ball bearings carried by a vertically extending boss 31 centrally disposed in the pump housing. As shown, the sun gear 15 is driven by the flywheel and, in turn, rotates the larger planet gear 28 and the smaller planet gear 29 attached thereto. The rotation of gear 29 in mesh with the stationary ring gear 16 causes the planet gears and the spider to revolve about the boss 31 at a speed less than the rotational speed of the sun gear 15. Attached to the spider sleeve 30 is a right angle bevel gear 19 which drives two bevel gears 20 and 21 that rotate in opposite directions on a common axis. Each of the driven gears 20 and 21 are connected to a crank arm 22 with a ballbearing roller 23 that bears against two flat bearing surface 32 and 33 on partial Scotch yokes 24 and 24'. As depicted, the flat bearing surfaces 32 and 33 of the Scotch yokes will provide a sinusodial blood pulse. If animal experiments indicate that a different blood pulse form is desirable, the Scotch yoke bearing surfaces can be contoured to produce other pulse forms. As the bevel gears and crank arms are rotated the rollers on the crank arms bear against the bearing surfaces 32 and 33 to cause a vertical displacement of the yokes. The yokes are tied together with beams and the beams are connected through pivots 34 to a pusher cup 35 which in turn displaces the blood pump diaphragm 25 to expel the blood in systole from a blood receiving chamber 26 defined within the pump housing by the latter and the diaphragm 25. Because the crank rollers can only push the yokes outward and cannot pull them back, the pump diaphragm is displaced inward by the blood returning to the pump. The volume displaced during diastole will depend on the amount of blood received from the pulmonary vein before the crank rollers re-engage in the systole portion of the pump cycle. The pusher cup 35 and the yoke assembly are supported in the transverse plane by means of a guide pin 37 which moves vertically in a ball bushing that is supported by the pump housing. The small yoke torque due to the friction of the crank roller is resisted by the bellows 26 that surrounds the driving mechanism. The drive system is fully balanced except for the small friction component. It is therefore essentially vibration-free.

In addition, because the two crank arms rotate in opposite directions, the crank rollers translate on the yoke assembly bearing surface in opposite directions and apply vertical loads which are balanced about the axis of the diaphragm pusher cup guide pin. This feature avoids side loads on the guide pin ball bushing. The yoke assembly is connected to the diaphragm pusher cup through pivots to insure that both crank rollers transmit power to the yoke assembly at all times. If, due to dimensional variations, only one crank pin attempts to drive the yoke assembly, the yoke connecting beam tilts and permits the other crank roller to also bear against the yoke assembly. Rolling element bearings are used throughout the pump driving mechanism to minimize the frictional power losses and the possibility of seizures which would render the mechanism inoperative.

The entire actuation space below the pump diaphragm is gas and vapor filled. Sealing of this space is accomplished by the pump diaphragm on one side and the compliance bladder 27 on the other. Since both of these sealing components will be made of reinforced silastic or other polymeric material, diffusions of water vapor and body absorbed gases (mostly air) to and from the space to reach an equilibrium condition can be expected.

Table I provides a listing of the materials to be used in a preferred embodiment of the present invention. Table 2 presents approximate weight of the various components used in the preferred embodiment.

TABLE I ______________________________________ MECHANICAL BLOOD PUMP MATERIALS Component Material ______________________________________ Pump Housing Titanium Diaphragm Silastic (Dacron rein- forced) Compliance Bag Silastic (Dacron rein- forced) Flexible Drive Shaft Shaft Stainless Steel Wire Guide Tube Teflon Bellows Titanium Ball Bearings Balls and Races A1S1 440 C Stainless Steel Retainer Rings Plastic (filled with lubricant) Flywheel Kennertium (95% Tungsten) Internal Bellows Titanium Diaphragm Pusher Cup Titanium Guide Pin Beam Titanium Yoke Assembly A1S1 440 C Stainless Steel Diaphragm Pusher Cup Guide Pin A1S1 440 C Stainless Steel Ball Bushing Balls and Outer Race Sleeve A1S1 440 C Stainless Steel Ball Retainer Plastic or Porous Metal Gears High Strength Plastic Crank Arm Titanium Drive Shafts and Planetary Spider Titanium ______________________________________

TABLE 2 ______________________________________ Component Weight (gm) ______________________________________ Housing 203 Flywheel and attached gears 88 Planetary gears and spider 29 Scotch yoke and bevel gears 19 Blood pump diaphragm assembly 32 Compliance bladder 25 Torsion bellows 44 Bearings and ball bushing 15 ______________________________________

Claims

We claim:

1. A blood pump of an artificial heart comprising:

a substantially hemispherical pump housing;

a drive shaft extending into said housing;

a rotatable flywheel disposed in said housing and having a diameter slightly less than the maximum inner diameter of said housing;

meshing bevel gears disposed on said shaft and said flywheel for rotating said flywheel;

a compound planetary gear set disposed within housing comprising a sun gear integral with said flywheel, a stationary ring gear affixed to said housing, compound planetary gears meshing with said sun gear and the ring gear, and a spider carrying said planetary gears and rotatable within said housing by said planetary gears at a speed less than the rotational speed of said flywheel;

a single bevel gear secured to and rotatable by said spider;

a pair of bevel gears meshing with said single bevel gear having their axis of rotation parallel to one another and rotatable by said single bevel gear;

a rotatable crank arm attached to each of said pair of bevel gears;

a pair of scotch yokes disposed within said housing with each of said yokes in contact with each of said cranks and vertically displaceable in response to the rotation of said cranks;

a diaphragm disposed within said housing above said scotch yokes and defining with said housing a blood receiving chamber; and

a pusher cup disposed intermediate said diaphragm and said scotch yokes and alternately displaceable by said scotch yokes upon the vertical displacement thereof by said crank for moving the diaphragm into said chamber and expelling blood therefrom and by the blood entering the chamber when said scotch yokes are not vertically displaced by said cranks.