Heart disease continues to take a heavy toll of human life. It is responsible for nearly a million deaths a year in the U.S. alone. The toll has been reduced to some extent by improved and new medical procedures, new drugs, pacemakers and most recently by the employment of ventricular assist devices. However, in many cases, replacement of the diseased heart with a healthy heart is the only manner of treating and curing the patient. One of the major problems with this method of treatment is that there are too few donors. For example, in 1978 only 31 people received transplanted hearts, whereas a panel of the National Heart, Lung and Blood Institute has estimated that from 17,000 to 50,000 people per year could use a transplanted heart.
A possible solution to this problem is a totally artificial heart. The development of such a device began in 1957. Since 1975 a number of artificial hearts have been developed and tested in animals. Unfortunately, most of the artificial hearts developed prior to 1970 were not successful for various reasons. In 1970 a series of developments made the prospect for the device look better. A major advance was the design of a heart whose pumping element was a diaphram. This principle was introduced by Clifford S. Kwan-Gett. Basically, the artificial heart developed by Kwan-Gett comprises a chamber containing a deformable diaphram. The heart was driven by an external pump which periodically pumps fluid into the heart chamber to deform the diaphram and thereby expel blood from the artificial heart chamber. Notwithstanding, the improved diaphram system, Kwan-Gett's artificial heart, along with other hearts of similar design and construction, did not prove to be as successful as had been hoped due to shape and size problems.
In 1972, the diaphram principle was used by Robert Jarvik to design a more anatomically acceptable artificial heart. In animal testing, the Jarvik artificial heart has been very successful. The most recent model, the Jarvik-7 heart which was developed in 1979 has been remarkably successful. The Jarvik-7 heart has been implanted in calves which subsequently have survived for considerable periods of time. Despite the success of the Jarvik heart, the system utilized to power the heart remains a major problem which has stymied the development of artificial hearts. The pneumatically powered artificial hearts, including the Jarvik-7 heart, that have proven successful in animals are not portable. The animal is confined to a cage, tethered to a large drive system and exercised only on a tread mill. Such conditions would be unacceptable for human beings. Even if compressed air devices were made portable, the large pneumatic tubes that enter the chest would be uncomfortable and would carry a high risk of infection at the point of entry.
Ventricular assist devices, which assist the natural heart by supplementing the function of the left ventricle have spurred the development of an improved power system. While not as large as artificial hearts, ventricular assist devices work on the same principle as the artificial heart. Thus, they too require a pneumatic or hydraulic power source. An example of one such ventricular assist device is disclosed in Runge U.S. Pat. No. 4,176,411. The device disclosed by Runge comprises a flexible dacron conduit disposed between the left atrium of the heart and the descending thoracic aorta and surrounded by an artificial muscle sheath. In operation, the artificial muscle sheath is electrically stimulated to contract against the flexible dacron conduit to force blood to flow from the left atrium in to the aorta, thus aiding corporeal circulation.
The most recent development in an improved power system is an electrohydraulic energy converter that is presently being design by Jarvik in collaboration with Milton Isaacson of New-Tech, Inc. This electrohydraulic energy converter has only one moving part. The impeller of an axial flow pump is attached to the rotor supported by a single hydrodynamic bearing. Reversing the rotation pump reverses the direction of the hydraulic flow. The hydraulic fluid (silicon oil of low viscosity) actuates the diaphram of a blood pump much as compressed air does. In a left ventricle cardiac assist device the axial flow pump moves the hydraulic fluid from a reservoir sack into the blood pump and back. In a total artificial heart the hydraulic fluid is pumped back and forth between the right and left ventricles. The energy converter is so small that it can be implanted without impinging on vital structures. The converter, however, requires an external battery and an electronics package which is connected to the heart by a small cable that passes through the chest. The batteries weigh from 2 to 5 lbs. and are worn in a vest or on a belt. It is necessary to replace the rechargable batteries once or twice a day. Although this device contains many of the desirable features of a portable artificial heart for human use, it nevertheless has many of the problems of the totally external pneumatic pumps. The electrohydraulic energy converter is not a completely internal power system, but rather is dependent upon an external power source. Also, like the external pneumatic pumps, this new device has wires that enter the chest which would result in a high risk of infection at the point of entry. Moreover, this new device is dependent on a battery system which must be continually recharged and which must be worn on a belt or vest.
The present invention solves the problems of the prior art pumping devices since it is directed to a totally internal system for powering artificial hearts, ventricular assist devices and the like.
The present invention was first disclosed to the U.S. Patent and Trademark Office in Disclosure Document 97,636 dated Feb. 10, 1981.