National Heart & Lung Institute, probably of either elastomeric or collagenous material. This material must be able to last for 1010 cycles in the lifetime of the heart, must be compatible with both body tissue and blood, and must be nonthrombogenic, i.e., will not cause blood clots. Recent accomplishments of the NH&LI program have been to test 75 artificial hearts with velour surfaces. These surfaces endothelialize to form a lining of the host's cells similar to scar tissue. This tissue covering the artificial ventricle surface appears to show many promising characteristics. The artificial heart shown duplicates the physiological function of the human heart by electronically monitoring the body's demand for blood, then controlling filling and pumping of the heart to meet this demand. The heart device may be controlled by varying both the beat rate and volumetric displacement in a manner similar to that of the patient's own heart. Artificial Heart Design The concept under development (Figure 7) utilizes the nuclear isotope Pu-238 as the source of energy. The unit is a cascaded thermoelectric Rankine system in which the thermal energy from the plutonium fuel is used to provide electric power for control of the small steam engine as well as mechanical pumping power from the engine which forces the blood through the patient's body. Size and Weight - By cascading a thermoelectric converter whose upper temperature is 868°C into a Rankine steam cycle whose hot temperature is 454°C, a very high theoretical efficiency is obtained 71% for the cascaded system versus 52% for a steam system. The energy available from the thermoelectric module is utilized to accomplish the work of operating valves, a feedwater pump and a control system. Thus, parasitic losses are reduced, enabling use of a smaller power source. The integrated design results in a unit only 1356 cubic centimeters in volume allowing a comfortable fit in the thoracic cavity. Moreover, the implanted weight of one pound is low enough to enable the unit to be supported by the patient's own pericardial sac. Quick connect fittings provide for ease of installation and connection to the patient's atria. Energy Source The Pu-238, over the 10-year life of the device, has a stored energy of 16 million compared to 40 watt hours per pound for a mercury battery. Since the half-life is 87.7 years, the energy is released in a comparatively uniform manner and provides the ultimate in reliability. |