HEAT FROM AN IMPLANTED POWER SOURCE IS MAINLY DISSIPATED BY BLOOD PERFUSION

Heat dissipation and its effects on tissue and blood interfaces are co mmon problems associated with the development and increased use of art ificial hearts, because all of the implantable actuators for artificia l hearts generate waste heat due to inefficiencies of energy conversio n. To determine the mechanisms of heat dissipation from artificial hea rts, heated disks producing constant heat fluxes of 0.08 watts/cm(2) w ere implanted adjacent to the left lung and the latissimus dorsi muscl e in calves for 2 weeks, 4 weeks, and 7 weeks. At the end of each expe riment, a series of acute studies was performed in which blood perfusi on to the heated tissue was decreased or stopped to observe the contri bution of blood perfusion to heat dissipation. The cooling effect of v entilation was also examined to determine its relative contribution to heat dissipation in lung tissue by decreasing the minute ventilation volume. The importance of blood perfusion for heat dissipation was dem onstrated by the temperature rise after cessation of blood perfusion t o the heated tissue. The contribution of ventilation to heat dissipati on in the heated lung tissue was minimal. Contribution of total blood perfusion to heat dissipation was increased with time in the muscle ti ssue, which has relatively low resting blood perfusion, but not in the lung tissue, which has relatively high blood perfusion. In the heated muscle tissue, the in vivo adaptive response to chronic heat was func tionally shown by the increased perfusion. In conclusion, blood perfus ion was the main mechanism of heat dissipation from tissues that were adjacent to an implanted power source.