Temperature and perfusion responses of muscle and lung tissue during chronic heating in vivo

For the first time, both temperature and perfusion responses have been obta ined from in vivo studies of chronically heated lung and muscle tissue of c alves. In each tissue, the spatial temperature distribution was measured by thermistors placed in needles at several distances from an implanted heate d disc. A perfusion parameter was defined for a bioheat transfer model that describes temperature dynamics with distance from the heated disc. Estimat es of perfusion were obtained by a least-squares fit of the model output to a step change in heat flux. Except for short transient experiments several times a week, a constant heat flux of 0.04, 0.06 or 0.08 W cm(-2) was main tained at the disc surface for up to seven weeks. At the higher heat fluxes , the steady-state tissue temperature decreased with heating duration. Also , the characteristic time constants of the tissues decreased with heating d uration. Muscle perfusion showed a statistically significant increase durin g chronic heating. Tissue adapts to chronic heating above 42 degreesC by al lowing more capillary blood flow that increases heat loss to reduce tissue temperature.