Local muscle blood flow and temperature responses to 915MHz diathermy as simultaneously measured and numerically predicted

The therapeutic benefits of diathermy are tied to the relationship thought to exist between tissue temperature and augmented blood flow (BF). To further define this relationship, simultaneous measurements of thigh muscle blood flow (MBF) and temperature have been made in 15 human subjects during 915MHz, direct-contact microwave diathermy (MWD) with simultaneous skin cooling. Tissue temperatures were measured invasively by special thermistor probes designed to minimize MW-induced artifacts, and the local rates of MBF were measured by monitoring the radioactive washout of injected Xenon¹³³ (Xe¹³³). The experimental results have shown that the initial MBF response is characterized by a 'critical temperature' behavior such that rapid increases in MBF occur for tissues above approximately 42C when diathermy power is sufficient. A proportionality between tissue temperature and MBF has not been found. To provide more useful descriptions of the temperature fields and diathermic BF responses, two-dimensional numerical thermal simulations of six of the subjects' treatments were constructed and recorded. An average peak simulated MBF of 48 ml/min-100 g was found for these subjects, a level in excess of previous estimates for maximum perfusion during diathermy.