The effects of fractionated hyperthermia on normal canine muscle blood flow

This study investigates the changes in normal canine muscle blood flow occurring during three fractions of 43 °C (60 min) hyperthermia. Blood flow was measured during heating at 1-, 3-, and 5-day intervals with a laser Doppler flowmeter. For 1-day intervals, blood flow oscillated during the first treatment reaching peak values of approximately 39 ml/min per 100 g of tissue after 8 min and 47 ml/min per 100 g of tissue after 40 min. Heatings at 1-day intervals showed both peaks in perfusion to persist during subsequent treatments with higher blood flows during later heatings. Results of the 3-day fractionated heating demonstrated lower blood flows during the second and third heatings than those at 1-day intervals. The third treatment of the 3-day fractionations showed a disappearance of the first peak and only a small increase in perfusion at the second peak (50 ml/min per 100 g of tissue). Perfusion studies at 5-day intervals demonstrated two peaks at approximately 15 and 40 min. Compared with the first treatment at 5-day intervals, the second and third treatments demonstrated decreased and increased peak perfusion values, respectively. This study suggests that the kinetics of blood flow changes during hyperthermia may be the result of several different mechanisms. There appear to be three different peaks which can be quantified during heating. These peaks may change during subsequent heating independently from one another. Further work must be performed to examine the physiological mechanisms responsible for each peak.