Abstract
Laser Doppler flowmetry has been applied to normal skin and to subepidermal tumours during localized ultrasound hyperthermia in the rat. In normal skin, 40°C hyperthermia only induced a marginal increase in the red blood cell flux. Significant increases occurred after 20 min at 42°C and after 4 min at 44°C. During 44°C hyperthermia maximum fluxes were reached after 24 min. Thereafter, the flow declined and finally approached preheating values. In contrast, in subepidermal tumours 40°C hyperthermia on the average induced a slight decrease of the flux. During 42°C hyperthermia a significant flow decrease was found after 40 min of heating. Following a transient increase in the laser Doppler flow during the heating-up period, 44°C hyperthermia led to a significant impairment of the flux after 24 min. A total shutdown of RBC flux was observed in about 30 per cent of the tumours at 44°C. Upon elevated tissue temperatures, pronounced inter-tumour variabilities in the time- and temperature-dependent changes of RBC flux were observed. Rhythmic oscillations of the RBC flux were found in some subepidermal tumours (0.40 ± 0.05 cycles/min). Upon heating, these periodic flow variations slowed down significantly (0.20 ± 0.04 cycles/min), whereas in normal skin the frequency of the flow fluctuations increased.