Laser Doppler flowmetry in subepidermal tumours and in normal skin of rats during localized ultrasound hyperthermia

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.degree.C hyperthermia only induced a marginal increase in the red blood cell flux. Signiificant increases occurred after 20 min at 42.degree.C and after 4 min at 44.degree.C. During 44.degree.C hyperthermia maximum fluxes were reached after 24 min. Thereafter, the flow declined and finally approached preheating values. In contrast, in subepidermal tumours 40.degree.C hyperthermia on the average induced a slight decrease of the flux. During 42.degree.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.degree.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.degree.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.