Blood flow, temperature, and heat loss of skin exposed to local radiative and convective cooling.

The relationship between skin blood flow (SBF) and temperature was evaluated and the heat loss calculated for locally applied thermal stimuli. In 10 subjects the palm was exposed to room climate, pure convective air currents, and pure radiation, which resulted in skin temperatures between 23 and 36 degrees C. Skin blood flow was estimated by laser Doppler flowmetry and local skin temperature was measured by a thermistor probe. Linear regression of SBF on skin temperature revealed significant correlations (r = 0.87, p less than 0.05) within subjects and large variations in estimated slopes (s/m = 34%) between subjects. Therefore, SBF was normalized to the room climate value in each separate experiment. When skin temperature and normalized SBF from all subjects were included in the regression analysis, a nearly linear relationship was confirmed (r = 0.88, p less than 0.0005). Radiative cooling (17 degrees C) doubled the heat loss, reduced skin temperature by 3.7 degrees C, and left SBF virtually unchanged compared with room climate values. When convective cooling (19 degrees C) was applied at 2 air current velocities (0.5 and 1.0 ms-1), palm blood flow diminished to 60 and 53%, respectively, of room climate values. Corresponding heat losses with convective cooling decreased to 68 and 70%, respectively, of room climate values. Linear regression of local heat loss on normalized SBF gave a significant correlation coefficient of 0.79 (p less than 0.001).