Heat-induced vasoconstriction in the fingers: a mechanism for reducing heat gain through the hand heated locally

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Abstract
This study examined the effect of local heating on the blood flow of the finger or forearm in male subjects in an environment of 35°C-40% (r.h.). One hand or forearm was immcrsed in a water bath the temperature of which (T w) was raised by 1°C every 10th min from 35° to 43°C, while the other hand or forearm was kept at a constantT w of 35°C. Blood-flow (BF) was measured by venous occlusion plethysmography, using temperature-compensated mercuryin-Silastic strain gauges. Finger BF in the heated hand was significantly lower than that in the control hand atT ws of 37°–41°C, mostly for the first few minutes of each heating period. Thereafter, finger BF in the heated hand gradually returned toward the previous values. AtT ws of 39°–40°C, liowever, finger BF in the heated hand remained lower than the control values for the entire period of heating. AtT ws of 42°–43°C, finger BF in the heated hand greatly increased after an initial transitory fall. In the forearm skin, however, no such vasoconstriction in response to local heating was observed. All this suggests that a rise in skin temperature to above the core temperature produces paradoxical vasoconstriction in the finger, which may be a mechanism to reduce heat gain through the hand heated locally at higher temperatures.

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