Heat Transfer in Man

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Abstract
Physical models of the body, incorporating heat and temp. generators, thermal conductances and capacities, were developed for the qualitative and semi-quantitative analysis of heat transfer in man. From the final model, one would expect symmetry in the thermal responses of deep and of superficial tissues to the imposition of heat loads from within, by exercise, and from without, by exposure to high ambient temps.; a definite "time constant" or time of adjustment of deep tissues to the imposition of any new heat load; and evidence of active control in heat exchange, i.e., the internal conductance of heat in the body and the evaporative conductance of heat from the body surface. Exptl. data were obtained which bear on these points by measuring the temp. of rectum, mean temp. of skin, and wt. of sweat excreted when heat loads were imposed successively from within and from without. The initial and primary response to heat in the 1st day of exposure is a marked increase in the internal conductance of heat which may be so great as to produce circulatory insufficiency. Reciprocal adjustments of heat transfer from the body surface by evaporation and of the internal conductance of heat within the body occur in acclimatization, whereby the former increases and thereby allows the internal conductance to decrease and consequently relieves circulatory strain. Both the increased sensitivity of the sweat mechanism on successive exposures to heat and the exhaustion phenomenon of sweating which occurs with time in a single exposure at high temps. have a close parallel with the characteristics of "training" and of "exhaustion" observed in psycho-motor activities.