Partitional calorimetric studies of man during exposures to thermal transients

Abstract

Three young men dressed in shorts were exposed for 1-hr, at a neutral temperature of 28 C, then quickly transferred for a 2 hr. exposure at 22 or at 18[degree] C, followed by another hour at 28[degree] C. Similar transfers were made between 18 and 22[degree] C, and 43[degree] C. The effect of a 4-hr, exposure at 18 and at 13[degree] C was also studied. Tympanic membrane temperature, rectal and average skin temperature, metabolic rate, and evaporative heat loss were measured. Heat balances were made for each 5-min. period by partitional calorimetry. During exposures to air temperatures 43[degree] C (sweat freely evaporated) the total increase in body heat content was limited to less than 30 kcal/m2. In the cold (13-18[degree] C) net heat loss continued at the rate of 20-40 kcal/m2 per hr. even at the end of a 2-hr, exposure when the body heat content had already decreased by 100 kcal/m2. Shivering was not observed at 18[degree] C after 2 hr. Sweating occurred if the average skin temperature was above 33.5[degree] C and the tympanic membrane temperature was above 36.6[degree] C at the same time. Evaporative heat loss during the thermal transients and the steady state could be accounted for by the product, [70 (Tskin 33.5) X (Tear - 36.6)] kcal/m2 per hr. if both terms are positive.