Body heat balance and urine excretion during a 4-day saturation dive at 4 ATA.

Five male volunteers were exposed for 4 days to a 4-ATA helium-oxygen saturation dive. Partitional calorimetry was performed during 2-h test periods at various ambient temperatures (Ta). Heat production during the period at 4 ATA in helium-oxygen was identical to that at 1 ATA in air. The nonevaporative heat loss (convective and radiant heat losses) was increased with a concomitant decrease in evaporative heat loss. The mean skin and mean body temperatures fell significantly at 4 ATA, and a slight reduction was observed in the rectal temperature. The conductive heat transfer coefficient from the core to skin (hk) was reduced, probably due to vasoconstriction at 4 ATA. Subjective thermal neutrality at rest at 4 ATA was obtained around Ta = 32 degrees C. A diuresis was observed at 4 ATA, but it disappeared with an increase in chamber temperature. An inverse relationship of urine flow to mean skin temperature was observed. An increase in urine flow at 4 ATA might be attributed to cold stress due to lower skin temperature that was caused by the increased nonevaporative heat loss.