Body temperature and metabolism in hyperbaric helium atmospheres.

Abstract

Five male deep-sea divers were observed during pressure chamber dives and decompression over a pressure range of 4.3-14.6 atmospheres absolute (Ata). Observation periods were begun 12 or more hours after reaching maximum depth and continued during decompression. The chamber atmosphere was He with small amounts of O2 and N2, and was quiescent and warm. Metabolic rate (seated, resting) increased only slightly above control, as large increases in connective heat transfer were accompanied by reductions in body heat transfer by radiation and evaporation. Mean skin temperature was reduced from its control value, and the high con-vective conductance (hc) of hyperbaric He narrowed the temperature gradient from skin to atmosphere to 1.6 C at 14.6 Ata. Rectal temperature was not reduced and shivering did not occur. Arterial blood pressure, respiratory rate and expired minute volume showed no systematic change under pressure, but relative bradycardia was noted. No adventitious neuromuscular activity was observed. The divers'' hc values match those generated by a mathematical model for a cylinder undergoing natural convection.