ADJUSTMENTS IN OXYGEN-TRANSPORT DURING HEAD-OUT IMMERSION IN WATER AT DIFFERENT TEMPERATURES

Respiratory gas exchange was investigated in human subjects immersed up to the shoulders in water at different temperatures (Tw = 25, 34, and 40°C). Cardiac output (Q̇C) and pulmonary tissue volume (Vti) were measured by a rebreathing technique with the inert gas Freon 22, and O2 consumption (V̇O2) was determined by the closed-circuit technique. Arterial blood gases (Pa(O2), Pa(CO2)) were analyzed by a micromethod, and alveolar gas (PA (O2)) was analyzed during quiet breathing with a mass spectrometer. The findings were as follows. 1) Immersion in a cold bath had no significant effect on Q̇(c) compared with the value measured at Tw = 34°C, whereas immersion in a hot bath led to a considerable increase in Q̇C. Vti was not affected by immersion at any of the temperatures tested. 2) A large rise in metabolic rate V̇O2 was only observed at Tw = 25°C (P < 0.001). 3) Arterial blood gases were not significantly affected by immersion, whatever the water temperature. 4) O2 transport during immersion is affected by two main factors: hydrostatic pressure and temperature. Above neutral temperature, O2 transport is improved because of the marked increase in Q̇(c) resulting from the combined actions of hydrostatic counter pressure and body heating. Below neutral temperature, O2 transport is altered; an increase in O2 extraction of the tissue is even calculated.