Body fluid compartments in humans during acute high-altitude exposure.

Body fluid compartments were studied in a group of sea level residents at sea level and during 12 d of acute exposure to an altitude to 3,500 m. Measurements of total body water and extracellular water were done on the third and 12th days of exposure, while plasma volume was measured on 12th day only. The intracellular water, blood volume, and red cell mass were computed from the above parameters. Total body water and extracellular water decreased progressively, the decrease being 4.7% (p less than 0.001) and 6.0% (p less than 0.05) respectively on the 12th day. Plasma volume and blood volume decreased significantly with a slight increase in red cell mass. Intracellular water, computed from total body water and extracellular water, decreased by 4.3% on 12th day. This study suggested hypohydration on acute altitude exposures.