[Investigations of human body liquids in long-duration space flight]

The hydration status of a Russian member on a six-month ISS mission was evaluated by bio-impedancemetry during monthly sessions of experiment Sprut (Octopus). Body liquids tended to diminish gradually and measured minimum values on the landing day. By the end of mission the total volume of liquids reduced by 18.9 %; the intracellular and extracellular portions lost 19.0 and 20.4 %, respectively. Time history of specific body liquids was identical in flight. Reductions in the body mass and lean mass (according to impedancemetry) reached 6.9 % and 8.0 %, respectively. These results point to a decrease in the human body hydration status during long-duration space flight concurrent to losses in the muscle mass. In two weeks after landing there was an implicit trend toward regaining the pre-flight hydration status and body mass; yet, both parameters were still below pre-flight values.