[Effect of short-term head-down tilt hypokinesia on the dynamics of the cardiorespiratory indices during graduated physical loading].

Seven healthy volunteers were exposed to head-down tilt at -15 degrees for 5 h. Before and after exposure they exercised on a bicycle ergometer in the supine and seated positions. During the study their respiration function, gas exchange, and arterialized blood parameters were measured. It was found that after exposure the physical aerobic performance diminished. The changes detected suggest that a lower exercise tolerance can be caused not only by a decreased circulating blood volume but also by increased energy expenditures of the cardiorespiratory system itself.