Physiological monitoring in the absence of gravity

Space flight provides the opportunity to study human physiology free of the influence of Earth´s gravitational field. The human body has evolved in one-gravity and operates in a steady state; blood pressure, fluid content, and other physiological conditions are stabilized at certain set points. In space, however, the body adapts to a new — microgravity — environment it establishes a new balance, or steady state, in a few days. Fluids redistribute to the upper body; muscle tone and cardiac conditioning decrease; bone mineral and muscle mass are lost; and the neurologic system exhibits changes. None of these changes have proved serious; all appear reversible after re-exposure to one gravity.