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.