[Water metabolism changes during prolonged hypokinesia with an antiorthostatic posture of the body].

Variations in the total content of body fluid and intravascular fluid were measured during a 49-day bed rest experiment and a 25-day recovery period. During the experiment the test subjects were kept in the head-down position at an angle of -4 degrees. The diminished motor activity led to a decrease of the absolute and, to a greater extent, of the relative content of water in the body which was associated with intravascular losses. The major changes in fluid balance occurred during the first two weeks of the bed rest experiment; this may be attributed to the head-down position of the test subjects.