Comparison of physiological effects of head-down tilting and immersion on the human body

Among the methods simulating weightlessness, effects on the human body, head-down tilting and water immersion are very useful. The purpose of the present investigation was to carry out a comparative study of water balance and water-protein composition of the blood using the above two methods to simulate the physiological effects typical of an acute stage of weightlessness adaptation. The results of the 7-d head-down tilting and immersion experiments allow the following conclusions: More pronounced changes in water balance and water-protein composition of the blood during immersion seem to indicate that immersion produces a greater effect on the human body; The pattern of changes during immersion and tilting suggests that the adaptation period to immersion takes a longer time; These findings give evidence that immersion, compared with head-down tilting, reproduces more closely effects of acute adaptation to simulated weightlessness.