Vertical and horizontal posture during suited immersion: similarity and differences according to some body functions

The role of axial body orientation was weighed during acute adaptation to suit immersion (SI) in 3 hr vertical (SIv, n=4) exposure series, and 3 d experiments in which six volunteers participated in both SIv and SIh. Various types of SI recruited different hormonal mechanisms to induce similar reactions of the water-electrolyte metabolism (WEM). Changes in the body position relative to the gravity vector modified equally strength and dynamics of the WEM regulation. The experimental data suggest that osmo- and volume-regulation reactions to SIv shown the response to the actual volumetric stimulus against the "distributed" weight-bearing reaction. They are less vigorous as compared to SIh and do not reach maximum within 3 hrs. Physiological reactions to SIh were marked by greater effects of ADH on the kidney when compared with dry immersion, and an additional stimulation of aldosterone secretion by the sympathetic nervous system and/or ACTH. SIh caused rapid and more heavy symptoms of motion sickness that correlated with body mass reduction, negative water balance, degradation of tolerance of classic physical tests executed after SI. Three-days SIv, as opposed to SIh, resulted in more profound hypervolemia in the upper body of the test-subjects.