Effect of partial immersion in water on response of healthy men to headward acceleration

Abstract

Protection against the effects of headward acceleration afforded by immersion in water has been assayed in the human centrifuge on 15 trained subjects. Immersion in water to the xyphoid afforded an average protection of 1.1 ± 0.1 G for vision and ear opacity and of 1.6 ± 0.2 G for ear pulse and heart rate. Deeper immersion, to the level of the third rib at the sternum increased the protection to 1.8 ± 0.1 G for vision and ear opacity and to 2.8 ± 0.2 G for ear pulse and heart rate. The protection afforded the various physiologic variables increased with the magnitude of acceleration tested. Protection against loss of consciousness may be greater than protection against blackout and is probably similar to the protection afforded the ear pulse and heart rate. The cardiovascular reactions produced by headward acceleration are qualitatively similar with and without water immersion. This finding does not support the concept that impediment to venous return is the primary determinant of man's tolerance to headward acceleration. Visual symptoms occurred at greater amplitudes of ear pulse, and presumably also at greater blood pressures at head level, during water immersion than during control runs. vision; arterial pressure; heart rate; venous return; arterial pulse in ear Submitted on May 13, 1963