The Effect of a 6-hour Immersion in Thermoneutral Water on Cardiovascular and Respiratory Systems in Man
Stone, Valerie J.
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A study of nine men (18-24 years) was undertaken to determine the effect of weightlessness on the human respiratory and cardiovascular functions of the body. Weightlessness was simulated by a six hour immersion in thermoneutral water (T=34.5 °C) of the whole body up to the neck level. The heart rate (HR), blood pressure (BP), ventilation (VE), and breathing rate (BR) were simultaneously monitored before and after immersion under conditions of lower body negative pressure (LBNP). A new apparatus, an LBNP "Box", was used to induce LBNP. The effects of immersion on oxygen uptake (Vo ) and work load capacity (WLC) were also studied at submaximal and maximal work levels on a magnetically-braked bicycle ergometer using pseudorandom-binary-sequences (PRBS). The results were then analyzed statistically to determine the significance of the differences observed. The HR was found to be higher in post-immersion than in pre-immersion, and to increase in both pre- and post-immersion as the LBNP became more negative. The systolic blood pressure showed a tendency to being less post-immersion, while the diastolic pressure did not significantly change post-immersion. The systolic blood pressure decreased with an increase in LBNP, while the diastolic blood pressure increased. This resulted in a decrease in pulse pressure (blood pressure amplitude) with increasing LBNP. The pulse pressure was not significantly different post-immersion as compared with pre-immersion. The breathing rate did not show significant differences before and after immersion and did not vary as the LBNP was made more negative. The minute ventilation showed a tendency to increase with increasing LBNP and tended to be lower after immersion. The work load capacity and the maximum oxygen consumption were lower after immersion. The respiratory and circulatory functions appeared to be affected by simulated weightlessness, but a study with sUbjects of more constant mass and fitness, as well as using a greater sample size, needs to be done to make a more reliable assessment of the effects of weightlessness.