Cardiovascular and metabolic responses at rest and to exercise during 48h head-out immersion : a case report

Head-out immersion in water (HIW) leads to several cardiovascular adjustments. Cardiac output (CO) increases by increasing stroke volume with no substantial changes in heart rate (HR) at rest. Therefore, total peripheral resistance (TPR) to blood flow declines, leading to an elevated O2 delivery. During exercise, CO increases for a given workload while HR response differs in relation to exercise intensity: it does not change for moderate exercise but decreases during intense exercise. Oxygen uptake does not change both at rest and during exercise. In this case report, we show data of cardiovascular and metabolic response of a 29 years old man at rest and during constant-load exercise (CLE) during 48 hours of HIW. Subject performed CLE on cycloergometer at 50%VO2max on laboratory (LAB) and during 48h HIW. Pulmonary gas exchange, VO2 kinetics, HR and RPE were determined. HR was similar but V’O2 increased in HIW relative to LAB at rest. During exercise, we recorded a similar metabolic cost of exercise and the same HR in LAB and HIW. V’O2 kinetics were faster in HIW. So, the cardiovascular and metabolic response at rest and during moderate exercise to few hours of HIW is not different from that during 48h.