The impact of repetitive long-duration water immersion on vascular function.

While physiological responses to water immersion (WI) are well-studied, the vascular responses after WI are less understood. Fifteen male subjects performed six-hour resting thermoneutral water immersions (WI) at 1.35 atmospheres absolute for four consecutive days, with follow-up on the fifth day.

Cardiovascular and autonomic responses to physiological stressors before and after six hours of water immersion.

The physiological responses to water immersion (WI) are known; however, the responses to stress following WI are poorly characterized. Ten healthy men were exposed to three physiological stressors before and after a 6-h resting WI (32-33°C): 1) a 2-min cold pressor test, 2) a static handgrip test to fatigue at 40% of maximum strength followed by postexercise muscle ischemia in the exercising forearm, and 3) a 15-min 70° head-up-tilt (HUT) test. Heart rate (HR), systolic and diastolic blood pressure (SBP and DBP), cardiac output (Q), limb blood flow (BF), stroke volume (SV), systemic and calf or forearm vascular resistance (SVR and CVR or FVR), baroreflex sensitivity (BRS), and HR variability (HRV) frequency-domain variables [low-frequency (LF), high-frequency (HF), and normalized (n)] were measured.