Breathing 100% oxygen during water immersion improves postimmersion cardiovascular responses to orthostatic stress

Abstract

Physiological compensation to postural stress is weakened after long‐duration water immersion (WI), thus predisposing individuals to orthostatic intolerance. This study was conducted to compare hemodynamic responses to postural stress following exposure to WI alone (Air WI), hyperbaric oxygen alone in a hyperbaric chamber (O2 HC), and WI combined with hyperbaric oxygen (O2 WI), all at a depth of 1.35 ATA, and to determine whether hyperbaric oxygen is protective of orthostatic tolerance. Thirty‐two healthy men underwent up to 15 min of 70° head‐up tilt (HUT) testing before and after a single 6‐h resting exposure to Air WI (N = 10), O2 HC (N = 12), or O2 WI (N = 10). Heart rate (HR), blood pressure (BP), cardiac output (Q), stroke volume (SV), forearm blood flow (FBF), and systemic and forearm vascular resistance (SVR and FVR) were measured. Although all subjects completed HUT before Air WI, three subjects reached presyncope after Air WI exposure at 10.4, 9.4, and 6.9 min. HUT time did not change after O2 WI or O2 HC exposures. Compared to preexposure responses, HR increased (+10 and +17%) and systolic BP (−13 and −8%), and SV (−16 and −23%) decreased during HUT after Air WI and O2 WI, respectively. In contrast, HR and SV did not change, and systolic (+5%) and diastolic BP (+10%) increased after O2 HC. Q decreased (−13 and −7%) and SVR increased (+12 and +20%) after O2 WI and O2 HC, respectively, whereas SVR decreased (−9%) after Air WI. Opposite patterns were evident following Air WI and O2 HC for FBF (−26 and +52%) and FVR (+28 and −30%). Therefore, breathing hyperbaric oxygen during WI may enhance post‐WI cardiovascular compensatory responses to orthostatic stress.

Endurance Exercise Performance Is Reduced after 6-h Dives at 1.35 ATA When Breathing 100% Oxygen Compared with Air

“…Previous work from our laboratory demonstrated that a 6-h water immersion while breathing air increased sympathetic nervous system activity, specifically leading to peripheral vascular resistance and a decrease in peripheral blood flow (i.e., forearm and calf muscles) (9). Interestingly, breathing 100% O 2 during the same conditions attenuated the decrease in peripheral blood flow compared with breathing air (32). It is possible that oxygen consumption during exercise after repeated long-duration diving with air was decreased as a result of decreased peripheral blood flow to the working muscles and, more generally, autonomic alterations after water immersions breathing air.…”

Pulmonary effects of repeated six-hour normoxic and hyperoxic dives

“…It seems reasonable to assume that a small translocated volume can generate local interstitial edema sufficient to irritate nerves without affecting overall pulmonary function parameters. However, the hypovolemia that follows from immersion [ 15 , 16 , 17 ] may have moderated the increased filtration pressures in the lungs in the wet divers despite the sustained increase in central venous pressure [ 18 ]. Hypovolemia was likely cumulative across the dive week [ 15 ], and perhaps more severe than that during the previous series of six-hour wet resting oxygen dives [ 2 ] when divers were less restricted.…”

Changes in Posture Following a Single Session of Long-Duration Water Immersion

“…The present study was conducted as part of a larger research project examining the neurophysiological response to repeated diving under a variety of conditions. 7,26 Participants completed a 6-hour dive once daily for 5 days with outcome measures collected before and after each dive. The analyses presented in this manuscript were limited to data collected during the first day (ie, immediately before and after the first dive exposure) so as to avoid effects related to training, learning, or chronic adaptation.…”