Cardiovascular and autonomic responses to stressors following 6 hours of water immersion

The physiological responses to water immersion (WI) are known; however, the responses to stress following WI are not wellcharacterized. Ten healthy men were exposed to three stressors before and after completing a 6hr resting WI: 1) 2min cold pressor test (CP), 2) static handgrip test (HG) to fatigue at 40% of max strength followed by forearm occlusion, and 3) a 15min 70 headup tilt test (HUT). Heart rate (HR), blood pressure (SBP, DBP), cardiac output (Q), limb blood flow (BF), stroke volume (SV), systemic, calf, or forearm vascular resistance (SVR, CVR, FVR), baroreflex sensitivity (BRS), and frequency (low, LF; high, HF; normalized, n) domain measures of heart rate variability (HRV) were measured. CP: PostWI HR, SBP, SV, Q, calf BF, LFnHRV, and LF/HFHRV were lower, and CVR and HFnHRV were higher, than preWI values (p<0.05). HG: Max strength and endurance was not affected by WI. HR, SBP, SV, Q, and calf BF were lower, and SVR and CVR were higher, than preWI values (p<0.05). During occlusion, HFnHRV increased from baseline after WI only, and postWI LFnHRV was lower than preWI values (p<0.05). HUT: PostWI SBP, DBP, SV, forearm BF, and BRS were lower, and HR, FVR, LF/HFHRV, and LFnHRV were higher, than preWI values (p<0.05). The changes suggest differential activation/depression during CP and HG (sympathetic/parasympathetic) and HUT (sympathetic/parasympathetic) following WI.Support: ONR and NAVSEA DSBDP

Cardiovascular and autonomic responses to stressors following 6 hours of water immersion Conference Paper