C-33 Free Communication/Poster - Acute Exercise - Cardiorespiratory Physiology Thursday, May 31, 2018, 7:30 AM - 12:30 PM Room: CC-Hall B
Dehydration reduces plasma volume and concentrates electrolytes, increasing plasma osmolality (pOsm). Water deprivation (WD) studies in animals demonstrate that elevated pOsm is associated with altered sympathetic outflow and blood pressure (BP) regulation. However, it remains unclear if WD augments BP responses to sympathoexcitatory stimuli in humans.
PURPOSE: We tested the hypothesis that WD elevates pOsm and consequently augments BP reactivity.
METHODS: Twenty healthy young adults were recruited (10M/10W; age: 24±1 yrs; BMI: 24±1 kg/m2; BP: 109±2/61±2 mmHg) to complete two hydration conditions, in random order. A normal hydration (NH) and WD visit were separated by at least one week. Daily water intake for the NH condition was 23mL H2O/kg bodyweight/day for 3 days prior to testing. The WD condition included a stepwise reduction in water intake over 3 days then a 16hr water restriction prior to testing. Beat-by-beat BP was measured continuously with finger photoplethysmography throughout a 10-min baseline, handgrip exercise (HG), post-exercise ischemia (PEI), and a cold pressor test (CPT). Isometric HG was performed at 30% of maximal voluntary contraction for 2 mins and PEI immediately followed with rapid upper arm cuff inflation to 250mmHg for 3 mins (to isolate the metaboreflex). Following HG & PEI, participants rested quietly for 10 mins prior to a 2-min hand-in-ice H2O CPT. Peak responses were calculated as the absolute change in BP during the final minute of each perturbation from the respective baseline.
RESULTS: Plasma volume, estimated by changes in hemoglobin and hematocrit, declined 5.6±1.4% during WD. POsm (287.0±1.0 vs. 290.0 ±1.0 mOsm/kg H2O), urine osmolality (481±137 vs. 708±42 mOsm/kg H2O), urine specific gravity (1.015±0.002 vs. 1.022±0.001), and thirst rating on a 0-10 scale (1.7±0.4 vs. 6.7±0.4) were higher for the WD condition (p<0.05 for all), suggesting mild dehydration. Mean BP responses were augmented following WD during HG (Δ12.8±1.7 vs. 18.7±2.0 mmHg, p<0.05), PEI (Δ8.8±1.0 vs. 14.7±2.4 mmHg, p<0.05), and CPT (Δ14.9±2.0 vs. 18.6±2.3 mmHg, p=0.05).
CONCLUSION: These preliminary findings suggest that short-term WD increases pOsm and augments BP responses during moderate intensity isometric HG exercise, PEI, and CPT, suggesting enhanced BP reactivity.