Hyper-hydration with a Carbohydrate-Electrolyte Solution Does Not Improve Orthostatic Tolerance in Healthy Young Individuals

A potential risk factor for astronauts is post-spaceflight orthostatic intolerance, which may be due to losses of plasma volume during spaceflight. One way to offset and minimize plasma volume loss is through a proper hydration strategy. The effects of hyper-hydration with Gatorade on orthostatic intolerance are unknown. Twenty-two individuals (12 men, 10 women) underwent a tilt table test [70⁰ head up tilt (HUT)] during two conditions: euhydrated and hyper-hydrated. Heart rate (HR) and blood pressure (systolic, SBP; diastolic, DBP) were measured at baseline (BL), HUT, and recovery (REC). SBP did not change with HUT and was similar between groups.  DBP was higher during HUT compared to BL (men: 63±7 to 80±10 mmHg, women: 72±7 to 80±7 mmHg, P=0.039) and overall higher in women (69±10 vs. 74±10 mmHg, for men vs. women, respectively, P=0.003). HR was higher during HUT and higher in women (men: 61±8 to 88±15, women: 71±11 to 104±16, for BL to HUT, respectively, P<0.001). Men had longer tilt times (33±15 vs. 18±12 min, euhydrated for men vs. women, respectively, P<0.001). Tilt times were similar between the two hydration conditions (men: 33±15 and 31±18, women: 19±12 and 16±7 min, for euhydration and hyper-hydration, respectively, P=0.442). In summary, men were more orthostatically tolerant than women. Gatorade did not improve orthostatic intolerance.

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