Influence of Hydration on Physiological and Renal Responses to Hypoxia

Fluid balance is known to alter with hypoxia and exercise, yet the combined effects have not been investigated using a controlled acute hypoxic exposure. Seven healthy participants were hypohydrated 24hrs prior to testing, using exercise and fluid restriction, causing a ~2.5% loss in body mass. Participants then rested in either normoxia with no fluid replacement (NH) or hypoxia (FIO2:0.12) with no fluid (HH), water (HW) or isotonic fluid (HI) replacement over the first 2 hrs of exposure. After 200mins of rest, participants completed an intermittent walking protocol at 50%VO2max. TBW, ICF, ECF, serum s100b, HSP70, ADH and urine hydration markers were taken pre and post exposure. HR, SaO2, core temperature and perceptual scales were monitored throughout. Fluid compartment volumes increased with rehydration and remained at similar values in the isotonic rehydration trial. HSP70 values increased in all trials (HH=1.48, HW=1.00, HI=0.95, NH=0.46pg/L), increases were greater in hypoxia. Serum s100b increased in all hypoxic trials (HH=0.28, HW=0.25, HI=0.09, NH=−0.005μg/L). Hypoxia and hypohydration induced similar physiological strain, which was exacerbated when the two were combined. Hypoxic disruption of the blood brain barrier increased with water intake, suggesting isotonic rehydration is necessary to reduce physiological strain and symptoms of headache and nausea.