Hypoxia effects on plasma volume shifts at rest, work, and recovery in supine posture

The purpose of this study was to determine the effects acute exposure to hypoxia (less than 1.5 h; gas mixture 12.6% O2-87.4% N2) has on plasma volume (PV) shifts during rest and exercise. Nine unacclimatized males performed identical protocols in the supine posture in both normoxic (N) and hypoxic (H) conditions. The protocol was rest 60 min, submaximal exercise (PWC 140, work rate eliciting a heart rate of 140 beats/min) for 30 min, immediately followed by maximal exercise, and 10 min of passive recovery. There were slight but significant losses of 2.7 and 1.4% PV at rest in H and N conditions, respectively. At the same relative intensity of submaximal exercise (work loads reduced by 22% in H conditions), PV losses were nearly identical (N = 11.2%, H = 11.8%). There was a further PV efflux subsequent to maximal exercise (N = 7.9%, H = 5.2%). The maximum PV efflux, from the beginning of rest to the end of maximal exercise, was 20% for both conditions. Total plasma protein (PP) content was unchanged during rest or exercise for either N or H conditions. After 10 min of recovery, restitution of PV was 10% below preexercise values for both N and H conditions. We conclude that acute hypoxic exposure does not influence the loss of VP or PP during submaximal or maximal exercise.