Operation Everest III: role of plasma volume expansion on Vo(2max) during prolonged high-altitude exposure

We hypothesize that plasma volume decrease (Delta PV) induced by high-altit ude (HA) exposure and intense exercise is involved in the limitation of max imal O-2 uptake ((V)over dot O-2max) at HA. Eight male subjects were decomp ressed for 31 days in a hypobaric chamber to the barometric equivalent of M t. Everest (8,848 m). Maximal exercise was performed with and without plasm a volume expansion (PVX, 219-292 mi) during exercise, at rea level (SL), at HA (370 mmHg, equivalent to 6,000 m after 10-12 days) and after return to SL (RSL, 1-3 days). Plasma volume (PTS) was determined at rest at SL, HA, a nd RSL by Evans blue dilution. PV was decreased by 26% (P < 0.01) at HA and was 10% higher at RSL than at SL. Exercise-induced Delta PV was reduced bo th by PVX and HA (P < 0.05). Compar ed with SL, (V)over dot O-2max was decr eased by 58 and 11% at HA and RSL, respectively. (V)over dot (2max) was enh anced by PVX at HA (+9%, P < 0.05) but not at SL or RSL. The more PV was de creased at HA, the more (V) over dot O-2 was improved by PVX (P < 0.05). At exhaustion, plasma renin and aldosterone were riot modified at HA compared with SL but were higher at RSL, whereas plasma atrial natriuretic factor w as lower at HA. The present results suggest that PV contributes to the limi tation of (V) over dot O-2 during acclimatization to HA. RSL-induced PVX, w hich may be due to increased activity of the renin-aldosterone system, coul d also influence the recovery of (V) over dot O-2.