Operation Everest III: COMEX '97.

Eight male volunteers, aged 23 to 37, were selected to participate in a simulated ascent to 8848 m in a hypobaric chamber. They were first preacclimatized in the Observatoire Vallot (4350 m) before entering the chamber. The chamber was progressively decompressed down to 253 mmHg barometric pressure, with a recovery period of 3 days at 5000 m from days 20 to 22. They spent a total of 31 days in the chamber. Seventeen protocols were organized by 14 European teams to explore the limiting factors of physical and psychological performance and the physiological and pathological changes in various systems (cardiac function, control of ventilation, autoregulation of cerebral blood flow, energy balance and body composition, muscle performance, erythropoiesis, and cognitive functions). All subjects reached 8000 m, and 7 of them reached the simulated altitude of 8848 m. Three subjects complained of transient neurological symptoms, which resolved rapidly with reoxygenation. At 8848 m (n = 5), Pa(O(2)) was 30.6 +/- 1.4 mmHg, Pc(O(2)) was 11.9 +/- 1.4 mmHg, and pH was 7.58 +/- 0.02 (arterialized capillary blood). V(O(2))max decreased by 59% at 7000 m and increased by 9% at 6000 m after plasma expansion, suggesting a role of altitude-induced plasma contraction in the reduction in V(O(2))max. Cardiac contractility was normal, but relaxation was slightly impaired. Autoregulation of cerebral blood flow was impaired at 8000 m. Negative energy balance was essentially caused by a decrease in appetite. Increased membrane lipid peroxidation could explain alterations in muscle or cognitive function. The subjects reached the "summit" in better physiological conditions than would have been possible in the mountains, probably because acclimatization and other environmental factors such as cold and nutrition were controlled.