Abstract

Operation Everest II was designed to examine the physiological responses to gradual decompression simulating an ascent of Mt Everest (8,848 m) to an inspired PO2 of 43 mmHg. The principal studies conducted were cardiovascular, respiratory, muscular-skeletal and metabolic responses to exercise. Eight healthy males aged 21-31 years began the ascent and six successfully reached the summit, where their resting arterial blood gases were PO2 = 30 mmHg and PCO2 = 11 mmHg, pH = 7.56. Their maximal oxygen uptake decreased from 3.98 +/- 0.2 l/min at sea level to 1.17 +/- 0.08 L/min at PO2 43 mmHg. The principal factors responsible for oxygen transport from the atmosphere to tissue were (1) Alveolar ventilation - a four fold increase. (2) Diffusion from the alveolus to endcapillary blood - unchanged. (3) Cardiac function (assessed by hemodynamics, echocardiography and electrocardiography) - normal - although maximum cardiac output and heart rate were reduced. (4) Oxygen extraction - maximal with PvO2 14.8 +/- 1 mmHg. With increasing altitude maximal blood and muscle lactate progressively declined although at any submaximal intensity blood and muscle lactate was higher at higher altitudes. Verf.-Referat