When Edmund Hillary and Tenzing Norgay reached the summit of Mt. Everest in 1953, it was the culmination of many attempts beginning in 1921. Alexander Kellas had actually predicted as early as 1920 that the mountain could be climbed, but the extreme altitude of 8848 m with the consequent oxygen deprivation had foiled previous attempts. One reason for the success of the 1953 expedition was the work done by the British physiologist Griffith Pugh in 1952 when he studied many of the physiological factors at high altitude including the oxygen requirements. Seven years later, Pugh and Hillary teamed up again for the Silver Hut Expedition in 1960-1961 that elucidated many of the problems of very high altitude. A group of physiologists spent several months at an altitude of 5800 m in a prefabricated hut and studied many aspects of exercise, pulmonary gas exchange, control of ventilation, and blood changes. Maximal exercise was measured as high as 7440 m and raised anew the question of whether Everest could ever be climbed without supplementary oxygen. The answer was shown to be yes in 1978 by Messner and Habeler, and 3 years later the American Medical Research Expedition to Everest clarified the physiological adaptations that allow humans to reach the highest point on earth. Five people reached the summit, the barometric pressure there was measured for the first time, and alveolar gas samples from the summit showed the critical importance of the extreme hyperventilation. However, the maximal oxygen consumption for the summit inspired PO2 of 43 mmHg was shown to be only about 1 l min(-1). In other words, the highest point on earth is very close to the limit of human tolerance to oxygen deprivation. As we celebrate the anniversary of Charles Darwin, it would be nice to have an evolutionary explanation for this, but in fact it is a cosmic coincidence.
Keywords: Ascent of Everest; Extreme altitude; Maximum oxygen uptake; Respiratory alkalosis; Severe hypoxia.