Between 1960 and 2003, 13 Chinese expeditions successfully reached the summit of Chomolungma (Mt Everest or Sagarmatha). Forty-five of the 80 summiteers were Tibetan highlanders. During these and other high-altitude expeditions in Tibet, a series of medical and physiological investigations were carried out on the Tibetan mountaineers. The results suggest that these individuals are better adapted to high altitude and that, at altitude, they have a greater physical capacity than Han (ethnic Chinese) lowland newcomers. They have higher maximal oxygen uptake, greater ventilation, more brisk hypoxic ventilatory responses, larger lung volumes, greater diffusing capacities, and a better quality of sleep. Tibetans also have a lower incidence of acute mountain sickness and less body weight loss. These differences appear to represent genetic adaptations and are obviously significant for humans at extreme altitude. This paper reviews what is known about the physiologic responses of Tibetans at extreme altitudes.

High altitude deterioration means a gradual diminution in man’s capacity to do work at great heights. This is associated with insomnia, lack of appetite, loss of weight and increasing lethargy. These symptoms appear after a prolonged stay above 18000 ft. and there is great individual variation. Man would deteriorate after a time at these heights even under the best con­ditions: if he is doing hard work and is subjected to many strains, mental and physical, other factors are brought to bear which will aggravate this basic state. Such factors are illness, exhaustion, starvation and dehydration. Symptoms similar to those of deterioration, but more acute in onset, appear if man goes too quickly to high altitudes without first acclimatizing. These symptoms of acute mountain sickness disappear if the subject returns to lower levels for some time. If he goes to moderate heights when acclimatizing he will be able to stay for reasonably long periods without undue trouble. Exhaustion at high altitudes is often only cured by coming down to lower levels, as above a certain height there seems to be little or no recovery.

The Tibetans probably originated in south-east Tibet, and are currently comprised largely of agriculturalists and nomads. In the 18th Century, about 20% were monks. Persons live at altitudes from 3600 m to 5400 m. This may be a factor in the incidence of chronic mountain sickness. Cold is combated by cultural methods, although some lamas are able to ‘warm without fire.’ Acute mountain sickness is well recognised. A low birth weight is common and menarche is delayed; age span does not appear to be increased. Goitre, measles, venereal diseases, chest infections and leprosy are common. Congenital cardiac abnormalities and pulmonary hypertension are often associated with systemic hypertension.

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Summary. Tests for inherited blood factors were done on samples from Lunana and Thimbu, Bhutan. Two persons in 31 from Lunana carried Haemoglobin E and five in 28 were Di (a+). Both populations appear to be related to the Tibetans, with some genes from South‐East Asia and, at Lunana, from India also.