Changes in human respiratory sensation induced by acute high altitude hypoxia.

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Respiratory sensation was studied in European low-landers at an altitude of 4382 m after a helicopter flight in order to investigate the acute and prolonged effects of high altitude hypoxia. At rest the ability to detect four inspiratory resistive loads can be used to create a sensitivity index P(A) without taking the response bias (B) into account, based on the Sensory Decision Theory. In 6 subjects respiratory sensitivity increased significantly under acute and prolonged hypoxia after 3-4 days of high altitude exposure. The respiratory sensitivity increased with the hyperventilation and mouth pressure increase induced by hypoxia. Hypoxia might also have feedback effects on the peripheral and central nervous integration of the respiratory sensation stimuli. One subject suffering from acute mountain sickness showed a severe decrease in his sensitivity index P(A) under hypoxic conditions, while the parameters of his cardiorespiratory function evolved in the same classical way as the other subjects who adapted well to altitude hypoxia. The increase in respiratory sensation may be the first necessary step in altitude acclimatization and might serve as a useful marker of this adaptation.