Peripheral chemoreceptors and human adaptation to high altitude.

Basal hypoxic chemoreflex drive values and respiratory responses to poikilocapnic hypoxic gas mixtures (pO2 = 9.33 kPa) were determined in 142 healthy residents of various Tien-Shan and Pamir altitudes (760 m, 2800 m, 3600 m). The age of the subjects ranged from 13 to 50 years. It was found that at 760 m and 2800 m (Tien-Shan) a chemoreflex mechanism maintains 13 to 18% of the total volume of eupnoic ventilation regardless of the age of the subject studied. No decreases in ventilation were observed at 3600 m following inhalation of two tidal volumes of oxygen, suggesting alterations in the chemoreflex components of respiratory regulation. Respiratory responses to poikilocapnic hypoxia were found to be qualitatively similar at all three altitudes. It is concluded that (1) the arterial chemoreceptor activity threshold is shifted towards lower PACO2 values at 3600 m; (2) this alteration in arterial chemoreceptor activity is related either to changes in their excitability during hypocapnia and/or prolonged hypoxia, or to central inhibition of arterial chemoreceptor activity; (3) respiratory centers are responsible for the blunted ventilatory hypoxic responses.