Peripheral chemoreflexes in the regulation of breathing of high altitude natives

Transient ventilatory response to 3 and 5 breaths of N₂ at rest and during exercise at sea level was determined in three high altitude natives acclimatized for 10 months and in three sea level natives. The striking differences were: 1) in the highlanders ventilation increased only when Pa_O2 fell to 50-60 mm Hg, whereas in the lowlanders any decrease in Pa_O2 from the resting value augmented ventilation; and 2 the increase in ventilation with P(Spao)In2 reduction was much less in the highlanders. The relative increase in ventilation during exercise from euoxic to hypoxic levels was also less in the highlanders than in the lowlanders. Transient relief of hypoxia at 4540 m by 2 breaths of O₂ during rest decreased ventilation by 10 per cent in the highlander and by 37 per cent in the lowlander. Thus ventilatory drive to transient O₂ stimulus in the highlander is low, and it remains low even after prolonged stay at sea level, suggesting irreversible insensitivity of the peripheral arterial chemoreflex mechanism to hypoxia.