The control of breathing at high altitude

The changes in the control of breathing in man at high altitude have been studied at 5,800 m (19,000 ft). The differences between 1owlanders and Sherpas were compared at 4,880 m (16,000 ft.). Ventilatory response to C0$_2$, hypoxia and exercise were studied, and acid-base status of the blood and CSF measured. Acclimatization to altitude is characterized by a shift of the C0$_2$ response curve to the left and an increase in its slope. The hypoxic sensitivity appears unchanged. On moderate exercise there results a progressive increase in ventilatory equivalent with increasing altitude. At maximum work rate ventilation increases more rapidly due to falling Sao$_2$. Sherpas show no significant difference in response to C0$_2$ but a remarkable lack of response to hypoxia. The C0$_2$ response showed little change in slope with change of P0 $_2$ and on exercise acutely changing PO$_2$had little effect on ventilation. Sherpas ventilate less on exercise and have higher maximum 0$_2$ intakes per kg than lowlanders. The arterial pH of highlanders is normal whereas in lowlanders it remains slightly elevated after k-6 weeks at altitude. CSF pH of highlanders is about 0.04 units more acid than lowlanders at the same altitude, indicating a greater central contribution to respiratory drive and a reduced peripheral component. The role of anaerobic cerebral metabolism in respiratory acclimatization is discussed