Differences in the control of breathing between Andean highlanders and lowlanders after 10 days acclimatization at 3850 m

We used Duffin's isoxic hyperoxic ( mmHg) and hypoxic ( mmHg) rebreathing tests to compare the control of breathing in eight (7 male) Andean highlanders and six (4 male) acclimatizing Caucasian lowlanders after 10 days at 3850 m. Compared to lowlanders, highlanders had an increased non-chemoreflex drive to breathe, characterized by higher basal ventilation at both hyperoxia (10.5 +/- 0.7 vs. 4.9 +/- 0.5 l min(1), P = 0.002) and hypoxia (13.8 +/- 1.4 vs. 5.7 +/- 0.9 l min(1), P < 0.001). Highlanders had a single ventilatory sensitivity to CO(2) that was lower than that of the lowlanders (P < 0.001), whose response was characterized by two ventilatory sensitivities (VeS1 and VeS2) separated by a patterning threshold. There was no difference in ventilatory recruitment thresholds (VRTs) between populations (P = 0.209). Hypoxia decreased VRT within both populations (highlanders: 36.4 +/- 1.3 to 31.7 +/- 0.7 mmHg, P < 0.001; lowlanders: 35.3 +/- 1.3 to 28.8 +/- 0.9 mmHg, P < 0.001), but it had no effect on basal ventilation (P = 0.12) or on ventilatory sensitivities in either population (P = 0.684). Within lowlanders, VeS2 was substantially greater than VeS1 at both isoxic tensions (hyperoxic: 9.9 +/- 1.7 vs. 2.8 +/- 0.2, P = 0.005; hypoxic: 13.2 +/- 1.9 vs. 2.8 +/- 0.5, P < 0.001), although hypoxia had no effect on either of the sensitivities (P = 0.192). We conclude that the control of breathing in Andean highlanders is different from that in acclimatizing lowlanders, although there are some similarities. Specifically, acclimatizing lowlanders have relatively lower non-chemoreflex drives to breathe, increased ventilatory sensitivities to CO(2), and an altered pattern of ventilatory response to CO(2) with two ventilatory sensitivities separated by a patterning threshold. Similar to highlanders and unlike lowlanders at sea-level, acclimatizing lowlanders respond to hypobaric hypoxia by decreasing their VRT instead of changing their ventilatory sensitivity to CO(2).