Pulmonary gas exchange at maximal exercise in Danish lowlanders during 8 wk of acclimatization to 4,100 m and in high-altitude Aymara natives

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Abstract
We aimed to test effects of altitude acclimatization on pulmonary gas exchange at maximal exercise. Six lowlanders were studied at sea level, in acute hypoxia (AH), and after 2 and 8 wk of acclimatization to 4,100 m (2W and 8W) and compared with Aymara high-altitude natives residing at this altitude. As expected, alveolar Po2was reduced during AH but increased gradually during acclimatization (61 ± 0.7, 69 ± 0.9, and 72 ± 1.4 mmHg in AH, 2W, and 8W, respectively), reaching values significantly higher than in Aymaras (67 ± 0.6 mmHg). Arterial Po2(PaO2) also decreased during exercise in AH but increased significantly with acclimatization (51 ± 1.1, 58 ± 1.7, and 62 ± 1.6 mmHg in AH, 2W, and 8W, respectively). PaO2in lowlanders reached levels that were not different from those in high-altitude natives (66 ± 1.2 mmHg). Arterial O2saturation (SaO2) decreased during maximum exercise compared with rest in AH and after 2W and 8W: 73.3 ± 1.4, 76.9 ± 1.7, and 79.3 ± 1.6%, respectively. After 8W, SaO2in lowlanders was not significantly different from that in Aymaras (82.7 ± 1%). An improved pulmonary gas exchange with acclimatization was evidenced by a decreased ventilatory equivalent of O2after 8W: 59 ± 4, 58 ± 4, and 52 ± 4 l·min·l O2−1, respectively. The ventilatory equivalent of O2reached levels not different from that of Aymaras (51 ± 3 l·min·l O2−1). However, increases in exercise alveolar Po2and PaO2with acclimatization had no net effect on alveolar-arterial Po2difference in lowlanders (10 ± 1.3, 11 ± 1.5, and 10 ± 2.1 mmHg in AH, 2W, and 8W, respectively), which remained significantly higher than in Aymaras (1 ± 1.4 mmHg). In conclusion, lowlanders substantially improve pulmonary gas exchange with acclimatization, but even acclimatization for 8 wk is insufficient to achieve levels reached by high-altitude natives.