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

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 PO2 was 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 (Pa-O2) 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). Pa-O2 in lowlanders reached levels that were not different from those in high-altitude natives ( 66 +/- 1.2 mmHg). Arterial O-2 saturation (Sa(O2)) 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, Sa(O2) in 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 O-2 after 8W: 59 +/- 4, 58 +/- 4, and 52 +/- 4 l . min . l O-2(-1), respectively. The ventilatory equivalent of O2 reached levels not different from that of Aymaras ( 51 +/- 3 l . min . l O-2(-1)). However, increases in exercise alveolar PO2 and Pa-O2 with acclimatization had no net effect on alveolar-arterial PO2 difference 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.