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ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

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

¹The Copenhagen Muscle Research Centre, 2100 Copenhagen Ø, Denmark; and ²Department of Physical Education, University of Las Palmas de Gran Canaria, Grand Canary, Spain

Submitted 22 December 2003 ; accepted in final form 25 May 2004

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 O₂ 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 O₂ after 8W: 59 ± 4, 58 ± 4, and 52 ± 4 l·min·l O₂^–1, respectively. The ventilatory equivalent of O₂ reached levels not different from that of Aymaras (51 ± 3 l·min·l O₂^–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.

chronic hypoxia; acute normoxia; ventilation

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