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Articles in PresS, published online ahead of print November 16, 2001
J Appl Physiol, 10.1152/jap.00093.2001
Submitted on January 30, 2001
Accepted on November 9, 2001
1 Division of Physiology, Department of Medicine, University of California, San Diego, La Jolla, CA, USA
2 Instituto Boliviano de Biologia de Altura, La Paz, Bolivia
3 Copenhagen Muscle Research Centre, Copenhagen, Denmark
* To whom correspondence should be addressed. E-mail: pdwagner{at}ucsd.edu, lrussell@ucsd.edu.
Pulmonary gas exchange and acid-base state were compared in 9 Danish lowlanders (L) acclimatized to 5260 m for 9 weeks and 7 native Bolivian residents (N) of La Paz (altitude 3600-4100 m) brought acutely to this altitude. We evaluated normalcy of arterial pH, and assessed pulmonary gas exchange and acid/base balance at rest and during peak exercise breathing room air and 55% O2. Despite 9 weeks at 5260 m and considerable renal bicarbonate excretion (arterial plasma [HCO3-]=15.1 meq/l), resting arterial pH in L was 7.48 ± 0.007 (significantly greater than 7.40). On the other hand, arterial pH in N was only 7.43±0.004 (despite arterial O2 saturation of 77%) after ascending from 3600-4000 m to 5260 m in two hours. Maximal power output was similar in the two groups breathing air, while on 55% O2, only L showed a significant increase. During exercise in air, arterial P was 8 Torr lower in L than N (p<0.001) yet P was the same such that at VO2MAX, AaPO2 was lower in N (5.3±1.3 Torr) than L (10.5±0.8 Torr), p=0.004. Calculated O2 diffusing capacity was 40% higher in N than L, and if referenced to maximal hyperoxic work capacity was 73% greater in N. Buffering of lactic acid was greater in N, with 20% less increase in base deficit per mmole/L rise in lactate. These data show in lowlanders persistent alkalosis even after 9 weeks at 5260 m and in natives: (1) insignificant reduction in exercise capacity breathing air at 5260 m compared to breathing 55% O2; (2) very little ventilatory response to acute hypoxemia (judged by arterial pH and arterial P responses to hyperoxia); (3) during exercise, greater pulmonary diffusing capacity than in L allowing maintenance of arterial P despite lower ventilation; and (4) better buffering of lactic acid. These results support and extend similar observations concerning adaptation in lung function in these and other high altitude native groups previously performed at much lower altitudes.
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