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3 Copenhagen Muscle Research Centre, Copenhagen, Denmark 2200; 2 Instituto Boliviano de Biologia de Altura, Bolivia; and 1 Division of Physiology, Department of Medicine, University of California, San Diego, La Jolla, California 92093
Pulmonary gas exchange
and acid-base state were compared in nine Danish lowlanders (L)
acclimatized to 5,260 m for 9 wk and seven native Bolivian residents
(N) of La Paz (altitude 3,600-4,100 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
when breathing room air and 55% O2. Despite 9 wk at 5,260 m and considerable renal bicarbonate excretion (arterial plasma
HCO3
concentration = 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 ascent
from 3,600-4,100 to 5,260 m in 2 h. Maximal power output was
similar in the two groups breathing air, whereas on 55% O2
only L showed a significant increase. During exercise in air, arterial
PCO2 was 8 Torr lower in L than in N
(P < 0.001), yet PO2 was the
same such that, at maximal O2 uptake,
alveolar-arterial PO2 difference was lower in N
(5.3 ± 1.3 Torr) than in L (10.5 ± 0.8 Torr),
P = 0.004. Calculated O2 diffusing capacity
was 40% higher in N than in 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 millimole per
liter rise in lactate. These data show in L persistent alkalosis even
after 9 wk at 5,260 m. In N, the data show 1) insignificant reduction in exercise capacity when breathing air at 5,260 m compared with breathing 55% O2; 2) very little
ventilatory response to acute hypoxemia (judged by arterial pH and
arterial PCO2 responses to hyperoxia);
3) during exercise, greater pulmonary diffusing capacity
than in L, allowing maintenance of arterial PO2
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.
hypoxia; ventilation; acid-base balance; diffusing capacity
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