JAP 00093-2001.R2 A:\chaclung 11 06 01.doc 1 11/09/01 PULMONARY GAS EXCHANGE AND ACID-BASE STATE AT 5260 m IN HIGH ALTITUDE BOLIVIANS AND ACCLIMATIZED LOWLANDERS

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 PCO2 was 8 Torr lower in L than N (p<0.001) yet PO2 was the same such that at V O2MAX, 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 i