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Effects of acetazolamide on aerobic exercise capacity and pulmonary hemodynamics at high altitudes

¹Laboratory of Physiology, Faculty of Medicine, Free University of Brussels, Brussels; ²Department of Cardiology, Erasme University Hospital, Brussels, Belgium; ³Laboratory of Physiology, University of Bordeaux 2, Bordeaux, France; ⁴Department of Pneumology, St, Elisabeth Hospital, Namur, Belgium; and ⁵Laboratory of Physiology, Institute of Sports and Physiotherapy, Free University of Brussels, Belgium

Submitted 12 February 2007 ; accepted in final form 28 June 2007

Aerobic exercise capacity is decreased at altitude because of combined decreases in arterial oxygenation and in cardiac output. Hypoxic pulmonary vasoconstriction could limit cardiac output in hypoxia. We tested the hypothesis that acetazolamide could improve exercise capacity at altitude by an increased arterial oxygenation and an inhibition of hypoxic pulmonary vasoconstriction. Resting and exercise pulmonary artery pressure (Ppa) and flow (Q) (Doppler echocardiography) and exercise capacity (cardiopulmonary exercise test) were determined at sea level, 10 days after arrival on the Bolivian altiplano, at Huayna Potosi (4,700 m), and again after the intake of 250 mg acetazolamide vs. a placebo three times a day for 24 h. Acetazolamide and placebo were administered double-blind and in a random sequence. Altitude shifted Ppa/Q plots to higher pressures and decreased maximum O₂ consumption (O_2max). Acetazolamide had no effect on Ppa/Q plots but increased arterial O₂ saturation at rest from 84 ± 5 to 90 ± 3% (P < 0.05) and at exercise from 79 ± 6 to 83 ± 4% (P < 0.05), and O₂ consumption at the anaerobic threshold (V-slope method) from 21 ± 5 to 25 ± 5 ml·min^–1·kg^–1 (P < 0.01). However, acetazolamide did not affect O_2max (from 31 ± 6 to 29 ± 7 ml·kg^–1·min^–1), and the maximum respiratory exchange ratio decreased from 1.2 ± 0.06 to 1.05 ± 0.03 (P < 0.001). We conclude that acetazolamide does not affect maximum exercise capacity or pulmonary hemodynamics at high altitudes. Associated changes in the respiratory exchange ratio may be due to altered CO₂ production kinetics.

echocardiography; cardiopulmonary exercise test; hypoxic pulmonary vasoconstriction; pulmonary vascular resistance

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