Effect of acetazolamide on pulmonary and muscle gas exchange during normoxic and hypoxic exercise

Acetazolamide (ACZ) is used to prevent acute mountain sickness at altitude. Because it could affect O-2 transport in several different and potentially conflicting ways, we examined its effects on pulmonary and muscle gas exchange and acid - base status during cycle exercise at similar to 30, 50 and 90% V-O2max in normoxia (F-IO2 = 0.2093) and acute hypoxia (F-IO2 = 0.125). In a double-blind, order-balanced, crossover design, six healthy, trained men (normoxic. V-O2max = 59 ml kg(-1) min(-1)) exercised at both F-IO2 values after ACZ ( 3 doses of 250 mg, 8 h apart) and placebo. One week later this protocol was repeated using the other drug ( placebo or ACZ). We measured cardiac output (Q(T)), leg blood flow (LBF), and muscle and pulmonary gas exchange, the latter using the multiple inert gas elimination technique. ACZ did not significantly affect. V-O2, QT, LBF or muscle gas exchange. As expected, ACZ led to lower arterial and venous blood [HCO3-], pH and lactate levels (P < 0.05), and increased ventilation (P < 0.05). In both normoxia and hypoxia, ACZ resulted in higher arterial P-O2 and saturation and a lower alveolar - arterial P-O2 difference (AaD(O2)) due to both less. V-A/Q mismatch and less diffusion limitation (P < 0.05). In summary, ACZ improved arterial oxygenation during exercise, due to both greater ventilation and more efficient pulmonary gas exchange. However, muscle gas exchange was unaffected.