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¹ Department of Medicine, University of California, San Diego, La Jolla, CA 92093-0623, USA

Acetazolamide (ACZ) is used to prevent acute mountain sickness at altitude. Because it could affect O₂ 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 30, 50 and 90% 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 = 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 , leg blood flow (LBF), and muscle and pulmonary gas exchange, the latter using the multiple inert gas elimination technique. ACZ did not significantly affect , , 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 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.

(Received 11 September 2006; accepted after revision 9 January 2007; first published online 11 January 2007)
Corresponding author P. D. Wagner: University of California, San Diego, Department of Medicine 0623A, 9500 Gilman Drive, La Jolla, CA 92093-0623, USA. Email: pdwagner{at}ucsd.edu

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