This is a randomized, placebo-controlled, double-blind parallel trial evaluating the effect of acetazolamide (375 mg per day) vs. placebo on lung water content by ultrasound in lowlanders with chronic obstructive pulmonary disease travelling to altitude. Participants living in the Bishkek area, Kyrgyzstan (760m), will be transferred by car within 4h to the Tuja Ashu high altitude clinic (3100 m), and stay there for 2 days. Acetazolamide 375mg/day (or placebo) will be administered 24 hours before departure at 760 m and during the stay at altitude. Outcomes will be assessed during the stay at 3100 m.
