This is a randomized, placebo-controlled, double-blind parallel trial evaluating the efficacy of dexamethasone prophylaxis in sleep related breathing disturbances in lowlanders with chronic obstructive pulmonary disease travelling to altitude. Participants living in the Bishkek area, Kyrgyzstan (700m), will be transferred by car within 4h to the Tuja Ashu high altitude clinic (3200 m), and stay there for 2 days. Dexamethasone 2x4mg/day (or placebo), will be administered before departure at 700 m and during the stay at altitude. Outcomes will be assessed during the stay at 3200 m
