BackgroundChronic obstructive pulmonary disease (COPD) may predispose to symptomatic pulmonary hypertension at high altitude. We investigated hemodynamic changes in lowlanders with COPD ascending to 3100m and evaluated whether preventive acetazolamide treatment would attenuate the altitude-induced increase in pulmonary artery pressure (PAP).MethodsIn this placebo-controlled, double-blind parallel-group trial, patients with COPD GOLD 2–3 living <800 m, SpO₂>92%, PaCO₂<6kPa, were randomized to receive either acetazolamide (125 0-250 mg d⁻¹) or placebo capsules starting 24h before ascent from 760 m and during a 2-day-stay at 3100 m. Echocardiography, pulse-oximetry and clinical assessments were performed at 760m and after the first night at 3100m. Primary outcome was PAP assessed by tricuspid regurgitation pressure gradient (TRPG).Results112 patients, 68% men, mean±sdage 59±8 y, FEV₁61±12%pred, SpO₂95±2% were included. TRPG increased from 22±7 to 30±10 mmHg in 54 allocated to placebo and from 20±5 to 24±7 mmHg in 58 allocated to acetazolamide (both p<0.05) resulting in a mean (95%CI) treatment effect of −5 (−9 to −1)mmHg (p=0.015). In patients assigned to placebo at 760/3100m, SpO₂was 95±2/88±3%, in the acetazolamide group respective values were 94±2/ 90±3% (both p<0.05) resulting in a treatment effect of +2(1 to 3)% (p= 0.001).ConclusionsIn lowlanders with COPD travelling to 3100m preventive acetazolamide treatment attenuated the altitude-induced rise in PAP and improved oxygenation.