• Hossein A Ghofrani, Frank Reichenberger, Markus G Kohstall, Eike H Mrosek, Timon Seeger, Horst Olschewski, Werner Seeger, and Friedrich Grimminger.
• University Hospital Giessen and Justus-Liebig University, Giessen, Germany.
• Ann. Intern. Med. 2004 Aug 3;141(3):169-77.

BackgroundAlveolar hypoxia causes pulmonary hypertension and enhanced right ventricular afterload, which may impair exercise tolerance. The phosphodiesterase-5 inhibitor sildenafil has been reported to cause pulmonary vasodilatation.ObjectiveTo investigate the effects of sildenafil on exercise capacity under conditions of hypoxic pulmonary hypertension.DesignRandomized, double-blind, placebo-controlled crossover study.SettingUniversity Hospital Giessen, Giessen, Germany, and the base camp on Mount Everest.Participants14 healthy mountaineers and trekkers.MeasurementsSystolic pulmonary artery pressure, cardiac output, and peripheral arterial oxygen saturation at rest and during assessment of maximum exercise capacity on cycle ergometry 1) while breathing a hypoxic gas mixture with 10% fraction of inspired oxygen at low altitude (Giessen) and 2) at high altitude (the Mount Everest base camp).InterventionOral sildenafil, 50 mg, or placebo.ResultsAt low altitude, acute hypoxia reduced arterial oxygen saturation to 72.0% (95% CI, 66.5% to 77.5%) at rest and 60.8% (CI, 56.0% to 64.5%) at maximum exercise capacity. Systolic pulmonary artery pressure increased from 30.5 mm Hg (CI, 26.0 to 35.0 mm Hg) at rest to 42.9 mm Hg (CI, 35.6 to 53.5 mm Hg) during exercise in participants taking placebo. Sildenafil, 50 mg, significantly increased arterial oxygen saturation during exercise (P = 0.005) and reduced systolic pulmonary artery pressure at rest (P < 0.001) and during exercise (P = 0.031). Of note, sildenafil increased maximum workload (172.5 W [CI, 147.5 to 200.0 W]) vs. 130.6 W [CI, 108.8 to 150.0 W]); P < 0.001) and maximum cardiac output (P < 0.001) compared with placebo. At high altitude, sildenafil had no effect on arterial oxygen saturation at rest and during exercise compared with placebo. However, sildenafil reduced systolic pulmonary artery pressure at rest (P = 0.003) and during exercise (P = 0.021) and increased maximum workload (P = 0.002) and cardiac output (P = 0.015). At high altitude, sildenafil exacerbated existing headache in 2 participants.LimitationsThe study did not examine the effects of sildenafil on normoxic exercise tolerance.ConclusionsSildenafil reduces hypoxic pulmonary hypertension at rest and during exercise while maintaining gas exchange and systemic blood pressure. To the authors' knowledge, sildenafil is the first drug shown to increase exercise capacity during severe hypoxia both at sea level and at high altitude.

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