Sildenafil and Exercise Capacity in the Elderly at Moderate Altitude

Objective Hypobaric hypoxia decreases exercise capacity and causes hypoxic pulmonary vasoconstriction and pulmonary hypertension. The phosphodiesterase-5 inhibitor sildenafil is a pulmonary vasodilator that may improve exercise capacity at altitude. We aimed to determine whether sildenafil improves exercise capacity, measured as maximal oxygen consumption (peak Vo₂), at moderate altitude in adults 60 years or older. Methods The design was a randomized, double-blind, placebo-controlled, crossover study. After baseline cardiopulmonary exercise testing at 1400 m, 12 healthy participants (4 women) aged 60 years or older, who reside permanently at approximately 1400 m and are regularly active in self-propelled mountain recreation above 2000 m, performed maximal cardiopulmonary cycle exercise tests in a hypobaric chamber at a simulated altitude of 2750 m after ingesting sildenafil and after ingesting a placebo. Results After placebo, mean peak Vo₂ was significantly lower at 2750 m than 1400 m: 37.0 mL · kg^-1 · min^-1 (95% CI, 32.7 to 41.3) vs 39.1 mL · kg^-1 · min^-1 (95% CI, 33.5 to 44.7; P =.020). After placebo, there was no difference in heart rate (HR) or maximal workload at either altitude (z = 0.182; P =.668, respectively). There was no difference between sildenafil and placebo at 2750 m in peak Vo₂ (P =.668), O₂ pulse (P =.476), cardiac index (P =.143), stroke volume index (z = 0.108), HR (z = 0.919), or maximal workload (P =.773). Transthoracic echocardiography immediately after peak exercise at 2750 m showed tricuspid annular plane systolic velocity was significantly higher after sildenafil than after placebo (P =.019), but showed no difference in tricuspid annular plane systolic excursion (P =.720). Conclusions Sildenafil (50 mg) did not improve exercise capacity in adults 60 years or older at moderate altitude in our study. This might be explained by a "dosing effect" or insufficiently high altitude.