Improvement in exercise capacity with nitric oxide inhalation in patients with precapillary pulmonary hypertension

Abstract

Background - Patients with precapillary pulmonary hypertension (PH) exhibit a poor exercise capacity due to an impaired vasodilatory response of their pulmonary arteries. By causing the pulmonary artery to dilate, inhaled nitric oxide (NO) may allow an increase in exercise capacity in patients with PH. Methods and Results - On 2 separate days, 3 days apart, 14 patients with precapillary PH (10 primary PH, 4 residual PH after correction of an intracardiac shunt; age, 40±12 years; mean pulmonary artery pressure, 60±23 mm Hg) performed exercise, with and without inhalation of 20 ppm NO, on a cycle ergometer. The work rate was increased 15 W/min until their symptom- limited maximum, with breath-by-breath gas analysis. Patients were randomly and blindly selected to inhale NO on either their first or second test. Peak exercise load and anaerobic threshold tended to increase, but not significantly. Peak oxygen consumption (V̇O2) and ΔV̇O2/ΔW ratio increased significantly, by 18% and 22%, respectively (peak V̇O2, 13.6±3.6 to 16.0±4.1 mL · kg-1 · min-1; ΔV̇O2/ΔW ratio, 5.8±2.4 to 7.1±2.3 mL · kg-1 · min-1 · W-1; both P<0.01). Peak V̇O2 increased > 10% in 12 of the 14 patients. However, respiratory quotient at peak exercise decreased from 1.22±0.15 to 1.09±0.15 (P<0.01). Conclusions - Inhaled NO substantially increases oxygen consumption at the same workload during exercise. This finding supports the possibility of ambulatory NO inhalation therapy in patients with precapillary PH.