The effect of inhaled nitric oxide on maximal oxygen consumption during exercise in acute hypoxia: a randomized double-blind crossover trial.

In moderate hypoxia [partial pressure of inspired oxygen ([Formula: see text]) = 85-111 mmHg], the reduction in maximal oxygen consumption (V̇o 2max ) has been attributed to arterial desaturation, whereas in severe hypoxia ([Formula: see text] < 85 mmHg), elevated pulmonary artery pressure (PAP) is thought to impair peak cardiac output ([Formula: see text]) and therefore V̇o 2max . The purpose of this study was to examine whether reducing PAP with inhaled nitric oxide (iNO, a selective pulmonary vasodilator) would increase V̇o 2max in moderate and severe acute hypoxia. Twelve young, healthy participants (mean V̇o 2max = 45.3 ± 12.2 mL/kg/min), with normal lung function completed the randomized double-blind crossover study over six sessions. Experimental cardiopulmonary exercise tests (CPET) were completed on separate days with participants under the following conditions: 1 ) acute moderate hypoxia ([Formula: see text] = 89 mmHg), 2 ) acute severe hypoxia ([Formula: see text] = 79 mmHg), 3 ) acute moderate hypoxia with 40 ppm iNO, and 4 ) acute severe hypoxia with 40 ppm iNO (order randomized). On separate days, rest, and exercise (60 W), echocardiography was conducted to determine right ventricular systolic pressure (RVSP/PAP) under conditions 1-4 . Resting RVSP was reduced by 2.5 ± 0.8 mmHg with iNO in moderate hypoxia ( P = 0.01) and 1.8 ± 0.2 mmHg in severe hypoxia ( P = 0.05); however, iNO had no effect on peak [Formula: see text] or V̇o 2max in either hypoxic condition. Despite reducing RVSP with iNO in hypoxia, peak [Formula: see text] and V̇o 2max were unaffected, suggesting that iNO may not improve exercise tolerance in healthy participants during hypoxic exercise. NEW & NOTEWORTHY The elevation of pulmonary artery pressure (PAP) with hypoxia may impair peak cardiac output ([Formula: see text]) and therefore V̇o 2max . Our novel findings show that despite reducing resting RVSP in acute moderate ([Formula: see text] = 89 mmHg) and severe hypoxia ([Formula: see text] = 79 mmHg) with inspired nitric oxide, peak [Formula: see text], and V̇o 2max were unaffected.