Hyperoxia improves exercise capacity in cardiopulmonary disease: a series of randomised controlled trials.

Background:The aim of this study was to investigate the overall and differential effect of breathing hyperoxia (inspiratory oxygen fraction (F IO2 ) 0.5) versus placebo (ambient air, F IO2 0.21) to enhance exercise performance in healthy people, patients with pulmonary vascular disease (PVD) with precapillary pulmonary hypertension (PH), COPD, PH due to heart failure with preserved ejection fraction (HFpEF) and cyanotic congenital heart disease (CHD) using data from five randomised controlled trials performed with identical protocols. Methods:91 subjects (32 healthy, 22 with PVD with pulmonary arterial or distal chronic thromboembolic PH, 20 with COPD, 10 with PH in HFpEF and seven with CHD) performed two cycle incremental (IET) and two constant work-rate exercise tests (CWRET) at 75% of maximal load (Wmax), each with ambient air and hyperoxia in single-blinded, randomised, controlled, crossover trials. The main outcomes were differences in Wmax (IET) and cycling time (CWRET) with hyperoxia versus ambient air. Results:Overall, hyperoxia increased Wmax by +12 W (95% CI: 9-16, p<0.001) and cycling time by +6:13 min (4:50-7:35, p<0.001), with improvements being highest in patients with PVD (Wmax/min: +18%/+118% versus COPD: +8%/+60%, healthy: +5%/+44%, HFpEF: +6%/+28%, CHD: +9%/+14%). Conclusion:This large sample of healthy subjects and patients with various cardiopulmonary diseases confirms that hyperoxia significantly prolongs cycling exercise with improvements being highest in endurance CWRET and patients with PVD. These results call for studies investigating optimal oxygen levels to prolong exercise time and effects on training.