The effect of increasing inspired oxygen on exercise performance in patients with chronic heart failure

Objective: Chronic heart failure is characterised by reduced exercise tolerance. We assessed the effects of different fractions of inspired oxygen (FiO2) on exercise capacity using cycle ergometry to see if there is a dose–response relationship between FiO2 and exercise performance. Methods: This was a single-centre, randomised, single-blinded, cross-over study. Thirty-one patients with chronic heart failure undertook three maximal incremental exercise tests. For each test, a different FiO2 was used: room air (20.9%), 28% or 40%. The patient had to breathe in via a venturi mask allowing the investigator to control the FiO2 and maintain the patient's blinding. The three tests were carried out in random order with a minimum of 4 days’ rest between any two tests. Results: Exercise time increased from (mean±standard deviations) 501±24.9 s on room air to 525±25.1 s (p=0.042) and 536±24.2 (p<0.001) seconds, with FiO2 of 28% and 40%, respectively. Maximal metabolic equivalents were 3.47±0.16 on room air and 3.67±0.16 (p=0.002) and 3.70±0.15 (p<0.001) on 28% and 40% oxygen, respectively. Maximal workload was 78.4±4.5 W on room air and 82.6±4.3 (p=0.021) and 84.2±4.2 (p=0.005) on 28% and 40% oxygen, respectively. Increasing FiO2 resulted in higher mean oxygen saturations during exercise. The mean heart rate during exercise was lower with FiO2 of 28% with no further drop at 40%. Changing FiO2 had no effect on blood pressure. Conclusions: Increasing FiO2 to 28% or 40% acutely improves exercise capacity in patients with chronic heart failure