STUDY QUESTION: We investigated whether domiciliary oxygen therapy (DOXT) increases exercise capacity and quality of life in patients with pulmonary arterial or distal chronic thromboembolic pulmonary hypertension (PAH/CTEPH) presenting with mild resting hypoxaemia and exercise-induced oxygen desaturation. MATERIALS AND METHODS: 30 patients with PAH/CTEPH, mean +/- SD age 60 +/- 15 years, pulmonary artery pressure 39 +/- 11 mmHg, resting arterial oxygen saturation measured by pulse oximetry (SpO2) >= 90%, SpO2 drop during a 6-min walk test >= 4%, on pulmonary hypertension-targeted medication, were randomised in a double-blind crossover protocol to DOXT and placebo (ambient air) treatment, each over 5 weeks, at 3 L/min via nasal cannula overnight and when resting during the day. Treatment periods were separated by 2 weeks of washout. Co-primary outcomes were changes in 6-min walk distance (6MWD, breathing ambient air) and physical functioning scale of the 36-item short-form medical outcome questionnaire during treatment periods. RESULTS: DOXT increased the 6MWD from baseline 478 +/- 113 m by a mean (95% CI) of 19 (6 to 32) m, and physical functioning from 52 +/- 29 by 4 (0 to 8) points. Corresponding changes with placebo were 1 (-11 to 13) m in 6MWD and -2 (-6 to 2) points in physical functioning. Between-treatment differences in changes were 6MWD 18 (1 to 35) m (p = 0.042) and physical functioning 6 (1 to 11) points (p = 0.029). DOXT significantly improved the New York Heart Association functional class versus placebo. ANSWER TO THE QUESTION: This first randomised trial in PAH/CTEPH patients with exercise-induced hypoxaemia demonstrates that DOXT improves exercise capacity, quality of life and functional class. The results support large long-term randomised trials of DOXT in PAH/CTEPH.
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