The effect of high altitude (2500 m) on incremental cycling exercise in patients with pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension: a randomised controlled crossover trial

Background Our objective was to investigate the effect of a day-long exposure to high altitude on peak exercise capacity and safety in stable patients with pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH). Methods In a randomised controlled crossover trial, stable patients with PAH or distal CTEPH without resting hypoxaemia at low altitude performed two incremental exercise tests to exhaustion: one after 3-5 h at high altitude (2500 m) and one at low altitude (470 m). Results In 27 patients with PAH/CTEPH (44% females, mean +/- sd age 62 +/- 14 years), maximal work rate was 110 +/- 64 W at 2500 m and 123 +/- 64 W at 470 m (-11%, 95% CI -16- -11%; p<0.001). Oxygen saturation measured by pulse oximetry and arterial oxygen tension at end-exercise were 83 +/- 6% versus 91 +/- 6% and 6.1 +/- 1.9 versus 8.6 +/- 1.9 kPa (-8% and -29%; both p<0.001) at 2500 versus 470 m, respectively. Maximal oxygen uptake was 17.8 +/- 7.5 Lmin(-1)kg(-1) at high altitude versus 20 +/- 7.4 Lmin(-1)kg(-1) at low altitude (-11%; p<0.001). At end-exercise, the ventilatory equivalent for carbon dioxide was 43 +/- 9 at 2500 m versus 39 +/- 9 at 470 m (9%, 95% CI 2-6%; p=0.002). No adverse events occurred during or after exercise. Conclusions Among predominantly low-risk patients with stable PAH/CTEPH, cycling exercise during the first day at 2500 m was well tolerated, but peak exercise capacity, blood oxygenation and ventilatory efficiency were lower compared with 470 m.