The effect of high altitude on exercise capacity and cardiorespiratory function in patients with pulmonary vascular disease after an overnight stay at 2500 m – a randomized cross-over study

Aim We investigated the effect of an overnight-stay at high altitude (HA, 2500 m) on constant work-rate exercise test (CWRET) time and cardiorespiratory function in patients with pulmonary vascular disease (PVD) and the impact of supplemental oxygen therapy (SOT) in case of severe altitude-induced hypoxemia. Methods In a randomized crossover trial, stable patients diagnosed with pulmonary arterial or distal chronic thromboembolic pulmonary hypertension (PVD, PAH/CTEPH) performed a symptom-limited cycling CWRET at 470 m and after an overnight stay at 2500 m. For safety, patients with a SpO 2 <80% for >30 min received SOT during the subsequent HA-stay. The primary outcome was CWRET-time, secondary outcomes were changes in ergospirometric parameters. Clinicaltrials.gov: NCT05107700 &NCT05112172. Results Of 27 PVD-patients (44% female; mean age 62±14 y, 20 PAH, 7 distal CTEPH), 10 (37%) required SOT. Overall at HA versus 470 m, CWRET-time decreased to 292±181 s versus 454±411 s (mean difference −162 s, 95%CI −290 to −34 s; p=0.026), driven by patients without need for SOT (261±187 s versus 519±497 s; p=0.017), who revealed lower resting PaO 2 (7.4±0.7 kPa versus 10.6±1.4 kPa, p<0.001) and ventilatory efficiency, but exercise-induced SpO 2 -desaturation was not significantly different (−0.9%, 95%CI −3.9 to 2). In 10/27 patients needing SOT, SOT restored CWRET time to 470 m-values (344±170 s versus 345±167 s; p=0.990), corrected altitude-induced hypoxemia and attenuated hyperventilation. Conclusion The majority of PVD-patients tolerated an overnight stay at 2500 m well. In those without need for SOT at HA, CWRET-time was reduced with increased hypoxemia and hyperventilation. In PVD-patients who received SOT due to severe nocturnal hypoxemia, SOT restored CWRET-time to 470 m levels and dampened the exercise-induced hypoxemia.