Constant work-rate cycling time and arterial blood gases in lowlanders with pulmonary arterial and chronic thromboembolic pulmonary hypertension on the second day at 2500m – a randomized cross-over study

<bold>Introduction:</bold> Mountain travel is popular, also for patients with chronic diseases including pulmonary vascular disease (PVD). We investigated the impact of overnight exposure to hypobaric hypoxia and the effect of supplemental oxygen in case of severe hypoxemia on constant work-rate exercise test (CWRET) time and arterial blood gas analysis (ABGA) in PVD-patients defined as pulmonary arterial or chronic thromboembolic hypertension (PAH/CTEPH). <bold>Methods:</bold> Adults with stable PVD underwent symptom-limited CWRET-cycling (75% of Wmax) at 470m (Zurich) and on the second day during a 30h overnight stay at 2500m (Mt. Säntis), according to a randomized, cross-over trial including >2 weeks wash-out. ABGA was performed at rest and at end-exercise. Oxygen supplementation (3l/min) was provided to patients experiencing severe hypoxemia (SpO2 <80% >30min) at 2500m. Mixed-linear-regression-models were performed and results are presented as mean±standard deviation, mean differences (95% confidence intervals) and statistical significance indicated by a two-sided p-value<0.05. <bold>Results:</bold> We included 27 patients (12 female, 44%; 20 PAH, 74%), age 62±14 years, of which 10 (37%) patients performed the CWRET on supplemental oxygen the second day at 2500m. <bold>Conclusion:</bold> The majority of PVD-patients did not require supplemental oxygen at 2500m but showed decreased exercise capacity along with hypoxemia at rest and at end-exercise, hyperventilation and lactatemia. In patients with predefined severe hypoxemia at altitude, supplemental oxygen restored exercise performance and resting hypoxemia to low altitude levels.