Introduction: Journeys to altitude touristic areas became increasingly popular also among potentially vulnerable groups such as precapillary pulmonary hypertension due to pulmonary vascular disease (PVD). Evidence to counsel PVD-patients for their upcoming HA trips is scarce.

Aims: We examined altitude-related adverse health events (ARAHE) during an overnight stay at 2500m and whether supplemental O2 reverses the effects of altitude.

Methods: In a randomized cross-over trial, 27 (44% female) stable patients with PVD were exposed to 2500m for around 30h. ARAHE requiring O2 therapy was defined as severe hypoxemia (SpO2<80% for >30min) Right heart function by echocardiography, acute mountain sickness (AMS), arterial blood gas and more were assessed the second day at altitude.

Results: 10/27 patients experienced severe hypoxemia according to predefined safety criteria and received O2, 6 experienced AMS. 1 patient required O2 the first day, all others during the night. All completed the study accordingly.

Significant differences between 470m and 2500m among patients not requiring O2 were present in tricuspid regurgitation pressure gradient (mean±SD) 40±19 and 61±23 (mean-difference and confidence interval) 21(7 to 35)mmHg, in PaCO2 4.5±0.4 and 4.2±0.4 kPa; -0.32(-0.6 to -0.04) and in PaO2 10.4 ± 1.5 and 7.2 ± 0.8; -3.42(-3.97 to -2.87) kPa, however not among patients receiving O2.

Conclusion: During a stay at 2500m, 37% experienced severe hypoxemia, which was reversed with supplemental O2. Significant physiological differences between 470m and 2500m among non-hypoxemic patients were detected, but no longer among those receiving O2.