To study the effect of acute normobaric hypoxia during exercise in patients with pulmonary hypertension on blood markers (serum markers of iron and red blood cell homeostasis and micro-RNAs known to be associated with PH).

Inclusion Criteria:

• Informed consent as documented by signature (Appendix Informed Consent Form)
• PH class I (PAH) or IV (CTEPH) diagnosed according to guidelines: mean pulmonary artery pressure >20 mmHg, pulmonary vascular resistance ≥3 wood units, pulmonary arterial wedge pressure ≤15 mmHg during baseline measures at the diagnostic right-heart catheterization

Exclusion Criteria:

• resting partial pressure of oxygen <8 kilopascal at Zürich altitude on ambient air
• exposure to an altitude >1000 m for ≥3 nights during the last 2 weeks before the study
• inability to follow the procedures of the study
• patients who take nitrates
• other clinically significant concomitant end-stage disease (e.g., renal failure, hepatic dysfunction)

We will share individual participant data after publication of the manuscript. The decision about the platform is ongoing.

After publication of the manuscript