High Altitude Residents With High Altitude Pulmonary Hypertension (HAPH), SDB Assessed at HA (3200 m) vs LA (760 m)

Inclusion Criteria: * Permanently living \>2500 m * HAPH diagnosed with a minimum RV/RA of 30 mmHg assessed by echocardiography at an altitude of 3200 m * Written informed consent Exclusion Criteria: * Highlanders who cannot follow the study investigations, * Patients with moderate to severe concomitant lung disease (FEV1\<70% or forced vital capacity \<70%), severe parenchymal lung disease, heavy smoking \>20 cigarettes/day or \>20 pack-years. * Coexistent unstable systemic hypertension or coronary artery disease that required adjustment of medication within the last 2 months * Regular use of medication that affects control of breathing (benzodiazepines, opioids, acetazolamide)