The Effect of Oxygen Therapy on 6MWD in PAH and CTEPH Patients With Hypoxemia

Study medication will be oxygen (O2) in diverse concentrations, titrated until a SaO2\>90% or pO2 \>60 mmHg is achieved, for 20 patients vs. no supplemental O2 for 20 patients over 90 ± 7 days. Patients of the control group will be offered to participate in the interventional treatment arm after they have terminated the control period (partial cross-over; secondary intervention group). After the end of the study it is up to the judgment of the investigator to prescribe oxygen to all patients who might benefit from the treatment.