Effect of Long-term Oxygen Therapy on Exercise Capacity and Quality of Life in Patients With Pulmonary Arterial and Chronic Thromboembolic Pulmonary Hypertension

Inclusion criteria: \- Adult patients with established diagnosis of pulmonary arterial or chronic thromboembolic pulmonary hypertension (class I and IV according to the latest WHO classification scheme of Dana Point 2008) on optimized medical therapy and in stable condition for at least 4 weeks, who desaturate in the 6 minute walking test by =4% to values \<92%. Exclusion criteria: * Patients in unstable conditions requiring frequent therapeutic adaption * pregnant women * patients with pulmonary venous hypertension due to left heart diseases * patients with relevant concomitant lung disease and severe daytime hypoxemia