Effect of Short-term Oxygen During CPET in Pulmonary Hypertension

Inclusion criteria: * diagnosis of pulmonary arterial 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 week * desaturate in the 6 minute walking test by at least 4% to values \<92% Exclusion criteria: * unstable conditions * pregnant women * patients with pulmonary venous hypertension * patients with relevant concomitant lung disease and severe daytime hypoxemia