Effect of Short-term Oxygen During CPET in COPD

Inclusion Criteria: * diagnosis of chronic obstructive pulmonary disease * 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 relevant concomitant lung disease and severe daytime hypoxemia