The purpose of this study is to investigate the effect of nocturnal oxygen therapy during a stay at moderate altitude on exercise performance of patients with chronic obstructive lung disease.

Patients with moderate to severe COPD living below 800 m, will be recruited to participate in a randomized cross-over field trial evaluating the hypothesis that exercise capacity during a 2 day sojourn at moderate altitude is improved by nocturnal oxygen therapy via a nasal cannula. Outcomes will be assessed during 2 days in Zurich (490 m, low altitude baseline), and during 2 days at St. Moritz Salastrains (2048 m).

Inclusion Criteria:

• chronic obstructive pulmonary disease (COPD), GOLD grade 2-3
• residents at low altitude (<800 m)

Exclusion Criteria:

• unstable condition, COPD exacerbation
• mild (GOLD 1) or very severe COPD (GOLD 4)
• requirement for oxygen therapy at low altitude residence
• hypoventilation
• pulmonary hypertension
• more than mild or unstable cardiovascular disease
• use of drugs that affect respiratory center drive
• internal, neurologic or psychiatric disease that interfere with protocol compliance including current heavy smoking (>20 cigarettes per day), inability to perform 6 min walk test.
• previous intolerance to moderate altitude (<2600m).
• exposure to altitudes >1500m for >2 days within the last 4 weeks before the study.
• pregnant or nursing patients