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

Patients with moderate to severe chronic obstructive pulmonary disease living below 800 m will be invited to participate in a randomized, cross-over field trial evaluating the hypothesis that nocturnal breathing and sleep during nights spent at moderate altitude are improved by oxygen therapy via a nasal cannula compared to room air (sham oxygen). Outcomes will be assessed at low altitude (Zurich, 490 m, baseline), and during 2 study periods of 2 nights each spent at moderate altitude (St. Moritz Salastrains, 2048 m) separated by a wash-out period of at least 2 weeks spent at low altitude (<800 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