The purpose of this study is to evaluate whether nocturnal breathing and sleep of patients with chronic obstructive pulmonary disease (COPD) are disturbed during a stay at moderate altitude.

This randomized cross-over trial evaluates the hypothesis that patients with chronic obstructive pulmonary disease experience nocturnal hypoxemia, periodic breathing and sleep disturbances when staying at moderate altitude. Sleep studies and clinical evaluations will be performed during 2 days in Zurich (490 m, low altitude baseline) and during 2 days at Davos Clavadel (1650 m), and 2 days at Davos Jakobshorn (2590 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