Early Signs of Altitude Illness in Patients With COPD

Inclusion criteria * Male and female patients, age 18-75 yrs. * COPD diagnosed according to GOLD, FEV1 40-80% predicted, SpO2 ≥92%, PaCO2 \<6 kPa at 760 m. * Born, raised and currently living at low altitude (\<800 m). * Written informed consent. Exclusion criteria * COPD exacerbation, very severe COPD with hypoxemia at low altitude (FEV1 \<40% predicted; oxygen saturation on room air \<92% or hypercapnia at 760 m). * Other lung disease or disorder of control of breathing * Comorbidities such as uncontrolled cardiovascular disease, i.e., unstable systemic arterial hypertension, coronary artery disease; previous stroke, internal, neurologic, rheumatologic or psychiatric disease that interfere with protocol compliance including current heavy smoking (\>20 cigarettes per day)