Long-term Oxygen Therapy in Patients With Chronic Obstructive Pulmonary Disease Who Live at High Altitude

Inclusion Criteria: * Men and women between ≥ 40 years and \< 85 years living in Bogotá or in a high - altitude city (\>2.500 - \<3.500 m). * Diagnosis of COPD defined by FEV1 / FVC \<LLN (Lower limit of normal value) and significant exposure to cigarette ≥ 10 packs / year or woodsmoke ≥ 10 years. * Diagnosis of ACO defined by FEV1 / FVC post BD \<70%, significant exposure to cigarette or woodsmoke and asthma diagnosed before 40 years and/or wheezing, cough with spirometry with a high respond to bronchodilator (FEV1 or FVC ≥ 15% and 400 ml) or eosinophil \>300 cels. * PaO2 ≥ 50 and ≤ 55 mmHg or oxygen desaturation during the six-minute walk test (at least in three of the measurements performed during the exam) or during sleep (SpO2 ≤ 85% in ≥ 30% of the total time of sleep) * No clinical signs of cor pulmonale * Clinically stable COPD defined as no exacerbations in the last three months. * Signature of informed consent. Exclusion Criteria: * BMI ≥40. * Paraclinical findings of chronic hypoxemia and pulmonary hypertension: * Hematocrit ≥ 55%. * Pulmonary hypertension (PH) defined by transthoracic echocardiography systolic pulmonary artery pressure \> 40 mmHg or indirect signs of PH: Pulmonary artery acceleration time \<100ms associated with a meso-systolic notch and flattening of the septum interventricular in systole. * Echocardiographic findings that could lead to pulmonary hypertension. * Left ventricular systolic dysfunction defined by an ejection fraction \<40% * Left ventricular diastolic dysfunction higher than grade I. * Valvular disease higher than moderate * Use of oxygen \> 12 hours a day for more than six months in the last year. * Comorbidities not controlled or deemed medically that can contribute to mortality during the study follow-up. * Diagnosis of severe sleep apnea-hypopnea syndrome without treatment * Plan of transfer of residence below 2.500 meters. * Medical, psychiatric, social and administrative conditions that define high probability of poor adherence to therapy with oxygen. * Active smoking