Inclusion Criteria:COPD patients 1) with at least two acute moderate or severe exacerbations during past 12 months, 2) who at the follow-up visit one month after an acute severe exacerbation of COPD are hypercapnic (capillary pCO2 >6.5 kPa) and not willing to use NIV or have used it less than 4 h/d during the last month despite optimal settings prescribed by an experienced pulmonologist, or if a patient at the follow-up one month after a severe exacerbation is hypercapnic and is willing to try NIV (initiated at the follow-up visit, not at the ward), but then uses it less than 4h/d during the following month. Acute moderate (treated with short acting bronchodilators plus antibiotics and/or oral corticosteroids) and severe (patient requires hospitalization or visits the emergency room) exacerbations of COPD are defined according to the GINA Guidelines (GOLD 2019).  Exclusion Criteria: 1) OSA (diagnosed OSA or high suspicion OSA because of regular snoring, witnessed apneas and daytime sleepiness), 2) neuromuscular or chest wall disease, 3) BMI>35 kg/m2 or 4) a patient is not able to give his/her informed consent for the study.