COPD is a heterogeneous disease composed by two main phenotypes: bronchitis (COPDb) and emphysema (COPDe) with different clinical presentation, physiology, imaging, response to therapy and decline in lung function.The aim of this study is to evaluate whether nocturnal hypoxemic COPDb and COPDe have a different behaviour during sleep and the effect of nocturnal oxygen supplementation (nO2LT).