[Sleep and COPD].

In COPD patients hypoxaemia does worsen during sleep and particularly during REM sleep. However, severe sleep-related O2 desaturation is only observed in patients who exhibit a marked daytime hypoxaemia. Nocturnal desaturation is due to the combination of alveolar hypoventilation and ventilation-perfusion mismatch; alveolar hypoventilation is the predominant mechanism, at least during REM sleep. Sleep-related hypoxaemia leads to peaks of pulmonary hypertension but also to cardiac arrhythmias. Hypoxaemia can be particularly severe when COPD is associated with a sleep apnoea syndrome (this association is rather frequent). A severe nocturnal desaturation needs a treatment with prolonged oxygen therapy, especially if daytime hypoxaemia (PaO2 < 55-60 mmHg) is present. The real benefit from oxygen therapy limited to sleep time in nocturnal desaturators who have not a significant daytime hypoxaemia, has not been yet demonstrated.