Sleep and chronic obstructive pulmonary disease

Patients with COPD who are hypoxaemic during wakefulness become more hypoxaemic during steep. The most severe episodes of nocturnal desaturation generally occur during REM steep. There is a strong relationship between nocturnal O-2 saturation and the level of daytime PaO2: the more pronounced daytime hypoxaemia, the more severe nocturnal hypoxaemia. The worsening of hypoxaemia is due to a variable combination of alveolar hypoventilation and ventilation - perfusion mismatching, alveolar hypoventilation being the predominant mechanism, at least during REM steep. The consequences of steep-related hypoxaemia include peaks of pulmonary hypertension due to hypoxic pulmonary vasoconstriction, generally observed in patients with marked daytime hypoxaemia. Cardiac arrhythmias have been described but their clinical relevance has not been established. The prevalence of obstructive steep apnoea syndrome (OSAS) is not greater in chronic obstructive pulmonary disease (COPD) patients than in the general population, but this association (Overlap Syndrome) is not rare since COPD and OSAS are both frequent diseases. Overlap patients are at a higher risk of developing respiratory insufficiency than are pure OSAS patients. Polysomnographyisonty indicated in COPD patients who are suspected of having OSAS. The treatment of nocturnal hypoxaemia is conventional O-2 therapy ( greater than or equal to 16/24 h) in COPD patients with marked daytime hypoxaemia (PaO2 < 55 - 60 mmHg) and conventional O-2 therapy plus nocturnal non-invasive ventilation in some patients with marked hypercapnia. At present data are not sufficient for justifying the use of isolated nocturnal oxygen therapy in COPD patients with nocturnal desaturation but with mild daytime hypoxaemia (PaO2 > 60 mmHg). (C) 2004 Elsevier Ltd. All rights reserved.