SLEEP-RELATED HYPOXEMIA IN CHRONIC OBSTRUCTIVE PULMONARY-DISEASE - CAUSES, CONSEQUENCES AND TREATMENT

Worsening of hypoxaemia during sleep in patients with chronic obstruct ive pulmonary disease has been extensively investigated in the past 20 years owing to the development of polysomnography and to the advent o f reliable transcutaneous oxymeters. Sleep-related hypoxaemia is chara cteristic of rapid-eye-movement (REM) sleep but may be present during other sleep stages. There is a strong relationship between nocturnal O -2 saturation and the level of daytime PaO2: the more pronounced dayti me hypoxaemia, the more severe nocturnal hypoxaemia. Sleep-related hyp oxaemia is due to a variable combination of alveolar hypoventilation a nd ventilation-perfusion mismatching, alveolar hypoventilation being t he preponderant mechanism during REM sleep. The deleterious effects of sleep-related hypoxaemia include cardiac arrhythmias, 'hypoxaemic str ess' on the coronary circulation and, especially, peaks of pulmonary h ypertension. The treatment of nocturnal hypoxaemia is conventional O-2 therapy (both nighttime and daytime) in patients who exhibit marked d aytime hypoxaemia (PaO2 < 55-60 mm Hg). At present data are not suffic ient for justifying the use of isolated nocturnal O-2 therapy in patie nts with nocturnal desaturation who do not qualify for conventional O- 2 therapy.