Overlap syndrome: obstructive sleep apnea in patients with chronic obstructive pulmonary disease.

Chronic obstructive pulmonary disease (COPD) and sleep apnea-hypopnea syndrome (SAHS) are both common diseases affecting respectively 10 and 5% of the adult population over 40 years of age, and their coexistence, which is denominated overlap syndrome, can be expected to occur in about 0.5% of this population. A recent epidemiologic study has shown that the prevalence of SAHS is not higher in COPD than in the general population, and that the coexistence of the two conditions is due to chance and not through a pathophysiologic linkage between these two diseases. Patients with overlap have a more important sleep-related O(2) desaturation than do patients with COPD with the same degree of bronchial obstruction. They have an increased risk of developing hypercapnic respiratory insufficiency and pulmonary hypertension when compared with patients with SAHS alone and with patients with "usual" COPD. In patients with overlap, hypoxemia, hypercapnia, and pulmonary hypertension can be observed in the presence of mild to moderate bronchial obstruction, which is different from "usual" COPD. Therapy of the overlap syndrome consists of nasal continuous positive airway pressure or nocturnal noninvasive ventilation (NIV), with or without associated nocturnal O(2). Patients who are markedly hypoxemic during daytime (Pa(O(2)) < 55-60 mm Hg) should be given conventional long-term O(2) therapy in addition to nocturnal ventilation.