Chronic obstructive pulmonary disease (COPD) and obstructive sleep apnea (OSA) represent two of the most prevalent chronic respiratory disorders and cardiovascular diseases are major co-morbidities in both.

Co-existence of both disorders (overlap syndrome) occurs in 1% of adults and overlap patients have worse nocturnal hypoxemia and hypercapnia than COPD and OSA patients alone. The present review discusses recent data concerning the pathophysiological and clinical significance of the overlap syndrome.

RECENT FINDINGS: The severity of obstructive ventilatory impairment and hyperinflation, especially the inspiratory capacity to total lung capacity (TLC) ratio, correlates with the severity of sleep-related breathing disturbances. Early treatment with continuous positive airway pressure (CPAP) improves survival, reduces hospitalization and pulmonary hypertension, and also reduces hypoxemia. Evidence of systemic inflammation and oxidative stress in COPD and sleep apnea provides insight into potential interactions between both disorders that may predispose to cardiovascular disease. Long-term outcome studies of overlap patients currently underway should provide further evidence of the clinical significance of the overlap syndrome.

SUMMARY: Studies of overlap syndrome patients at a clinical, physiological and molecular level should provide insight into disease mechanisms and consequences of COPD and sleep apnea, in addition to identifying potential relationships with cardiovascular disease.