The overlap syndrome: chronic obstructive pulmonary disease and obstructive sleep apnea.

The overlap syndrome defines the relationship between obstructive sleep apnea (OSA) and chronic obstructive pulmonary disease (COPD), and is a commonly noted but poorly studied disorder. Individuals who have the overlap syndrome have been recognized to have greater risk for pulmonary hypertension, right heart failure, and hypercapnia than patients who have either disorder alone. In patients who have advanced-stage COPD, concomitant OSA likely has significant adverse consequences. The interaction between these two diseases is unclear, however. Further clinical trials of the overlap syndrome are urgently needed.