Sleep-disordered breathing and COPD: the overlap syndrome

Abstract

Sleep-disordered breathing (mainly obstructive sleep apnea [OSA]) and COPD are among the most common pulmonary diseases, so a great number of patients have both disorders; this "overlap syndrome" causes more severe nocturnal hypoxemia than either disease alone. This common combination of OSA and COPD has important implications for diagnosis, treatment, and outcome. Specifically, patients with COPD and OSA have a substantially greater risk of morbidity and mortality, compared to those with either COPD or OSA alone. Only now are the interactions between these 2 systemic diseases being determined and appreciated. Many questions remain, however, with regard to disease definition, prognosis, and optimal treatment. Treatment currently consists of continuous positive airway pressure, and oxygen as needed. Noninvasive ventilation may be helpful in overlap syndrome patients, but this has not yet been well studied.

Fig. 1

Example of nocturnal oxygen desaturation. The top graph shows the electroencephalogram (EEG) sleep stages (rapid-eye-movement sleep [REM] in bold). The lower graph shows transcutaneous oxygen measurements during sleep in a subject with COPD. Hypoxemia worsens during sleep, most substantially during REM sleep. (Adapted from Reference , with permission.)

Fig. 2

COPD and obstructive sleep apnea (OSA) are systemic disorders that cause cardiovascular disease via various common pathways. Both inflammatory and oxidative stress pathways may be critical to the pathogenesis of OSA and COPD complications. Hypoxia is central to the pathogenesis of both OSA and COPD, although the continuous hypoxia of COPD may be somewhat different biologically from the intermittent hypoxia of OSA syndrome (OSAS). The study of these pathways is complicated by covariates, especially smoking and obesity. TNF = tumor necrosis factor. CRP = C-reactive protein. (Adapted from Reference , with permission.)

Fig. 3

Kaplan-Meier survival curves for outcomes among COPD patients, overlap patients on CPAP, and overlap patients not on CPAP. CPAP treatment was not randomly assigned, which is a source of potential bias, although markers of disease severity were similar, on average, in the treated and untreated groups. (Adapted from Reference , with permission.)