Nocturnal hypoxemia coupled with chronic obstructive pulmonary disease (COPD) increased the risk for cardiovascular events and mortality in female patients with suspected obstructive sleep apnea (OSA), according to a study published in the Annals of the American Thoracic Society.

A cohort of patients seen at an urban academic hospital in Toronto, Canada, whose healthcare data were linked to provincial health administrative data was enrolled in the study. The cohort comprised 10,149 patients with suspected OSA who underwent a first diagnostic polysomnography between 1994 and 2010.

Investigators considered severe OSA as defined by an apnea hypopnea index (AHI) >30 events per hour and the degree of nocturnal hypoxemia as 2 primary OSA exposures of interest. Time from the first diagnostic sleep study to either the first hospitalization for myocardial infarction, congestive heart failure, or stroke; cardiac revascularization; or all-cause mortality comprised the primary outcome.

Patients with COPD

Approximately 30% of patients had AHI >30 events per hour, 12% had COPD, and 25% had spent ≥10 minutes in sleep with an oxygen saturation of <90%. During a median 9.4-year follow-up, 16.4% of the population experienced one of the primary outcomes. Patients with COPD who had spent ≥10 minutes in sleep with oxygen saturation level <90% had a greater risk for experiencing one of the primary outcomes (hazard ratio, 1.91; 95% CI, 1.60-2.28).

Synergistic effect

A synergistic effect between COPD and nocturnal hypoxemia was observed in female patients (related excess risk due to interaction [RERI]=1.18; 95% CI, 0.05-2.30) but not in male patients (RERI=–0.08; 95% CI, –0.47 to 0.32). The co-occurrence of AHI >30 events per hour and COPD in untreated individuals (hazard ratio, 2.01; 1.55-2.62) was associated with the highest risk for one of the primary outcomes.

“In patients with COPD and suggestive symptoms who are diagnosed with nocturnal hypoxemia, [polysomnography] may be a useful tool to exclude coexistent OSA as a treatable cause of nocturnal hypoxemia,” the researchers concluded, “given that pulse oximetry tracing interpretation has been shown to have solely modest diagnostic value in identifying OSA in patients with moderate to severe COPD.”