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Combined effects of sleep disordered breathing and metabolic syndrome on endothelial function: the Wisconsin Sleep Cohort study.

STUDY OBJECTIVES
To examine the combined impact of sleep disordered breathing (SDB) and metabolic syndrome (MetS) in endothelial dysfunction.


DESIGN
Cross-sectional assessment of endothelial function, MetS and SDB status in a population-based sample.


SETTING
Community-based cohort.


PARTICIPANTS
Participants (n = 431) from the Wisconsin Sleep Cohort were studied between 2004 and 2007. MetS was defined following the National Cholesterol Education Program criteria. SDB severity was defined by the apnea-hypopnea index ([AHI] events/h of sleep) during overnight polysomnography. Fasting lipids, glucose, and insulin were measured and homeostasis model assessment was calculated to quantify insulin resistance (HOMA-IR). Multivariable linear regression was used to assess associations of brachial artery flow-mediated dilation (FMD) with SDB, MetS, and their interaction.


INTERVENTION
None.


MEASUREMENTS AND RESULTS
Participants averaged 60.2 years of age (SD 7.8 years), 44% were female, and 97% Caucasian. MetS was present in 35%; 22% had AHI ≥ 15 events/hour. Of the no-MetS group, 7% had AHI ≥ 15 events/hour. FMD (mean 5.5%; SD 3.5%) was inversely associated with age (r = -0.16, P = 0.001) and mean brachial artery diameter (r = -0.29, P < 0.001). Multivariate linear models adjusted for CVD risk factors showed that the negative association between SDB and FMD was present among subjects with MetS (β FMD(per unit log2(AHI+1)) = -0.55%, P = 0.014), but not among subjects with normal metabolic function (β = 0.13, not significant), P for interaction = 0.011.


CONCLUSION
Sleep disordered breathing and concurrent metabolic syndrome are synergistically associated with worse endothelial function. Individuals with both of these conditions appear to be at a significantly higher risk for cardiovascular disease complications.