Does obstructive sleep apnea cause endothelial dysfunction? A critical review of the literature.

Endothelial dysfunction is characterized by impaired endothelium-dependent vasodilatation and is an independent predictor of adverse cardiovascular consequences. The ease with which endothelial function can be assessed has led to it becoming a useful marker of cardiovascular diseases in research studies. Obstructive sleep apnea (OSA) has been independently associated with endothelial dysfunction which may explain the increased risk for cardiovascular and all-cause mortality in this population. One possible mechanism for the development of endothelial dysfunction in OSA is through the cyclical pattern of hypoxia and re-oxygenation. This creates a haemostatic imbalance in which nitric oxide bio-availability is reduced and pro-inflammatory and pro-thrombotic forces prevail. Furthermore the repair capacity of the endothelium to protect itself against this increased damage is diminished. All of these pathways contribute to vascular disease which ultimately gives rise to adverse cardiovascular consequences. This review aims to provide a critical appraisal of the cross-sectional and interventional studies which have investigated micro- and macro-vascular endothelial dysfunction in OSA with emphasis on randomised controlled studies.