Inflammatory cardiovascular risk markers in obstructive sleep apnoea syndrome

Obstructive sleep apnoea syndrome (OSAS) represents a highly prevalent disease and is recognized as a major public health burden. Large-scale epidemiological studies have demonstrated an independent relationship between OSAS and various cardiovascular disorders. The pathogenesis of cardiovascular complications in OSAS is not completely understood, but given the complexity of the disorder, a multifactorial etiology is likely. Inflammatory processes have emerged as critical in the pathogenesis of atherosclerosis in general and they mediate many of the stages of atheroma formation. Circulating levels of several markers of inflammation have been associated with future cardiovascular risk. These markers include cell adhesion molecules such as intercellular adhesion molecule-1 (ICAM-1) and selectins, cytokines such as tumour necrosis factor alpha (TNF-alpha) and interleukin 6 (IL-6), chemokines such as IL-8, and C-reactive protein (CRP). There is increasing evidence that inflammatory processes also play a central role in the cardiovascular pathophysiology of OSAS. This is supported by cell culture and animal studies identifying a preferential activation of inflammatory pathways by intermittent hypoxia (IH), the hallmark of OSAS. A number of studies have selectively examined the expression of inflammatory factors in OSAS patients with different conclusions. These different findings may have been contributed to by a number of methodological factors such as small subject numbers, inadequately matched study populations, particularly in terms of body mass index (BMI), and inclusion of patients with pre-existing cardiovascular or metabolic diseases. This review will focus on the potential role of various inflammatory markers in OSAS with a critical analysis of the current literature.