Biology of peripheral blood cells in obstructive sleep apnea--the tip of the iceberg.

Obstructive sleep apnea (OSA), a highly prevalent breathing disorder in sleep, characterized by intermittent and recurrent pauses in respiration, has emerged as an independent risk factor for cardiovascular morbidity and mortality. Accumulated evidence implicates Leukocyte-endothelial cell activation and adhesion as critical components that induce inflammation and injury to the vasculature resulting in the development of cardiovascular complications. Similar cellular interactions were described in conditions of ischemia/reperfusion, and various components of the metabolic syndrome as hypercholesterolemia and hypertension. The hallmark of sleep apnea--the multiple cycles of hypoxia/reoxygenation--promote oxidative stress and inflammation. These facilitate increased interactions of blood cells with endothelial cells, resulting in endothelial cell injury and dysfunction. Such events can promote atherosclerosis and the development of cardiovascular morbidities in OSA. However, inter-individual differences in response to intermittent hypoxia and activation of anti-inflammatory cytokine profiles in T lymphocytes can serve as protective mechanisms.