Clinical Assessment of Endothelial Function

The vascular endothelium plays a critical role in the regulation of arterial function through the synthesis and elaboration of a number of antiatherogenic factors such as nitric oxide (NO). “Endothelial dysfunction” represents a pathophysiological state in which normal homeostatic properties of the vasculature are impaired or lost, thereby supporting a vasospastic, prothrombotic, and proinflammatory atherogenic milieu.1 Impaired arterial function is associated with multiple cardiac risk factors and is detectable early in the progression of atherosclerosis, thus making it an ideal target for primary preventive intervention. It is also fundamental to mechanisms of advanced disease playing a critical role in the pathophysiology of acute cardiovascular syndromes such as myocardial infarction and stroke. The concept that endothelial phenotype serves as an overall barometer of vascular health and may shape clinical disease has prompted significant interest in its clinical assessment.2,3Article see p 371Clinical measurement of endothelial function is challenging, owing to its heterogeneous functions, because no single test provides a comprehensive physiological thumbprint of the entire vascular tree. As such, most studies have focused primarily on the regulation of arterial tone as a means of assessing vasoreactivity through interrogation of NO-mediated, endothelium-dependent vasodilator responses to specific agonists such as acetylcholine or shear stress that normally provoke vasodilation. Paradoxical constriction or attenuated dilator responses develop in disease states, reflecting impaired vasomotor function and reduced NO bioactivity. Although such studies were initially performed in coronary arteries, the technique has migrated to the surrogate forearm circulation, which permits more practical studies that are noninvasive and repeatable.4A number of noninvasive techniques are now available for assessment of forearm vascular reactivity, and presently the most frequently used method involves flow-mediated dilation (FMD) of the brachial artery, using ultrasound imaging. In this method, brachial diameter is measured at baseline and after …