The endothelium plays a central role in the initiation, progression and clinical outcomes of atherosclerosis. Flow-mediated dilation (FMD) of the brachial artery is an established non-invasive method used to assess endothelial function. The method was introduced by Celermajer et al. in 1992, and over the last 20 years has become increasingly important since several studies have shown that an impaired FMD response is related to cardiovascular risk factors such as smoking, hypercholesterolemia, hypertension, diabetes and aging, and is an independent predictor of cardiovascular events. Indeed, thousands of papers have established that endothelial dysfunction is one of the earliest detectable signs of atherosclerosis in patients ranging from youngsters to adults.
FMD can be measured by ultrasound imaging, as described in the guidelines of the International Brachial Artery Reactivity Task Force (Corretti et al., 2002). The examination consists in measuring brachial artery diameter at rest and after reactive hyperemia induced by ischemia of the forearm. The measurement is made on a B-mode section of the artery, which is imaged above the antecubital fossa in the longitudinal plane.