Flow-Mediated Dilation (FMD)

FMD was performed with high-resolution vascular ultrasound (Vivid i, GE Medical Systems, Tirat Carmel, Israel), by measuring the vessel dilation (endothelium-dependent dilation) of the brachial artery, as previously described.26 Briefly, subjects lay at rest for at least 10 minutes and a first resting scan was recorded. Then, an increased flow was induced by inflation of a sphygmomanometer cuff, located distally to the brachial artery in the forearm, to supra-systolic pressure (about 20 to 30 mmHg) for 5 minutes. The cuff was emptied and the flow and dilatation of the vessel, provided by the shear stress, was recorded. The difference between the basal diameter and the diameter after dilation was evaluated.