The endothelial covers the vascular lumen and has been recognized as an organ that responds to physical and chemical signals by producing some vasoactive substances. The early detection of endothelial dysfunction(ED) is essential to intervene and prevent its progression as ED is considered as an initial step of atherosclerosis.
Many studies have been reported the relationship between vascular endothelial cells and cardiovascular disease since Furchgott (Nobel prize in medicine awarded in 1998) proved nitric oxide (NO) was the endothelium derived relaxing factor.
Flow mediated dilation (FMD), developed by Celermajer in 1992, is an index of vasomotor function that measures arterial diameter to dilate in response to a shear stress stimulus that produces a NO dependent response (induced by the cuff inflation and then deflation).


FMD can be calculated as follows: