Flow Mediated Dilation

Flow-mediated dilation (FMD) refers to dilation (widening) of an artery when blood flow increases in that artery.[1][2] The primary cause of FMD is release of nitric oxide by endothelial cells.[1]

To determine FMD, brachial artery dilation following a transient period of forearm ischemia is measured using ultrasound.[3] Because the value of FMD can be compromised when improperly applied, attempts have been made to standardize the methodology for measuring FMD.[4]

Source: https://en.wikipedia.org/wiki/Flow-mediated_dilation