Flow-mediated dilatation (FMD)

Flow-mediated dilatation (FMD) is a specialist ultrasound test that assesses endothelial function — how well the inner lining of your arteries relaxes and dilates in response to increased blood flow. Endothelial dysfunction is one of the very earliest changes in the development of cardiovascular disease, often present years before any structural change to the artery wall. The test is performed on the brachial artery in the arm. A blood pressure cuff is briefly inflated for five minutes and the artery's response is measured before and afterwards with high-resolution ultrasound. It's painless, uses no radiation, and takes around 30–45 minutes. FMD is used most often in specialist cardiovascular assessment, in research studies, and where a very early marker of vascular health is needed — for example in young patients with a strong family history, or to track the effect of a prevention programme over time.