Evaluation of Endothelial Dysfunction: Flow-Mediated Dilation

By the time the clinical findings of atherosclerotic disease appear, involvement is usually at an advanced stage and procedures after this stage are usually palliative or aimed at secondary protection. On the other hand, prevention can be achieved by the detection and treatment of endothelial dysfunction, which is one of the most important changes in the early subclinical stage of atherosclerotic disease. When the systemic involvement of endothelial dysfunction is taken into consideration, checking from the peripheral arteries with noninvasive methods gives one-to-one correct information. Currently, endothelial dysfunction can be detected using simple, inexpensive, and noninterventional methods. Particularly, easily accessible localization of the brachial artery is ideal for the evaluation of endothelial dysfunction. Flow-mediated dilation method (FMD; endothelial-dependent vasodilation), which can be carried out noninvasively with ultrasonography on the brachial artery, is a frequently used method for the assessment of endothelial dysfunction. A sphygmomanometer is placed on the forearm to create a flow stimulation in the brachial artery. The sphygmomanometer is inflated until the systolic pressure is above 50 mm Hg, thus stopping the antegrade blood flow and creating ischemia. Consequently, vasodilation occurs at the resistance arteries distal to where the flow is blocked. When the sphygmomanometer is deflated, a reactive hyperemia occurs in the brachial artery. The % difference between the diameter measured after reactive hyperemia and the basal diameter is taken as FMD. The effects of the treatments on endothelial dysfunction can be monitored with this method. Studies have shown that angiotensin-converting enzyme (ACE) inhibitors, angiotensin 1 (AT1) receptor blockers, latest-generation beta blockers such as nebivolol and carvediol, statins, estrogen treatment, diet, and exercise increase FMD. Before this method becomes a part of routine clinical evaluation of cardiovascular disease (CVD) risk, measurement technique and FMD values need to be standardized.