Testing endothelial function using ultrasound.

Endothelial dysfunction appears to be a key early event in a number of important cardiovascular disease states, including atherosclerosis and hypertension. Testing endothelial function in vivo has proved challenging. Although the endothelium releases a number of products, no single blood test has yet proved useful to determine normal endothelial function or early abnormalities. The most common test of endothelial function used to date in vivo depends on measuring endothelium-dependent dilatation in response to pharmacologic or physiologic stimuli. This depends mostly on the endothelial ability to release nitric oxide (NO), not only a potent vasodilator but also an inhibitor of platelet aggregation, monocyte adhesion, and smooth muscle proliferation. Over the past decade, endothelium-dependent dilatation has been tested using high-resolution external vascular ultrasound. The major advantage of this method is that it is completely noninvasive, accurate, and reproducible. The major disadvantage is that the coronary arteries cannot be imaged directly with ultrasound, and therefore the test is usually applied to peripheral arteries, such as the brachial or femoral conduit vessels. Using such ultrasound techniques, many groups have documented endothelial dysfunction in children and young adults at risk for atherosclerosis and have performed a variety of studies concerning reversibility of early arterial damage, using potentially important antiatherogenic strategies.