When the endothelium is functioning like it is supposed to, it helps to regulate blood clotting, assists the body's immune response, controls the volume of fluid and the amount of electrolytes and other substances that pass from the blood into the tissues, and produces dilation or constriction of the blood vessels. When endothelial dysfunction is present, the ability to perform one or more of these functions is reduced.
Actually measuring a patient's endothelial function is not routinely done, but is accomplished by measuring the ability of the blood vessels to dilate and/or constrict in response to drug administration.
Endothelial dysfunction is thought to play a major role in the development of atherosclerosis. Endothelial dysfunction can be caused by several conditions, including diabetes or metabolic syndrome, hypertension, smoking, and physical inactivity.