One of the major developments in medicine during the last two decades is the delineation of the role of endothelium in the development of cardiovascular disease. Soon after the first observations in animals, methods were devised that could evaluate endothelial function in humans. The initial methods were invasive, but subsequently noninvasive methods were established. During the last decade, these noninvasive methods have been standardized and widely used for the clinical research, while the possibility of using them in standard clinical practice is also raised. In this chapter we review the most commonly employed methods for assaying endothelium dependent vasodilation in both the macro- and microcirculation.

MACROCIRCULATION

Endothelium-Dependent versus

Endothelium-Independent Vasodilation

Although the endothelium regulates the vascular tone by the balanced secretion of vasoconstrictors and vasodilators, it should be remembered that this is mainly achieved by the action of these vasomodulators on the vascular smooth muscle cell (VSMC). This can have serious implications in the interpretation of the results of various tests in humans. Thus, in the theoretical case in which VSMC vasodilatory capacity is impaired, those tests that assess the ability of endothelial cells (ECs) to produce vasodilators such as nitric oxide (NO) –; endothelium-dependent vasodilation – will be abnormal. Therefore, correct interpretation of the data requires the consideration of both the endothelium-dependent and -independent vasodilation measurements that are collectively referred to as vascular reactivity measurements.

Venous Plethysmography

Venous plethysmography, or venous occlusive plethysmography, was the first technique used to measure vascular reactivity (1). This technique employs a mercury in-silastic strain gauge coupled to a plethysmograph. The gauge is placed at the upper third of the forearm.