Evaluation of Macrocirculatory Endothelium-Dependent and Endothelium-Independent Vasoreactivity in Vascular Disease

Macrocirculatory endothelium-dependent and independent vasodilatation is integral to tissuebed oxygen delivery and homeostasis. Dysfunction of macrocirculatory vasoreactivity is a precursor to atherosclerosis and occurs in a similar fashion in multiple tissue beds long before the onset of symptoms. Impaired macrocirculatory vasodilatation has been shown to occur in certain disease states including diabetes mellitus, hypercholesterolemia, chronic renal failure, peripheral arterial atherosclerosis, and abdominal aortic aneurysms, as well as secondary to smoking, advanced age, menopause, high-fat diet, and sedentary lifestyle. Brachial artery vasoreactivity is a noninvasive means of assessing macrocirculatory vasodilatory capacity that may help identify patients at increased risk for peripheral and cardiovascular disease and allow for objective assessment and monitoring of treatment. Endothelium-dependent vasoreactivity, or flow-mediated dilatation, is measured after brachial artery occlusion with a pneumatic blood pressure cuff, and endothelium-independent vasoreactivity is measured after the administration of sublingual nitroglycerin. The accuracy of brachial artery vasoreactivity is dependent on hematologic variables, as well as diurnal, day-to-day, ultrasound operator, and reader variations; however, the overall coefficient of variation is only 1.8%. We discuss the importance of the macrocirculation, investigative methods for evaluating macrocirculatory vasoreactivity, and review the literature of vasoreactivity in these different states.