Flow mediated dilation of the brachial artery: an investigation of methods requiring further standardization

Twenty-six healthy volunteers underwent repeated brachial artery diameter measurements by B-mode ultrasound. Following baseline diameter recordings we assessed endothelium-dependent flow mediated dilation by inflating a blood pressure cuff either on the upper arm (proximal) or on the forearm (distal).Thirty-seven measures were performed using proximal occlusion and 25 with distal occlusion. Following proximal occlusion relative to distal occlusion, FMD was larger (16.2 ± 1.2% vs. 7.3 ± 0.9%, p < 0.0001) and elongated (107.2 s vs. 67.8 s, p = 0.0001). Measurement of the test repeatability showed that differences between the repeated measures were greater on average when the measurements were done using the proximal method as compared to the distal method (2.4%; 95% CI 0.5–4.3; p = 0.013).These findings suggest that forearm compression holds statistical advantages over upper arm compression. Added to documented physiological and practical reasons, we propose that future studies should use forearm compression in the assessment of endothelial function.Impaired endothelial function is recognized as an early and modulating process in the pathophysiology of atherosclerotic cardiovascular disease[1]. Endothelial function is often quantified by flow-mediated dilation (FMD), which represents the endothelium-dependent relaxation of a conduit artery-typically the brachial artery – due to an increased blood flow. Brachial artery reactivity is a frequently used non-invasive ultrasonographic assessment of FMD that indicates endothelium-dependent response to shear stress[2]. This measure is a marker for increased cardiovascular risk[3], and correlates with impaired endothelium-dependent relaxation in the coronary arteries[4]. Due to lack of a standardized method to measure brachial artery reactivity[5,6], we sought to evaluate the impact of different circulatory occlusion sites (upper arm and forearm occlusion locations) and timing of measurements, in order to establish a consisten