Brachial Artery Response to Reactive Hyperemia: Describing High-Flow-Mediated Constriction in Healthy Children, Adolescents and Adults, and the Intra- and Inter-day Reproducibility of High-Flow-Mediated Constriction Response in Adults

Abstract

Endothelial dysfunction has been shown to be an important precursor in the atherosclerotic process. A widely used, non-invasive method of assessing endothelial function is flow-mediated dilation (FMD). This method of vascular health assessment utilizes ultrasound imaging and has historically focused on the degree of vessel dilation in response to reactive hyperemia to ascertain endothelial function. The brachial artery's ideal vessel diameter and its nitric oxide-mediated response to reactive hyperemia make it the preferred site of assessment. Also, a strong correlation between endothelial function in coronary and brachial arteries has been reported, which allows brachial FMD to be a surrogate measure of coronary function. Additionally, many studies have shown impairment of FMD in response to a range of cardiovascular risk factors and has been inversely associated with future CVD events. However, a biphasic response, where vessel constriction occurs prior to dilation, has been observed during reactive hyperemia. The constriction phase during reactive hyperemia has been largely overlooked in FMD research, termed high-flow-mediated constriction (H-FMC). Therefore, the purpose of the following dissertation was to perform a cross-sectional examination of children, adolescents and adults to quantify the frequency and magnitude of H-FMC, determine potential influences of sex, age, body composition, cardiovascular and metabolic factors on H-FMC, and report the reproducibility of an H-FMC in young adults to lend further insight to the existing body of research surrounding FMD and H-FMC assessment.