Abstract 460: Intra- and Inter-Day Reproducibility of Low-Flow Mediated Constriction Response in Young Adults

Abstract

Purpose: When assessing vasomotor endothelial function of the brachial artery by reactive hyperemia, blood flow is stopped and creates a period of low-flow mediated constriction (L-FMC). Little is known about how this parameter influences flow-mediated vasodilation (FMD). The purpose of this study was to better understand this relationship and to determine the intra- and inter-day reproducibility of brachial L-FMC in healthy adults. Methods: Brachial L-FMC and FMD were measured on 26 healthy, young adults (13 males, 13 females; 24.6 ± 2.7 years). Each subject had two assessments conducted on two separate visits, separated by a minimum of seven days. Brachial artery pre-occlusion baseline diameter was imaged during rest and prior to cuff-occlusion. Continuous imaging of the artery was captured during the last 20 seconds of cuff-occlusion to 180 seconds post-cuff release. An L-FMC was considered present if the relative change from pre-occlusion baseline to L-FMC artery diameter was less than -0.1%. Peak FMD was measured as the greatest 10-second average in brachial artery diameter following occlusion compared to pre-occlusion baseline. Results: Overall, there was a strong, positive correlation between increased brachial L-FMC and blunted FMD (visit 1 test 1: r=0.758, p <0.001; visit 1 test 2: r=0.706, p <0.001; visit 2 test 1: r=0.836, p <0.001; visit 2 test 2: 0.857, p <0.001). The reproducibility of intra- and inter-day L-FMC diameter were ICC = 0.627, CV = 54.4% and ICC = 0.734, CV = 43.5%, respectively. Conclusion: The results of the present study suggest that the degree of vasoconstriction to low-flow conditions influences the subsequent maximal dilation during reactive hyperemia. However, L-FMC in young adults is variable as evidenced by the weak inter- and intra-day reproducibility of the measure. Further research is needed to study brachial L-FMC reproducibility among varying subject populations and the implications L-FMC has on the interpretation of FMD results.