Intra and inter-rater repeatability of brachial artery ultrasound estimates of flow-mediated slowing and flow-mediated dilation.

Flow-mediated slowing (FMS) is a non-invasive measure of endothelial function measured through reactive hyperemia-induced changes in pulse wave velocity (PWV). FMS is suggested to mitigate known pitfalls of flow-mediated dilation (FMD) including suboptimal repeatability and high-operator dependency. However, the few single-rater studies that examined FMS repeatability have shown controversial results and used only regional measurements of PWV, which might not reflect local brachial artery stiffness responses to reactive hyperemia. We assessed the inter- and intra-rater repeatability of ultrasound-based changes in local PWV (FMS) and diameter (FMD). Twenty-four healthy male participants aged 23-75 yr, were examined on two separate days. Reactive hyperemia-induced changes in PWV were calculated using a tailored R-script. The inter- and intra-rater repeatability were tested with the intraclass correlation coefficient (ICC), coefficient of variation (CV), and the Bland-Altman plot estimates. The inter-rater repeatability of FMS (bias: -0.08%; ICC: 0.85; 95% CI: 0.65 to 0.93; CV: 11%) and FMD (bias: -0.02%; ICC: 0.98; 95% CI: 0.97 to 0.99; CV: 7%) showed overall good repeatability over different days. The intra-rater repeatability of FMD (1st rater: bias: 0.27%; ICC: 0.90; 95% CI: 0.78 to 0.96; CV: 14%; 2nd rater: bias: 0.60%; ICC: 0.85; 95% CI: 0.64 to 0.94; CV: 18%) was better than FMS (1st rater: bias: -1.03%; ICC: 0.76; 95% CI: 0.44 to 0.91; CV: 21%; 2nd rater: bias:-0.49%; ICC: 0.70; 95% CI: 0.34 to 0.80; CV: 23%) but not different between raters. Ultrasound-based local measurements of PWV deceleration reactive hyperemia were repeatable among the raters.