Assessment of Endothelial Reactivity using Brachial Pulse Wave Velocity Response to Shear.

Non-invasive assessment of endothelial reactivity (ER) is done by analyzing the relative change in brachial artery diameter in response to transient forearm ischemia. However, confounding factors such as flow velocity that mediates to dilation of the artery are not considered while calculating the ER index (FMD%). Therefore, we propose a technique for the assessment of ER using the measurement of local pulse wave velocity (PWV) during reactive hyperemia (RH). Continuous diameter and flow velocity were recorded on 10 healthy subjects during baseline, RH and recovery phases and corresponding PWV was calculated using the flow-area (QA) and ln(diameter)-velocity (DU) method. After $54\pm 32s$ of cuff release, PWV increased to 35.53% and 18.45% compared to baseline, and recovered to 45.6% and 55.62% from RH in $78\pm 16s$ for both QA and DU methods. The study was repeated for 2 consecutive days. Repeatable diameter and flow measurements were obtained $(ICC 0.6)$. There existed a significant mean difference in estimation of PWV using QA and DU methods $(P0.05)$. The ICC for PWV derived ER was 30% higher than FMD%. Hence, analyzing temporal response of local PWV to ischemia is a reliable technique for assessment of ER. Direct methods for evaluating PWV during the course of the experiment can be a potential and simpler technique for assessment of ER.