Abstract 3686: Time to Peak Flow-Mediated Dilation as a Measure of Vascular Endothelial Function is both Variable and not Repeatable: Implications for the Accurate Assessment of Endothelial Function
BACKGROUND: The measurement of flow-mediated dilation (FMD) is the most common method to noninvasively assess endothelial function. Traditionally, the evaluation of peak diameter has been made within 60 seconds post cuff deflation although this practice has been questioned by recent findings of temporal heterogeneity in the maximal FMD response.
OBJECTIVES: To quantify and compare the time-course (TC) of FMD of healthy subjects, smokers, as well as patients with hypertension (HTN), heart failure (HF), and coronary artery disease (CAD). A secondary objective was to determine the reliability of TC by testing its repeatability.
METHODS: 40 healthy volunteers, 16 smokers, 17 HTN, 13 CAD, and 14 HF patients were studied. 27 of the healthy subjects were studied on 2 separate occasions ≥ 24 hours apart. FMD was performed by placing a pneumatic cuff above the wrist, distal to the site of arterial measurement, and inflating it to 250 mmHg for 4 minutes and 30 seconds. Arterial diameter was measured continuously for 1 minute before cuff inflation, during cuff inflation and for 4 minutes and 30 seconds after deflation.
RESULTS: The TC values of peak FMD ranged from 11 to 184 seconds in all groups, with only 58% of all subjects achieving maximum dilatation within 1 minute of cuff deflation. TC values were not significantly different between groups (p=0.55). The correlation between TC values of repeated visits in healthy subjects was non-significant (r2=0.013, intraclass correlation coefficient=0.17, p=0.37). The coefficient of repeatability calculated from the Bland-Altman assessment of agreeability was 92.5% with 95% limits of agreement of −103.584 and 89.834.
CONCLUSION: The TC of peak FMD is a highly variable measure often falling outside the traditional 60-second period following cuff deflation, suggesting that continuous arterial diameter measurements are more appropriate than measurements at fixed time points. TC values were not significantly different between healthy controls and those with compromised cardiovascular health status, indicating that the measurement of this variable does not complement that of traditional FMD. The unrepeatable nature of the TC measure suggests that this variable is not useful as an adjunct measure of endothelial health.