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1 University Medical Centre Nijmegen
2 Liverpool John Moores University
3 Radboud University Nijmegen Medical Centre
* To whom correspondence should be addressed. E-mail: d.thijssen{at}fysiol.umcn.nl.
Flow-mediated dilatation (FMD) has become a commonly applied approach for assessment of vascular function and health in humans. Recent studies emphasize the importance of 'normalizing' the magnitude of FMD to its apparent eliciting stimulus, the post-deflation arterial shear. However, the relation between shear stress and magnitude of FMD may differ between groups. The aim of this study was to examine the relationship between the brachial FMD and 4 different indices of post deflation shear rate (SR) in healthy children (n=51, 10±1 yrs), young (n=57, 27±6 yrs) and older (n=27, 58±4 yrs) subjects. SR was calculated from deflation (time 0) until 9 s (peak), 30 s (0-30), 60 s (0-60) or until the time-to-peak peak diameter in each individual (0-ttp). Edge-detection and wall-tracking of high resolution B-mode arterial ultrasound images was used to calculate conduit artery diameter. In young adults, brachial artery FMD demonstrated a significant correlation with the SR-AUC 0-30 s (r2=0.12, P=0.009), 0-60 s (r2=0.14, P=0.005) and 0-ttp (r2=0.14, P=0.005), but not for the peak SR-AUC 0-9 s (r2=0.04, P=0.12). In children and older adults, the magnitude of brachial artery FMD did not correlate with any of the 4 SR-AUC stimuli. These findings suggest that in young subjects, post-deflation SR-AUC correlates moderately with the magnitude of the FMD response. However, the relationship between FMD and post deflation shear appears to be age dependent, with less evidence for association in younger and older subjects. Therefore, we support presenting SR-AUC stimuli, but not 'normalizing' FMD-responses for the SR-AUC when utilizing this technique.
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