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1Research Institute for Sport and Exercise Science, Liverpool John Moores University, Liverpool, United Kingdom; 2Department of Physiology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands; and 3School of Sport Science, Exercise and Health, The University of Western Australia, Crawley, Western Australia
Submitted 9 September 2008 ; accepted in final form 12 November 2008
Flow-mediated dilatation (FMD) has become a commonly applied approach for the 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 postdeflation arterial shear. However, the relationship between shear stress and the magnitude of FMD may differ between groups. The aim of this study was to examine the relationship between the brachial FMD and four different indexes of postdeflation shear rate (SR) in healthy children (n = 51, 10 ± 1 yr) and young (n = 57, 27 ± 6 yr) and older (n = 27, 58 ± 4 yr) adults. 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 diameter in each individual (0-ttp). Edge detection and wall tracking of high resolution B-mode arterial ultrasound images were used to calculate the conduit artery diameter. In young adults, the brachial artery FMD demonstrated a significant correlation with the area under the SR curve (SRAUC) 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 SRAUC 0–9 s (r2 = 0.04, P = 0.12). In children and older adults, the magnitude of the brachial artery FMD did not correlate with any of the four SRAUC stimuli. These findings suggest that in young subjects, postdeflation SRAUC correlates moderately with the magnitude of the FMD response. However, the relationship between FMD and postdeflation shear appears to be age dependent, with less evidence for an association in younger and older subjects. Therefore, we support presenting SRAUC stimuli but not normalizing FMD responses for the SRAUC when using this technique.
eliciting stimulus; Doppler; blood flow; methodology
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