Wall shear rate and brachial artery flow-mediated dilatory response between healthy young and older populations using multi-gate spectral Doppler ultrasound

Background: Ageing is associated with an impaired brachial artery flow-mediated dilatation (FMD) response and a reduced wall shear rate (WSR) stimulus may contribute to this response. However, a detailed analysis of the WSR-FMD response is lacking due to inherent difficulties of WSR estimation near the arterial wall by conventional ultrasound. We have overcome this limitation by using an integrated multi-gate Doppler FMD evaluation system, and in this study, we compared the WSR-FMD relationship between a healthy young and older population. Methods: Data from 33 young (YNG: 27.5±4.9yrs) and 33 older (OLD: 64.9±3.6yrs) individuals were analysed. FMD was assessed using Ultrasound Advanced Open Platform (ULA-OP). Acquired raw data were post-processed using custom-designed software to obtain WSR and diameter parameters. Results: Peak WSR [WSRpk: 635(585–685) vs 424(374–473) s−1] and absolute WSR increase [WSRΔ: 548(504–592) vs 356(313–400) s−1] were greater in YNG than OLD (both p < 0.05). WSR area under the curve until its return to baseline value (WSRauc) was also greater in YNG than OLD [18632(16395–20868) vs 13049(10812–15285) au, p < 0.05]. WSRpk, WSRΔ and WSRauc were associated with both absolute and percentage diameter increases in YNG (all p < 0.05). However, none of the WSR parameters in OLD were associated with absolute or percentage diameter increases. Conclusions: These results demonstrate 1) a reduced WSR stimulus during reactive hyperaemia in OLD compared with YNG, and 2) the absence of an association between WSR parameters and FMD response in OLD. These observations suggest that in older adults, diminished WSR together with WSR-independent factors are important determinants of the FMD response.