Key result
Compared to Newtonian fluids, non-Newtonian blood analogues reduced mean oscillatory shear index by 9-19% and predicted smaller regions of low and oscillatory wall shear stress in carotid models.
Why the study?
Carotid bifurcation atherosclerosis is influenced by local variations in wall shear stress magnitude, direction, and flow complexity.
Using a physiological non-Newtonian fluid model alters predicted wall shear stress and flow disturbances in carotid bifurcation models compared to a Newtonian assumption.
Answers are grounded in this paper and cite their sources.
Non-Newtonian fluid models alter carotid shear predictions; leaves open improved clinical risk stratification pending human validation.
The development of atherosclerosis at the carotid bifurcation is impacted by local variations in wall shear stress (WSS) magnitude and direction, as well as flow complexity within the vessel. In this study, stereoscopic particle image velocimetry (PIV) was used to investigate multidirectional WSS and disturbed flow for idealized models of the carotid bifurcation with varying eccentric stenosis of the internal carotid artery (ICA) and both Newtonian (N-fluid) and non-Newtonian (nN-fluid) blood analogues. Turbulence intensity (TI) was reduced with the nN-fluid compared to N-fluid for mild to moderate stenosis, and comparable for more severely stenosed (70%) models. Differences in maximum TI due to viscosity model ranged from 0.02 m/s to 0.06 m/s compared to much larger differences due to geometry of up to 0.29 m/s between mild and severe stenosis. The level of time-averaged WSS (TAWSS) increased with stenosis severity from 5 Pa to 32 Pa, and nN-fluid led to higher WSS on average than N-fluid counterparts. Regions of elevated oscillatory shear index (OSI) demarcated recirculation regions, and mean OSI in the ICA branch was reduced for nN-fluid models by 9-19% compared to N-fluid. Transverse WSS (transWSS) increased with WSS magnitude and again was higher in nN-fluid models. Surface area exposure to shear metrics indicated that a Newtonian viscosity assumption predicted larger regions of low and oscillatory WSS, while predicting reduced regions of high transWSS, in comparison to the more physiological shear thinning fluid.
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DiCarlo et al. (2019) studied Carotid artery stenosis. Non-Newtonian (nN-fluid) blood analogues vs. Newtonian (N-fluid) blood analogues was evaluated on Multidirectional wall shear stress (WSS) and disturbed flow metrics (TI, TAWSS, OSI, transWSS). Compared to Newtonian fluids, non-Newtonian blood analogues reduced mean oscillatory shear index by 9-19% and predicted smaller regions of low and oscillatory wall shear stress in carotid models.
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