However, in the low-velocity areas, the true viscosity is much higher than this constant, when non-Newtonian rheological models could simulate the blood viscosity variations in different shear strain rates ( Gijsen et al., 1999 Jahangiri et al., 2017). With increasing flow velocity and shear strain rate, blood flows more smoothly ( Moon et al., 2014) and its viscosity decreases toward a constant, which has been commonly used as the viscosity of blood in a Newtonian model ( Jahangiri et al., 2017). In most of the previous CFD studies on ICAS, blood was simulated as a Newtonian fluid for simplicity ( Leng et al., 2014, 2019 Nam et al., 2016 Liu et al., 2018 Chen et al., 2020), despite the fact that blood is a non-Newtonian fluid with a shear-thinning nature ( Nader et al., 2019). Both indices have been associated with the risk of stroke relapse in patients with symptomatic ICAS: those with a lower PR (i.e., larger translesional pressure gradient) and excessively elevated focal WSS at the ICAS lesion had significantly higher risk of recurrent stroke despite optimal medical treatment ( Leng et al., 2019). On the other hand, the relative change of wall shear stress (WSS) at the stenotic throat as compared to WSS at proximal “normal” vessel segment, has also been proposed to reflect the hemodynamic impact of an ICAS lesion on plaque growth and rupture ( Lan et al., 2020). For instance, translesional pressure ratio (PR), calculated as the ratio of the pressures distal and proximal to an ICAS lesion obtained in a CFD model, has been put forward to reflect the hemodynamic significance of ICAS ( Liebeskind and Feldmann, 2013). In recent years, computational fluid dynamics (CFD) modeling based on conventional neurovascular imaging has been applied to simulate in vivo cerebral blood flow and quantify cerebral hemodynamic metrics in the presence of ICAS, which cannot be achieved with conventional neurovascular imaging alone ( Liebeskind et al., 2016 Linfang Lan, 2017 Liu et al., 2018 Chen et al., 2020).Ĭomputational fluid dynamics modeling studies have indicated that global and focal cerebral hemodynamics may play an important role in governing the risk of stroke recurrence in patients with symptomatic ICAS ( Leng et al., 2014, 2019). Intracranial atherosclerotic stenosis (ICAS) is a major cause for ischemic stroke and transient ischemic attack (TIA) in Asian populations ( Wong, 2006). In the transient model, the rheological difference of WSS areas with low WSS was enhanced, especially during diastolic period.Ĭonclusion: Newtonian fluid model could be applicable for PR calculation, but caution needs to be taken when using the Newtonian assumption in simulating WSS especially in severe ICAS cases. As to WSS, in static models (virtual and patient-specific), the rheological difference was not obvious in areas with high WSS, but observable in low WSS areas. Results: In all the static and transient simulations, the Newtonian/non-Newtonian difference on PR value was negligible. In all the simulations, we compared the PR and WSS values in CFD models derived with Newtonian, Casson, and Carreau-Yasuda fluid assumptions. We measured translesional pressure ratio (PR) and wall shear stress (WSS) values in all CFD models, to reflect the changes in pressure and WSS across a stenotic lesion. We also performed transient simulations on another patient-specific model. We performed static simulations on these models with Newtonian and two non-Newtonian (Casson and Carreau-Yasuda) fluid models. We also constructed CFD models in three patients with ICAS of different severities in the luminal stenosis. Methods: We built a virtual artery model with an eccentric 75% stenosis and performed static CFD simulation. We aimed to investigate the differences of cerebral hemodynamic metrics quantified in CFD models built with Newtonian and non-Newtonian fluid assumptions, in patients with ICAS. 4Shenzhen Research Institute, The Chinese University of Hong Kong, Shenzhen, Chinaīackground: Newtonian fluid model has been commonly applied in simulating cerebral blood flow in intracranial atherosclerotic stenosis (ICAS) cases using computational fluid dynamics (CFD) modeling, while blood is a shear-thinning non-Newtonian fluid.
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