Proposal of hematocrit-based non-Newtonian viscosity model and its significance in intracranial aneurysm blood flow simulation

Abstract

• A hematocrit-based non-Newtonian model was determined from measured blood samples • The model was verified by computational fluid dynamics (CFD) of cerebral aneurysms • The model can predict apparent patient-specific non-Newtonian viscosities • The model does not require a viscosity measurement if a hematocrit is available • The model is a practical viscosity model for CFD simulations of cerebral aneurysms Common viscosity models that do not consider patient-specific viscosity variations have been used in computational fluid dynamics (CFD) analyses of intracranial aneurysms (IAs). However, because blood viscosity varies among patients, these results may be unreliable. Therefore, to perform reliable CFD analyses based on realistic computational conditions, a model that can easily estimate patient-specific viscosities is required. In this study, a practical non-Newtonian viscosity model to estimate patient-specific apparent viscosities from a clinically available hematocrit value was employed using patient data. In addition, the differences between important parameters computed using the measured viscosities, common viscosity models, and this applied model were verified. The apparent viscosities were measured from blood samples using a falling needle rheometer. Finally, a hematocrit-based non-Newtonian model (Hct model) was determined from the measured data obtained from 15 patients. In addition, a patient-specific non-Newtonian viscosity model as a ground truth and additional four simplified Newtonian models were defined. Subsequently, CFD analysis was performed for 21 patient-specific IA morphologies. Two parameters (average velocity and wall shear stress) simulated using the simplified models were compared to those simulated using the patient-specific non-Newtonian viscosity model. Significant differences were not observed in the parameters with the Hct model (P > 0.05) regardless of the inlet boundary conditions, unlike with the other simplified models (P < 0.05). The CFD results obtained using the Hct model were similar to those obtained by the patient-specific viscosity model, which does not require a viscosity measurement. Thus, the Hct model is a practical viscosity model for CFD simulations of IAs.