Effect of Infrarenal Flow Waveform on Hemodynamics of Abdominal Aortic Aneurysms and Selection of Rheology Models

The infrarenal flow waveform (IFW) demonstrates distinct patterns in response to varying cardiac conditions, raising questions regarding the applicability of the Newtonian model due to variations of the shear rate (|γ ̇ |) distribution across different IFW patterns. This study aims to investigate the hemodynamic conditions generated by different IFW patterns within an Abdominal Aortic Aneurysm (AAA) model, and their impact on the predictions of various rheological models. Numerical simulations are conducted using a simplified, axisymmetric AAA geometry. Three IFW patterns, with varying peak systolic, diastolic, and mean flow rates are applied to the Newtonian, several shear-thinning and viscoelastic (Oldroyd-B) models. The hemodynamic conditions are compared by monitoring important wall shear stress (WSS) descriptors including time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), endothelial cell activation potential (ECAP); with |γ ̇ | distributions and the evolution of vortex patterns. The results demonstrate that even small changes of IFW influence the vortex transport mechanism (VTM) considerably. The transportation time of the vortices from proximal to distal regions within the bulge decreases by up to 50% with an increase in the mean flow rate. These alterations in the VTM affect |γ ̇ | distribution, causing significant variations in the predictions of the rheological models. Even at high mean flow rates, the Newtonian predicts an OSI_(max ) twice as large as that predicted by the Carreau and Power models, along with an ECAP_(max ) that is 5 times greater. However, the differences obtained by the Oldroyd-B model are relatively minor when compared to the viscous shear-thinning models. Therefore, the Newtonian model is not appropriate for the AAA simulations, even in cases characterized by high mean flow rates. Employing the Carreau and Power models, by integrating the patient-specific constants, might exhibit a potential in providing more accurate hemodynamic predictions. Moreover, together with |γ ̇ |, a comprehensive assessment of IFW pattern and resulting VTM prior to the rheological model selection is critical and recommended.