A novel residence-time based blood rheology model: Are we overestimating the non-Newtonian behavior of blood in patient-specific models?

The choice of blood rheology is often considered an important assumption in patient-specific modeling of cardiovascular disease. Blood is known as a non-Newtonian fluid where red blood cell (RBC) aggregation and rouleaux formation contribute to the shear-thinning behavior of blood. Current non-Newtonian models prescribe viscosity as a function of shear rate. However, rouleaux formation requires not only low shear rates but also high residence-time. Herein, a novel hybrid blood rheology model is presented where the non-Newtonian effects are only activated in high residence-time regions where RBCs have enough time to form rouleaux structures. Patient-specific abdominal aortic and cerebral aneurysm models are considered. Highly resolved numerical simulations of blood flow are performed using Oasis, a minimally dissipative solver. Rouleaux formation likelihood is modeled using a backward particle residence-time measure. The hybrid residence-time based non-Newtonian model shows reduced shear-thinning effects and estimates hemodynamics qualitatively indistinguishable and quantitatively close to the Newtonian model. Our results suggest that current non-Newtonian models commonly used in the literature overestimate the non-Newtonian behavior of blood.