Computational Analysis of Flow-Induced Stresses in Cerebral Aneurysms during Normal and Exercise Conditions

Abstract-This study numerically investigates the hemodynamic behavior of cerebral aneurysms under two distinct physiological states–rest and exercise–using a non-Newtonian Casson fluid model. Four patient-specific aneurysm geometries located in the anterior cerebral artery (ACA), middle cerebral artery (MCA), internal carotid artery (ICA), and basilar artery (BAS) were simulated using the finite-volume solver ANSYS Fluent. Blood was modeled as an incompressible Casson fluid with a hematocrit level of 0.42, and the vessel walls were assumed rigid (non-FSI). Transient simulations were performed for three cardiac cycles with a time step of 0.00297 s. Time-dependent inlet mass flow and outlet pressure waveforms were applied to reproduce physiological pulsatility at both rest and exercise states. Results demonstrated that exercise significantly amplifies flow velocity, wall shear stress (WSS), and pressure throughout the aneurysm domain. The maximum and average WSS increased by more than threefold under exercise conditions, reaching peak systolic values up to 10 Pa, while wall pressure rose proportionally with flow rate and systemic pressure. Time-averaged WSS (AWSS) and oscillatory shear index (OSI) analyses revealed that exercise enhances shear uniformity but reduces low-shear oscillatory regions, suggesting a shift toward more directional, high-energy flow. Increased vorticity and jet impingement during exercise further intensified the local hemodynamic stresses at the aneurysm neck. These findings highlight the critical influence of physiological activity on intra-aneurysmal flow dynamics and may provide insights into the biomechanical factors governing aneurysm growth and rupture risk.