The influence of transient physiological factors on patient-specific cerebral aneurysm hemodynamics*

Hemodynamic factors are known to play a critical role in the growth and rupture of an intracranial aneurysm (IA). However, conflicting findings regarding the specific role of individual flow parameters have been reported, suggesting confounding factors not considered among studies to date may exist. Current studies, regardless of the modality used, consider aneurysmal flow fields only from a single, fixed set of inflow conditions, typically assumed by or based on in vivo 4D-Flow magnetic resonance imaging (MRI) data. However, IAs inherently exist within a dynamic system, and are subject to transient factors. For example, changes in the patient’s vitals alter aneurysmal inflow conditions; the aneurysm is rotated depending on if the patient is standing, laying down, or moving actively; etc. It is not clear the extent to which these factors alter aneurysmal hemodynamics or affect IA progression. In this work, we address this question. Using 4D particle tracking velocimetry (PTV), we evaluate how changes to heart rate, blood pressure, and aneurysm orientation affect hemodynamic factors affect the flow in patient-specific IA geometries. We also evaluate how vessel compliance may affect IA hemodynamics. Flow parameters known to influence aneurysm progression including wall shear stress (WSS), oscillatory shear index (OSI), flow complexity, and high-frequency velocity fluctuations are evaluated across the varying physiological conditions. Overall, through this analysis, we comment on the extent to which transient physiological factors must be considered when studying IA flow and risk of progression as well as if these factors may have contributed to the conflicting results reported to date.