A rational approach to defining principal axes of multidirectional wall shear stress in realistic vascular geometries, with application to the study of the influence of helical flow on wall shear stress directionality in aorta.

The distribution of arterial lesions is attributed by the prevalent mechanistic theory to the proatherogenic role played by low and oscillatory wall shear stress (WSS). However, discrepancies observed when comparing WSS distribution with location of regions with lesion prevalence challenge this theory and have recently stimulated the idea that a role in endothelial mechanosensing is played by WSS multidirectionality, which could contribute to explain the observed discrepancies. Here an approach is presented for analyzing the multidirectional nature of WSS in complex vascular geometries. Using an essential geometric attribute of the vessel (its centerline), the local WSS vector is projected along an "axial" direction (aligned with the tangent to the vessel׳s centerline), and "secondary" direction (orthogonal to centerline׳s tangent), which is related to secondary flow. The WSS projection scheme is applied: (1) to a realistic computational hemodynamic model of human aorta, with the aim to come up with a plausibility checking regarding its consistency; and (2) to investigate if an aortic hemodynamics characterized by different amount and topology of helical flow (HF) could influence WSS directionality. The projection scheme confirmed its consistency and plausibility in realistic arterial geometries and allowed to get insight into the relationship between aortic intravascular fluid structures and WSS directionality. The findings of this study clearly show the potential of the projection scheme as quantitative tool for an in depth investigation of the WSS multidirectional nature. The proposed approach enriches the arsenal of tools available to study and exploit the role played by local hemodynamics in vascular disease.