Helical flow in carotid bifurcation as surrogate marker of exposure to disturbed shear.

The main purpose of the study is to verify if helical flow might be a surrogate marker of the exposure to disturbed shear in normal carotid bifurcations. Based on hemodynamic simulations data of 50 carotid bifurcations, we defined appropriate helicity-based bulk flow descriptors and multivariate linear regression analysis was performed to assess the potential for a combination of helicity-based indicators in describing the exposure to disturbed shear. To select the optimal combination of helicity-based descriptors in the regression model, the Akaike information criterion was applied. The identified statistical model is composed of two bulk flow descriptors proposed here to quantify helicity intensity and the balance between counter-rotating helical flow patterns in the flow field. The model revealed the existence of a significant relationship with adjusted squared Pearson's correlation coefficient in the range 0.4-0.7 (P<0.0001). In detail, while a high helicity intensity is instrumental in suppressing flow disturbances, this protective effect could be moderated when one direction of rotation is dominant in the flow field. The in vivo quantification of the bulk flow features emerging in this study would offer a practical way to infer the presence of disturbed shear in large-scale in vivo studies of local risk factors in atherosclerosis.