Peak systolic or maximum intra-aneurysmal hemodynamic condition? Implications on normalized flow variables

Abstract

Background: CFD has been used to assess intra-aneurysmal hemodynamics. Nevertheless, the lack of patient-specific flow information has triggered the possibility of implementing a wide variety of physiological flow conditions. Due to these uncertainties in the patient flow conditions, the normalization of the intra-aneurysmal hemodynamics is generally conducted.

Purpose: To investigate how intra-aneurysmal and arterial hemodynamics change over time when different physiological flow conditions are imposed.

Material and method: Eleven image-based aneurysm models were used in this study. CFD simulations were performed under pulsatile flows. Velocity magnitude and wall shear stress (WSS) were calculated during one cardiac cycle.

Results: Maximum hemodynamic condition does not necessarily occurred at peak systole. The shifted time from peak systole to the time where the maximum hemodynamic condition occurs inside the aneurysm depends on the aneurysm size, flow rate, surrounding vasculature and the stabilities of flow patterns. Larger shifted times were observed with increasing aneurysm size as well as with reducing the flow rate. Moreover, the maximum hemodynamic condition can occur earlier than peak systole if flow patterns at parent artery change. Differences between peak systolic WSS and maximum WSS can be up to 65%. Moreover, the velocity magnitude and WSS depend on the selected segment of the parent artery, with relatively larger variability near peak systole than the rest of the cardiac cycle. More than 50% of differences were found between two arterial segments arbitrary selected for a given flow rate.

Conclusions: Our results indicate that if the highest intra-aneurysmal stress is calculated, then it is preferable to use the time instance where the maximum WSS occurred instead of the peak systolic WSS. Additionally, the normalization of intra-aneurysmal hemodynamics should be done with variables that do not depend on any arbitrary segment of the parent artery.

Keywords: CFD; Cerebral aneurysms; Flow rate; Hemodynamics; Wall shear stress.