Numerical Simulation of Flow Pulse Propagation in Elastic Pipes with Local Cross-Sectional Area Changes

Abstract

Arterial stiffness can be indirectly estimated by measuring the Pulse Wave Velocity (PWV). The PWV can be assessed with non-invasive techniques in patients and it was shown to correlate with geometrical and biomechanical parameters of the artery wall. For straight tubular vessels of constant diameter and thickness, the pressure and flow waves at the inlet propagate with a PWV determined by the Moens-Korteweg (M-K) equation. If the pipe has a heterogeneous cross-sectional area, bifurcations or changes in the wall distensibility, the pressure and flow pulses are no longer simple waves due to reflections and the M-K equation might no longer be valid. This occurs in a vessel with an aneurysm, where the pressure and flow waves undergo significant disturbances. In order to study the effects of an aneurysm on the PWV, we performed three-dimensional simulations of flow pulses in straight elastic pipes including different levels of localized cross-sectional dilatation and wall thickness. The flow was assumed incompressible and with Newtonian behaviour and the pipe wall was modeled as a linear elastic solid. The fluid transport properties, the pipe size and the mechanical properties of the pipe wall had physiologically realistic values similar to those found in representative abdominal aorta aneurysms. Several configurations were analyzed, including variations in the diameter of the dilated region that emulated the aneurysm and in the wall thickness. A PWV was computed based on the Time-To-Foot of the pulse in every transversal plane for different percentages of the maximum local flow rate. The results obtained for the PWV were compared with the M-K prediction and it was found that this theoretical value overestimates the PWV computed from the simulation in the region of area increase. These results might give some insight into clinical applications of PWV estimations for dilated vessels.