Vortex dynamics and transport phenomena in stenotic aortic models using Echo-PIV

TL;DR

This study combines ultrasound imaging with advanced flow analysis techniques to investigate blood flow and vortex behavior in realistic models of stenotic aortas, revealing how flow structures evolve with different occlusion levels and flow conditions.

Contribution

It introduces a novel ultrasound-based method integrating Eulerian and Lagrangian descriptors to analyze flow dynamics in realistic arterial models, advancing understanding of vortex transport and stenosis progression.

Findings

Vortex propagation velocity increases with Reynolds number.

Lagrangian Coherent Structures influence flow transport behind stenosis.

A significant portion of fluid remains in the stenosis over multiple pulsatile cycles.

Abstract

In this work, we propose a novel approach which combines ultrasound with Eulerian and Lagrangian descriptors, to analyse blood flow dynamics and fluid transport in stenotic aortic models with morphology, mechanical and optical properties close to those of real arteries. To this end, vorticity, particle residence time (PRT), particle's final position (FP) and finite time Lyapunov's exponents (FTLE) were computed from the experimental fluid velocity fields acquired using ultrasonic particle imaging velocimetry (Echo-PIV). For the experiments, CT-images were used to create morphological realistic models of the descending aorta with 0%, 35% and 50% occlusion degree with same mechanical properties as real arteries. Each model was connected to a circuit with a pulsatile programmable pump which mimics physiological flow and pressure conditions. The pulsatile frequency was set to 0.9 Hz (55 bpm) and the upstream peak Reynolds number (Re) was changed from 1100 to 2000. Flow in the post-stenotic region was composed of two main structures: a high velocity jet over the stenosis throat and a recirculation region behind the stenosis where vortex form and shed. We characterized vortex kinematics showing that vortex propagation velocity increases with Re. Moreover, from the FTLE field we identified Lagrangian Coherent Structures (i.e. material barriers) that dictate transport behind the stenosis. The size and strength of those barriers increased with Re and the occlusion degree. Finally, from the PRT and FP, we showed that independently of Re, the same amount of fluid remains on the stenosis over more than a pulsatile period, which combined with large FTLE values may provide an alternative way to understand stenosis growth.