In vitro characterization of Lagrangian fluid transport downstream of a dysfunctional bileaflet mechanical aortic valve

Ahmed Darwish,Giuseppe Di Labbio,Wael Saleh,Lyes Kadem

doi:10.1063/5.0021372

Ahmed Darwish, Giuseppe Di Labbio + Show 2 more

Open Access

https://doi.org/10.1063/5.0021372

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Journal: AIP Advances	Publication Date: Sep 1, 2020
Citations: 6	License type: cc-by

Affiliation: Concordia University, Polytechnique Montréal

Abstract

This experimental study aims to explore the Lagrangian nature of fluid transport downstream of a bileaflet mechanical aortic valve under different malfunction scenarios that might be encountered clinically. Time-resolved planar particle image velocimetry measurements are performed to extract instantaneous velocity fields downstream of the bileaflet mechanical valve implanted in an elastic aortic model. The results show an increase in particle residence time with the severity of malfunction. This is attributed to the expansion of the recirculation regions downstream of the valve. The time-evolution of Lagrangian coherent structures over one cardiac cycle (using finite-time Lyapunov exponent fields) shows the effect of valve dysfunction on the material transport and its barriers inside the aorta. The unbalanced flow through the dysfunctional leaflets leads to a significant redistribution of the LCS, thus the fluid transport along the ascending aorta. Moreover, a new technique for the evaluation of the highest accumulated shear stresses is applied along the Lagrangian trajectory of particles being released from the extracted Lagrangian coherent structures where the highest stretching occurs. Finally, the induced non-laminar flow behavior by the valve dysfunction is analyzed using the time-frequency spectra of velocity signals at selected points in the ascending aorta.

Highlights

The aorta is the largest artery that carries the main blood supply in our body
Two interesting points can be noticed from the particle residence time (PRT) and particle residence index (PRI) analyses: (1) the particles remaining in the ascending aorta beyond two consecutive cycles, despite their low relative percentage, have the tendency to be more localized in a region lower than one valve diameter from the valve
If the dysfunctional leaflet is the one facing the sinus of Valsalva (SLP and sinus leaflet totally blocked (SLT)), the percentage of particles retained in the ascending aorta appears to be significantly higher

Summary

Introduction

The aorta is the largest artery that carries the main blood supply in our body. It is connected to the left ventricle through a native valve called the aortic valve (AV). Another complication that appears with BMAVs is pannus formation around the suture location.10 Both thrombosis and pannus formation can restrict the movement of the leaflets causing a significant disturbance to the flow inside the ascending aorta.. The trajectories of platelets become longer within the wake region leading to a larger harvest of shear stresses. They observed a phenomenon called vortex pairing, where adjacent vortices combine to form a larger vortical structure that brings activated platelets together.. Bluestein et al. reported the shear stress induced on the platelets when the valve is tilted relative to the aortic root They noticed that the platelets near the leaflets can be activated within only one cardiac cycle.. In the case of leaflet dysfunction, velocity magnitudes in the ascending aorta downstream of the free moving leaflet increase significantly exceeding the normal expected values. with an increasing degree of dysfunction, the vortical structures downstream of the valve occupy a larger area in the ascending aorta, which can promote platelet aggregation.

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