Material transport in the left ventricle with aortic valve regurgitation

This experimental in vitro work investigates material transport properties in a model left ventricle in the case of aortic regurgitation, a valvular disease characterized by a leaking aortic valve and consequently double-jet filling within the elastic left ventricular geometry. This study suggests that material transport phenomena are strongly determined by the motion of the counterrotating vortices driven by the regurgitant aortic and mitral jets. The overall particle residence time appears to be significantly longer with moderate aortic regurgitation, attributed to the dynamics resulting from the timing between the onset of the two jets. Increasing regurgitation severity is shown to be associated with higher frequencies in the time-frequency spectra of the velocity signals at various points in the flow, suggesting nonlaminar mixing past moderate regurgitation. Additionally, a large part of the regurgitant inflow is retained for at least one cardiac cycle. Such an increase in particle residence time accompanied by the occurrence and persistence of a number of attracting Lagrangian coherent structures presents favorable conditions and locations for activated platelets to agglomerate within the left ventricle, potentially posing an additional risk factor for patients with aortic regurgitation

On the Evolution of Flows in Straight Circular Pipes subject to a Localized Transverse Impulsive Body Force

In blunt traumatic aortic injury, it is highly debated whether an abrupt deceleration alone is sufficient to cause aortic rupture. Motivated by this debate, this fundamental study investigates the effects of a localized transverse impulsive body force acting on a straight circular pipe through numerical simulation for both constant and pulsatile inlet velocity profiles. Application of this impulsive force results in a transverse pressure gradient which skews counterclockwise with flow acceleration. This pressure gradient induces two counter-rotating streamwise vortices at the boundaries of the forced section with secondary flows developing in conjunction which act to restore the unforced velocity profile. The development of the secondary flow was observed to occur later for an accelerating flow and earlier for a decelerating flow. A dimensionless parameter, Ψ, was developed to characterize flows based on the ratio of transverse to streamwise pressure gradients. Lower Reynolds number flows (higher Ψ), were observed to be most readily affected by the body force. Maximum skewing of the velocity profile occurred during the impact rather than at the end except for a decelerating flow, with larger skewing occurring for higher Ψ. The temporal decay of kinetic energy was observed to be faster for larger Reynolds numbers and is governed by a power law decay. An alternating exchange in energy between the axial and secondary flows was also observed

In-Vitro Investigation Of The Effect Of A Dysfunctional Bileaflet Mechanical Aortic Valve On Flow Characteristics In The Ascending Aorta

Heart valve replacement is still the optimal solution in young patients with severe symptomatic heart valve disease. In those patients, bileaflet mechanical heart valves (BMHV) are preferred to biological valves because of their higher durability. However, thrombus formation has been reported as a common complication following BMHV implantation despite a permanent anticoagulation therapy. Thrombus formation can lead to valve leaflet dysfunction, a lifethreatening event that requires immediate surgical intervention. This study aims to investigate the fluid dynamics downstream of a dysfunctional bileaflet mechanical aortic valve. A bileaflet ON-X mechanical aortic valve is used with different dysfunctional configurations. In this study, partially and totally blocked configurations of one of the leaflets is investigated relative to its orientation with the sinus of Valsalva. Time-resolved two-dimensional particle image velocimetry measurements are performed to investigate flow field characteristics in the ascending aorta in terms of velocity and vorticity fields and circulation. Vorticity and circulation in the aorta are significantly affected by the valve orientation with respect to the sinus of Valsalva

P0006: Hearts on Fire

ABSTRACT: The left ventricle is the heart's powerhouse, responsible for pumping oxygen- and nutrient-rich blood to each and every tissue throughout the body. By consequence, diseases affecting this laborious chamber are not only more common but often more serious. The fluid dynamics in the healthy left ventricle is characterized by the impulsive formation of a vortex ring during its filling phase which facilitates the following ejection with very little energy loss. In the case of a leaking aortic valve however, the left ventricle will fill from two sides, resulting in the interaction between two pulsatile jets in a confined elastic vessel, marking a new and unique fluid dynamics problem. Here, we show the backward finite-time Lyapunov exponent in the healthy and diseased left ventricles, revealing the attracting Lagrangian coherent structures associated with the aortic (A) and mitral (M) inflows. The background shows the time-frequency spectra of velocity signals over one cardiac cycle taken at the entrance of the mitral (right) and aortic (left) inflows for the healthy (top) and diseased (bottom) cases. The overlay and perceptually-uniform colormap (thanks to Stéfan van der Walt and Nathaniel Smith) are such that the high frequency bursts (up to 200 Hz) occurring early in the filling phase give the appearance of fire

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

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