Kinematic, Dynamic, and Energy Characteristics of Diastolic Flow in the Left Ventricle

Blood flow characteristics in the normal left ventricle are studied by using the magnetic resonance imaging, the Navier-Stokes equations, and the work-energy equation. Vortices produced during the mitral valve opening and closing are modeled in a two-dimensional analysis and correlated with temporal variations of the Reynolds number and pressure drop. Low shear stress and net pressures on the mitral valve are obtained for flow acceleration and deceleration. Bernoulli energy flux delivered to blood from ventricular dilation is practically balanced by the energy influx and the rate change of kinetic energy in the ventricle. The rates of work done by shear and energy dissipation are small. The dynamic and energy characteristics of the 2D results are comparable to those of a 3D model

Combined CFD/MRI analysis of blood flow in human left ventricle.

The study is to simulate blood flow processes in a human left ventricular (LV) via a combination of computational fluid dynamics (CFD) and magnetic resonance imaging (MRI). Cardiac MR images from normal and patient subjects are segmented and transformed to generate time-resolved two-dimensional (2D) and three-dimensional (3D) moving grids for blood flow using the arbitrary Lagrangian-Eulerian (ALE) formulation of the Navier-Stokes equations. The numerical solution of the Navier-Stokes equations yields pressure gradient in LV which is well correlated with the acceleration and deceleration of the diastolic and systolic flow. The complexity of transient spiral flow produced by the LV dilation and contraction is difficult to analyze and graphically presented. Thus 2D and 3D models of LV have been used to capture the main characteristics of blood flow in LV. The numerical simulation is performed for (i) 2D model of three normal and three heart failure subjects without valve leaflets (ii) 2D model of LV with and without mitral and aortic valve leaflets for a normal case (iii) 3D model of LV for a normal case (iv) 3D model of LV for a patient case before and after surgery. The results of the 2D modeling for three normal and three heart failure cases without valve leaflets show that the number of vortices and pressure difference between basal and apical for normal cases is higher than abnormal cases. The effect of leaflets on fluid patterns during diastole and systole are assessed. The flow patterns are highly altered with presence of valve leaflets. The work-energy equation is well used to quantify the energy transfer from the contraction and dilation of the ventricle to the pulsating flow processes. The results show that the valve leaflets can not change the rate of energy transfer from LV in comparison with LV without valve leaflets. Furthermore, the pressure and vorticity contours in LV associated with net pressure and shear stress on leaflets are derived. The results show low shear stress on leaflets during diastole and systole. In a 3D model of LV, the 3D flow processes are analyzed by calculating the Lagrange stream function on a sequence of longitudinal planes. The net rate of energy transfer from the wall motion to the blood flow in the ventricle is primarily contributed by the rate of kinetic energy. For the normal subject, the work done by shear stresses and the dissipation of energy are rather small. The results of energy characteristics show an optimal filling and ejection for a normal case. Moreover, the kinematic, dynamics and energy characteristics of blood flow in a LV before and after surgery are quantified. All mentioned characteristics are improved for after surgery LV. The Theoretical and numerical assessment of LV blood flow might provide a basic understanding of fluid mechanics of normal and abnormal ventricular dilation and contraction.DOCTOR OF PHILOSOPHY (MAE

Three-dimensional MRI-based computational fluid modeling of the left ventricle for patient before and after surgical ventricular restoration

This study was to simulate the left ventricular (LV) flow in the human heart via combination of computational fluid dynamics (CFD) and magnetic resonance imaging (MRI). MRI was performed for a heart failure (HF) patient before and 4- month after surgical ventricular restoration. The geometry included LV, left atrium (LA) and ascending aorta derived for 25 frames during one cycle from MRI data. After reconstruction of time dependent geometries and producing intermediate grids, 3D CFD modeling is performed for both before and after surgery. Intermediate geometries are generated to provide fine enough time steps for CFD modeling and discontinue time step fashion is used. The results showed that velocity of blood in LV increased after surgery and more powerful vortices exist than before surgery LV. Combined CFD/MRI for patients before and after surgery with different heart diseases could facilitate better understanding of flow pattern and research into ways to optimize and refine surgical treatment approaches in the future

Fluid Dynamic Characteristics of Systolic Blood Flow of the Left Ventricle

Ejection of blood from the left ventricle to the aorta is studied using two-dimensional Navier–Stokes equations, the work-energy equation and the magnetic resonance imaging of a normal ventricular motion. Vortex shedding in the sinuses of Valsalva is dominated by the aortic jet, flow acceleration and valve motion. Momentums produced by ventricular contraction are in concert with vortices in the ventricle for blood ejection. Shear stresses and net pressures on the aortic valve are calculated during valve opening and closing. The rate of work done by shear and the energy dissipation in the ventricle are small. The Bernoulli energy flux delivered to blood from ventricular contraction is practically balanced by energy flux at the aortic root and the rate change of kinetic energy in the ventricle.ASTAR (Agency for Sci., Tech. and Research, S’pore)Accepted versio

Fluid-dynamics modelling of the human left ventricle with dynamic mesh for normal and myocardial infarction : preliminary study

Pulsating blood flow patterns in the left ventricular (LV) were computed for three normal subjects and three patients after myocardial infarction (MI). Cardiac magnetic resonance (MR) images were obtained, segmented and transformed into 25 frames of LV for a computational fluid dynamics (CFD) study. Multi-block structure meshes were generated for 25 frames and 75 intermediate grids. The complete LV cycle was modelled by using ANSYS-CFX 12. The flow patterns and pressure drops in the LV chamber of this study provided some useful information on intra-LV flow patterns with heart diseases