Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session L15: Bio: Cardiovascular Flow III |
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Chair: Oscar Flores, Universidad Carlos III de Madrid Room: E143/144 |
Monday, November 21, 2016 4:30PM - 4:43PM |
L15.00001: Patient-specific analysis of blood stasis in the left atrium Oscar Flores, Alejandro Gonzalo, Manuel Garcia-Villalba, Lorenzo Rossini, Albert Hsiao, Elliot McVeigh, Andrew M. Kahn, Juan C. del Alamo Atrial fibrillation (AF) is a common arrhythmia in which the left atrium (LA) beats rapidly and irregularly. Patients with AF are at increased risk of thromboembolic events (TE), particularly stroke. Anticoagulant therapy can reduce the risk of TE in AF, but it can also increase the risks of adverse events such as internal bleeding. The current lack of tools to predict each patient's risk of LA thrombogenesis makes it difficult to decide whether to anticoagulate patients with AF. The aim of this work is to evaluate blood stasis in patient-specific models of the LA, because stasis is a known thrombogenesis risk factor. To achieve our aim, we performed direct numerical simulations of left atrial flow using an immersed boundary solver developed at the UC3M, coupled to a 0D model for the pulmonary circulation. The LA geometry is obtained from time-resolved CT scans and the parameters of the 0D model are found by fitting pulmonary vein flow data obtained by 4D phase contrast MRI. Blood stasis is evaluated from the flow data by computing blood residence time together with other kinematic indices of the velocity field (e.g. strain and kinetic energy). We focus on the flow in the left atrial appendage, including a sensitivity analysis of the effect of the parameters of the 0D model. [Preview Abstract] |
Monday, November 21, 2016 4:43PM - 4:56PM |
L15.00002: Vortex and energy characteristics of flow in the left ventricle following progressive severities of aortic valve regurgitation Giuseppe Di Labbio, Lyes Kadem During the heart's filling phase, a notorious vortex is known to develop in the left ventricle (LV). Improper development and poor energetic behavior of this vortex can be correlated with cardiac disease. In particular, during aortic valve regurgitation (leakage of blood through the aortic valve during LV filling), this vortex is forced to interact with a jet emanating from a regurgitant orifice in the valve. The ensuing flow in the left ventricle subject to this disease has yet to be fully characterized and may lead to new indices for evaluation of its severity. As such, this experimental work investigates flow in a model LV subject to aortic regurgitation on a novel double-activation left heart duplicator for six progressive grades of regurgitation (beginning from the healthy case). Double-activation (independent activation of the atrium and ventricle) is critical to the simulation of this pathology. Regurgitation is induced by restricting the closure of the aortic valve to a centralized orifice. The velocity fields for each case are acquired using 2D time-resolved particle image velocimetry. Viscous energy dissipation and vortex formation time are investigated and found to significantly increase as the pathology progresses, while a histogram of vorticity tends toward a shifted and depressed Gaussian distribution. Proper orthogonal decomposition reveals significant disruption of the dominant energetic coherent structures. [Preview Abstract] |
Monday, November 21, 2016 4:56PM - 5:09PM |
L15.00003: Flow in patients with left ventricular thrombus using optimized echo PIV-PTV Kaushik Sampath, Thura T Harfi, Richard T George, Joseph Katz Applications of echocardiographic particle image velocimetry and particle tracking velocimetry (echo PIV-PTV) for characterizing cardiovascular flows have been expanding. It involves acquisition and processing of time-resolved contrast echocardiograms of in vivo flows seeded with micro bubbles. Here, a set of image enhancement and particle tracking methods are implemented on in-vivo data from five patients with history of past or current confirmed left ventricular thrombus (LVT). Our aim is to correlate the LV mixing with thrombogenicity. For cases with persistent LVT and low cardiac efficiency, results show low velocities around the clot as well as low penetration depth of the jet at the exit from the mitral valve and strength of the associated LV vortex. The speeds increase with increasing kinesis (wall motion) and distance from the clot. Patients with recovering cardiac function and diminishing clot size exhibit improved flow, LV vortex strength and penetration even when their efficiency is lower than normal. Trends of the apical washing are consistent with those predicted by the E-wave propagation index. [Preview Abstract] |
Monday, November 21, 2016 5:09PM - 5:22PM |
L15.00004: Experimental study of the intraventricular filling vortex in diastolic dysfunction Arvind Santhanakrishnan, Milad Samaee, Nicholas Nelsen Heart failure with normal ejection fraction (HFNEF) is a clinical syndrome that is prevalent in over half of heart failure patients. HFNEF patients typically show diastolic dysfunction, caused by a decrease in relaxation capability of the left ventricular (LV) muscle tissue and/or an increase in LV chamber stiffness. Numerous studies using non-invasive medical imaging have shown that an intraventricular filling vortex is formed in the LV during diastole. We conducted 2D particle image velocimetry and hemodynamics measurements on a left heart simulator to investigate diastolic flow under increasing LV wall stiffness, LV wall thickness and heart rate (HR) conditions. Flexible-walled, optically clear LV physical models cast from silicone were fitted within a fluid-filled acrylic chamber. Pulsatile flow within the LV model was generated using a piston pump and 2-component Windkessel elements were used to tune the least stiff (baseline) LV model to physiological conditions. The results show that peak circulation of the intraventricular filling vortex is diminished in conditions of diastolic dysfunction as compared to the baseline case. Increasing HR exacerbated the circulation of the filling vortex across all cases. [Preview Abstract] |
Monday, November 21, 2016 5:22PM - 5:35PM |
L15.00005: Patient-specific assessment of left ventricular thrombogenesis risk after acute myocardial infarction: a pilot clinical study L Rossini, A Khan, J C del Alamo, P Martinez-Legazpi, C Pérez del Villar, Y Benito, R Yotti, A Barrio, A Delgado-Montero, A Gonzalez-Mansilla, F Fernandez-Avilés, J Bermejo Left ventricular thrombosis (LVT) is a major complication of acute myocardial infarction (AMI). In these patients, the benefits of chronic anticoagulation therapy need to be balanced with its pro-hemorrhagic effects. Blood stasis in the cardiac chambers, a risk factor for LVT, is not addressed in current clinical practice. We recently developed a method to quantitatively assess the blood residence time (RT) inside the left ventricle (LV) based on 2D color-Doppler velocimetry (echo-CDV). Using time-resolved blood velocity fields acquired non-invasively, we integrate a modified advection equation to map intraventricular stasis regions. Here, we present how this tool can be used to estimate the risk of LVT in patients with AMI. 73 patients with a first anterior-AMI were studied by echo-CDV and RT analysis within 72h from admission and at a 5-month follow-up. Patients who eventually develop LVT showed early abnormalities of intraventricular RT: the apical region with RT>2s was significantly larger, had a higher RT and a longer wall contact length. Thus, quantitative analysis of intraventricular flow based on echocardiography may provide subclinical markers of LV thrombosis risk to guide clinical decision making. [Preview Abstract] |
Monday, November 21, 2016 5:35PM - 5:48PM |
L15.00006: Patient-Specific Modeling of Interventricular Hemodynamics in Single Ventricle Physiology Vijay Vedula, Jeffrey Feinstein, Alison Marsden Single ventricle (SV) congenital heart defects, in which babies are born with only functional ventricle, lead to significant morbidity and mortality with over 30{\%} of patients developing heart failure prior to adulthood. Newborns with SV physiology typically undergo three palliative surgeries, in which the SV becomes the systemic pumping chamber. Depending on which ventricle performs the systemic function, patients are classified as having either a single left ventricle (SLV) or a single right ventricle (SRV), with SRV patients at higher risk of failure. As the native right ventricles are not designed to meet systemic demands, they undergo remodeling leading to abnormal hemodynamics. The hemodynamic characteristics of SLVs compared with SRVs is not well established. We present a validated computational framework for performing patient-specific modeling of ventricular flows, and apply it across 6 SV patients (3SLV $+$ 3SRV), comparing hemodynamic conditions between the two subgroups. Simulations are performed with a stabilized finite element method coupled with an immersed boundary method for modeling heart valves. We discuss identification of hemodynamic biomarkers of ventricular remodeling for early risk assessment of failure. [Preview Abstract] |
Monday, November 21, 2016 5:48PM - 6:01PM |
L15.00007: Velocity and Vorticity in the Right Heart from 4DMRI Measurements Jean Hertzberg, James Browning, Brett Fenster Measurements of blood flow in the human heart were made using time-resolved 3D cardiac magnetic resonance phase contrast flow imaging (4DMRI). This work focuses on blood flow in the right ventricle (RV) and right atrium (RA) in both normal subjects and patients with pulmonary hypertension (PH). Although cardiac output is unchanged early in the disease, details of the flow field differ between normals and PH patients. In particular, vorticity at peak diastole has been found to correlate with PH. The underlying physics of this difference are being explored by a qualitative visual comparison of 3D flow structures in the vena cava, RA, and RV between healthy subjects and pulmonary hypertensive patients. [Preview Abstract] |
Monday, November 21, 2016 6:01PM - 6:14PM |
L15.00008: Hemodynamic Assessment of Compliance of Pre-Stressed Pulmonary Valve-Vasculature in Patient Specific Geometry Using an Inverse Algorithm Ullhas Hebbar, Anup Paul, Rupak Banerjee Image based modeling is finding increasing relevance in assisting diagnosis of Pulmonary Valve-Vasculature Dysfunction (PVD) in congenital heart disease patients. This research presents compliant artery -- blood interaction in a patient specific Pulmonary Artery (PA) model. This is an improvement over our previous numerical studies which assumed rigid walled arteries. The impedance of the arteries and the energy transfer from the Right Ventricle (RV) to PA is governed by compliance, which in turn is influenced by the level of pre-stress in the arteries. In order to evaluate the pre-stress, an inverse algorithm was developed using an in-house script written in MATLAB and Python, and implemented using the Finite Element Method (FEM). This analysis used a patient specific material model developed by our group, in conjunction with measured pressure (invasive) and velocity (non-invasive) values. The analysis was performed on an FEM solver, and preliminary results indicated that the Main PA (MPA) exhibited higher compliance as well as increased hysteresis over the cardiac cycle when compared with the Left PA (LPA). The computed compliance values for the MPA and LPA were 14{\%} and 34{\%} lesser than the corresponding measured values. Further, the computed pressure drop and flow waveforms were in close agreement with the measured values. In conclusion, compliant artery -- blood interaction models of patient specific geometries can play an important role in hemodynamics based diagnosis of PVD. [Preview Abstract] |
Monday, November 21, 2016 6:14PM - 6:27PM |
L15.00009: Image-based modeling of blood flow and oxygen transfer in feto-placental capillaries Philip Pearce, Oliver Jensen During pregnancy, oxygen diffuses from maternal to fetal blood through the placenta. At the smallest scale of the feto-placental vasculature are the “terminal villi”, bulbous structures that are thought to be the main sites for oxygen transfer in the final trimester of pregnancy. The objective of this study is to investigate blood flow and oxygen transfer in the terminal villi of the placenta. Three-dimensional representations of villous and capillary surfaces, obtained from confocal laser scanning microscopy, are converted to finite-element meshes. Simulations of blood flow and oxygen transfer are performed to calculate the vascular flow resistance of the capillaries and the total oxygen transfer rate from the maternal blood. Scaling arguments, which predict the oxygen transfer across a range of Peclet numbers, are shown to be an efficient tool for quantifying the effect of statistical variability and experimental uncertainty. The effect of commonly observed localised dilations in the fetal vasculature on oxygen transfer is quantified using an idealised model in a simplified geometry. The model predicts how, for a fixed pressure drop through a capillary, oxygen transfer is maximised by an optimal shape of the dilation, leading to an increase in oxygen transfer of up to 15%. [Preview Abstract] |
Monday, November 21, 2016 6:27PM - 6:40PM |
L15.00010: Dynamic Mode Decomposition Bio-Markers for Left Ventricle Flow Maria Borja, Pablo Martinez-Legazpi, Yolanda Benito, Raquel Yotti, Francisco Fernandez-Aviles, Javier Bermejo, Juan C. del Alamo Dynamic mode decomposition (DMD) is a tool used in the fluid community to extract a set of modes that describe the underling fluid dynamics in a set of flow fields generated experimentally or by numerical simulations. Despite advances in medical imaging, characterization of some cardiac dysfunctions has remained a challenge and diagnosis is often subjective. This study presents a novel DMD method to objectively characterize left ventricular (LV) flow in healthy volunteers and patients with dilated cardiomyopathy (DCM) and hypertrophic cardiomyopathy (HCM). Our approach is based on assessing temporal evolution dependent mode structures from two-dimensional velocity fields, obtained experimentally using echocardiographic color Doppler velocimetry, and defined with a common unit normal moving LV coordinate system. Using the mode structures as a basis, we reconstruct the flow field, determine the key contributing modes, and obtain a reduce order model. Using 20 healthy volunteers, 20 DCM patients and 20 HCM patients, our results show quantitative and qualitative differences between healthy and in the DCM and HCM patients. This study suggests that temporal evolution dependent modes can be used as bio-markers to asses in-vivo LV flow. [Preview Abstract] |
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