Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session L30: Biological Fluid Dynamics : Cardiac Flows I |
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Chair: Niema Pahlevan, USC Room: 612 |
Monday, November 25, 2019 1:45PM - 1:58PM |
L30.00001: Designing a Low Reynolds Number Ejector Pump for Infants with a Single Ventricle Dongjie Jia, Mahdi Esmaily, Matthew Peroni, Tigran Khalayan Simulations have shown modifying stage-1 operation on single ventricles to incorporate an ejector pump presents several advantages, including improved oxygen delivery and low heart load. However, the efficient operation of an ejector pump relies on sufficient mixing to transfer energy and pump low-pressure fluid. Thus, the standard design of an ejector pump cannot operate effectively in infants where the blood flow Reynolds number is low. To address this issue, we present a novel design of an ejector pump that can effectively operate at a low Reynolds number environment. The performance of this ejector pump will then be demonstrated through implementation in the assisted bidirectional Glenn procedure that treats Hypoplastic heart syndrome. The further potential use of the device will be discussed. [Preview Abstract] |
Monday, November 25, 2019 1:58PM - 2:11PM |
L30.00002: Artificial Right Atrium Design for Univentricular Heart Patients Heng Wei, Cynthia Herrington, John Cleveland, Vaughn Starnes, Niema Pahlevan Infants born with single ventricle pose a large challenge. The Fontan operation for univentricular heart patients creates a unique circulation whereby systemic veins get connected to the pulmonary arteries without passing through the cardiac chambers. As getting older, individuals with single ventricle tend to develop long-term complications like heart failure and require heart transplant. Previous studies have attempted to mechanically support these patients with standard left ventricular assist devices (LVAD). The primarily difficulty in establishing mechanical support for Fontan is that there is no blood reservoir in the closed Fontan circulation. An artificial right atrium is one of the treatments that could be implanted into the Fontan graft and provide a reservoir for blood and allow for full circulatory support. We investigated the optimum geometrical design of artificial right atrium by minimizing the particle residence time to reduce the chance of blood stagnation and clotting. Non-Newtonian Fluid-Structure Interaction (FSI) simulations employing Lattice-Boltzmann and immersed boundary method were utilized to evaluate Fontan hemodynamics. Our results indicate that the artificial atrium optimum shape is similar to the real human atrium. [Preview Abstract] |
Monday, November 25, 2019 2:11PM - 2:24PM |
L30.00003: Is 3D Measurement Necessary for Quantifying Fluid Mechanics in a Left Ventricle? Zhenglun Wei, Keshav Kohli, Yingnan Zhang, Vahid Sadri, Ikechukwu Okafor, Ajit Yoganathan Left ventricle (LV) fluid mechanics has been broadly investigated \textit{in vivo}, \textit{in vitro}, and \textit{in silico} over the past few decades. Previous studies have successfully demonstrated clinical relevance for hemodynamic metrics of the LV, e.g., energy dissipation, washout time, and vortex formation time, etc. A majority of these studies extracted conclusions based on 2D measurements. Additionally, 2D phase-contrast magnetic resonance imaging (PC-MRI) and echocardiography are the most common measurement tools in clinical practice since current 3D tools have technical challenges or have significantly higher demand. Unfortunately, previous literature marginally discussed the validity of reducing the order of LV hemodynamic metrics (from 3D to 2D). In this study, an \textit{in silico} LV model is developed and firstly validated against 4D PC-MRI in an \textit{in vitro}, patient-specific, 3D LV phantom. Then, the settings of the \textit{in silico} model are adjusted to mimic diseased states. The center-plane of the 3D phantom is extracted to represent a 2D measurement plane. The necessity of 3D measurement is elucidated based on the comparison between the LV hemodynamic metrics obtained from 3D and 2D measurements. [Preview Abstract] |
Monday, November 25, 2019 2:24PM - 2:37PM |
L30.00004: Theoretical and Experimental Evidence for the Role of Vorticity in Ventricular Flow Alejandro Roldán-Alzate, Ryan Pewowaruk In the ventricular flow literature, vorticity is a frequently reported parameter that is credited for being a key marker of blood flow dynamics and particularly flow efficiency. However, the exact role of vorticity in ventricular flow efficiency has yet to be explained. We apply the concept of enstrophy from turbulence and geophysical fluid dynamics to ventricular flow to explain the relationship between vorticity and viscous energy dissipation. Theoretically, enstrophy predicts a quadratic relationship between vorticity and viscous energy dissipation. Magnetic resonance velocimetry is performed in pigs using a high spatial resolution, radial acquisition (PC-VIPR). Velocity derived vorticity and viscous energy dissipation in both the left and right ventricle of pigs show strong agreement with the theoretical quadratic relationship (R$^{\mathrm{2}}=$0.94). This work is the first rigorous explanation of the importance of vorticity in ventricular flow and we hope the concept of enstrophy is further applied in cardiovascular research. Additionally, experimental evidence shows strong agreement with theory, highlighting the ability of magnetic resonance velocimetry to quantify key aspects of cardiovascular fluid dynamics in living subjects. [Preview Abstract] |
Monday, November 25, 2019 2:37PM - 2:50PM |
L30.00005: Cardiac Triangle Mapping: A Novel Systems Approach for Noninvasive Evaluation of Left Ventricular End Diastolic Pressure. Niema Pahlevan, Melissa Ramos, Ray Matthews Left ventricular end diastolic pressure (LVEDP) is an important measure of global left ventricle (LV) function. Elevated LVEDP is indicative of poor LV function in both heart failure with preserved ejection fraction and in heart failure with reduced ejection fraction. This highlights LVEDP's importance as quantitative biomarker for diagnosis, chronic monitoring, and evaluating response to therapy. Here, we introduce a new systems approach, called Cardiac Triangle Mapping (CTM), for non-invasive and instantaneous measurement of LVEDP. CTM uses arterial pressure waves and ECG to map the global ventricular function; hence, allowing computation of LVEDP. The accuracy and validity of CTM have been shown using retrospective clinical data. Here, we present the validity and accuracy of CTM method using data from a prospective clinical study at the Keck Medical Center of USC. [Preview Abstract] |
Monday, November 25, 2019 2:50PM - 3:03PM |
L30.00006: Patient-Specific Computational Fluid-Structure Interaction (FSI) Modeling of Full Cardiac Cycle Mohammad Mehri, Matthew Fig, Maysam Mousaviraad A patient-specific computational fluid-structure interaction (FSI) model of full-cycle cardiac dynamics is presented. One-way and two-way coupling simulations are carried out for 2D and 3D geometries. The patient-specific 3D left ventricle (LV) geometry is constructed from 2D echocardiography images based on biplane ellipsoid model. One-way coupling studies use the wall motions and the pressure-volume (PV) loop data to specify the solid and fluid boundary conditions. The two-way coupled simulations model the myocardium passive dynamics with anisotropic Mooney-Rivlin method. Active contractions are modeled by stiffening and softening the myocardial material properties calculated as part of the one-way studies. The compressibility of blood is included in the model to produce the entire curve of the PV loop. The wall motions and PV loop data are used to validate the two-way results. Next steps will include invariant-based orthotropic models for passive behavior of myocardium and electrophysiology models for active contractions. The valvular dynamics will also need to be included for improved vorticity dynamics modeling. [Preview Abstract] |
Monday, November 25, 2019 3:03PM - 3:16PM |
L30.00007: Elastohydrodynamics of the heart Vamsi Spandan, Emmanuel Virot, Lauren Niu, Wim van Rees, L Mahadevan Animal hearts are deformable shells pumping large volumes of blood which guarantees oxygen for cells. Here we suggest a scaling for the heart rate based on a simple idea: Elastohydrodynamic resonance of a fluid-loaded soft elastic shell that is capable of bending and twisting as it ejects fluid over a contraction cycle. Such a mechanism can yield ejection fractions of 40\% with relatively small strains, suggesting a solution to a long-standing puzzle in heart physiology. Our study provides a general principle to characterize the heart rate of an organism as a function of its geometry, while suggesting design principles for artificial pumps made of soft shells, and may even shed light on their pathologies. [Preview Abstract] |
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