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https://www.readbyqxmd.com/read/29770490/functional-magnetic-resonance-electrical-impedance-tomography-fmreit-sensitivity-analysis-using-an-active-bidomain-finite-element-model-of-neural-tissue
#1
Rosalind J Sadleir, Fanrui Fu, Munish Chauhan
PURPOSE: A direct method of imaging neural activity was simulated to determine typical signal sizes. METHODS: An active bidomain finite-element model was used to estimate approximate perturbations in MR phase data as a result of neural tissue activity, and when an external MR electrical impedance tomography imaging current was added to the region containing neural current sources. RESULTS: Modeling-predicted, activity-related conductivity changes should produce measurable differential phase signals in practical MR electrical impedance tomography experiments conducted at moderate resolution at noise levels typical of high field systems...
May 16, 2018: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
https://www.readbyqxmd.com/read/29751215/a-docked-state-conformational-dynamics-model-to-explain-the-ionic-strength-dependence-of-fmn-heme-electron-transfer-in-nitric-oxide-synthase
#2
Andrei V Astashkin, Jinghui Li, Huayu Zheng, Yubin Miao, Changjian Feng
The FMN-heme interdomain electron transfer (IET) in nitric oxide synthase (NOS) is a key stage of the electron transport chain, which supplies the catalytic heme site(s) with the NADPH-derived electrons. While there is a recognition that this IET depends on both the electron tunneling and the conformational dynamics, the detailed mechanism remains unclear. In this work, the IET kinetics were measured by laser flash photolysis for a bidomain oxygenase/FMN (oxyFMN) construct of human inducible NOS (iNOS) over the ionic strength range from 0...
March 26, 2018: Journal of Inorganic Biochemistry
https://www.readbyqxmd.com/read/29674971/a-numerical-study-of-scalable-cardiac-electro-mechanical-solvers-on-hpc-architectures
#3
Piero Colli Franzone, Luca F Pavarino, Simone Scacchi
We introduce and study some scalable domain decomposition preconditioners for cardiac electro-mechanical 3D simulations on parallel HPC (High Performance Computing) architectures. The electro-mechanical model of the cardiac tissue is composed of four coupled sub-models: (1) the static finite elasticity equations for the transversely isotropic deformation of the cardiac tissue; (2) the active tension model describing the dynamics of the intracellular calcium, cross-bridge binding and myofilament tension; (3) the anisotropic Bidomain model describing the evolution of the intra- and extra-cellular potentials in the deforming cardiac tissue; and (4) the ionic membrane model describing the dynamics of ionic currents, gating variables, ionic concentrations and stretch-activated channels...
2018: Frontiers in Physiology
https://www.readbyqxmd.com/read/29575751/numerical-approximation-of-the-electromechanical-coupling-in-the-left-ventricle-with-inclusion-of-the-purkinje-network
#4
Mikel Landajuela, Christian Vergara, Antonello Gerbi, Luca Dedé, Luca Formaggia, Alfio Quarteroni
In this work, we consider the numerical approximation of the electromechanical coupling in the left ventricle with inclusion of the Purkinje network. The mathematical model couples the 3D elastodynamics and bidomain equations for the electrophysiology in the myocardium with the 1D monodomain equation in the Purkinje network. For the numerical solution of the coupled problem, we consider a fixed-point iterative algorithm that enables a partitioned solution of the myocardium and Purkinje network problems. Different levels of myocardium-Purkinje network splitting are considered and analyzed...
March 25, 2018: International Journal for Numerical Methods in Biomedical Engineering
https://www.readbyqxmd.com/read/29459293/determining-the-most-significant-input-parameters-in-models-of-subendocardial-ischaemia-and-their-effect-on-st-segment-epicardial-potential-distributions
#5
Barbara M Johnston, Peter R Johnston
There is considerable interest in simulating ischaemia in the ventricle and its effect on the electrocardiogram, because a better understanding of the connection between the two may lead to improvements in diagnosis of myocardial ischaemia. In this work we studied subendocardial ischaemia, in a simplified half-ellipsoidal bidomain model of a ventricle, and its effect on ST segment epicardial potential distributions (EPDs). We found that the EPD changed as the ischaemic depth increased, from a single minimum (min1) over the ischaemic region to a maximum (max) there, with min1 over the border of the region...
April 1, 2018: Computers in Biology and Medicine
https://www.readbyqxmd.com/read/29130137/assessment-of-the-equivalent-dipole-layer-source-model-in-the-reconstruction-of-cardiac-activation-times-on-the-basis-of-bspms-produced-by-an-anisotropic-model-of-the-heart
#6
Arno M Janssen, Danila Potyagaylo, Olaf Dössel, Thom F Oostendorp
Promising results have been reported in noninvasive estimation of cardiac activation times (AT) using the equivalent dipole layer (EDL) source model in combination with the boundary element method (BEM). However, the assumption of equal anisotropy ratios in the heart that underlies the EDL model does not reflect reality. In the present study, we quantify the errors of the nonlinear AT imaging based on the EDL approximation. Nine different excitation patterns (sinus rhythm and eight ectopic beats) were simulated with the monodomain model...
November 13, 2017: Medical & Biological Engineering & Computing
https://www.readbyqxmd.com/read/29072834/light-regulated-synthesis-of-cyclic-di-gmp-by-a-bidomain-construct-of-the-cyanobacteriochrome-tlr0924-sesa-without-stable-dimerization
#7
Matthew Blain-Hartung, Nathan C Rockwell, J Clark Lagarias
Phytochromes and cyanobacteriochromes (CBCRs) use double-bond photoisomerization of their linear tetrapyrrole (bilin) chromophores within cGMP-specific phosphodiesterases/adenylyl cyclases/FhlA (GAF) domain-containing photosensory modules to regulate activity of C-terminal output domains. CBCRs exhibit photocycles that are much more diverse than those of phytochromes and are often found in large modular proteins such as Tlr0924 (SesA), one of three blue light regulators of cell aggregation in the cyanobacterium Thermosynechococcus elongatus...
November 21, 2017: Biochemistry
https://www.readbyqxmd.com/read/29066291/in-silico-assessment-of-the-effects-of-various-compounds-in-mea-hipsc-cm-assays-modeling-and-numerical-simulations
#8
Emanuela Abbate, Muriel Boulakia, Yves Coudière, Jean-Frédéric Gerbeau, Philippe Zitoun, Nejib Zemzemi
We propose a mathematical approach for the analysis of drugs effects on the electrical activity of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) based on multi-electrode array (MEA) experiments. Our goal is to produce an in silico tool able to simulate drugs action in MEA/hiPSC-CM assays. The mathematical model takes into account the geometry of the MEA and the electrodes' properties. The electrical activity of the stem cells at the ion-channel level is governed by a system of ordinary differential equations (ODEs)...
January 2018: Journal of Pharmacological and Toxicological Methods
https://www.readbyqxmd.com/read/29060329/design-and-application-of-a-novel-gastric-pacemaker
#9
Saeed Alighaleh, Timothy R Angeli, Shameer Sathar, Gregory O'Grady, Leo K Cheng, Niranchan Paskaranandavadivel
Omnipresent bioelectrical events known as slow waves are responsible for coordinating motility in the gastrointestinal tract. Functional motility diseases, such as gastroparesis, are associated with slow wave dysrhythmias. Electrical stimulation is a potential therapy to correct abnormal slow wave patterns. We present the design and application of a new gastric pacemaker. Real-time changes to the stimulation parameters such as period, amplitude and pulse width were applied using a graphical user interface, which communicated with the microcontroller to deliver the stimulus...
July 2017: Conference Proceedings: Annual International Conference of the IEEE Engineering in Medicine and Biology Society
https://www.readbyqxmd.com/read/29023795/real-time-ecg-simulation-for-hybrid-mock-circulatory-loops
#10
Leonie Korn, Daniel Rüschen, Niklas Zander, Steffen Leonhardt, Marian Walter
Classically, mock circulatory loops only simulate mechanical properties of the circulation. To connect the hydraulic world with electrophysiology, we present a real-time electrical activity model of the heart and show how to integrate this model into a real-time mock loop simulation. The model incorporates a predefined conduction pathway and a simplified volume conductor to solve the bidomain equations and the forward problem of electrocardiography, resulting in a physiological simulation of the electrocardiogram (ECG) at arbitrary electrode positions...
February 2018: Artificial Organs
https://www.readbyqxmd.com/read/28964127/incorporating-inductances-in-tissue-scale-models-of-cardiac-electrophysiology
#11
Simone Rossi, Boyce E Griffith
In standard models of cardiac electrophysiology, including the bidomain and monodomain models, local perturbations can propagate at infinite speed. We address this unrealistic property by developing a hyperbolic bidomain model that is based on a generalization of Ohm's law with a Cattaneo-type model for the fluxes. Further, we obtain a hyperbolic monodomain model in the case that the intracellular and extracellular conductivity tensors have the same anisotropy ratio. In one spatial dimension, the hyperbolic monodomain model is equivalent to a cable model that includes axial inductances, and the relaxation times of the Cattaneo fluxes are strictly related to these inductances...
September 2017: Chaos
https://www.readbyqxmd.com/read/28964126/modeling-bipolar-stimulation-of-cardiac-tissue
#12
Suran K Galappaththige, Richard A Gray, Bradley J Roth
Unipolar stimulation of cardiac tissue is often used in the design of cardiac pacemakers because of the low current required to depolarize the surrounding tissue at rest. However, the advantages of unipolar over bipolar stimulation are not obvious at shorter coupling intervals when the tissue near the pacing electrode is relatively refractory. Therefore, this paper analyzes bipolar stimulation of cardiac tissue. The strength-interval relationship for bipolar stimulation is calculated using the bidomain model and a recently developed parsimonious ionic current model...
September 2017: Chaos
https://www.readbyqxmd.com/read/28964121/effects-of-mechanical-feedback-on-the-stability-of-cardiac-scroll-waves-a-bidomain-electro-mechanical-simulation-study
#13
P Colli Franzone, L F Pavarino, S Scacchi
In this work, we investigate the influence of cardiac tissue deformation on re-entrant wave dynamics. We have developed a 3D strongly coupled electro-mechanical Bidomain model posed on an ideal monoventricular geometry, including fiber direction anisotropy and stretch-activated currents (SACs). The cardiac mechanical deformation influences the bioelectrical activity with two main mechanical feedback: (a) the geometric feedback (GEF) due to the presence of the deformation gradient in the diffusion coefficients and in a convective term depending on the deformation rate and (b) the mechano-electric feedback (MEF) due to SACs...
September 2017: Chaos
https://www.readbyqxmd.com/read/28964111/numerical-sensitivity-analysis-of-a-variational-data-assimilation-procedure-for-cardiac-conductivities
#14
Alessandro Barone, Flavio Fenton, Alessandro Veneziani
An accurate estimation of cardiac conductivities is critical in computational electro-cardiology, yet experimental results in the literature significantly disagree on the values and ratios between longitudinal and tangential coefficients. These are known to have a strong impact on the propagation of potential particularly during defibrillation shocks. Data assimilation is a procedure for merging experimental data and numerical simulations in a rigorous way. In particular, variational data assimilation relies on the least-square minimization of the misfit between simulations and experiments, constrained by the underlying mathematical model, which in this study is represented by the classical Bidomain system, or its common simplification given by the Monodomain problem...
September 2017: Chaos
https://www.readbyqxmd.com/read/28933043/quantifying-the-effect-of-uncertainty-in-input-parameters-in-a-simplified-bidomain-model-of-partial-thickness-ischaemia
#15
Barbara M Johnston, Sam Coveney, Eugene T Y Chang, Peter R Johnston, Richard H Clayton
Reduced blood flow in the coronary arteries can lead to damaged heart tissue (myocardial ischaemia). Although one method for detecting myocardial ischaemia involves changes in the ST segment of the electrocardiogram, the relationship between these changes and subendocardial ischaemia is not fully understood. In this study, we modelled ST-segment epicardial potentials in a slab model of cardiac ventricular tissue, with a central ischaemic region, using the bidomain model, which considers conduction longitudinal, transverse and normal to the cardiac fibres...
May 2018: Medical & Biological Engineering & Computing
https://www.readbyqxmd.com/read/28823052/sensitivity-analysis-of-ventricular-activation-and-electrocardiogram-in-tailored-models-of-heart-failure-patients
#16
C Sánchez, G D'Ambrosio, F Maffessanti, E G Caiani, F W Prinzen, R Krause, A Auricchio, M Potse
Cardiac resynchronization therapy is not effective in a variable proportion of heart failure patients. An accurate knowledge of each patient's electroanatomical features could be helpful to determine the most appropriate treatment. The goal of this study was to analyze and quantify the sensitivity of left ventricular (LV) activation and the electrocardiogram (ECG) to changes in 39 parameters used to tune realistic anatomical-electrophysiological models of the heart. Electrical activity in the ventricles was simulated using a reaction-diffusion equation...
March 2018: Medical & Biological Engineering & Computing
https://www.readbyqxmd.com/read/28819329/efficient-computation-of-electrograms-and-ecgs-in-human-whole-heart-simulations-using-a-reaction-eikonal-model
#17
Aurel Neic, Fernando O Campos, Anton J Prassl, Steven A Niederer, Martin J Bishop, Edward J Vigmond, Gernot Plank
Anatomically accurate and biophysically detailed bidomain models of the human heart have proven a powerful tool for gaining quantitative insight into the links between electrical sources in the myocardium and the concomitant current flow in the surrounding medium as they represent their relationship mechanistically based on first principles. Such models are increasingly considered as a clinical research tool with the perspective of being used, ultimately, as a complementary diagnostic modality. An important prerequisite in many clinical modeling applications is the ability of models to faithfully replicate potential maps and electrograms recorded from a given patient...
October 1, 2017: Journal of Computational Physics
https://www.readbyqxmd.com/read/28744962/inverse-estimation-of-cardiac-activation-times-via-gradient-based-optimization
#18
Siri Kallhovd, Mary M Maleckar, Marie E Rognes
Computational modeling may provide a quantitative framework for integrating multiscale data to gain insight into mechanisms of heart disease, identify and test pharmacological and electrical therapy and interventions, and support clinical decisions. Patient-specific computational cardiac models can help guide such procedures, and cardiac inverse modeling is a promising alternative to adequately personalize these models. Indeed, full cardiac inverse modeling is currently becoming computationally feasible; however, fundamental work to assess the feasibility of emerging techniques is still needed...
February 2018: International Journal for Numerical Methods in Biomedical Engineering
https://www.readbyqxmd.com/read/28512434/evaluation-of-a-rapid-anisotropic-model-for-ecg-simulation
#19
Simone Pezzuto, Peter Kal'avský, Mark Potse, Frits W Prinzen, Angelo Auricchio, Rolf Krause
State-of-the-art cardiac electrophysiology models that are able to deliver physiologically motivated activation maps and electrocardiograms (ECGs) can only be solved on high-performance computing architectures. This makes it nearly impossible to adopt such models in clinical practice. ECG imaging tools typically rely on simplified models, but these neglect the anisotropic electric conductivity of the tissue in the forward problem. Moreover, their results are often confined to the heart-torso interface. We propose a forward model that fully accounts for the anisotropic tissue conductivity and produces the standard 12-lead ECG in a few seconds...
2017: Frontiers in Physiology
https://www.readbyqxmd.com/read/28507234/modelling-far-field-pacing-for-terminating-spiral-waves-pinned-to-ischaemic-heterogeneities-in-cardiac-tissue
#20
E Boccia, S Luther, U Parlitz
In cardiac tissue, electrical spiral waves pinned to a heterogeneity can be unpinned (and eventually terminated) using electric far field pulses and recruiting the heterogeneity as a virtual electrode. While for isotropic media the process of unpinning is much better understood, the case of an anisotropic substrate with different conductivities in different directions still needs intensive investigation. To study the impact of anisotropy on the unpinning process, we present numerical simulations based on the bidomain formulation of the phase I of the Luo and Rudy action potential model modified due to the occurrence of acute myocardial ischaemia...
June 28, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
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