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130 results on '"Al Abed, Amr"'

14. First biopotential recordings from a liquid crystal optrode

Author

Silvestri, Leonardo, primary, Al Abed, Amr, additional, Revol, Emilie C. M., additional, Firth, Josiah, additional, Wei, Yuan, additional, Wang, Han, additional, Gouailhardou, Nathalie, additional, Lehmann, Torsten, additional, Lovell, Nigel H., additional, and Ladouceur, Francois, additional

Published
2020
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19. Neurotrophin gene augmentation by electrotransfer to improve cochlear implant hearing outcomes

Author

Pinyon, Jeremy L., primary, von Jonquieres, Georg, additional, Crawford, Edward N., additional, Duxbury, Mayryl, additional, Al Abed, Amr, additional, Lovell, Nigel H., additional, Klugmann, Matthias, additional, Wise, Andrew K., additional, Fallon, James B., additional, Shepherd, Robert K., additional, Birman, Catherine S., additional, Lai, Waikong, additional, McAlpine, David, additional, McMahon, Catherine, additional, Carter, Paul M., additional, Enke, Ya Lang, additional, Patrick, James F., additional, Schilder, Anne G.M., additional, Marie, Corinne, additional, Scherman, Daniel, additional, and Housley, Gary D., additional

Published
2019
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36. Electrical activity of atrial tissue: an experimental and computational study

Author

Al Abed, Amr

Subjects
Computational biology, Multiscale modelling, Cardiac electrophysiology, Sino-atrial node, Computational cardiology, Optimisation, Action potential, Cardiac cell ionic model, Curvilinear gradient, Arrhythmia, Atrial electrophysiology, Intracellular microelectrode electrophysiological recording
Abstract

Intracellular action potentials were recorded from rabbit heart sinoatrial node (SAN) and atrial intact tissue preparations. The tissue-intact myocytes exhibited heterogeneous action potential waveforms and electrical restitution properties. A generic cell ionic model was used to fit the experimental waveforms, based on a single background current and a user-defined number of time-dependent ionic currents. In order to optimise the model parameters in the presence of electrotonic loading from neighbouring regions, an axisymmetric 2D disc model was utilised. The disc was divided into concentric electrophysiologically-distinct regions. Action potential waveforms generated from selective points were fitted to experimental recordings from tissue-intact myocytes. The root mean square of residuals was less than 5 mV for each tissue-intact myocyte. A 3D anatomically-realistic atrial geometry was reconstructed from cryosection images of the male Visible Human, including central and peripheral SAN regions and pulmonary veins. A realistic thickness atrial wall mesh and an epicardial shell mesh were generated based on this geometry. Distinct ionic model parameters, obtained from the optimisation process, were assigned to the central and peripheral SAN, right and left atria, and pulmonary vein regions. Heterogeneous tissue conductivity values were applied in different regions to produce physiologically realistic conduction velocities (~150 cm.s^{-1}, ~ 40 cm.s^{-1} and ~ 80 cm.s^{-1} for fast and slow conducting pathways, and bulk atrial myocardium respectively). The 3D models were able to reproduce action potential waveforms similar to those recorded experimentally, including spontaneous activation of the SAN (cycle length ~ 770 ms), and electric propagation into the surrounding atrium. Several types of arrhythmia were simulated either by pacing of specific myocardial regions or induction of spontaneous activity in one of the pulmonary veins. The novel methodology developed in this thesis allows the systemic link between experimental and computational cardiac electrophysiology, paving the way for patient-specific simulations.

Published
2011
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40. The role of infarct transmural extent in infarct extension: A computational study.

Author

Leong, Chin‐Neng, Lim, Einly, Andriyana, Andri, Al Abed, Amr, Lovell, Nigel Hamilton, Hayward, Christopher, Hamilton‐Craig, Christian, and Dokos, Socrates

Subjects
MYOCARDIAL infarction, COMPUTER simulation, NUMERICAL analysis, HYPOXEMIA, ASPHYXIA
Abstract

Infarct extension, a process involving progressive extension of the infarct zone (IZ) into the normally perfused border zone (BZ), leads to continuous degradation of the myocardial function and adverse remodelling. Despite carrying a high risk of mortality, detailed understanding of the mechanisms leading to BZ hypoxia and infarct extension remains unexplored. In the present study, we developed a 3D truncated ellipsoidal left ventricular model incorporating realistic electromechanical properties and fibre orientation to examine the mechanical interaction among the remote, infarct and BZs in the presence of varying infarct transmural extent (TME). Localized highly abnormal systolic fibre stress was observed at the BZ, owing to the simultaneous presence of moderately increased stiffness and fibre strain at this region, caused by the mechanical tethering effect imposed by the overstretched IZ. Our simulations also demonstrated the greatest tethering effect and stress in BZ regions with fibre direction tangential to the BZ-remote zone boundary. This can be explained by the lower stiffness in the cross-fibre direction, which gave rise to a greater stretching of the IZ in this direction. The average fibre strain of the IZ, as well as the maximum stress in the sub-endocardial layer, increased steeply from 10% to 50% infarct TME, and slower thereafter. Based on our stress-strain loop analysis, we found impairment in the myocardial energy efficiency and elevated energy expenditure with increasing infarct TME, which we believe to place the BZ at further risk of hypoxia. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Published
2017
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49. Convolution based method for calculating inputs from dendritic fields in a continuum model of the retina.

Author

Al Abed, Amr, Yin, Shijie, Suaning, Gregg J., Lovell, Nigel H., and Dokos, Socrates

Abstract

Computational models are valuable tools that can be used to aid the design and test the efficacy of electrical stimulation strategies in prosthetic vision devices. In continuum models of retinal electrophysiology, the effective extracellular potential can be considered as an approximate measure of the electrotonic loading a neuron's dendritic tree exerts on the soma. A convolution based method is presented to calculate the local spatial average of the effective extracellular loading in retinal ganglion cells (RGCs) in a continuum model of the retina which includes an active RGC tissue layer. The method can be used to study the effect of the dendritic tree size on the activation of RGCs by electrical stimulation using a hexagonal arrangement of electrodes (hexpolar) placed in the suprachoroidal space. [ABSTRACT FROM PUBLISHER]

Published
2012
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50. Numerical investigation of the effect of cannula placement on thrombosis.

Author

ChiWei Ong, Dokos, Socrates, BeeTing Chan, Einly Lim, Al Abed, Amr, Abu Osman, Noor Azuan Bin, Kadiman, Suhaini, and Lovell, Nigel H.

Subjects
HEART assist devices, LEFT heart ventricle, FLUID-structure interaction, AXIAL flow, VORTEX motion
Abstract

Despite the rapid advancement of left ventricular assist devices (LVADs), adverse events leading to deaths have been frequently reported in patients implanted with LVADs, including bleeding, infection, thromboembolism, neurological dysfunction and hemolysis. Cannulation forms an important component with regards to thrombus formation in assisted patients by varying the intraventricular flow distribution in the left ventricle (LV). To investigate the correlation between LVAD cannula placement and potential for thrombus formation, detailed analysis of the intraventricular flow field was carried out in the present study using a two way fluid structure interaction (FSI), axisymmetric model of a passive LV incorporating an inflow cannula. Three different cannula placements were simulated, with device insertion near the LV apex, penetrating one-fourth and mid-way into the LV long axis. The risk of thrombus formation is assessed by analyzing the intraventricular vorticity distribution and its associated vortex intensity, amount of stagnation flow in the ventricle as well as the level of wall shear stress. Our results show that the one-fourth placement of the cannula into the LV achieves the best performance in reducing the risk of thrombus formation. Compared to cannula placement near the apex, higher vortex intensity is achieved at the one-fourth placement, thus increasing wash out of platelets at the ventricular wall. One-fourth LV penetration produced negligible stagnation flow region near the apical wall region, helping to reduce platelet deposition on the surface of the cannula and the ventricular wall. [ABSTRACT FROM AUTHOR]

Published
2013
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