ORCID Profile
0000-0002-7399-2712
Current Organisation
University of New South Wales
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Biomedical Engineering | Rehabilitation Engineering | Simulation And Modelling | Integrated Circuits | Medical Devices | Biomaterials | Optimisation | Biomaterials | Biomechanical Engineering | Animal Physiology—Biophysics | Biomedical Engineering Not Elsewhere Classified | Wireless Communications |
ANZSRC Socio-Economic Objective (SEO)
Hearing, vision, speech and their disorders | Clinical health not specific to particular organs, diseases and conditions | Medical Instruments | Nervous System and Disorders | Nervous system and disorders | Cardiovascular system and diseases | Medical instrumentation | Biological sciences | Hearing, Vision, Speech and Their Disorders | Mathematical sciences
Related Links
Publications
Chapter 6. Hypostasizing Socrates
Publisher: University of Pennsylvania Press
Date: 31-12-2014
Modeling of pharyngoesophageal segment during tracheoesophageal phonation in total laryngectomy patients with preliminary validation
Publisher: IEEE
Date: 08-2016
SOCRATES
Publisher: Cambridge University Press
Date: 03-01-1932
Continuum model of light response in the retina
Publisher: IEEE
Date: 08-2011
Introduction: Karl Popper, the Viennese Socrates 1
Publisher: Peter Lang
Symplectic geometry spectrum regression for prediction of noisy time series
Publisher: American Physical Society (APS)
Date: 20-05-2016
Activation of retinal ganglion cells following epiretinal electrical stimulation with hexagonally arranged bipolar electrodes
Publisher: IOP Publishing
Date: 18-05-2011
DOI: 10.1088/1741-2560/8/3/035004
Abstract: We investigated retinal ganglion cell (RGC) responses to epiretinal electrical stimulation delivered by hexagonally arranged bipolar (Hex) electrodes, in order to assess the feasibility of this electrode arrangement for future retinal implant devices. In vitro experiments were performed using rabbit retinal preparations, with results compared to a computational model of axonal stimulation. Single-unit RGC responses to electrical stimulation were recorded with extracellular microelectrodes. With 100 µs hase biphasic pulses, the threshold charge densities were 24.0 ± 11.2 and 7.7 ± 3.2 µC cm(-2) for 50 and 125 µm diameter Hex electrodes, respectively. Threshold profiles and response characteristics strongly suggested that RGC axons were the neural activation site. Both the model and in vitro data indicated that localized tissue stimulation is achieved with Hex electrodes.
Impact of myocardial infarction on intraventricular vortex and flow energetics assessed using computational simulations.
Publisher: Wiley
Date: 25-04-2019
DOI: 10.1002/CNM.3204
Abstract: Flow energetics have been proposed as early indicators of progressive left ventricular (LV) functional impairment in patients with myocardial infarction (MI), but its correlation with in idual MI parameters has not been fully explored. Using electro-fluid-structure interaction LV models, this study investigated the correlation between four MI parameters: infarct size, infarct multiplicity, regional enhancement of contractility at the viable myocardium area (RECVM), and LV mechanical dyssynchrony (LVMD) with intraventricular vortex and flow energetics. In LV with small infarcts, our results showed that infarct appearance lified the energy dissipation index (DI), where substantial viscous energy loss was observed in areas with high flow velocity and near the infarct-vortex interface. The LV with small multiple infarcts and RECVM showed remarkable DI increment during systole and diastole. In correlation analysis, the systolic kinetic energy fluctuation index (E') was positively related to ejection fraction (EF) (R
A hybrid continuum-discrete computational model of electrical stimulation of the retinal network
Publisher: IEEE
Date: 04-2015
A Cardiovascular Mathematical Model of Graded Head-Up Tilt
Publisher: Public Library of Science (PLoS)
Date: 29-10-2013
Challenging the optimality of rectangular pulse stimulation for neuroprosthetic devices
Publisher: IEEE
Date: 11-2013
Stimulation of the Retinal Network in Bionic Vision Devices: From Multi-Electrode Arrays to Pixelated Vision
Publisher: Springer Berlin Heidelberg
Date: 2010
Computational Models of Neural Retina
Publisher: Springer New York
Date: 2015
Differential electrical responses in retinal ganglion cell subtypes: Effects of synaptic blockade and stimulating electrode location
Publisher: IOP Publishing
Date: 06-06-2018
Abstract: Visual prostheses have shown promising results in restoring visual perception to blind patients. The ability to differentially activate retinal ganglion cell (RGC) subtypes could further improve the efficacy of these medical devices. Using whole-cell patch cl , we investigated membrane potential differences between ON and OFF RGCs in the mouse retina when their synaptic inputs were blocked by synaptic blockers, and examined the differences in stimulation thresholds under such conditions. By injecting intracellular current, we further confirmed the relationship between RGC stimulation thresholds and resting membrane potentials (RMPs). In addition, we investigated the effects of stimulating electrode location on the differences in stimulation thresholds between ON and OFF RGCs. With synaptic blockade, ON RGCs became significantly more hyperpolarized (from -61.8 ± 1.4 mV to -70.8 ± 1.6 mV), while OFF RGCs depolarized slightly (from -60.5 ± 0.7 mV to -58.6 ± 0.9 mV). RGC stimulation thresholds were negatively correlated with their RMPs (Pearson r value: -0.5154 p-value: 0.0042). Thus, depriving ON RGCs of synaptic inputs significantly increased their thresholds (from 14.7 ± 1.3 µA to 22.3 ± 2.1 µA) over those of OFF RGCs (from 13.2 ± 0.7 µA to 13.1 ± 1.1 µA). However, with control solution, ON and OFF RGC stimulation thresholds were not significantly different. Finally, placement of the stimulating electrode away from the axon enhanced differences in stimulation thresholds between ON and OFF RGCs, facilitating preferential activation of OFF RGCs. Since ON and OFF RGCs have antagonistic responses to natural light, achieving differential RGC activation could convey more natural visual information, leading to better visual prosthesis outcomes.
Secondary flow in bifurcations – Important effects of curvature, bifurcation angle and stents
Publisher: Elsevier BV
Date: 12-2021
DOI: 10.1016/J.JBIOMECH.2021.110755
Abstract: Coronary bifurcations have complex flow patterns including secondary flow zones and helical flow, which directly affect pathophysiological mechanisms such as the development of atherosclerosis. The objective of this study was to generate insights into the effects of curvature, bifurcation angle and the presence of stents on flow patterns and resulting haemodynamics in coronary left main bifurcations. The blood flow and associated metrics were modelled in both idealised and patient-specific bifurcations with varying curvature and bifurcation angles with and without stents, resulting in a total of 128 geometries considered. The results showed that larger curvature of bifurcating vessels has a significant influence on secondary flow, especially with distance to the bifurcation region, causing a skew, spin and asymmetry of Dean vortices, an increase in helical flow intensity with symmetry loss, and a decrease in adversely low time-average wall shear stress (TAWSS). Generally, asymmetric flow patterns coincided with adversely low TAWSS regions. In identical stented geometries, the presence of the stents induced local recirculation immediately adjacent to the stent struts, thus generating adversely low TAWSS in these areas, with some effect on the overall secondary flow. Overall, the effect of stents outweighed the effect of curvature and BA. This new knowledge contributes to a better understanding of the joint effects of curvature, bifurcation angle, and stents on flow patterns and haemodynamics in coronary bifurcations.
Epilogue: Socrates or Plato?
Publisher: Wiley
Date: 10-09-2009
A computational modelling study of transcranial direct current stimulation montages used in depression.
Publisher: Elsevier BV
Date: 02-2014
DOI: 10.1016/J.NEUROIMAGE.2013.11.015
Abstract: Transcranial direct current stimulation (tDCS) is a neuromodulatory technique which involves passing a mild electric current to the brain through electrodes placed on the scalp. Several clinical studies suggest that tDCS may have clinically meaningful efficacy in the treatment of depression. The objective of this study was to simulate and compare the effects of several tDCS montages either used in clinical trials or proposed, for the treatment of depression, in different high-resolution anatomically-accurate head models. Detailed segmented finite element head models of two subjects were presented, and a total of eleven tDCS electrode montages were simulated. Sensitivity analysis on the effects of changing the size of the anode, rotating both electrodes and displacing the anode was also conducted on selected montages. The F3-F8 and F3-F4 montages have been used in clinical trials reporting significant antidepressant effects and both result in relatively high electric fields in dorsolateral prefrontal cortices. Other montages using a fronto-extracephalic or fronto-occipital approach result in greater stimulation of central structures (e.g. anterior cingulate cortex) which may be advantageous in treating depression, but their efficacy has yet to be tested in randomised controlled trials. Results from sensitivity analysis suggest that electrode position and size may be adjusted slightly to accommodate other priorities, such as skin discomfort and damage.
Anisotropic scattering of discrete particle arrays
Publisher: Optica Publishing Group
Date: 04-2010
The Sources for Socrates
Publisher: Bloomsbury Academic
Differential effect of brief electrical stimulation on voltage-gated potassium channels
Publisher: American Physiological Society
Date: 05-2017
Abstract: Electrical stimulation of neuronal tissue is a promising strategy to treat a variety of neurological disorders. The mechanism of neuronal activation by external electrical stimulation is governed by voltage-gated ion channels. This stimulus, typically brief in nature, leads to membrane potential depolarization, which increases ion flow across the membrane by increasing the open probability of these voltage-gated channels. In spiking neurons, it is activation of voltage-gated sodium channels (Na V channels) that leads to action potential generation. However, several other types of voltage-gated channels are expressed that also respond to electrical stimulation. In this study, we examine the response of voltage-gated potassium channels (K V channels) to brief electrical stimulation by whole cell patch-cl electrophysiology and computational modeling. We show that nonspiking amacrine neurons of the retina exhibit a large variety of responses to stimulation, driven by different K V -channel subtypes. Computational modeling reveals substantial differences in the response of specific K V -channel subtypes that is dependent on channel kinetics. This suggests that the expression levels of different K V -channel subtypes in retinal neurons are a crucial predictor of the response that can be obtained. These data expand our knowledge of the mechanisms of neuronal activation and suggest that K V -channel expression is an important determinant of the sensitivity of neurons to electrical stimulation. NEW & NOTEWORTHY This paper describes the response of various voltage-gated potassium channels (K V channels) to brief electrical stimulation, such as is applied during prosthetic electrical stimulation. We show that the pattern of response greatly varies between K V channel subtypes depending on activation and inactivation kinetics of each channel. Our data suggest that problems encountered when artificially stimulating neurons such as cessation in firing at high frequencies, or “fading,” may be attributed to K V -channel activation.
Fuzzy central tendency measure for time series variability analysis with application to fatigue electromyography signals
Publisher: IEEE
Date: 07-2013
Slotted Monopole Patch Antenna for Microwave-Based Head Imaging Applications
Publisher: MDPI AG
Date: 23-09-2022
DOI: 10.3390/S22197235
Abstract: A modified monopole patch antenna for microwave-based hemorrhagic or ischemic stroke recognition is presented in this article. The designed antenna is fabricated on a cost-effective FR-4 lossy material with a 0.02 loss tangent and 4.4 dielectric constant. Its overall dimensions are 0.32 λ × 0.28 λ × 0.007 λ, where λ is the lower bandwidth 1.3 GHz frequency wavelength. An inset feeding approach is utilized to feed the antenna to reduce the input impedance (z = voltage/current). A total bandwidth (below −10 dB) of 2.4 GHz (1.3–3.7 GHz) is achieved with an effective peak gain of over 6 dBi and an efficiency of over 90%. A time-domain analysis confirms that the antenna produces minimal signal distortion. Simulated and experimental findings share a lot of similarities. Brain tissue is penetrated by the antenna to a satisfactory degree, while still exhibiting a safe specific absorption rate (SAR). The maximum SAR value measured for the head model is constrained to be equal to or below 0.1409 W/kg over the entire usable frequency band. Evaluation of theoretical and experimental evidence indicates the intended antenna is appropriate for Microwave Imaging (MWI) applications.
Revisiting frontoparietal montage in electroconvulsive therapy: clinical observations and computer modeling: a future treatment option for unilateral electroconvulsive therapy.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 03-2015
A pilot study of alternative transcranial direct current stimulation electrode montages for the treatment of major depression.
Publisher: Elsevier BV
Date: 10-2014
DOI: 10.1016/J.JAD.2014.06.022
Abstract: Typically, transcranial direct current stimulation (tDCS) treatments for depression have used bifrontal montages with anodal (excitatory) stimulation targeting the left dorsolateral prefrontal cortex (DLPFC). There is limited research examining the effects of alternative electrode montages. This pilot study aimed to examine the feasibility, tolerability and safety of two alternative electrode montages and provide preliminary data on efficacy. The montages, Fronto-Occipital (F-O) and Fronto-Cerebellar (F-C), were designed respectively to target midline brain structures and the cerebellum. The anode was placed over the left supraorbital region and the cathode over the occipital and cerebellar region for the F-O and F-C montages respectively. Computational modelling was used to determine the electric fields produced in the brain regions of interest compared to a standard bifrontal montage. The two montages were evaluated in an open label study of depressed participants (N=14). Mood and neuropsychological functioning were assessed at baseline and after four weeks of tDCS. Computational modelling revealed that the novel montages resulted in greater activation in the anterior cingulate cortices and cerebellum than the bifrontal montage, while activation of the DLPFCs was higher for the bifrontal montage. After four weeks of tDCS, overall mood improvement rates of 43.8% and 15.9% were observed under the F-O and F-C conditions, respectively. No significant neuropsychological changes were found. The clinical pilot was open-label, without a control condition and computational modelling was based on one healthy participant. Results found both montages safe and feasible. The F-O montage showed promising antidepressant potential.
A symplectic geometry-based method for nonlinear time series decomposition and prediction
Publisher: AIP Publishing
Date: 29-07-2013
DOI: 10.1063/1.4817181
Abstract: We present a technique to decompose a time series into the sum of a small number of independent and interpretable components based on symplectic geometry theory. The proposed symplectic geometry spectrum analysis technique consists of embedding, symplectic QR decomposition of the matrix into an orthogonal matrix and a triangular matrix, grouping, and diagonal averaging steps. As an ex le application, the noisy Lorenz series demonstrate the effectiveness of this technique in nonlinear prediction.
Acousto-optic modulation by pulsed optical excitation: implications to imaging in turbid media
Publisher: The Optical Society
Date: 13-08-2010
DOI: 10.1364/OL.35.002780
Distributed Systems Modelling with Partial Differential Equations
Publisher: Springer Berlin Heidelberg
Date: 2017
Numerical Integration of Ordinary Differential Equations
Publisher: Springer Berlin Heidelberg
Date: 2017
Modelling Electrical Stimulation of Tissue
Publisher: Springer Berlin Heidelberg
Date: 2017
The Finite Element Method
Publisher: Springer Berlin Heidelberg
Date: 2017
Solid Mechanics
Publisher: Springer Berlin Heidelberg
Date: 2017
Models of Diffusion and Heat Transfer
Publisher: Springer Berlin Heidelberg
Date: 2017
Fluid Mechanics
Publisher: Springer Berlin Heidelberg
Date: 2017
Modeling extracellular electrical stimulation: II. Computational validation and numerical results
Publisher: IOP Publishing
Date: 27-11-2012
DOI: 10.1088/1741-2560/9/6/065006
Abstract: The validity of approximate equations describing the membrane potential under extracellular electrical stimulation (Meffin et al 2012 J. Neural Eng. 9 065005) is investigated through finite element analysis in this paper. To this end, the finite element method is used to simulate a cylindrical neurite under extracellular stimulation. Laplace's equations with appropriate boundary conditions are solved numerically in three dimensions and the results are compared to the approximate analytic solutions. Simulation results are in agreement with the approximate analytic expressions for longitudinal and transverse modes of stimulation. The range of validity of the equations describing the membrane potential for different values of stimulation and neurite parameters are presented as well. The results indicate that the analytic approach can be used to model extracellular electrical stimulation for realistic physiological parameters with a high level of accuracy.
Cells-in-Touch: 3D Printing in Reconstruction and Modelling of Microscopic Biological Geometries for Education and Future Research Applications
Publisher: MDPI AG
Date: 05-06-2023
DOI: 10.3390/BIOENGINEERING10060687
Abstract: Additive manufacturing (3D printing) and computer-aided design (CAD) still have limited uptake in biomedical and bioengineering research and education, despite the significant potential of these technologies. The utility of organ-scale 3D-printed models of living structures is widely appreciated, while the workflows for microscopy data translation into tactile accessible replicas are not well developed yet. Here, we demonstrate an accessible and reproducible CAD-based methodology for generating 3D-printed scalable models of human cells cultured in vitro and imaged using conventional scanning confocal microscopy with fused deposition modeling (FDM) 3D printing. We termed this technology CiTo-3DP (Cells-in-Touch for 3D Printing). As a proof-of-concept, we created dismountable CiTo-3DP models of human epithelial, mesenchymal, and neural cells by using selectively stained nuclei and cytoskeletal components. We also provide educational and research context for the presented cellular models. In the future, the CiTo-3DP approach can be adapted to different imaging and 3D printing modalities and comprehensively present various cell types, subcellular structures, and extracellular matrices. The resulting CAD and 3D printed models could be used for a broad spectrum of education and research applications.
A gap junction-based cardiac electromechanics model
Publisher: IEEE
Date: 08-2015
Lumped Parameter Modelling with Ordinary Differential Equations
Publisher: Springer Berlin Heidelberg
Date: 2017
Introduction to Modelling in Bioengineering
Publisher: Springer Berlin Heidelberg
Date: 2017
Focalised stimulation using high definition transcranial direct current stimulation (HD-tDCS) to investigate declarative verbal learning and memory functioning.
Publisher: Elsevier BV
Date: 08-2015
DOI: 10.1016/J.NEUROIMAGE.2015.05.019
Abstract: Declarative verbal learning and memory are known to be lateralised to the dominant hemisphere and to be subserved by a network of structures, including those located in frontal and temporal regions. These structures support critical components of verbal memory, including working memory, encoding, and retrieval. Their relative functional importance in facilitating declarative verbal learning and memory, however, remains unclear. To investigate the different functional roles of these structures in subserving declarative verbal learning and memory performance by applying a more focal form of transcranial direct current stimulation, "High Definition tDCS" (HD-tDCS). Additionally, we sought to examine HD-tDCS effects and electrical field intensity distributions using computer modelling. HD-tDCS was administered to the left dorsolateral prefrontal cortex (LDLPFC), planum temporale (PT), and left medial temporal lobe (LMTL) to stimulate the hippoc us, during learning on a declarative verbal memory task. Sixteen healthy participants completed a single blind, intra-in idual cross-over, sham-controlled study which used a Latin Square experimental design. Cognitive effects on working memory and sustained attention were additionally examined. HD-tDCS to the LDLPFC significantly improved the rate of verbal learning (p=0.03, η(2)=0.29) and speed of responding during working memory performance (p=0.02, η(2)=0.35), but not accuracy (p=0.12, η(2)=0.16). No effect of tDCS on verbal learning, retention, or retrieval was found for stimulation targeted to the LMTL or the PT. Secondary analyses revealed that LMTL stimulation resulted in increased recency (p=0.02, η(2)=0.31) and reduced mid-list learning effects (p=0.01, η(2)=0.39), suggesting an inhibitory effect on learning. HD-tDCS to the LDLPFC facilitates the rate of verbal learning and improved efficiency of working memory may underlie performance effects. This focal method of administrating tDCS has potential for probing and enhancing cognitive functioning.
Numerical Optimization Studies of Cardiovascular–Rotary Blood Pump Interaction
Publisher: Wiley
Date: 10-04-2012
DOI: 10.1111/J.1525-1594.2012.01449.X
Abstract: A heart-pump interaction model has been developed based on animal experimental measurements obtained with a rotary blood pump in situ. Five canine experiments were performed to investigate the interaction between the cardiovascular system and the implantable rotary blood pump over a wide range of operating conditions, including variations in cardiac contractility and heart rate, systemic vascular resistance (SVR), and total blood volume (V(total) ). It was observed in our experiments that SVR decreased with increasing mean pump speed under the healthy condition, but was relatively constant during the speed r study under reduced cardiac contractility conditions. Furthermore, we also found a significant increase in pulmonary vascular resistance with increasing mean pump speed and decreasing total blood volume, despite a relatively constant SVR. Least squares parameter estimation methods were utilized to fit a subset of model parameters in order to achieve better agreement with the experimental data and to evaluate the robustness and validity of the model under various operating conditions. The fitted model produced reasonable agreement with the experimental measurements, both in terms of mean values and steady-state waveforms. In addition, all the optimized parameters were within physiological limits.
Effects of macroscopic heterogeneity on propagation in a computationally inexpensive 2D model of the heart
Publisher: IEEE
Date: 08-2014
Repeatability of brain phase-based magnetic resonance electric properties tomography methods and effect of compressed SENSE and RF shimming
Publisher: Springer Science and Business Media LLC
Date: 30-03-2023
DOI: 10.1007/S13246-023-01248-1
Abstract: Magnetic resonance electrical properties tomography (MREPT) is an emerging imaging modality to noninvasively measure tissue conductivity and permittivity. Implementation of MREPT in the clinic requires repeatable measurements at a short scan time and an appropriate protocol. The aim of this study was to investigate the repeatability of conductivity measurements using phase-based MREPT and the effects of compressed SENSE (CS), and RF shimming on the precision of conductivity measurements. Conductivity measurements using turbo spin echo (TSE) and three-dimensional balanced fast field echo (bFFE) with CS factors were repeatable. Conductivity measurement using bFFE phase showed smaller mean and variance that those measured by TSE. The conductivity measurements using bFFE showed minimal deviation with CS factors up to 8, with deviation increasing at CS factors 8. Subcortical structures produced less consistent measurements than cortical parcellations at higher CS factors. RF shimming using full slice coverage 2D dual refocusing echo acquisition mode (DREAM) and full coverage 3D dual TR approaches further improved measurement precision. BFFE is a more optimal sequence than TSE for phase-based MREPT in brain. Depending on the area of the brain being measured, the scan can be safely accelerated with compressed SENSE without sacrifice of precision, offering the potential to employ MREPT in clinical research and applications. RF shimming with better field mapping further improves precision of the conductivity measures.
Erratum: Optimisation of a generic ionic model of cardiac myocyte electrical activity (Computational and Mathematical Methods in Medicine)
Publisher: Hindawi Limited
Date: 2013
DOI: 10.1155/2013/213563
Multiscale Two-Directional Two-Dimensional Principal Component Analysis and Its Application to High-Dimensional Biomedical Signal Classification
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 07-2016
Clinical Pilot Study and Computational Modeling of Bitemporal Transcranial Direct Current Stimulation, and Safety of Repeated Courses of Treatment, in Major Depression.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 12-2015
A pilot study: Can heart rate variability (HRV) be determined using short-term photoplethysmograms?
Publisher: F1000 Research Ltd
Date: 22-09-2016
DOI: 10.12688/F1000RESEARCH.9556.1
Abstract: To date, there have been no studies that investigate the independent use of the photoplethysmogram (PPG) signal to determine heart rate variability (HRV). However, researchers have demonstrated that PPG signals offer an alternative way of measuring HRV when electrocardiogram (ECG) and PPG signals are collected simultaneously. Based on these findings, we take the use of PPGs to the next step and investigate a different approach to show the potential independent use of short 20-second PPG signals collected from healthy subjects after exercise in a hot environment to measure HRV. Our hypothesis is that if the PPG--HRV indices are negatively correlated with age, then short PPG signals are appropriate measurements for extracting HRV parameters. The PPGs of 27 healthy male volunteers at rest and after exercise were used to determine the HRV indices: standard deviation of heartbeat interval (SDNN) and the root-mean square of the difference of successive heartbeats (RMSSD). The results indicate that the use of the $aa$ interval, derived from the acceleration of PPG signals, is promising in determining the HRV statistical indices SDNN and RMSSD over 20-second PPG recordings. Moreover, the post-exercise SDNN index shows a negative correlation with age. There tends to be a decrease of the PPG--SDNN index with increasing age, whether at rest or after exercise. This new outcome validates the negative relationship between HRV in general with age, and consequently provides another evidence that short PPG signals have the potential to be used in heart rate analysis without the need to measure lengthy sequences of either ECG or PPG signals.
Parameter fitting using multiple datasets in cardiac action potential modeling
Publisher: IEEE
Date: 08-2011
Modelling Organs, Tissues, Cells and Devices
Publisher: Springer Berlin Heidelberg
Date: 2017
Cell-specific modeling of retinal ganglion cell electrical activity
Publisher: IEEE
Date: 07-2013
A continuum neuronal tissue model based on a two-compartmental representation of cells
Publisher: IEEE
Date: 07-2013
Chapter 10. The Many-Voiced Socrates: Neoplatonist Sensitivity to Socrates’ Change of Register
Publisher: University of Pennsylvania Press
Date: 31-12-2014
Learning-Based Coronal Spine Alignment Prediction Using Smartphone-Acquired Scoliosis Radiograph Images
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2021
Cells-In-Touch: 3D Printing in Reconstruction and Modelling of Microscopic Biological Geometries for Research and Education
Publisher: MDPI AG
Date: 10-05-2022
DOI: 10.20944/PREPRINTS202205.0136.V1
Abstract: Additive manufacturing (3D printing) and computer-aided design (CAD) still have limited up-take in biomedical and bioengineering research and education, despite the significant potential of these technologies. The utility of organ-scale 3D-printed models of living structures is widely appreciated, while the workflows for microscopy data translation into tactile-accessible replicas are not well developed yet. Here, we demonstrate an accessible and reproducible CAD-based methodology for generating 3D-printed scalable models of human cells cultured in vitro and imaged using conventional scanning confocal microscopy and fused deposition modelling (FDM) 3D printing. We termed this technology CiTo-3DP (Cells-in-Touch for 3D Printing). As a proof-of-concept, we created CiTo-3DP models of human pancreatic cancer cells and healthy dermal fibroblasts by using selectively stained nuclei and the cytoskeleton components (f-actin and & alpha -smooth muscle actin). The production of dismountable sets of cellular components was al-so shown. The CiTo-3DP approach can be adapted to comprehensively present various cell types, subcellular structures and extracellular matrices. We envisage that the resulting CAD and 3D printed models could be used for further applications, including but not limited to in silico simulations for biology, medicine, pharmacological research, tissue engineering, morphometrical analysis, multiphysics modelling, education, rehabilitation of visually impaired people, and integration into virtual reality.
A Simplified 3D Model of Whole Heart Electrical Activity and 12-Lead ECG Generation
Publisher: Hindawi Limited
Date: 2013
DOI: 10.1155/2013/134208
Abstract: We present a computationally efficient three-dimensional bidomain model of torso-embedded whole heart electrical activity, with spontaneous initiation of activation in the sinoatrial node, incorporating a specialized conduction system with heterogeneous action potential morphologies throughout the heart. The simplified geometry incorporates the whole heart as a volume source, with heart cavities, lungs, and torso as passive volume conductors. We placed four surface electrodes at the limbs of the torso: , , and and six electrodes on the chest to simulate the Einthoven, Goldberger-augmented and precordial leads of a standard 12-lead system. By placing additional seven electrodes at the appropriate torso positions, we were also able to calculate the vectorcardiogram of the Frank lead system. Themodel was able to simulate realistic electrocardiogram (ECG) morphologies for the 12 standard leads, orthogonal , , and leads, as well as the vectorcardiogram under normal and pathological heart states. Thus, simplified and easy replicable 3D cardiac bidomain model offers a compromise between computational load and model complexity and can be used as an investigative tool to adjust cell, tissue, and whole heart properties, such as setting ischemic lesions or regions of myocardial infarction, to readily investigate their effects on whole ECG morphology.
Performance optimization of current focusing and virtual electrode strategies in retinal implants
Publisher: Elsevier BV
Date: 11-2014
DOI: 10.1016/J.CMPB.2014.06.012
Abstract: The electrode configuration in an implanted visual prosthesis array affects the spatial electric field distribution within the retina, contributing to current focusing and virtual electrode (VE) stimulation strategies. In this paper, a finite element model incorporating various electrode configurations was used to study the interaction between electrode size and electrode-to-cell distance in current focusing and VE stimulation paradigms. The electrode array unit comprises an active electrode, six flanking return electrodes and a distant monopolar return. A quasi-monopolar (QMP) fraction is defined as the proportion of current which can be preferentially returned through the distant return, in comparison with the more adjacent flanking electrodes. The simulation results indicate that current focusing and VE strategies can be optimized by tuning the QMP fraction. The QMP fraction is adjusted to optimize the electric field spread based on retinal ganglion cell (RGC) density in the degenerate retina, thereby offsetting the effect of inhomogeneous distribution of surviving RGCs and leading to a uniform stimulation paradigm across electrodes. Importantly, there is negligible difference in functional performance across electrode configurations for distances less than the electrode diameter, implying that the stimulation mode does not significantly affect activation threshold or activated retinal area for electrode diameters greater than the retinal thickness. Furthermore, the QMP fraction has a significant effect on VE performance, defined by activation threshold and activated retinal area, when threshold current is evenly ided between two adjacent active electrodes.
A review of computational models of transcranial electrical stimulation.
Publisher: Begell House
Date: 2013
DOI: 10.1615/CRITREVBIOMEDENG.2013007163
Abstract: Transcranial electrical stimulation (tES), which includes transcranial direct current stimulation (tDCS) and electroconvulsive therapy (ECT), has played an important role in the treatment of various psychiatric disorders. Decades of empirical research and clinical experience have led to new and improved brain stimulation techniques, but the mechanisms underlying treatment efficacy and side effects are poorly understood. As part of the ongoing research effort in tES, the value of computational models of transcranial electric current flow has been increasingly recognized, and a proliferation of modeling studies have been published. The complexity of these tES models ranges from simple sphere-based models of the head to high-resolution anatomical reconstructions based on head-image scans. This review provides an up-to-date description and comparison of existing computational models of tES (primarily tDCS and ECT), focusing on the modeling approaches adopted in previous studies and their significant finding.
Quasi-Monopolar Stimulation: A Novel Electrode Design Configuration for Performance Optimization of a Retinal Neuroprosthesis
Publisher: Public Library of Science (PLoS)
Date: 26-08-2013
Mimicking natural neural encoding through retinal electrostimulation
Publisher: IEEE
Date: 05-2017
The role of end‐diastolic myocardial fibre stretch on infarct extension
Publisher: Wiley
Date: 04-12-2019
DOI: 10.1002/CNM.3291
Abstract: Myocardial infarct extension, a process involving the enlargement of infarct and border zone, leads to progressive degeneration of left ventricular (LV) function and eventually gives rise to heart failure. Despite carrying a high risk, the causation of infarct extension is still a subject of much speculation. In this study, patient-specific LV models were developed to investigate the correlation between infarct extension and impaired regional mechanics. Subsequently, sensitivity analysis was performed to examine the causal factors responsible for the impaired regional mechanics observed in regions surrounding the infarct and border zone. From our simulations, fibre strain, fibre stress and fibre stress-strain loop (FSSL) were the key biomechanical variables affected in these regions. Among these variables, only FSSL was correlated with infarct extension, as reflected in its work density dissipation (WDD) index value, with high WDD indices recorded at regions with infarct extension. Impaired FSSL is caused by inadequate contraction force generation during the isovolumic contraction and ejection phases. Our further analysis revealed that the inadequacy in contraction force generation is not necessarily due to impaired myocardial intrinsic contractility, but at least in part, due to inadequate muscle fibre stretch at end-diastole, which depresses the ability of myocardium to generate adequate contraction force in the subsequent systole (according to the Frank-Starling law). Moreover, an excessively stiff infarct may cause its neighbouring myocardium to be understretched at end-diastole, subsequently depressing the systolic contractile force of the neighbouring myocardium, which was found to be correlated with infarct extension.
Selective activation of on and off retinal ganglion cells to high-frequency electrical stimulation: A computational modeling study
Publisher: IEEE
Date: 08-2014
A computational model of direct brain excitation induced by electroconvulsive therapy: Comparison among three conventional electrode placements
Publisher: Elsevier BV
Date: 07-2012
DOI: 10.1016/J.BRS.2011.07.004
Abstract: Electroconvulsive therapy (ECT) is a highly effective treatment for severe depressive disorder. Efficacy and cognitive outcomes have been shown to depend on variations in electrode placement and other stimulus parameters, presumably because of differences in the pattern of neuronal activation. This latter effect, however, is poorly understood. In this study, we present an anatomically accurate human head computational model to stimulate neuronal excitation during ECT, to better understand the effects of varying electrode placement and stimulus parameters. Electric field and current density throughout the head, as well as direct neural activation within the brain, were computed using the finite element method. Regions representing passive volume conductors (skin, skull, cerebrospinal fluid) were extracellularly coupled to an excitable neural continuum region representing the brain. The skull was modeled with anistropic electrical conductivity. Simulation results indicated that direct activation of the brain occurred immediately beneath the electrodes on the scalp, consistent with existing imaging studies. In addition, we found that the brainstem was also activated using a right unilateral electrode configuration. Simulation also demonstrated that a reduction in stimulus litude or pulse width led to a reduction in the spatial extent of brain activation. The novel model described in this study was able to simulate direct excitation of the brain during ECT, was useful in characterizing differences in neuronal activation as electrode placement, pulse width, and litude were altered, and is proposed as a tool for further exploring the effects of variations in ECT stimulation approaches. Results from the simulations assist in understanding recently described clinical phenomena, in particular, the reduction in cognitive side effects with ultrabrief pulse width stimulation, and greater effects of the ECT stimulus on cardiovascular function with unilateral electrode placement.
Shear properties of passive ventricular myocardium
Publisher: American Physiological Society
Date: 12-2002
DOI: 10.1152/AJPHEART.00111.2002
Abstract: We examined the shear properties of passive ventricular myocardium in six pig hearts. S les (3 × 3 × 3 mm) were cut from adjacent regions of the lateral left ventricular midwall, with sides aligned with the principal material axes. Four cycles of sinusoidal simple shear (maximum shear displacements of 0.1–0.5) were applied separately to each specimen in two orthogonal directions. Resulting forces along the three axes were measured. Three specimens from each heart were tested in different orientations to cover all six modes of simple shear deformation. Passive myocardium has nonlinear viscoelastic shear properties with reproducible, directionally dependent softening as strain is increased. Shear properties were clearly anisotropic with respect to the three principal material directions: passive ventricular myocardium is least resistant to simple shear displacements imposed in the plane of the myocardial layers and most resistant to shear deformations that produce extension of the myocyte axis. Comparison of results for the six different shear modes suggests that simple shear deformation is resisted by elastic elements aligned with the microstructural axes of the tissue.
The unique characteristics of on and off retinal ganglion cells: A modeling study
Publisher: IEEE
Date: 08-2014
Revisiting QRS Detection Methodologies for Portable, Wearable, Battery-Operated, and Wireless ECG Systems
Publisher: Public Library of Science (PLoS)
Date: 07-01-2014
Sensitivity Analysis of Left Ventricle with Dilated Cardiomyopathy in Fluid Structure Simulation
Publisher: Public Library of Science (PLoS)
Date: 25-06-2013
A gradient model of cardiac pacemaker myocytes
Publisher: Elsevier BV
Date: 06-2004
Current Steering in Retinal Stimulation via a Quasimonopolar Stimulation Paradigm
Publisher: Association for Research in Vision and Ophthalmology (ARVO)
Date: 21-06-2013
Abstract: Research to restore some degree of vision to patients suffering from retinal degeneration is becoming increasingly more promising. Several groups have chosen electrical stimulation of the remaining network of a degenerate retina as a means to generate discrete light percepts (phosphenes). Approaches vary significantly, with the greatest difference being the location of the stimulating electrode itself. Suprachoroidal positioning offers excellent mechanical stability and surgical simplicity however, at the cost of activation thresholds and focused stimulation due to the distance from the electrodes to the target neurons. Past studies proposed a hexapolar electrode configuration to focus the cortical activation and minimize cross-talk between electrodes during concurrent stimulation. The high impedance nature of the choroid and pigment epithelium, however, cause current to shunt between the stimulating and return electrodes, resulting in even higher activation thresholds. In our study, we analyzed the effect of stimulating the feline retina using a quasimonopolar stimulation by simultaneously stimulating a hexapolar and distant monopolar return configurations. Results of in vivo studies showed that quasimonopolar stimulation can be used to maintain the activation containment properties of hexapolar stimulation, while lowering the activation threshold to values almost equivalent to those of monopolar stimulation. The optimal stimulus was found to be composed of a subthreshold monopolar stimulus combined with a suprathreshold hexapolar stimulation. This resulted in a decrease of activation threshold of 60% with respect to hexapolar alone, but with no discernible deleterious effect on the charge containment of a pure hexapolar stimulation.
Vagal Control of Sinoatrial Rhythm: a Mathematical Model
Publisher: Elsevier BV
Date: 09-1996
Abstract: The ionic mechanisms underlying vagal control of the cardiac pacemaker were investigated using a new single cell mathematical model of sinoatrial node electrical activity. The model was formulated from a wide range of electrophysiological data available in the literature, with particular reference to whole cell recordings from enzymatically isolated sinoatrial node cells. Development of the model was prompted by the lack of an existing physiologically accurate formulation of sinoatrial node activity that could reproduce the known complex chronotropic response of the pacemaker to brief-burst vagal stimulation, as observed in whole animal and isolated sinus node preparations. Features of the model include the dynamic modulation of the hyperpolarisation-activated current (i(f)) and the L-type calcium current (iCa,L) by acetylcholine, the improved characterisation of the muscarinic potassium current (iK,ACh), assigning the entire background potassium current (ib,K) to spontaneous openings of its channels, and the utilisation of second order kinetics for acetylcholine within the neuroeffector junction. Simulations performed using brief vagal stimuli elicited a strong hyperpolarisation of the membrane which prolonged the cycle in which it was delivered in a phase-dependent manner. This phase-dependency was presented in the form of a standard phase response curve which was characterised by a positive linear slope region, a breakpoint characteristic and a "no effect" zone in which the vagal pulse could no longer prolong the cycle. The breakpoint was manifested as a discontinuity in the curve which was examined by bracketing this point at the limit of the double precision arithmetic employed. At these boundary points on either side of the breakpoint, the vagal stimulus was able to activate outward iK,ACh in such a manner as to finely balance the increasing inward iCa,L trying to generate phase 0 upstroke. On decay of iK,ACh, the membrane either subsequently repolarised or fired to produce an action potential depending on the precise phase of the stimulus. The positive linear slope portion of the PRC was characterised by a strong resetting type behaviour in which the membrane hyperpolarised to approximately the same value, irrespective of the phase of stimulus delivery. For vagal stimulus bursts applied throughout the "no effect" zone, outward iK,ACh was not sufficiently activated in order to overcome the strong inward drive of iCa,L and could not prevent upstroke occurring. For these vagal stimuli, the subsequent cycle was hyperpolarised and prolonged. The size of the "no effect" zone was directly related to the inherent latency incorporated in the activation characteristic of iK,ACh. In contrast to previous models of vagal pacemaker control, our new model was able to reproduce the classical triphasic chronotropic response to brief vagal stimulation characterised by a primary inhibition response, a postinhibitory rebound and a secondary inhibition response. In particular, the postinhibitory rebound was due to activation of the inward hyperpolarisation-activated current by the vagally-induced membrane hyperpolarisation, whilst the secondary inhibition phase resulted from the inhibition of the hyperpolarisation-activated current by acetylcholine. The model suggests that the complex chronotropic responses of the cardiac pacemaker to brief vagal stimulation arises from inherent ionic mechanisms operating within the sinoatrial node.
Optimisation of ionic models to fit tissue action potentials: Application to 3D atrial modelling
Publisher: Hindawi Limited
Date: 2013
DOI: 10.1155/2013/951234
Abstract: A 3D model of atrial electrical activity has been developed with spatially heterogeneous electrophysiological properties. The atrial geometry, reconstructed from the male Visible Human dataset, included gross anatomical features such as the central and peripheral sinoatrial node (SAN), intra-atrial connections, pulmonary veins, inferior and superior vena cava, and the coronary sinus. Membrane potentials of myocytes from spontaneously active or electrically paced in vitro rabbit cardiac tissue preparations were recorded using intracellular glass microelectrodes. Action potentials of central and peripheral SAN, right and left atrial, and pulmonary vein myocytes were each fitted using a generic ionic model having three phenomenological ionic current components: one time-dependent inward, one time-dependent outward, and one leakage current. To bridge the gap between the single-cell ionic models and the gross electrical behaviour of the 3D whole-atrial model, a simplified 2D tissue disc with heterogeneous regions was optimised to arrive at parameters for each cell type under electrotonic load. Parameters were then incorporated into the 3D atrial model, which as a result exhibited a spontaneously active SAN able to rhythmically excite the atria. The tissue-based optimisation of ionic models and the modelling process outlined are generic and applicable to image-based computer reconstruction and simulation of excitable tissue.
A continuum model of electrical stimulation of multi-compartmental retinal ganglion cells
Publisher: IEEE
Date: 07-2017
A Method for Control of an Implantable Rotary Blood Pump for Heart Failure Patients Using Noninvasive Measurements
Publisher: Wiley
Date: 08-2011
DOI: 10.1111/J.1525-1594.2011.01268.X
Abstract: We propose a deadbeat controller for the control of pulsatile pump flow (Q(p) ) in an implantable rotary blood pump (IRBP). Noninvasive measurements of pump speed and current are used as inputs to a dynamical model of Q(p) estimation, previously developed and verified in our laboratory. The controller was tested using a lumped parameter model of the cardiovascular system (CVS), in combination with the stable dynamical models of Q(p) and differential pressure (head) estimation for the IRBP. The control algorithm was tested with both constant and sinusoidal reference Q(p) as input to the CVS model. Results showed that the controller was able to track the reference input with minimal error in the presence of model uncertainty. Furthermore, Q(p) was shown to settle to the desired reference value within a finite number of s ling periods. Our results also indicated that counterpulsation yields the minimum left ventricular stroke work, left ventricular end diastolic volume, and aortic pulse pressure, without significantly affecting mean cardiac output and aortic pressure.
Optimal stimulus profiles for neuroprosthetic devices: Monophasic versus biphasic stimulation
Publisher: IEEE
Date: 07-2013
The role of infarct transmural extent in infarct extension: A computational study
Publisher: Wiley
Date: 09-06-2016
DOI: 10.1002/CNM.2794
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.
Modeling aortic valve closure under the action of a ventricular assist device
Publisher: IEEE
Date: 07-2013
An image processing pipeline for segmenting the retinal layers from optical coherence tomography images
Publisher: IEEE
Date: 11-2013
Understanding the retina: A review of computational models of the retina from the single cell to the network level
Publisher: Begell House
Date: 2014
DOI: 10.1615/CRITREVBIOMEDENG.2014011732
Abstract: The vertebrate retina is a clearly organized signal-processing system. It contains more than 60 different types of neurons, arranged in three distinct neural layers. Each cell type is believed to serve unique role(s) in encoding visual information. While we now have a relatively good understanding of the constituent cell types in the retina and some general ideas of their connectivity, with few exceptions, how the retinal circuitry performs computation remains poorly understood. Computational modeling has been commonly used to study the retina from the single cell to the network level. In this article, we begin by reviewing retinal modeling strategies and existing models. We then discuss in detail the significance and limitations of these models, and finally, we provide suggestions for the future development of retinal neural modeling.
A generic cardiac biventricular fluid-electromechanics model
Publisher: IEEE
Date: 07-2017
Practical Considerations in Retinal Neuroprosthesis Design
Publisher: Wiley
Date: 10-04-2006
Vagal entrainment of heart rate is simulated by an integrator with feedback
Publisher: Springer Science and Business Media LLC
Date: 06-2001
DOI: 10.1007/BF03178351
Implications of ultrasound beam shape on the modulation of diffuse light: analysis using spatio-temporal perturbation of the refractive index
Publisher: Springer Science and Business Media LLC
Date: 09-2010
Ion Currents Underlying Sinoatrial Node Pacemaker Activity: A New Single Cell Mathematical Model
Publisher: Elsevier BV
Date: 08-1996
Abstract: The ionic currents underlying autorhythmicity of the mammalian sinoatrial node and their wider contribution to each phase of the action potential have been investigated in this study using a new single cell mathematical model. The new model provides a review and update of existing formulations of sinoatrial node membrane currents, derived from a wide range of electrophysiological data available in the literature. Simulations of spontaneous activity suggest that the dominant mechanism underlying pacemaker depolarisation is the inward background Na+ current, ib,Na. In contrast to previous models, the decay of the delayed rectifying K+ current, iK, was insignificant during this phase. Despite the presence of a pseudo-outward background current throughout the pacemaker range of potentials (Na-K pump+leak currents), the hyperpolarisation-activated current i(f) was not essential to pacemaker activity. A closer inspection of the current-voltage characteristics of the model revealed that the "instantaneous" time-independent current was inward for holding potentials in the pacemaker range, which rapidly became outward within 2 ms due to the inactivation of the L-type Ca2+ current, iCa,L. This suggests that reports in the literature in which the net background current is outward throughout the pacemaker range of potentials may be exaggerated. The magnitudes of the action potential overshoot and the maximum diastolic potential were determined largely by the reversal potentials of iCa,L and iK respectively. The action potential was sustained by the incomplete deactivation of iCa,L and the Na-Ca exchanger, iNaCa. Despite the incorporation of "square-root" activation by [K]o of all K+ currents, the model was unable to correctly simulate the response to elevated [K]o.
Socrates contra Socrates in Plato
Publisher: Cambridge University Press
Date: 11-04-1991
Optimisation of a generic ionic model of cardiac myocyte electrical activity
Publisher: Hindawi Limited
Date: 2013
DOI: 10.1155/2013/706195
Abstract: A generic cardiomyocyte ionic model, whose complexity lies between a simple phenomenological formulation and a biophysically detailed ionic membrane current description, is presented. The model provides a user-defined number of ionic currents, employing two-gate Hodgkin-Huxley type kinetics. Its generic nature allows accurate reconstruction of action potential waveforms recorded experimentally from a range of cardiac myocytes. Using a multiobjective optimisation approach, the generic ionic model was optimised to accurately reproduce multiple action potential waveforms recorded from central and peripheral sinoatrial nodes and right atrial and left atrial myocytes from rabbit cardiac tissue preparations, under different electrical stimulus protocols and pharmacological conditions. When fitted simultaneously to multiple datasets, the time course of several physiologically realistic ionic currents could be reconstructed. Model behaviours tend to be well identified when extra experimental information is incorporated into the optimisation.
Intermittent KHz-frequency electrical stimulation selectively engages small unmyelinated vagal afferents
Publisher: Cold Spring Harbor Laboratory
Date: 02-2021
DOI: 10.1101/2021.01.30.428827
Abstract: Afferent and efferent vagal fibers mediate bidirectional communication between the brain and visceral organs. Small, unmyelinated C-afferents constitute the majority of vagal fibers, play critical roles in numerous interoceptive circuits and autonomic reflexes in health and disease and may contribute to the efficacy and safety of vagus nerve stimulation (VNS). Selective engagement of C-afferents with electrical stimuli has not been feasible, due to the default fiber recruitment order: larger fibers first, smaller fibers last. Here, we determine and optimize an electrical stimulus that selectively engages vagal C-afferents. Intermittent KHz-frequency electrical stimulation (KES) activates motor and, preferentially, sensory vagal neurons in the brainstem. During KES, asynchronous activity of C-afferents increases, while that of larger fibers remains largely unchanged. In parallel, KES effectively blocks excitability of larger fibers while moderately suppressing excitability of C-afferents. By compiling selectivity indices in in idual animals, we find that optimal KES parameters for C-afferents are KHz frequency and 7-10 times engagement threshold (×T) intensity in rats, 15-25×T in mice. These effects can be explained in computational models by how sodium channel responses to KES are shaped by axonal size and myelin. Our results indicate that selective engagement of vagal C-afferents is attainable by intermittent KES.
A hybrid symplectic principal component analysis and central tendency measure method for detection of determinism in noisy time series with application to mechanomyography
Publisher: AIP Publishing
Date: 06-2013
DOI: 10.1063/1.4812287
Abstract: We present a hybrid symplectic geometry and central tendency measure (CTM) method for detection of determinism in noisy time series. CTM is effective for detecting determinism in short time series and has been applied in many areas of nonlinear analysis. However, its performance significantly degrades in the presence of strong noise. In order to circumvent this difficulty, we propose to use symplectic principal component analysis (SPCA), a new chaotic signal de-noising method, as the first step to recover the system dynamics. CTM is then applied to determine whether the time series arises from a stochastic process or has a deterministic component. Results from numerical experiments, ranging from six benchmark deterministic models to 1/f noise, suggest that the hybrid method can significantly improve detection of determinism in noisy time series by about 20 dB when the data are contaminated by Gaussian noise. Furthermore, we apply our algorithm to study the mechanomyographic (MMG) signals arising from contraction of human skeletal muscle. Results obtained from the hybrid symplectic principal component analysis and central tendency measure demonstrate that the skeletal muscle motor unit dynamics can indeed be deterministic, in agreement with previous studies. However, the conventional CTM method was not able to definitely detect the underlying deterministic dynamics. This result on MMG signal analysis is helpful in understanding neuromuscular control mechanisms and developing MMG-based engineering control applications.
Comparison of three right-unilateral electroconvulsive therapy montages.
Publisher: IEEE
Date: 07-2013
Multiphysics Computational Modelling of the Cardiac Ventricles
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2022
Simulation of motor current waveform as an index for aortic valve open-close condition during ventricular support
Publisher: IEEE
Date: 08-2014
Multipolar Field Shaping in a Suprachoroidal Visual Prosthesis
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2017
Mathematical studies of the effects of acetylcholine on pacemaker activity in the mammalian sinoatrial node
Publisher: IEEE
Date: 10-2014
Effects of modifying the electrode placement and pulse width on cognitive side effects with unilateral ECT: A pilot randomised controlled study with computational modelling
Publisher: Elsevier BV
Date: 11-2021
DOI: 10.1016/J.BRS.2021.09.014
Abstract: The electrode placement and pulse width for electroconvulsive therapy (ECT) are important treatment parameters associated with ECT related retrograde memory side-effects. Modification of these parameters with right unilateral (RUL) ECT may have utility for further reducing these side-effects. This study explored use of the frontoparietal (FP) placement for reducing retrograde memory side effects with ECT. We hypothesised that superior retrograde memory outcomes would occur with FP compared to temporoparietal (TP) placement and with ultrabrief (UB: 0.3 ms) compared to brief pulse (BP: 1.0 ms) width ECT. In this randomised cross-over, double-blinded study, participants received a single treatment of BP TP, BP FP, UB TP and UB FP ECT. Neuropsychological testing was conducted prior to and immediately following each treatment. Computational modelling was conducted to explore associations between E-fields in regions-of-interest associated with memory. Nine participants completed the study. The FP placement was not superior to TP for retrograde memory outcomes. For both electrode placements UB pulse width was associated with significantly better visual retrograde memory compared to BP (p < .05). With TP ECT, higher E-fields in regions-of-interest were significantly associated with greater visual retrograde memory side-effects (hippoc i: r = -0.77, p = .04 inferior frontal gyri: r = -0.92, p < .01 middle frontal gyri: r = -0.84, p = .02). Modification of pulse-width had greater effects than electrode placement for reducing retrograde memory side-effects with RUL ECT. Preliminary findings suggested that higher E-fields may be associated with greater cognitive side-effects with ECT.
Computational evaluation of an extra-aortic elastic-wrap applied to simulated aging anisotropic human aorta models
Publisher: Springer Science and Business Media LLC
Date: 27-12-2019
DOI: 10.1038/S41598-019-56609-2
Abstract: Structural changes occurring to the aortic wall can result in vascular stiffening. This is represented by a loss of vascular compliance during pulsatile flow, resulting in increased systolic and pulse blood pressure, particularly in populations aged 50 and over. Aortic stiffness is thought to be permanent and an active de-stiffening strategy is yet to be developed. Extra aortic elastic wrapping has been proposed as a surgical technique to boost aortic distensibility and treat hypertension in the elderly. Previously, in-vivo and in-vitro testing have suggested a pulse-pressure reduction potential of elastic wrapping in the stiffened aortas. Herein, we explore the feasibility of elastic aortic wrapping to improve simulated aortic compliance across the age span. Detailed computational studies of the anisotropic aortic wall mechanics, using data from human subjects, were performed, evaluating key performance properties for the interaction between the aortic wall and elastic aortic wrap procedure. Main determinants of the procedure’s efficiency are identified using a pre-defined aortic stiffness and wrap elasticity. Finite element analysis predicts that segmental aortic distensibility can be increased if elastic wrapping is applied to a simulated stiff aorta. Elastic aortic wrapping is calculated to have little impact on the compliance of an initially distensible aorta.
Computational Models of Neural Retina
Publisher: Springer New York
Date: 2014
The Effect of Transcranial Direct Current Stimulation (tDCS) Electrode Size and Current Intensity on Motor Cortical Excitability: Evidence From Single and Repeated Sessions
Publisher: Elsevier BV
Date: 2016
DOI: 10.1016/J.BRS.2015.08.003
Abstract: Current density is considered an important factor in determining the outcomes of tDCS, and is determined by the current intensity and electrode size. Previous studies examining the effect of these parameters on motor cortical excitability with small s le sizes reported mixed results. This study examined the effect of current intensity (1 mA, 2 mA) and electrode size (16 cm(2), 35 cm(2)) on motor cortical excitability over single and repeated tDCS sessions. Data from seven studies in 89 healthy participants were pooled for analysis. Single-session data were analyzed using mixed effects models and repeated-session data were analyzed using mixed design analyses of variance. Computational modeling was used to examine the electric field generated. The magnitude of increases in excitability after anodal tDCS was modest. For single-session tDCS, the 35 cm(2) electrodes produced greater increases in cortical excitability compared to the 16 cm(2) electrodes. There were no differences in the magnitude of cortical excitation produced by 1 mA and 2 mA tDCS. The repeated-sessions data also showed that there were greater increases in excitability with the 35 cm(2) electrodes. Further, repeated sessions of tDCS with the 35 cm(2) electrodes resulted in a cumulative increase in cortical excitability. Computational modeling predicted higher electric field at the motor hotspot for the 35 cm(2) electrodes. 2 mA tDCS does not necessarily produce larger effects than 1 mA tDCS in healthy participants. Careful consideration should be given to the exact positioning, size and orientation of tDCS electrodes relative to cortical regions.
Simulation of aortic valve dynamics during ventricular support
Publisher: IEEE
Date: 08-2015
Numerical investigation of the effect of cannula placement on thrombosis
Publisher: Springer Science and Business Media LLC
Date: 16-05-2013
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.
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