1,721,022 research outputs found
Dynamical effects of myocardial ischemia in anisotropic cardiac models in three dimensions
No full textThe interaction between the presence of moderate or severe
subendocardial ischemic regions and the anisotropic structure of the cardiac
muscle is investigated here by means of numerical simulations based on
anisotropic Bidomain and Monodomain models. The ischemic effects on cardiac
excitation, recovery and distribution of action potential duration are
discussed, showing the presence of ischemic epicardial markers. Extracellular
potential distributions during the ST and TQ intervals are computed separately
using non-stationary models. During the ST interval, the extracellular
potential patterns differ from those simulated with stationary models used in
the literature. These differences are explained by decomposing the cardiac
current sources into conormal, axial and orthogonal components and determining
which component is dominant during the ST and TQ intervals
Prevention and control of OQDS (olive quick decline syndrome) outbreaks caused by Xylella fastidiosa
No full textIn Southern Italy, since 2013, there has been an ongoing Olive Quick Decline Syndrome (OQDS) outbreak, due to the bacterium Xylella fastidiosa, which has caused a dramatic impact from both socio-economic and environmental points of view. The main players involved in OQDS are represented by the insect vector, Philaenus spumarius, its host plants (olive trees and weeds) and the bacterium, X. fastidiosa. Current agronomic practices are mainly based on uprooting the sick olive trees and their surrounding ones, with later installment of olive cultivars more resistant to the bacterium infection. Unfortunately, both of these practices are having an undesirable impact on the environment (most of these olive trees were monumental ones) and on the economy. Based on a mathematical model expressed in terms of a nontrivial system of ordinary differential equations, our analysis has provided a clear picture of all possible steady states (feasible equilibria) and their stability properties, corresponding to a variety of different parameter scenarios; all of this has been illustrated by a set of computational experiments. A significant original contribution of this paper is the proof of the global asymptotic stability of each of the feasible equilibria under its existence assumptions, a fact that excludes multiple equilibria under the given conditions. It has emerged that the removal of a suitable amount of weed biomass (host plants of the juvenile stages of the insect vector of X. fastidiosa) from olive orchards and surrounding areas leads to the eradication of the epidemic, without requiring neither the removal nor the substitution of the existing olive trees
A reliability analysis of cardiac repolarization time markers
No full textTwo widely used markers of cardiac repolarization time are the time RT of minimum
derivative during the downstroke of the transmembrane action potential (TAP) and the
time RT90 when the TAP reaches 90\% of its resting value. These two markers are
generally taken as the gold standards for comparison with other markers assessing
repolarization time from the T wave of the unipolar electrogram.The results show a high correlation between the extracellular and transmembrane markers,
irrespective of T wave polarity.
However, the extracellular markers may be locally inaccurate in estimating the repolarization sequence
and large discrepancies may ensue when they are compared with transmembrane markers.
As a consequence, the spatial distribution of activation-recovery intervals (ARI)
is not always an accurate estimate of the spatial distribution of action potential durations (APD)
Computing cardiac recovery maps from electrograms and monophasic action potentials under heterogeneous and ischemic conductions
No full textVirtual Element Method and Topology Optimization on polygonal meshes
Full text linkTopology optimization is a fertile area of research that is mainly concerned with the automatic generation of optimal layouts to solve design problems in Engineering. The classical formulation addresses the problem of finding the best distribution of an isotropic material that minimizes the work of the external loads at equilibrium, while respecting a constraint on the assigned amount of volume. This is the so-called minimum compliance formulation that can be conveniently employed to achieve stiff truss-like layout within a two-dimensional domain. A classical implementation resorts to the adoption of four node displacement-based finite elements that are coupled with an elementwise discretization of the (unknown) density field. When regular meshes made of square elements are used, well-known numerical instabilities arise, see in particular
the so-called checkerboard patterns. On the other hand, when unstructured meshes are needed to cope with geometry of any shape, additional instabilities can steer the optimizer towards local minima instead of the expected global one. Unstructured meshes approximate the strain energy of truss-like members with an accuracy that is strictly related to the geometrical features of the discretization, thus remarkably affecting the achieved layouts. In this talk we will consider several benchmarks of truss design and explore the performance of the Virtual Element Method (VEM) in driving the topology optimization procedure. In particular, we will show how the capability of VEM of efficiently approximating elasticity equations on very general polygonal meshes can contribute to overcome the aforementioned mesh-dependent instabilities exhibited by classical finite element based discretization techniques
Determining recovery times from transmembrane action potentials and unipolar electrograms in normal heart tissue
No full textIn this study, we quantitatively analyze some frequently used
markers of recovery time, derived from the transmembrane action potentials
and from unipolar extracellular electrograms. To this end, we
performed 3D numerical simulations by using the anisotropic bidomain
model of normal cardiac tissue, coupled with the Luo-Rudy phase I membrane
model. We show that the extracellular markers considered are very
accurate estimates of (and very well correlated with) the transmembrane
action potential markers of the repolarization phase, irrespective of Twave
polarity, repolarization sequence, and transmural distribution of
intrinsic properties of the cell membrane
GDSW preconditioners for composite Discontinuous Galerkin discretizations of multicompartment reaction–diffusion problems
Full text linkThe aim of the present work is to design, analyze theoretically, and test numerically, a generalized Dryja–Smith–Widlund (GDSW) preconditioner for composite Discontinuous Galerkin discretizations of multicompartment parabolic reaction–diffusion equations, where the solution can exhibit natural discontinuities across the domain. We prove that the resulting preconditioned operator for the solution of the discrete system arising at each time step converges with a scalable and quasi-optimal upper bound for the condition number. The GDSW preconditioner is then applied to the EMI (Extracellular - Membrane - Intracellular) reaction–diffusion system, recently proposed to model microscopically the spatiotemporal evolution of cardiac bioelectrical potentials. Numerical tests validate the scalability and quasi-optimality of the EMI-GDSW preconditioner, and investigate its robustness with respect to the time-step size as well as jumps in the diffusion coefficients
Effects of anisotropy and transmural hetrogeneity on the T-wave polarity of simulated electrograms
No full texthe major determinants of the T wave polarity in electrocardiograms (ECGs) are still a debated issue.
The aim of this work is to investigate the effects of tissue anisotropy, cellular action potential
duration (APD) heterogeneities and excitation wavefront shape on the T wave polarity in unipolar and bipolar ECGs,
simulated in a conducting medium surrounding the cardiac tissue at some distance fom endo to epicardium.
The study is based on three-dimensional anisotropic Monodomain simulations of the entire depolarization
and repolarization phases of propagating action potentials in a parallelepipedal slab.
The results show that the T wave of unipolar ECGs is positive at all sites explored
and its shape and polarity are
mainly determined by the anisotropy of the cardiac tissue, irrespective of cellular
APD heterogeneities and shape of the excitation wavefront.
On the other hand, bipolar ECGs are mainly affected by their isotropic component and their T wave
turns out to be positive for single site stimulations
in the presence of transmural APD heterogeneity, while it becomes always negative in case of multiple sites
stimulation generating
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