95 research outputs found
Overdrive pacing of spiral waves in a model of human ventricular tissue
High-voltage electrical defibrillation remains the only reliable method of quickly controlling life-threatening cardiac arrhythmias. This paper is devoted to studying an alternative approach, low-voltage cardioversion (LVC), which is based on ideas from non-linear dynamics and aims to remove sources of cardiac arrhythmias by applying high-frequency stimulation to cardiac tissue. We perform a detailed in-silico study of the elimination of arrhythmias caused by rotating spiral waves in a TP06 model of human cardiac tissue. We consider three parameter sets with slopes of the APD restitution curve of 0.7, 1.1 and 1.4, and we study LVC at the baseline and under the blocking of INa and ICaL and under the application of the drugs verapamil and amiodarone. We show that pacing can remove spiral waves; however, its efficiency can be substantially reduced by dynamic instabilities. We classify these instabilities and show that the blocking of INa and the application of amiodarone increase the efficiency of the method, while the blocking of ICaL and the application of verapamil decrease the efficiency. We discuss the mechanisms and the possible clinical applications resulting from our study
Upper limit on the ultra-high-energy photon flux from AGASA and Yakutsk data
We present the interpretation of the muon and scintillation signals of
ultra-high-energy air showers observed by AGASA and Yakutsk extensive air
shower array experiments. We consider case-by-case ten highest energy events
with known muon content and conclude that at the 95% confidence level (C.L.)
none of them was induced by a primary photon. Taking into account statistical
fluctuations and differences in the energy estimation of proton and photon
primaries, we derive an upper limit of 36% at 95% C.L. on the fraction of
primary photons in the cosmic-ray flux above 10^20 eV. This result disfavors
the Z-burst and superheavy dark-matter solutions to the GZK-cutoff problem.Comment: revtex, 8 pages, 4 figure
Scroll wave with negative filament tension in a model of the left ventricle of the human heart and its overdrive pacing
Nonlinear waves of electrical excitation initiate cardiac contraction. Abnormal wave propagation in the heart, e.g., spiral waves, can lead to sudden cardiac arrest. This study analyzed the dynamics of spiral waves under the influence of an instability called negative filament tension, and examined how the spiral waves can be eliminated through high-frequency pacing. A generic anatomical model of the left ventricle of the human heart and the Aliev-Panfilov model for cardiac tissue were used. The study showed that the source of such arrhythmia is elongated filaments with lengths that can be 10-20 times greater than the characteristic thickness of the heart wall. In anisotropic tissue, the filament elongated before it was annihilated at the base of the heart. The spiral waves were eliminated through overdrive pacing with stimulation periods from 0.8 to 0.95 relative to the spiral wave period. The minimum time for the expulsion was about 10 s. © 2021 American Physical Society.Russian Science Foundation, RSF: 17-71-20024Our work involved simulations at the “Uran” cluster of IMM UB RAS (Ekaterinburg). Our research is supported by a Russian Science Foundation grant (Project 17-71-20024)
Induced Drift of Scroll Waves in the Aliev-Panfilov Model and in an Axisymmetric Heart Left Ventricle
The low-voltage cardioversion-defibrillation is a modern sparing electrotherapy method for such dangerous heart arrhythmias as paroxysmal tachycardia and fibrillation. In an excitable medium, such arrhythmias relate to appearance of spiral waves of electrical excitation, and the spiral waves are superseded to the electric boundary of the medium in the process of treatment due to high-frequency stimulation from the electrode. In this paper we consider the Aliev-Panfilov myocardial model, which provides a positive tension of three-dimensional scroll waves, and an axisymmetric model of the left ventricle of the human heart. Two relations of anisotropy are considered, namely, isotropy and physiological anisotropy. The periods of stimulation with an apical electrode are found so that the electrode successfully entrains its rhythm in the medium, the spiral wave is superseded to the base of the ventricle, and disappears. The results are compared in two-dimensional and three-dimensional media. The intervals of effective stimulation periods are sufficiently close to each other in the two-dimensional case and in the anatomical model. However, the use of the anatomical model is essential in determination of the time of superseding. © 2020 Walter de Gruyter GmbH, Berlin/Boston 2020.The work was supported by the Russian Science Foundation (project No. 17–71–20024). The work was performed with the use of the ‘URAN’ supercomputer of IMM UB RAS
The use of the Cherenkov radiation and the fluorescence light to calibrate the energy of giant air showers
In terms of the quark-gluon string model the analysis of the classic
procedure to estimate the energy of giant air showers with help of the
parameter s(600) (a density of energy deposition in the scintillator at a
distance of 600 m from the shower core) have been carried out. Simulations of
the signal s(600) with help of the CORSIKA code in terms of the hybrid scheme
show energy estimates which are approximately a factor of 1.6 times lower than
adopted at the Yakutsk array. The energy estimates calculated with the help of
the Cherenkov radiation coincide with the experimental data. Simulations of
deposited energy distributions in the atmosphere with help of the GEANT4 code
and the CORSIKA code show that more than 20% of this energy may be deposited at
distances above 100 m from the shower axis.Comment: 10 pages, 5 figure
Cosmic Rays: The Second Knee and Beyond
We conduct a review of experimental results on Ultra-High Energy Cosmic Rays
(UHECR's) including measurements of the features of the spectrum, the
composition of the primary particle flux and the search for anisotropy in event
arrival direction. We find that while there is a general consensus on the
features in the spectrum -- the Second Knee, the Ankle, and (to a lesser
extent) the GZK Cutoff -- there is little consensus on the composition of the
primaries that accompany these features. This lack of consensus on the
composition makes interpretation of the agreed upon features problematic. There
is also little direct evidence about potential sources of UHECRs, as early
reports of arrival direction anisotropies have not been confirmed in
independent measurements.Comment: 46 pages, 30 figures. Topical Review to appear in J. Physics
Measuring extensive air showers with Cherenkov light detectors of the Yakutsk array: The energy spectrum of cosmic rays
The energy spectrum of cosmic rays in the range 10^15 eV to 6*10^19 eV has
been studied using the air Cherenkov light detectors of the Yakutsk array. The
total flux of photons produced by relativistic electrons (including positrons
as well, hereafter) of extensive air showers in the atmosphere is used as the
energy estimator of the primary particle initiating a shower. The resultant
differential flux of cosmic rays exhibits, in accordance with previous
measurements, a knee and ankle features at energies 3*10^15 and ~10^19 eV,
respectively. A comparison of observational data with simulations is made in
the knee and ankle regions in order to choose the models of galactic and
extragalactic components of cosmic rays which describe better the energy
spectrum measured.Comment: 27 pages, 22 figures, accepted for publication in New Journal of
Physics (Focus Issue
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