Military Academy

About: Military Academy is a based out in . It is known for research contribution in the topics: Population & Context (language use). The organization has 2478 authors who have published 3003 publications receiving 33188 citations.

Cardiac Rhythm Variability: Approaches to Mechanisms

Abstract: Physiological mechanisms of cardiac rhythm variability (CRV) are reviewed. The results of original experiments are discussed together with the history of the problem and data available from the literature. Special emphasis is placed on the spectral analysis of cardiac rhythm. Various mechanisms of the generation of periodic and aperiodic components of CRV are considered. Although the variability of cardiac rhythm has been studied for many years in many laboratories worldwide, fine mechanisms of CRV remain obscure. However, a number of specific features of CRV are presently widely recognized. Periodic CRV components isolated from short-term records in patients at rest are represented by high-frequency, low-frequency, and very low-frequency oscillations. Fourier-transform spectral analysis of cardiac rhythm is the most appropriate method of the detection of these oscillations. High-frequency components are associated with respiration and represent the effects of the parasympathetic nervous system on myocardium. Low-frequency components are due to the activity of the postganglionic sympathetic fibers and represent the processes of cardiac rhythm modulation by the sympathetic nervous system. Genesis of very low-frequency oscillations is still uncertain. Most probably, these oscillations are associated with the effects of suprasegmental (primarily, hypothalamic) centers of autonomic regulation. Aperiodic CRV components represent random events associated with the reflex regulation of the heart rate by external or internal factors. Because aperiodic components significantly modify the results of the CRV analysis, the effects of these factors should be eliminated. It is concluded that because many problems associated with cardiac rhythm variability remain to be solved, extensive research in this direction should be continued.

Atrial Fibrillation Dynamics and Ionic Block Effects in Six Heterogeneous Human 3D Virtual Atria with Distinct Repolarization Dynamics

Abstract: Atrial fibrillation (AF) usually manifests as reentrant circuits propagating through the whole atria creating chaotic activation patterns. Little is yet known about how differences in electrophysiological and ionic properties between patients modulate reentrant patterns in AF. The goal of this study is to quantify how variability in action potential duration (APD) at different stages of repolarization determines AF dynamics and their modulation by ionic block using a set of virtual whole-atria human models. Six human whole-atria models are constructed based on the same anatomical structure and fibre orientation, but with different electrophysiological phenotypes. Membrane kinetics for each whole-atria model are selected with distinct APD characteristics at 20, 50 and 90% repolarization, from an experimentally-calibrated population of human atrial action potential models including AF remodeling and acetylcholine parasympathetic effects. Our simulations show that in all whole-atria models, reentrant circuits tend to organize around the pulmonary veins and the right atrial appendage, thus leading to higher dominant frequency (DF) and more organized activation in the left atrium than in the right atrium. Differences in APD in all phases of repolarization (not only APD90) yielded quantitative differences in fibrillation patterns with long APDs associated with slower and more regular dynamics. Long APD50 and APD20 were associated with increased inter-atrial conduction block and inter-atrial differences in DF and OI, creating reentry instability and self-termination in some cases. Specific inhibitions of IK1, INaK or INa reduce DF and organization of the arrhythmia by enlarging wave meandering, reducing the number of secondary wavelets and promoting inter-atrial block in all six virtual patients, especially for the phenotypes with short APD at 20, 50 and/or 90% repolarization. This suggests that therapies aiming at prolonging the early phase of repolarization might constitute effective anti-arrhythmic strategies for the pharmacological management of AF. In summary, simulations report significant differences in atrial fibrillatory dynamics resulting from differences in APD at all phases of repolarization.

Magnetoelectronic properties of nanographite ribbons

Abstract: Magnetoelectronic structures of the AA- and AB-stacked nanographite ribbons, which strongly depend on magnitude and direction of magnetic field, ribbon edges, and interribbon interactions, are studied within the frame of tight-binding model. First, the origins of Landau subbands and additional spectra, induced by the perpendicular magnetic field B ⊥ , chiefly changing the intraribbon interaction, are analytically studied in the zigzag systems. This method allows us to intuitively understand the magnetoband structures of the finite size systems. Then, the interribbon interactions modify Landau subbands and change energy dispersions, energy spacing, bandwidth and oscillation period of Landau subbands. On the other hand, the parallel magnetic field B ∥ changes the interribbon interactions and leads to the Landau levels along k ^ z . Furthermore, B ∥ can induce the metal–insulator transition in the AB-stacked armchair ribbons. Above all, magnetic field and interribbon interactions vitalize the magnetoband structures. So, there are rich structures in density of states: sharp peaks, square-root peaks, logarithmic divergences and oscillating structures. Finally, DOS can clearly exhibit 0D, 1D and 2D characteristics. And this specific is expected to have great effects on the physical properties, e.g. optical, magnetic and transport properties, of the stacked ribbons.