Generation Of Beats Research Articles

Повышение акустической безопасности производственного помещения

Sound-emitting production and technological as well as engineering equipment located within the enclosed space of industrial premises can form paired interacting sound fields with similar values of expressed dominant emission frequencies in the spectra, ultimately causing the formation of a physical process of sound vibration beats. The process manifests in negative psychoacoustic impacts on a human characterized by pulsating sound pressure levels over time with a pulsation frequency equal to the difference between similar frequency values of discrete components of interacting sound fields. The article provides the results of experimental studies to determine the required value of frequency mismatch of sound fields for individual sources of noise emissions mounted in industrial premises. The industrial premises have been presented as a rectangular parallelepiped with rigid sound-reflective fences. Simulation experiments have been carried out using an electroacoustic sound-emitting system represented as two autonomous sound-emitters — electroacoustic loudspeakers. The loudspeakers have simulated noise-generating engineering units with the specified passport steady-state speed operating modes ns and accompanied by the respective established physical processes of sound energy emission whose spectral composition contains specific discrete values of operating dominant functional sound frequencies fs. The technical result of the study is achieved by the implementation of a sufficient degree of frequency mismatch of expressed discrete components of sound emissions of individual autonomous sources of noise preventing the formation of the physical process of generation of intense sound vibration beats. The suggested technical method aiming to increase the acoustic safety of industrial premises assumes that the discrete values of operating dominant functional sound frequencies fs differ from each other by a limiting value Δf exceeding the value of 5 Hz.

Ectopic beats arise from micro-reentries near infarct regions in simulations of a patient-specific heart model

Ectopic beats are known to be involved in the initiation of a variety of cardiac arrhythmias. Although their location may vary, ectopic excitations have been found to originate from infarct areas, regions of micro-fibrosis and other heterogeneous tissues. However, the underlying mechanisms that link ectopic foci to heterogeneous tissues have yet to be fully understood. In this work, we investigate the mechanism of micro-reentry that leads to the generation of ectopic beats near infarct areas using a patient-specific heart model. The patient-specific geometrical model of the heart, including scar and peri-infarct zones, is obtained through magnetic resonance imaging (MRI). The infarct region is composed of ischemic myocytes and non-conducting cells (fibrosis, for instance). Electrophysiology is captured using an established cardiac myocyte model of the human ventricle modified to describe ischemia. The simulation results clearly reveal that ectopic beats emerge from micro-reentries that are sustained by the heterogeneous structure of the infarct regions. Because microscopic information about the heterogeneous structure of the infarct regions is not available, Monte-Carlo simulations are used to identify the probabilities of an infarct region to behave as an ectopic focus for different levels of ischemia and different percentages of non-conducting cells. From the proposed model, it is observed that ectopic beats are generated when a percentage of non-conducting cells is near a topological metric known as the percolation threshold. Although the mechanism for micro-reentries was proposed half a century ago to be a source of ectopic beats or premature ventricular contractions during myocardial infarction, the present study is the first to reproduce this mechanism in-silico using patient-specific data.

Killing Many Birds With Two Stones: Hypoxia and Fibrosis Can Generate Ectopic Beats in a Human Ventricular Model.

During cardiac diseases many types of anatomical and functional remodeling of cardiac tissue can occur. In this work, we focus on two conditions: hypoxia and fibrosis, which are part of complex pathological modifications that take place in many cardiac diseases (hypertrophic cardiomyopathy, hypertensive heart disease, and recurrent myocardial infarction) and respiratory diseases (obstructive pulmonary disease, obstructive sleep apnea, and cystic fibrosis). Using computational models of cardiac electrophysiology, we evaluate if the interplay between hypoxia and fibrosis is sufficient to trigger cardiac arrhythmia. We study the mechanisms behind the generation of ectopic beats, an arrhythmic trigger also known as premature ventricular contractions (PVCs), in regions with high hypoxia and fibrosis. First, we modify an electrophysiological model of myocytes of the human left ventricle to include the effects of hypoxia. Second, diffuse fibrosis is modeled by randomly replacing cardiac myocytes by non-excitable and non-conducting cells. The Monte Carlo method is used to evaluate the probability of a region to generate ectopic beats with respect to different levels of hypoxia and fibrosis. In addition, we evaluate the minimum size of three-dimensional slabs needed to sustain reentries for different stimulation protocols. The observed mechanism behind the initiation of ectopic beats is unidirectional block, giving rise to sustained micro-reentries inside the region with diffuse fibrosis and hypoxia. In summary, our results suggest that hypoxia and fibrosis are sufficient for the creation of a focal region in the heart that generates PVCs.

Correlated microtiming deviations in jazz and rock music.

Musical rhythms performed by humans typically show temporal fluctuations. While they have been characterized in simple rhythmic tasks, it is an open question what is the nature of temporal fluctuations, when several musicians perform music jointly in all its natural complexity. To study such fluctuations in over 100 original jazz and rock/pop recordings played with and without metronome we developed a semi-automated workflow allowing the extraction of cymbal beat onsets with millisecond precision. Analyzing the inter-beat interval (IBI) time series revealed evidence for two long-range correlated processes characterized by power laws in the IBI power spectral densities. One process dominates on short timescales (t < 8 beats) and reflects microtiming variability in the generation of single beats. The other dominates on longer timescales and reflects slow tempo variations. Whereas the latter did not show differences between musical genres (jazz vs. rock/pop), the process on short timescales showed higher variability for jazz recordings, indicating that jazz makes stronger use of microtiming fluctuations within a measure than rock/pop. Our results elucidate principles of rhythmic performance and can inspire algorithms for artificial music generation. By studying microtiming fluctuations in original music recordings, we bridge the gap between minimalistic tapping paradigms and expressive rhythmic performances.

Experimental Observation of Chaotic Beats in Oscillators Sharing Nonlinearity

This paper deals with the generation of chaotic beats in a system of two forced dissipative LCR oscillators sharing a nonlinear element. The presence of two external periodic excitations and a common nonlinear element in the chosen system enables the facile generation of chaotic beats. Thus rendered chaotic beats were characterized in both time domain and phase space. Lyapunov exponents and envelope of the beats were computed to diagnose the chaotic nature of the signals. The role of common nonlinearity on the complexity of the generated beats is discussed. Real-time experimental hardware implementation has also been done to confirm the subsistence of the phenomenon, for the first time. Extensive Multisim simulations were carried out to understand, a bit more about the shrinkage and revivals of state variables in phase space.

Simulation of Ectopic Pacemakers in the Heart: Multiple Ectopic Beats Generated by Reentry inside Fibrotic Regions.

The inclusion of nonconducting media, mimicking cardiac fibrosis, in two models of cardiac tissue produces the formation of ectopic beats. The fraction of nonconducting media in comparison with the fraction of healthy myocytes and the topological distribution of cells determines the probability of ectopic beat generation. First, a detailed subcellular microscopic model that accounts for the microstructure of the cardiac tissue is constructed and employed for the numerical simulation of action potential propagation. Next, an equivalent discrete model is implemented, which permits a faster integration of the equations. This discrete model is a simplified version of the microscopic model that maintains the distribution of connections between cells. Both models produce similar results when describing action potential propagation in homogeneous tissue; however, they slightly differ in the generation of ectopic beats in heterogeneous tissue. Nevertheless, both models present the generation of reentry inside fibrotic tissues. This kind of reentry restricted to microfibrosis regions can result in the formation of ectopic pacemakers, that is, regions that will generate a series of ectopic stimulus at a fast pacing rate. In turn, such activity has been related to trigger fibrillation in the atria and in the ventricles in clinical and animal studies.

Generation of undamped exciton-biexciton beats in InAs quantum dots using six-wave mixing

Generation of undamped exciton-biexciton beats in InAs quantum dots using six-wave mixing

Partial Uncoupling of Impulse Source to Atrial Tissue by Ablation Triggers De Novo Ectopic Beats Through Paradoxical Improvement of Impulse Propagation

Background A source-sink mechanism plays a crucial role in transmission of electrical impulse to tissue. We hypothesized that partial uncoupling of impulse source to tissue by ablation might generate ectopic beats. Methods Canine right atrial preparations (n = 5) were coronary perfused and optically mapped using ANBDQBS, a near-infrared voltage-sensitive dye, to assess the origin and spread of excitation in transmural layers. The sinus node (SN) and surrounding atrial tissue in the field of view were reconstructed after Masson-trichrome, H&E, and immunofluorescence. Masson-trichrome histology was merged with the optical mapping. Cryoablation at –70°C for >3 minutes was performed in the SN and the atrial tissue. Results At baseline, sinus impulse originated from a specific cluster of the histologically demarcated SN (n = 5, 124 ± 23 bpm). Random extensive cryoablation on the SN and atrial tissue caused de novo activation of the ectopic foci outside the field of view (n = 3/5). We also observed the ectopic focus outside the histologic SN independently producing only spontaneous electrical oscillatory waves at baseline before ablation (n = 1), which was composed of HCN4 + cells in immunohistochemistry. However, this isolated electrical activity failed to propagate to the large atrium, as evidenced by the inability of this cluster to generate P waves on the pseudo-ECG. We created partial uncoupling of the nonpropagated ectopic source to the large atrium by cryoablation. In contrast to preablation, the nonpropagated ectopic source acquired the ability to propagate to the surviving atrial myocardium and generated ectopic beats. Conclusions The current study suggests that incomplete ablation may induce ectopic beats through paradoxical improvement of impulse conduction to the cardiac tissue by reducing coupling of impulse source to atrial sink. The current study may provide a mechanistic insight and clinical implications on generation of ectopic beats.

Loss of H3K4 methylation destabilizes gene expression patterns and physiological functions in adult murine cardiomyocytes

Histone H3 lysine 4 (H3K4me) methyltransferases and their cofactors are essential for embryonic development and the establishment of gene expression patterns in a cell-specific and heritable manner. However, the importance of such epigenetic marks in maintaining gene expression in adults and in initiating human disease is unclear. Here, we addressed this question using a mouse model in which we could inducibly ablate PAX interacting (with transcription-activation domain) protein 1 (PTIP), a key component of the H3K4me complex, in cardiac cells. Reducing H3K4me3 marks in differentiated cardiomyocytes was sufficient to alter gene expression profiles. One gene regulated by H3K4me3 was Kv channel-interacting protein 2 (Kcnip2), which regulates a cardiac repolarization current that is downregulated in heart failure and functions in arrhythmogenesis. This regulation led to a decreased sodium current and action potential upstroke velocity and significantly prolonged action potential duration (APD). The prolonged APD augmented intracellular calcium and in vivo systolic heart function. Treatment with isoproterenol and caffeine in this mouse model resulted in the generation of premature ventricular beats, a harbinger of lethal ventricular arrhythmias. These results suggest that the maintenance of H3K4me3 marks is necessary for the stability of a transcriptional program in differentiated cells and point to an essential function for H3K4me3 epigenetic marks in cellular homeostasis.

Synchronization of Spontaneous Calcium Waves in Cardiac Muscle

Spontaneous sarcoplasmic reticulum (SR) Ca2+ release due to abnormal cardiac ryanodine receptor (RyR2) function is thought to play an important role in the genesis of arrhythmia by activation of delayed afterdepolarizations and extrasystolic action potentials (APs). While the molecular and subcellular steps linking spontaneous Ca2+ release to extrasystolic APs are relatively well established and are known to involve Ca2+-dependent depolarizing currents, the multicellular mechanisms of generation of ectopic beats remain to be defined. Because myocytes are electrically coupled, any depolarization signals that arise in individual myocytes would be dampened due to dissipation of the depolarizing currents into neighboring myocytes. Therefore, it is reasonable to propose that a synchronization mechanism exists that temporally aligns spontaneous Ca2+ releases in neighboring cells as part of arrhythmogenesis. In the present study, we directly tested this hypothesis by examining synchrony of spontaneous Ca2+ waves and after-contractions in multicellular cardiac preparations. Rat cardiac trabeculae preparations were loaded with the fluorescent Ca2+ indicator, Fluo-4, and spatially resolved changes in Ca2+ were monitored along with total contractile force at different pacing rates. Exposure of trabeculae to caffeine (0.5-1 mM) and isoproterenol (1 μM) resulted in the occurrence of regular spontaneous Ca2+ waves and after-contractions. Spontaneous Ca2+ waves occurred in most myocytes in the image plane with a high degree of synchrony during sequential contraction-relaxation cycles. Interestingly, despite their high synchrony, spontaneous Ca2+ waves led predominantly to sub-maximal contractions and only rarely (>0.1%) gave rise to full-strength extrasystolic beats. These results suggest that spontaneous Ca2+ release caused by altered RyR2 function shows a high level of synchrony across cardiac tissue. However, other factors beside spontaneous Ca2+ release synchrony are likely to critically contribute to the generation of ectopic activity.

Feeling the Beat: Premotor and Striatal Interactions in Musicians and Nonmusicians during Beat Perception

Little is known about the underlying neurobiology of rhythm and beat perception, despite its universal cultural importance. Here we used functional magnetic resonance imaging to study rhythm perception in musicians and nonmusicians. Three conditions varied in the degree to which external reinforcement versus internal generation of the beat was required. The "volume" condition strongly externally marked the beat with volume changes, the "duration" condition marked the beat with weaker accents arising from duration changes, and the "unaccented" condition required the beat to be entirely internally generated. In all conditions, beat rhythms compared with nonbeat control rhythms revealed putamen activity. The presence of a beat was also associated with greater connectivity between the putamen and the supplementary motor area (SMA), the premotor cortex (PMC), and auditory cortex. In contrast, the type of accent within the beat conditions modulated the coupling between premotor and auditory cortex, with greater modulation for musicians than nonmusicians. Importantly, the response of the putamen to beat conditions was not attributable to differences in temporal complexity between the three rhythm conditions. We propose that a cortico-subcortical network including the putamen, SMA, and PMC is engaged for the analysis of temporal sequences and prediction or generation of putative beats, especially under conditions that may require internal generation of the beat. The importance of this system for auditory-motor interaction and development of precisely timed movement is suggested here by its facilitation in musicians.

Arrhythmogenicity of Low‐Flow Reperfusion Following Acute Local Ischemia in Excised Rat Hearts

Clinical studies show that impaired myocardial reperfusion following thrombolytic therapy for coronary occlusions increases the incidence of ventricular arrhythmias; however the mechanisms are poorly understood. We studied arrhythmias during controlled low‐flow reperfusion (LFRP) in excised Langendorff‐perfused hearts (n=6). The left anterior coronary artery (LAD) was cannulated. An HPLC pump delivered perfusate to the LAD at a rate of 2 mL/min, followed by 20 min of local ischemia (0 mL/min) and then 20 min of LFRP (0.2 mL/min). The electrical response at each flow rate was monitored using an ECG and fluorescence imaging of epicardial potentials. We found that the highest heart rates and lowest heart rate variability occurred during LFRP (p&lt;0.05). LFRP also resulted in the highest incidence of VF (p&lt;0.05). During ischemia heart rate variability was highest and the incidence of VF was much lower than during LFRP (p&lt;0.05). Fluorescence images revealed periodic ectopic beats during ischemia and numerous ectopic beats during LFRP. During LFRP, frequent episodes of monomorphic VT were driven by a single rotor and VF was driven by multiple transient rotors. In summary, LFRP fuels the continuous generation of ectopic beats that precede VT/VF. These findings match with our previous in‐vitro studies where we hypothesized that microreperfusion of ischemic border zones could result in ectopic beats and arrhythmias.

CHAOTIC BEATS IN A NONAUTONOMOUS SYSTEM GOVERNING SECOND-HARMONIC GENERATION OF LIGHT

This letter proposes a procedure for generation and control of chaotic beats in a dynamical system that is initially in the periodic state. The dynamical system describes a simple nonlinear optical process — second-harmonic generation of light. The periodic states of the system are found to be in analytical forms. We also investigate some aspects of synchronization of chaotic beats in two systems, detuned in the pump fields.

Hyperchaotic beats and their collapse to the quasiperiodic oscillations

The letter shows the possibility of generation of hyperchaotic beats characterized by four, three or two positive Lyapunov exponents. The beats are a result of linear coupling of two identical nonlinear subsystems describing second-harmonic generation of light (SHG). The rapid transition from highly chaotic beats to quasiperiodic oscillations is studied.

Generation of Chaotic Beats in a Modified Chua's Circuit Part I: Dynamic Behaviour

This paper and the companion one [Cafagna, D. and Grassi, G., Nonlinear Dynamics, this issue] present the new phenomenon of chaotic beats in non-autonomous Chua's circuit, driven by two sinusoidal inputs with slightly different frequencies. In particular, in this paper the behaviour of the proposed circuit is analyzed both in time-domain and state-space, confirming the chaotic nature of the phenomenon and the effectiveness of the design.

Generation of Chaotic Beats in a Modified Chua's Circuit Part II: Circuit Design

This paper and the companion one [Cafagna, D., and Grassi, G., Nonlinear Dynamics, this issue] describe the new phenomenon of chaotic beats in a modified version of the Chua's circuit, driven by two sinusoidal inputs with slightly different frequencies. In particular, this paper presents the circuit design, including a novel implementation of the Chua diode, and investigates the beats phenomenon generated by the considered circuit.

Electrophysiological Characteristics of Arterially-Perfused Canine Pulmonary Veins: Role of the Delayed Afterdepolarization-Induced Triggered Activity

Background and Objectives：The mechanism responsible for the generation of ectopic beats in pulmonary veins (PVs) remains to be well defined. The present study examines the electrophysiological characteristics of the PVs and other regions of the canine left atrium (LA) under low dose (300 μM) caffeine condition. Materials and Methods：Transmembrane action potentials were recorded from the left superior PVs, PV-LA junctions (PLJ, atrium <5 mm from the PV ostium), LA appendage (LAA) or Bachmann’s bundle (BB) in arterially perfused canine LA-PV preparations, using floating glass microelectrodes. Rapid atrial pacing (cycle lengths 140-300 ms, 10 sec) was used to induce delayed afterdepolarizations (DAD) at the baseline and under low dose (300 μM) caffeine conditions. Results：Spontaneous diastolic depolarization or triggered activity (TA) was not observed in any of the recording area under the baseline condition. DAD and TA were induced by caffeine in 4/8 PVs and in 3/8 PLJs, but in no LAA (0/6) or BB (0/5). These TA and DAD were also observed after termination of pacing-induced atrial tachyarrhythmia. DAD was abolished by pretreatment of the atria with verapamil or propranolol (1.0 μM). Conclusion：Spontaneous diastolic depolarization was not present in perfused canine left atria or proximal PV. Pulmonary veins and adjacent areas displayed an increased susceptibility to develop DAD-induced TA under low dose caffeine condition. This distinctive electrophysiological property of the PV and PLJ area may contribute to the arrhythmogenic substrate responsible for the ectopic activity that initiates atrial fibrillation. (Korean Circulation J 2005;35:643-648)

The Computation of Evoked Heart Rate and Blood Pressure

Abstract For many years psychophysiologists have been interested in stimulus related changes in heart rate and blood pressure. To represent these evoked heart rate and blood pressure patterns, heart rate and blood pressure data have to be transformed into equidistant time series. This paper presents an extensive comparison between two methods. The most often used method is based on linear interpolation, also known as weighted averaging. The low pass filtering method presented here is based on a well-known model for the generation of heart beats, the integral pulse frequency modulation model (IPFM). The comparison shows that the results of the filtering and interpolation procedures are virtually identical. Practically, small differences between the methods disappear in the averaging process. Therefore, the interpolation method is a suitable practical alternative to the computationally complex filtering method.

Surf zone dynamics simulated by a Boussinesq type model. Part II: surf beat and swash oscillations for wave groups and irregular waves

This is the second of three papers on the modelling of various types of surf zone phenomena. In the first paper the general model was described and it was applied to study cross-shore motion of regular waves in the surf zone. In this paper, part II, we consider the cross-shore motion of wave groups and irregular waves with emphasis on shoaling, breaking and runup as well as the generation of surf beats. These phenomena are investigated numerically by using a time-domain Boussinesq type model, which resolves the primary wave motion as well as the long waves. As compared with the classical Boussinesq equations, the equations adopted here allow for improved linear dispersion characteristics and wave breaking is modelled by using a roller concept for spilling breakers. The swash zone is included by incorporating a moving shoreline boundary condition and radiation of short and long period waves from the offshore boundary is allowed by the use of absorbing sponge layers. Mutual interaction between short waves and long waves is inherent in the model. This allows, for example, for a general exchange of energy between triads rather than a simple one-way forcing of bound waves and for a substantial modification of bore celerities in the swash zone due to the presence of long waves. The model study is based mainly on incident bichromatic wave groups considering a range of mean frequencies, group frequencies, modulation rates, sea bed slopes and surf similarity parameters. Additionally, two cases of incident irregular waves are studied. The model results presented include transformation of surface elevations during shoaling, breaking and runup and the resulting shoreline oscillations. The low frequency motion induced by the primary-wave groups is determined at the shoreline and outside the surf zone by low-pass filtering and subsequent division into incident bound and free components and reflected free components. The model results are compared with laboratory experiments from the literature and the agreement is generally found to be very good. Finally the paper includes special details from the breaker model: time and space trajectories of surface rollers revealing the breakpoint oscillation and the speed of bores; envelopes of low-pass filtered radiation stress and surface elevation; sensitivity of surf beat to group frequency, modulation rate and bottom slope is investigated. Part III of this work (Sørensen et al., 1998) presents nearshore circulations induced by the breaking of unidirectional and multi-directional waves.

Generation and propagation of ectopic beats induced by spatially localized Na-K pump inhibition in atrial network models.

A biophysically detailed two-dimensional network model of the cardiac atrium has been implemented on the Thinking Machines massively parallel CM-5 supercomputer. The model is used to study the effects of spatially localized inhibition of the Na-K pump. Na overloading produced by pump inhibition can induce spontaneous, propagating ectopic beats within the network. At a cell-to-cell coupling value yielding a realistic plane wave conduction velocity of 0.6 m s-1, pump inhibition in roughly 1000 cells can induce propagating ectopic beats in a 512 x 512 lattice of cells.