Generation and escape of local waves from the boundary of uncoupled cardiac tissue

We aim to understand the formation of abnormal waves of activity from myocardial regions with diminished cell-to-cell coupling. In route to this goal, we studied the behavior of a heterogeneous myocyte network in which a sharp coupling gradient was placed under conditions of increasing network automaticity. Experiments were conducted in monolayers of neonatal rat cardiomyocytes using heptanol and isoproterenol as means of altering cell-to-cell coupling and automaticity respectively. Experimental findings were explained and expanded using a modified Beeler-Reuter numerical model. The data suggests that the combination of a heterogeneous substrate, a gradient of coupling and an increase in oscillatory activity of individual cells creates a rich set of behaviors associated with self-generated spiral waves and ectopic sources. Spiral waves feature a flattened shape and a pin-unpin drift type of tip motion. These intercellular waves are action-potential based and can be visualized with either voltage or calcium transient measurements. A source/load mismatch on the interface between the boundary and well-coupled layers can lock wavefronts emanating from both ectopic sources and rotating waves within the inner layers of the coupling gradient. A numerical approach allowed us to explore how: i) the spatial distribution of cells, ii) the amplitude and dispersion of cell automaticity, iii) and the speed at which the coupling gradient moves in space, affects wave behavior, including its escape into well-coupled tissue.Comment: 28 pages, 10 figures, submitted to Biophysical Journa

Using the dipole particles for simulation of 3d vortex flow of a viscous incompressible fluid

A fully lagrangian numerical method for simulation of 3D nonstationary flow of viscous and ideal incompressible fluid is developed in this work. This method is based on the representation of a vortex field as a set of dipole particles [1]. The introduced vector-function D describes density of dipole momentum. The equation for this function is in accordance with Navier-Stokes equations [2]. The vorticity is equal to curl of dipole momentum density. Thus vortex field is always solenoidal. The dipole particles are generated at a body surface and are moving interacting. The region where function D is essentially non-zero approximately coincides with the vortex region. Each dipole particle induces the velocity field which is equal to field of a point dipole at large distance from the particle. But near a particle the induced velocity field is another taking into account the particle volume and viscosity of the liquid. The method can be applied for simulation of an ideal and viscous flows

Evolution of spiral and scroll waves of excitation in a mathematical model of ischaemic border zone

Abnormal electrical activity from the boundaries of ischemic cardiac tissue is recognized as one of the major causes in generation of ischemia-reperfusion arrhythmias. Here we present theoretical analysis of the waves of electrical activity that can rise on the boundary of cardiac cell network upon its recovery from ischaemia-like conditions. The main factors included in our analysis are macroscopic gradients of the cell-to-cell coupling and cell excitability and microscopic heterogeneity of individual cells. The interplay between these factors allows one to explain how spirals form, drift together with the moving boundary, get transiently pinned to local inhomogeneities, and finally penetrate into the bulk of the well-coupled tissue where they reach macroscopic scale. The asymptotic theory of the drift of spiral and scroll waves based on response functions provides explanation of the drifts involved in this mechanism, with the exception of effects due to the discreteness of cardiac tissue. In particular, this asymptotic theory allows an extrapolation of 2D events into 3D, which has shown that cells within the border zone can give rise to 3D analogues of spirals, the scroll waves. When and if such scroll waves escape into a better coupled tissue, they are likely to collapse due to the positive filament tension. However, our simulations have shown that such collapse of newly generated scrolls is not inevitable and that under certain conditions filament tension becomes negative, leading to scroll filaments to expand and multiply leading to a fibrillation-like state within small areas of cardiac tissue.Comment: 26 pages, 13 figures, appendix and 2 movies, as accepted to PLoS ONE 2011/08/0

Predictors of fatal cardiac outcomes during the long-term observation of patients with chronic ischemic heart disease after coronary grafting

The aim of investigation was to determine predictors of fatal cardiac outcomes in patients with stable angina (SA) after coronary grafting during the long-term observation. Material and methods. This investigation included 120 patients with SA of 2-4 functional classes aged 55+18 years, duration of ischemic heart disease consisted 4±2.1 years. Myocardial infarction in anamnesis had 86.7% of patients, aneurysm of left ventricular had 9.2% of patients. Ejection fraction (EF) of left ventricular consisted 52±2.5%. Arterial hypertension had 87.5% of patients, chronic obstructive lung disease had 9.2% of patients, diabetes mellitus was registered in 11.7% of patients. Duration of artificial circulation consisted 82±13 minutes, time of aorta occlusion consisted 51 ±17 minutes, average amount of grafts in one patient consisted 2,7. Results. 11 patients were lost during follow-up period. During observation period 8 (7.4%) patients died: 4 patients died from myocardial infarction and 4 patients died suddenly. Independent predictors of lethal outcomes were: age above 70 years, EF less than 40%, diabetes mellitus, chronic obstructive lung disease, duration of artificial lung ventilation more than 24 hours.Цель работы - выявление независимых предикторов фатальных сердечно - сосудистых осложнений при проспективном наблюдении больных стабильной стенокардией (СС), перенесших коронарное шунтирование (КШ). Материал и методы. В исследование включено 120 больных СС II-IV ФК в возрасте 55±18 лет с длительностью ИБС 4±2,1 года. Инфаркт миокарда (ИМ) ранее перенесли 86,7% больных, аневризма левого желудочка имелась у 11 (9,2%) лиц. Фракция выброса левого желудочка (ФВЛЖ) составила 52±2.5%. Артериальная гипертония (АГ) имелась у 105 (87,5%), хроническая обструктивная болезнь легких (ХОБ/1) - у 11 (9,2%), сахарный диабет (СД) - у 14 (11,7%) больных. Средняя продолжительность искусственного кровообращения при КШ составила 82±13 минут, время окклюзии аорты - 51 ±17 минута. Среднее количество шунтов на одного пациента составило 2,7±0,3. Результаты. Выбыло из исследования 11 пациентов. За период наблюдения умерло 8 (7,4%) больных, из них вследствие ИМ - 4 (3,3%), внезапно - 4 (3,3%). Независимыми предикторами сердечной смерти больных явились: возраст старше 70 лет, ФВЛЖ менее 40%, СД, ХОБЛ, длительность искусственной вентиляция легких более 24 часов

Verified and potential pathogens of predatory mites (Acari: Phytoseiidae)

Several species of phytoseiid mites (Acari: Phytoseiidae), including species of the genera Amblyseius, Galendromus, Metaseiulus, Neoseiulus, Phytoseiulus and Typhlodromus, are currently reared for biological control of various crop pests and/or as model organisms for the study of predator¿prey interactions. Pathogen-free phytoseiid mites are important to obtain high efficacy in biological pest control and to get reliable data in mite research, as pathogens may affect the performance of their host or alter their reproduction and behaviour. Potential and verified pathogens have been reported for phytoseiid mites during the past 25 years. The present review provides an overview, including potential pathogens with unknown host effects (17 reports), endosymbiotic Wolbachia (seven reports), other bacteria (including Cardinium and Spiroplasma) (four reports), cases of unidentified diseases (three reports) and cases of verified pathogens (six reports). From the latter group four reports refer to Microsporidia, one to a fungus and one to a bacterium. Only five entities have been studied in detail, including Wolbachia infecting seven predatory mite species, other endosymbiotic bacteria infecting Metaseiulus (Galendromus, Typhlodromus) occidentalis (Nesbitt), the bacterium Acaricomes phytoseiuli infecting Phytoseiulus persimilis Athias-Henriot, the microsporidium Microsporidium phytoseiuli infecting P. persimilis and the microsporidium Oligosproridium occidentalis infecting M. occidentalis. In four cases (Wolbachia, A. phytoseiuli, M. phytoseiuli and O. occidentalis) an infection may be connected with fitness costs of the host. Moreover, infection is not always readily visible as no obvious gross symptoms are present. Monitoring of these entities on a routine and continuous basis should therefore get more attention, especially in commercial mass-production. Special attention should be paid to field-collected mites before introduction into the laboratory or mass rearing, and to mites that are exchanged among rearing facilities. However, at present general pathogen monitoring is not yet practical as effects of many entities are unknown. More research effort is needed concerning verified and potential pathogens of commercially reared arthropods and those used as model organisms in research

Microscopic analysis of the microbiota of three commercial Phytoseiidae species (Acari: Mesostigmata)

Microbes associated with the external and internal anatomy of three commercially available predatory mite species, Phytoseiulus persimilis, Typhlodromips (=Amblyseius) swiskii, and Neoseiulus (=Amblyseius) cucumeris were examined using light microscopy, confocal laser scanning microscopy and fluorescence in-situ hybridization (FISH). Four microbe morphotypes were observed on external body regions. These included three microfungi-like organisms (named T1, T2 and T3) and rod-shaped bacteria (T4). Morphotypes showed unique distributions on the external body regions and certain microbes were found only on one host species. Microfungi-like T1 were present in all three species whereas T2 and T3 were present in only P. persimilis and T. swirskii respectively. T1 and T2 microbes were most abundant on the ventral structures of the idiosoma and legs, most frequently associated with coxae, coxal folds, ventrianal shields and epigynal shields. T3 microbes were most abundant on legs and dorsal idiosoma. T4 microbes were less abundant and were attached to epigynal shields of N. cucumeris and T. swirskii. Significant differences in distribution between seasons (spring and winter) suggest that there are fluctuations in the microbiota of phytoseiids in mass reared systems. FISH using the EUB338 (I-III) probes showed bacteria within the alimentary tract, in Malpighian tubules and anal atria. It is possible these have a role in absorbing excretory products or maintaining gut physiology. We suggest how microbes might be transmitted to offspring and throughout populations. The implications of these findings for commercial mass rearing are discussed. This study highlights the necessity of understanding the intrinsic microbiota of Phytoseiidae and other Acari

Locations of ectopic beats coincide with spatial gradients of NADH in a regional model of low-flow reperfusion

We studied the origins of ectopic beats during low-flow reperfusion after acute regional ischemia in excised rat hearts. The left anterior descending coronary artery was cannulated. Perfusate was delivered to the cannula using an high-performance liquid chromatography pump. This provided not only precise control of flow rate but also avoided mechanical artifacts associated with vessel occlusion and deocclusion. Optical mapping of epicardial transmembrane potential served to identify activation wavefronts. Imaging of NADH fluorescence was used to quantify local ischemia. Our experiments suggest that low-flow reperfusion of ischemic myocardium leads to a highly heterogeneous ischemic substrate and that the degree of ischemia between adjacent patches of tissue changes in time. In contrast to transient ectopic activity observed during full-flow reperfusion, persistent ectopic arrhythmias were observed during low-flow reperfusion. The origins of ectopic beats were traceable to areas of high spatial gradients of changes in NADH fluorescence caused by low-flow reperfusion