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The spatial–temporal organization of the activation, repolarization and hemodynamics of the heart ventricle in rainbow trout, Oncorhynchus mykiss, adapted to a temperature of 5–7 °C, were studied from the normal sinus rhythm (21.6 ± 4.9 bpm) to the highest possible heart rhythm (HR) (60 bpm), during which deterioration of the contractile activity of the myocardium occurred. Regardless of the HR, the main pattern of excitation of the heart ventricle was the movement of the depolarization wave from the dorsal areas of the base in the base-apical and ventral directions with the capture of the entire thickness of the walls, with a slight difference in the time of activation of the subendocardium compared to the subepicardium. The increase in HR above the sinus rhythm caused significant shortening of local repolarization durations in all areas and layers (endocardial, intramural and subepicardial) of the heart ventricle. Changes in local durations of repolarization led to an increase in the heterogeneity of repolarization of the ventricular myocardium; as a result, a deterioration of its contractility was observed. In relation to the sinus rhythm, the maximal systolic pressure in the heart ventricle decreased, the diastolic and end-diastolic pressure increased, and the maximum rates of pressure rise and fall decreased. In rainbow trout adapted to a temperature of 5–7 °C at sinus rhythm, the pumping function of the heart was probably within the upper limit of the physiological norm, and a further increase in the heart rate led to a decline in myocardial contractility.

In this work, we report on the construction, training and functional assessment of an electronic nose (called ‘E-Nose’) that is capable of monitoring the microbial contamination onboard space ships under microgravity conditions. To this end, a commercial electronic nose was modified to allow for the sampling of microbial volatile organic compounds (MVOCs) emitted from relevant bacterial and fungi species. Training of the modified ‘E-Nose’ was performed by establishing an MVOC database consisting of two Gram-positive bacteria strains (Bacillus subtilis and Staphylococcus warneri) and two fungi strains (Aspergillus versicolor and Penicillium expansum). All these strains are known to exist onboard the International Space Station (ISS) and to form important parts of its microbial contamination. All cultures were grown on four kinds of structural materials also in use onboard the ISS. The MVOCs emitted during the different growth phases of these cultures were monitored with an array of ten different metal oxide gas sensors inside the ‘E-Nose’. Principal component analysis of the array data revealed that B. subtilis and S. warneri form separate clusters in an optimized score plot, while the two fungi strains of A. versicolor and P. expansum form a large common cluster, well discriminated against to the bacteria clusters.

Depolarization of the heart ventricles at an increasing heart rate was investigated in a rainbow trout Oncorhynchus mykiss (n = 14). It was shown that at an imposed supraventricular rhythm ranging from 30 to 60 bpm the depolarization wave initially propagates from the loci of earliest atrial excitation located near the atrioventricular orifice to the subendocardial trabecular layer of the noncompact myocardium and then travels towards the epicardium as well as along the wall. This indicates some preferential pathways of cardiac excitation conduction from the pacemaker zone to subendocardial myocytes. Regardless of the heart rate, the basic pattern of ventricular excitation in the rainbow trout heart consists in the propagation of the depolarization wave, which captures the entire thickness of the myocardial wall and activates the subendocardium faster than the subepicardium, from the dorsal regions of the cardiac base in basoapical and ventral directions. At a rhythm of 50–60 bpm, propagation of the depolarization wave in the basal ventricular areas is inverted from the dorsoventral to ventrodorsal direction.

We studied the combined effect of hypokinesia and external cooling on structural and morphological changes in the ventricular myocardium and parameters of homeostasis of the blood system in male and female WKY (normotensive) and SHR (hypertensive) rats. Simultaneous exposure to hypokinesia and cold caused destructive processes in the myocardium and high dynamics of heart remodeling with diverse structural and morphological changes in the left ventricle in rats of both sexes. The thickness of the left ventricular wall most rapidly decreased in male hypertensive SHR rats. The thickness of the wall of the right ventricle significantly increased in male and female rats of both strains. In WKY and SHR females, structural transformations in the heart were less pronounced than in males. The key role in different degree of morphological remodeling of the myocardium in male and female probably belongs to sex hormones.

In this work two-phase Stefan problem for the cylindrical heat equation is considered. One of the phase turns to zero at initial time. In this case, it is difficult to solve by radial heat polynomials because the equations are singular. The solution is represented in linear combination series of special functions Laguerre polynomial and confluent hyper-geometric function. The free boundary is given and heat flux is found. The numerical and approximate test problem is compared graphically. The undetermined coefficients are founded. The convergence of series proved.

We studied the effect of hypokinesia alone and in combination with cold exposure on HR and total cholesterol content in the blood serum of Wistar, WKY, and SHR rats. Irrespectively of the season, hypokinesia was associated with a decrease in HR, which is probably a result of reduced body needs due to deceleration of metabolic processes. A significant increase in total cholesterol was found under conditions of cold exposure combined with hypokinesia, which indicates qualitative structural rearrangement of energy metabolism under the influence of environmental factors. In winter, the increase in total cholesterol concentration was more pronounced (by 51.5%) in the group of hypertensive animals. Presumably, the increase in the serum concentration of total cholesterol under conditions of hypokinesia and cold exposure is a predictor of structural changes in the heart.

Two novel antimicrobial surface coatings were assessed for their lasting antibacterial effect under simulated space conditions during the SIRIUS-19 study. Because long-term space travel can affect the human immune system, astronauts are particularly susceptible to infectious disease. Moreover, the space flight environment can alter the composition of microbial communities within the spacecraft and increase bacterial virulence and resistance to antibiotics. In addition to protecting the crew from infection by human pathogens, prevention and elimination of bacterial contamination is important to avoid corrosion and damage of the technical equipment. The antimicrobial coating AGXX(R)consists of micro-galvanic cells composed of silver and ruthenium which damage bacterial cells through the release of reactive oxygen species. Over the last years, several studies on the antimicrobial effect of AGXX(R)have demonstrated an effective inhibition of growth and even complete elimination of many pathogenic bacteria - including multiresistant microorganisms - as well as their biofilms. The second antimicrobial coating, GOX, consists of chemically modified graphene oxide. Through a positive surface charge and its flexible scaffold, GOX can multivalently bind and immobilize bacteria via electrostatic attraction. Here, AGXX(R)and GOX were applied to non-metallic carriers not previously tested. The antimicrobial coated materials, as well as uncoated control samples, were exposed in the SIRIUS artificial space module and analyzed at different time points during the 4-months isolation study. Survival and growth of airborne heterotrophic, aerobic bacteria on the surfaces were assessed by cultivation-based methods, employing growth conditions suitable for potential human pathogens. Human-associated, biofilm-forming Staphylococcus spp. (S. hominis, S. haemolyticus, and S. epidermidis) strongly dominated at all time points, most were resistant against erythromycin, kanamycin, and ampicillin. AGXX(R)coatings completely inhibited growth of these opportunistic pathogens on all tested surface materials. Particularly, AGXX(R)-cellulose fleece achieved a clear reduction in bacterial load able to recover post contact. GOX-cellulose fleece effectively immobilized bacteria. Sequence analysis of 16S rRNA gene amplicons revealed that the isolated Staphylococcus spp. did not dominate the overall bacterial community, accounting for only 0.1-0.4% of all sequences. Instead, molecular data revealed Lactobacillus, Comamonas, Pseudomonas, Sporosarcina, and Bacillusas the dominant genera across all samples and time points.

In this research the inverse Stefan problem in spherical model where heat flux has to be determined is considered. This work is continuing of our research in electrical engineering that when heat flux passes through one material to the another material at the point where they contact heat distribution process takes the place. At free boundary α (t) contact spot starts to boiling and at β (t) stars to melting and there appear two phase: liquid phase and solid phase. Our aim to calculate temperature in liquid and solid phase, then find heat flux entering into contact spot. The exact solution of problem represented in linear combination of series for radial heat polynomials and integral error functions. The recurrent formulas for determine unknown coefficients are represented. The effectiveness of method is checked by test problem and approximate problem in which exact solution and approximate solution of heat flux is compared. The coefficients of heat at liquid and solid phases and heat flux are found. The heat flux equation is checked by testing problem by using Mathcad program.Key words: Stefan problem, radial heat polynomials, Faa-di Bruno, collocation method.

The effects of therapeutic or preventive-therapeutic administration of water-soluble echinochrome analog U-441 on arrhythmia severity assessed by a set of myocardial spatio-temporal depolarization and repolarization parameters were examined on the model of acute myocardial ischemia in cats. Coronary occlusion increased activation time and decreased repolarization time in the ischemic zone; in addition, it increased both global and borderline (local) dispersions of repolarization. The linear regression model showed that only activation time values measured at the initial state and at termination of occlusion were associated with total arrhythmia score during ischemia (regression coefficient β=0.338, 95%CI=0.074-0.602, p=0.015 and β=0.720, 95%CI=0.323-1.117, p=0.001, respectively). The study revealed no association between administration of echinochrome analog U-441 and arrhythmia severity.

Aim of the study was to find out which myocardial repolarization parameters predict reperfusion ventricular tachycardia and fibrillation (VT/VF) and determine how these parameters express in ECG.Coronary occlusion and reperfusion (30/30min) was induced in 24 cats. Local activation and end of repolarization times (RT) were measured in 88 intramyocardial leads. Computer simulations of precordial electrograms were performed.Reperfusion VT/VF developed in 10 animals. Arrhythmia-susceptible animals had longer RTs in perfused areas [183(177;202) vs 154(140;170) ms in susceptible and resistant animals, respectively, P0.05]. In logistic regression analysis, VT/VFs were associated with prolonged RTs in the perfused area (OR 1.068; 95% CI 1.012-1.128; P=0.017). Simulations demonstrated that prolonged repolarization in the perfused/border zone caused precordial terminal T-wave inversion.The reperfusion VT/VFs were independently predicted by the longer RT in the perfused zone, which was reflected in the terminal negative phase of the electrocardiographic T-wave.

Background To understand electrophysiological mechanisms that underlie the progression of compensated right ventricular hypertrophy (RVH) to heart failure, the purpose of the study was to evaluate remodeling of ventricular repolarization in connection with hemodynamic abnormalities and vulnerability of the heart ventricles to arrhythmias in RVH rats with pulmonary arterial hypertension (PAH) and heart failure. Methods PAH followed by heart failure was induced by monocrotaline in adult female Wistar rats. Unipolar epicardial electrograms and cardiac hemodynamic parameters were recorded in situ. Vulnerability to ventricular arrhythmias was measured as the threshold dose of aconitine required to produce sustained ventricular tachycardia. Histological examination of the heart ventricles was performed. Activation–recovery intervals (ARIs) and ARI dispersions were used as indices of durations and heterogeneity of repolarization respectively to assess ventricular repolarization. Results and conclusions The development of compensated RVH was characterized by the dramatic prolongation of repolarization against the less expressed increase in repolarization heterogeneity, whereas the dramatic increase in repolarization heterogeneity against the less expressed but inhomogeneous prolongation of repolarization occurred in the progression of compensated RVH to heart failure. These changes increased vulnerability of the failing heart but not the compensated heart to aconitine-induced ventricular arrhythmias.

The effect of preventive administration of melatonin on the arrhythmogenic substrate in the myocardium was studied in the rabbit model of acute ischemia/reperfusion in vivo. The animals treated with melatonin 60 min before ischemia induction had shorter median activation time compared to the control group (p=0.039), less pronounced shortening of repolarization durations in the ischemic zone during coronary occlusion (p=0.008), and more complete recovery of repolarization during reperfusion (p=0.027). In the melatonin group, the dispersion of repolarization was less than in the control group during both ischemic period (p=0.043) and reperfusion (p=0.038). Thus, preventive administration of melatonin mitigated the arrhythmogenic substrate in the heart under conditions of ischemia/reperfusion.

Dynamics of melting and welding of closed electrical contacts is analyzed for ac current half-wave. It is shown that in the range of low current and contact load the spherical model introduced by R. Holm describes satisfactorily the contact heating. The special attention is focused on the influence of softening of contact material on the current density and temperature field. All consecutive stages of contact heating including pre-softening, softening, melting and welding processes are described by the mathematical model based on the Stefan free boundary problems for the spherical heat equation. The relationship between current, contact load, parameters of the contact material and the radius of contact welded zone is obtained, discussed and compared with experimental data. It was found that for the certain range of contact parameters the influence of contact softening is very important and should be taken into account.

Background Myocardial ischemic electrophysiological alterations are associated with the generation of reactive oxygen species. However, electrophysiological effects of antioxidants are unclear. Our objective was to determine the effects of the antioxidant echinochrome on ventricular repolarization in a feline model of 30-min ischemia. Methods and results Activation–recovery intervals were measured from 64 ventricular electrograms recorded before and during the LAD ligation in untreated animals (controls, n = 5) and animals given echinochrome (1 mg/kg, n = 5 and 2 mg/kg, n = 7). In controls, ischemia resulted in the increase of repolarization dispersion, QTc and Tpeak–Tend intervals and precordial T wave amplitude dispersion. Echinochrome attenuated the ischemic increase of repolarization dispersion. The increased dose of echinochrome abolished the ischemic ECG repolarization changes but did not modify the incidence of ventricular arrhythmias. Conclusion Echinochrome modified ischemic alterations of repolarization dispersion that were associated with the changes of the body surface T wave amplitude dispersion and Tpeak–Tend interval.

Two mathematical models, spherical and axisymmetric, describing the temperature field in closed electrical contacts are compared and the rightness of their application is discussed. The ranges of the contact radius, time and current are determined for which one or another model could be applied with the required accuracy. The temperature field in the axisymmetric model is found in the form of alternative series where the first term represents the solution in the spherical model. It enables us to estimate the error in calculation of the temperature using the spherical model with respect to the axisymmetric model. Some applications to the experimental data are considered.

The mathematical model describing welding at contact closure is elaborated. All consecutive stages of contact closure are considered including the first touch of micro-asperities with micro-arcing, initial contact heating, softening, melting and boiling of the contact surface. Two possible phenomena are discussed, welding and bouncing. It is shown that everything depends on the relationship between dynamical characteristics of heating and contact motion such as spreading of melting and softening zones on the contact surface, action of elastic-plastic, electrodynamic and contact spring forces, metallic vapors pressure, parameters of the contact material, circuit parameters and some other factors. The mathematical model is based on the axisymmetric Stefan problem which takes into account phase transformations of the contact material. Some new methods for the solution of this problem are presented. The results of calculation are compared with experimental data.

Doxorubicin, one of the most effective anticancer drugs, is characterized by severe cardiotoxic effects, which induce cardiac remodeling and congestive heart failure. The aim of the study was to evaluate remodeling of ventricular repolarization heterogeneity in chronic doxorubicin cardiotoxicity in rats. Doxorubicin cardiotoxicity was produced by six equal intraperitoneal injections of the drug in a cumulative dose of 15 mg/kg in a 2-week period. Electrophysiological mapping of the ventricular epicardium in situ was performed 6 weeks after the last injection of doxorubicin. Activation-recovery intervals (ARIs) were used for the evaluation of the heterogeneity in repolarization durations. The major findings were as follows: (1) ARIs on the ventricular epicardium of both ventricles were significantly prolonged in the doxorubicin group and (2) this inhomogeneous prolongation of ARIs on the ventricular epicardium resulted in (i) the increase in the dispersion of repolarization across the ventricular epicardium and (ii) the inhomogeneous alterations of the regional ARI gradients on the ventricular epicardium. These changes in repolarization could explain the electrocardiographic alterations, that is, the prolongation of the QT interval and flattening of the T wave.

Objective—To characterize systolic intervals of the left ventricle and their relationship with heart rate in conscious sheep. Animals—11 healthy Romanov sheep (age range, 3 months to 10 years). Procedures—Systolic intervals and indices of myocardial contractility of the left ventricle were measured in conscious sheep by use of polycardiography. Results—The mean ± SD pre-ejection period was 59 ± 12 milliseconds, and the mean left ventricular ejection time was 194 ± 34 milliseconds. The mean myocardial tension index was 0.22 ± 0.05, and the mean ratio of the pre-ejection period to ejection time was 0.30 ± 0.09. Total electromechanical systole, mechanical systole, and ejection time varied inversely with heart rate. The electromechanical delay and pre-ejection period were not correlated with heart rate, nor were the myocardial tension index and the ratio of the pre-ejection period to ejection time. The isovolumetric contraction index and isovolumetric contraction time were not significantly correlated with heart rate, although the values for the correlation coefficient were moderate (r = −0.561 and r = −0.482, respectively). Conclusions and Clinical Relevance—Although a larger study would be needed to provide reference intervals for healthy sheep, the results of the study reported here provided useful information for the cardiac evaluation of sheep.

Aim: Prolongation of ventricular repolarization is characteristic of myocardial cooling. In the present study, we investigated whether this prolongation is uniform or not throughout ventricular epicardium and how these hypothermia-induced changes express in the body surface potential distribution. Methods: Epicardial and body surface potential mapping from 64 unipolar leads was carried out in 18 anaesthetized adult rabbits. Mild hypothermia documented by lowering the mediastinal and rectal temperature from 38 to 32 °C was elicited by perfusion of the mediastinum with cooled saline. Activation times, repolarization times and activation–recovery intervals were determined in each epicardial lead. Results: Baseline activation–recovery intervals distributed non-uniformly on the ventricular epicardium, increasing progressively from the apex to the base and from the left ventricular (LV) sites to the right ventricular (RV) sites (P

Based on a multichannel synchronous mapping of heart electric potentials, the sequence in time of the ventricle myocardium depolarization was compared with dynamics of distribution of cardioelectric potentials on the dog body surface. The cardioelectric field on the dog body surface at the period of the initial ventricular activity has been shown to be characterized by the presence of two inversions of the mutual disposition of areas of positive and negative potentials. Contribution to formation of distribution of the cardioelectric potentials on the body surface at each moment of the period of initial ventricular activity was made by all myocardial layers involved in excitation.

Mathematical models describing phenomena of heat and mass transfer in electrical contacts are based on systems of partial differential equations for temperature and electromagnetic fields. The influence of Joule, Kohler and Thomson heat sources on the temperature field in closed contacts is discussed. The mathematical model of the ring-shaped welding in closed contacts is presented. Dynamics of contact opening is considered as consecutive stages including the initial stage of heating up to the melting point, the stage of a liquid bridge, metallic and gaseous arc stages. The dimensionless criteria of Thomson and Kohler are introduced which may be responsible for the displacement of the hottest isotherms of a bridge from its middle and corresponding bridge material transfer. The conditions for self-restrained bridge transfer are discussed. Phenomenon of contact floating due to metallic vapour pressure produced by a vacuum micro-arc is investigated experimentally and then described by a mathematical model. A mathematical model is presented describing transient phenomena accompanied a vacuum short arc at the initial stage of contact opening. It enables to describe the evolution of transient short anode dominated arc, which appears just after the rupture of molten bridge, into diffusive cathode dominated arc. The mechanisms of arc erosion are described by several models due to evaporation, droplets ejection, Marangoni effect, ejection of solid particles at thermo-elastic stresses. The hybrid mathematical model is elaborated to describe dynamics of the arc and forces acting in contact gap. It includes experimental oscillograms of current, voltage and contact displacement and nonlinear equations for arc, anode and cathode temperature fields and contact motion. It is shown theoretically and confirmed experimentally that in the range of high current the force of metallic vapour pressure at arcing in vacuum is comparable with magnetic repulsion force and should be taken into consideration.The mathematical model describing transition from arc to glow at contact opening in circuits with a high inductance and small current is elaborated and identified experimentally. The mechanism of thermionic emission from the cathode surface based on Richardson-Dushman equation is corrected by addition of another emission mechanism due to electrochemical phenomena in melted pool on the cathode. The influence of current frequency on the rate of the arc erosion at contact opening is investigated using the model of transition of the metallic arc phase into gaseous phase.

The aim of the study was to advance our knowledge regarding the activation process of the ventricular myocardium in birds in which Purkinje fibres penetrate into the ventricular wall to reach the epicardium. A depolarization pattern of the left ventricular free wall was studied in chickens (Gallus gallus) during ventricular paced beats. Duration of the activation process of the left ventricular free wall is significantly increased during ventricular ectopic excitation as compared with sinus rhythm. Its lowest increase occurs during subendocardial pacing of the middle part of the left ventricle, but its greatest increase is observed during subepicardial pacing of the left ventricular base. Multifocality and mosaicity of depolarization of the left ventricular free wall myocardium in chicken are expressed in a considerably less degree during ventricular paced beats in comparison with sinus rhythm. During ventricular paced beats, excitation of the left ventricular free wall is mostly due to the successive spreading of the depolarization wave from pacing sites.

The avian cardiovascular system is of special interest because avian hearts are relatively larger than mammalian hearts, and activation of ventricular myocardium in birds has a "flash" pattern. Systolic time intervals and indices of myocardial contractility were examined in anaesthetized open-chest chickens by polycardiography, including synchronous recordings of electrocardiogram, phonocardiogram, and apex cardiogram. The asynchronous contraction time, isometric contraction time, pre-ejection period and ejection time were 26 +/- 3 (Mean +/- SD), 21 +/- 9, 47 +/- 12, and 83 +/- 23 ms, respectively, for heart rates of 260 +/- 57 bpm. The myocardial tension index, isometric contraction index and the pre-ejection period/ejection time ratio were 0.39 +/- 0.11, 0.42 +/- 0.10, and 0.54 +/- 0.14, respectively. A "flash" pattern of ventricular myocardial depolarization causes more rapid excitation and as a consequence shorter asynchronous contraction time of relatively larger chicken hearts compared with rabbit hearts. Inverse relation (P0.05) of the asynchronous contraction time to the heart rate in chickens is probably associated with the specific activation pattern of avian ventricles. Establishment of the values of systolic time intervals will facilitate a better understanding of cardiac function in birds. The obtained results are discussed in comparison with the rabbit. The indices calculated from the systolic time intervals show disadvantageous contractile function of chicken heart compared to rabbit heart.

Cardioelectric field (CEF) on the body surface of birds (hen and pigeon) at the period of atrial excitation was studied by the method of the 64-channel synchronous electrocardiotopography. At the period of the atrial depolarization in the birds the zone of CEF negative potentials on the body surface is located cranially with respect to the zone of positive potentials. At the initial moments of P wave the minimum is located in the cranial (hen) or middle (pigeon) third of the dorsal body surface, while the maximum—in the area of the heart projection onto the ventral (hen) or left-lateral (pigeon) body surface. The maximum and minimum of the potential reach the greatest value at the period of the middle part of the P wave (near the peak), their amplitude being higher in pigeons. The distribution dynamics of the CEF potentials on the body surface is similar in different bird species and is characterized by stability in mutual disposition of positive and negative zones. The interspecies and intraspecies CEF variability on the body surface at the period of the atrial activation seems to be due to differences in the heart disposition in the chest. At the period of the atrial myocardium activation, CEF on the bird body surface reflects adequately projection of the potential distribution on epicardium and the sequence of spreading of excitation in the atrial myocardium, including that in the presence of several fronts of depolarization waves.

The present study is the first attempt to examine the effect of left ventricular hypertrophy (LVH) on the excitation pattern of the ventricular epicardium in experimental hypertensive rats. The left renal artery was clipped in Wistar rats (n = 8; 6-8 months old; weight, 174-295 g) to produce two-kidney one-clip (2K1C) hypertension. After 4 weeks, blood pressure was measured, and epicardial potential mapping was performed under sinus rhythm from 64 unipolar electrodes regularly distributed over the ventricular epicardium. Systolic blood pressure was approximately 40% higher in the rats with a clipped renal artery (162 +/- 14 mmHg, mean +/- s.d.) than in the normotensive rats (115 +/- 3 mmHg). LVH (approximately 23% increase in the ratio of the left ventricular weight to the body weight, P < 0.05) was observed in the 2K1C hypertensive rats. The depolarization pattern of the ventricular epicardium in the normotensive rats was similar to that in the rats with 2K1C hypertensive LVH. The duration of ventricular epicardial activation was shown to increase (approximately 35%, P < 0.05) in the hypertensive rats as compared to the normotensive animals. This study provides an explanation for alterations of the body surface potential distribution in hypertensive patients with LVH.

Studies have been conducted of AgCu contacts to investigate the influence of current frequency on the rate of the arc erosion at contact opening. The work is performed on a special designed test rig at the current of 100 A, frequencies ranging from 50 Hz to 1000 Hz, operating voltage of 110 V, contact gap of 3 mm for 1000 operations. It was found that that the rate of erosion depends nonmonotonically on the current frequency and decreases at a frequency greater than 500Hz. The mathematical model is presented to explain this phenomena. It is based on the system of differential equations describing dynamics of arc temperature, energy and material transfer from one contact to another. The results of calculation show that the arc temperature maximum shifts to a greater time values when the current frequency increases. Shifting of the arc temperature maximum in time entails the change of the time duration Δt when the arc temperature is greater than the temperature of gas ionisation (~ 5000 K) at which evaporation is more intensive. These phenomena can explain nonmonotonical dependence arc erosion on the current frequency. The main result is that erosion decreases at the current frequency greater than 500 Hz

The right atrioventricular valve of adult birds is a muscular unicuspid structure and unlike the right atrioventricular valve in the adult mammalian heart. The aim of this study is to test the hypothesis that the avian muscular valve (MV) is a part of the cardiac wall during systole and contributes to the right ventricle pump function. Six adult hens Gallus gallus domesticus were examined with a focus on MV structure and function. The thickness of the right ventricle (RV) wall and MV were examined post-mortem. RV wall and MV end-systolic thickness were estimated echocardiographically. The frame-by-frame processing of RV images was applied for the analysis of MV and RV free wall motion. According to the post-mortem measurements, no significant difference in the thickness between RV free wall and MV (1.8±0.3 and 1.6±0.4 mm, respectively) was found. In the course of the entire cardiac cycle, MV demonstrated the excursion of 10.3±0.9 mm. To the end of RV systole, MV thickness was increased roughly by a factor of two (2.9±0.57 mm), and reached almost the same value (3.0±0.25 mm) in RV free wall. Based on the findings obtained, we concluded that the MV may play specific and non-specific roles in the avian heart. First, MV determines the blood flow separation between the right heart chambers. Second, MV performs contractility to support for RV pump function.

Spatial and temporal non-uniform and polyfocal depolarization of the subendocardial, intramural, and subepicardial layers of the ventricle myocardium in the chicken have been established experimentally. Different depth and time of formation of activation centers in the ventricular myocardium provide the appearance of groups of multiple depolarization foci on the epicardial surface of the ventricles. During the initial ventricular activity the cardioelectric field (CEF) on the chicken body surface is characterized by three periods of the dynamics of distribution of potentials: (1) the period of their gradual changes reflecting the electrical activity of excitation foci in the subendocardial, intramural, and subepicardial ventricular layers of myocardium on CEF; (2) the period of inversion consisting of an alteration of the mutual arrangement of the positive and negative CEF areas, this alteration corresponding in time to polyfocal depolarization of the epicardial surface of the ventricles; (3) the period of stability, during which the arrangement of the positive and negative CEF regions does not change, which is due to depolarization of multiple myocardium zones at the final phase of the heart ventricle activation.

The statistical analysis is performed of changes of the bimolecular rate constant value (Δlog kII) of inhibition of human AChE, mouse AChE, AChE of flies Musca domestica and Calliphora vicina, and horse BuChE by dialkylphosphates with the general formula (AlkO) 2P(O)X at elongation of alkyl radicals and change of their branching in comparison with three physical-chemical characteristics (hydrophobicity, polarity, and volume of the side chain) of 6 amino acid residues in acyl and alkoxyl pockets variable in the studied ChE (Nos. 282, 287, 288, 290, 330, 335 in Torpedo ray AChE sequence). It has been shown that depending on structure of alkyl radicals, the rate of ChE interaction with OPI is determined by sterical hindrances to sorption (residues 282, 287, 290, 335), hydrophobic interactions (288) or polarity of microenvironment (287). This dependence in most cases is statistically significant; however, rather low values of the correlation coefficient indicate influence of structure of the OPI leaving part. The decrease of the statistical significance with elongation of alkyl radicals seems to be due to an increase of the number of possible conformational states of the OPI molecule.

By the method of synchronous multielectrode cartography (24-unipolar leads), distribution of durations and time of end of repolarization were studied on ventricular epicardium of pikes (Esox lucius) and frogs (Rana esculenta) and in ventricular intramural layers of toads (Bufo bufo) at the ectopic heart excitation. The time of arrival of the excitation wave and of the end of repolarization in each lead was determined from the minimum of time derivative of potential at the period of the QRS complex and by minimum of the T wave, respectively. It has been established that at the ventricle electrostimulation, alongside with deceleration and a change of sequence of the myocardium activation, there occurs redistribution of local repolarization durations: in areas of late activation the repolarization being longer than in zones of early activation (p0.05). At stimulation, the apicobasal gradient of repolarization is predominantly changed due to electrophysiological processes in the apical areas. In all studied species. at ectopical excitation of the heart ventricle the sequence of its repolarization repeats the depolarization sequence due to delay of activation (in fish) and redistribution of repolarization durations (in amphibians).

Summary Isoproterenol in high doses induces infarction-like myocardial damage and structural and functional remodelling of the ventricular myocardium. The purpose of the present study was to investigate ventricular repolarization in a rat model of isoproterenol-induced heart failure. Isoproterenol was administered twice to female Wistar rats (170 mg/kg, s.c., 24 h apart). Four weeks after the injections, cardiac output was measured and unipolar epicardial ventricular electrograms were recorded in situ. Activation–recovery intervals were calculated to assess repolarization. Histological examination of the heart ventricles was also performed. Heart failure in rats treated with isoproterenol was indicated by myocardial histopathological damage and reduced cardiac output. In rats with heart failure, the regional differences in activation–recovery interval prolongation over the ventricular epicardium resulted in increasing heterogeneity in the activation–recovery interval distribution and increasing repolarization heterogeneity of the ventricular subepicardium. Myocardial damage and haemodynamic changes in heart failure induced by isoproterenol were accompanied by significant changes in ventricular repolarization, which were not associated with myocardial hypertrophy.

Erosion of electrical contacts in vacuum depends essentially on the time of the initial arc immobility when the temperature on the contact spot rises rapidly up to the boiling point. The mechanism of arc root motion is very complicated and there is no universally recognized model until now which could explain it in general case. Immobility time depends on many factors, and it is very important to understand the predominant cause provoking instability of arc spot on the contact surface, which leads to the arc collapse. The model of arc evolution and instability in vacuum based on the dynamics of arc root is presented in this paper. It takes into account the parameters of electrical circuit, properties of contact material, heating, melting and evaporation during interaction of the arc with the electrode surface. It is shown that arc root immobility is conditioned by the dynamics of contact evaporation and rise of arc resistivity which depends on the vapor density in the arc and entails arc instability at certain critical current. The time and the critical contact distance of arc root immobility can be found from the conditions defining the change of the direction of heat fluxes into the arc for the opposite vector. The time of existence of a cathode spot and arc instability is found for various contact materials and current densities. Phenomenon of arc-to glow transition in low current inductive electrical circuits in vacuum due to arc instability is considered as a special case. The conditions required for this transition are obtained in dependence of contact material properties, characteristics of an electrical circuit, opening velocity and gas pressure. Special experiments with arc-to-glow transition have been carried out to verify obtained theoretical results. Comparison shows a good agreement. These results can be applied for elaboration of new electrical contact systems for vacuum circuit breakers with reduced arc duration and erosion.

Anthracycline chemotherapy produces cardiac repolarization abnormalities and arrhythmias because of cardiac toxicity of drugs. Ventricular arrhythmogenesis is attributable to increase in repolarization heterogeneity that is characterized by spatial dispersion of repolarization. The purpose of this work was to study the delayed effects of doxorubicin, the most frequently used anthracycline, on repolarization heterogeneity of the ventricular epicardium. Doxorubicin was administered to rats in a cumulative dose of 15 mg/kg (six equal intraperitoneal injections over a period of 2 weeks). Six weeks after the last injection, electrophysiological mapping of the ventricular epicardium was performed by sequential superimposition of a 64-electrode array on the left ventricular base, left ventricular apex, right ventricular base, and right ventricular apex. Activation–recovery intervals (ARIs) were measured. In doxorubicin-treated rats, ARIs were inhomogeneously prolonged, the overall ARI dispersion and local ARI dispersions were increased, and the interregional differences in ARI dispersion were decreased. These data demonstrate that doxorubicin-induced inhomogeneous prolongation of repolarization of the ventricular epicardium results in increasing heterogeneity of ventricular repolarization because of increasing intraregional heterogeneity while interregional differences are lost. Repolarization of the right ventricle is more sensitive to doxorubicin than that of the left one.

Parameters of cardioelectric field on body surface and propagation of excitation in ventricular myocardium during initial activation were studied using multichannel synchronous electrocardiotopography. It was shown that inversion of areas of negative and positive potentials of cardioelectric field on body surface at the moment of excitation propagation to the epicardium reflected changes in the main direction of excitation wavefront in ventricles.

Repolarization properties of left ventricular (LV) myocardium change during its hypertrophy of various genesis. Aim of this work was to study repolarization of epicardial surface of the right ventricle (RV) in experimental model of LV hypertrophy caused by renovascular hypertension in rats. We registered 32 unipolar electrograms on the surface of cardiac ventricles and calculated duration of activation recovery intervals for assessment of repolarization. In hypertensive rats relative LV mass was 26% greater than in control rats, while relative mass of RV was similar in both groups. Length of activation recovery intervals in hypertension was 1.7 times greater than in control group on both LV and RV surfaces. Dispersion of activation recovery intervals did not differ significantly between groups. Thus in LV hypertrophy in rats caused by renovascular hypertension electrical remodeling of myocardium occurs not only in left but also in right ventricle.

The pump function of the right heart ventricle has been studied in anesthetized dogs and hens at sinus rhythm, supraventricular rhythm, and subepicardial ectopic excitation of base and apex of the right and left ventricles. Dynamics of the ventricle intracavital pressure was recorded by transmural catheterization. The pump function of the right ventricle in hen (as compared with sinus rhythm) retained to the greater degree at stimulation of the left ventricle apex and deteriorated significantly at stimulation of the right ventricle, whereas in dog (as compared with supraventricular rhythm) it retained to the greater degree at stimulation of the left ventricle base and deteriorated at stimulation of the right ventricle apex. Changes of the pump function of the right heart ventricle at ectopic ventricle stimulation are similar in birds and mammals. Differences in changes of dog and hen pump functions under effect of location of the ectopic excitation seem to be due to morphofunctional peculiarities of heart ventricles.

The pump function of the heart ventricles was studied in chest-open anaesthetized adult female chickens under sinus rhythm and ectopic excitation of different localization. The intraventricular pressure in the right and left heart ventricles was measured by insertion of catheters through the ventricular free walls. Maximum systolic pressure, end-diastolic pressure, contractility (dP/dtmax) and relaxation (dP/dtmin) of both heart ventricles, and duration of the asynchronous contraction time of the left ventricle were analyzed. It was revealed that reduction of the pump function of the left ventricle tends to be greater under right ventricular ectopic excitation compared with left ventricular one. In comparison with the sinus rhythm, the pump function of the right ventricle was preserved to a greater extent under stimulation of the left ventricular apex and was significantly impaired under right ventricular ectopic excitation. Relaxation of both heart ventricles was more susceptible to ventricular ectopic excitation than contractility, and was more vulnerable in the right ventricle than in the left one. The direction of changes of the pump function of the heart ventricles in chickens under ventricular ectopic excitation was similar to changes of the pump function of mammalian hearts.

Effects of ectopic pacing on left ventricular repolarization were studied in six anesthetized open-chest chickens. In each animal, unipolar electrograms were acquired from as many as 98 sites with 14 plunge needles (seven transmural locations between epicardium and endocardium in each needle). Activation-recovery intervals (ARIs), corrected to the cycle length, were used for estimating repolarization. At baseline, the nonuniform ARI distribution in the left ventricle resulted in the apicobasal differences being greater than the transmural gradient. Nonuniform ARI prolongation caused by ectopic pacing resulted in decreasing the transmural repolarization gradient and increasing the differences in the apex-to-base direction. The basal, but not apical transmural differences contributed to the total left ventricular transmural gradient. The total left ventricular apicobasal gradient was contributed by the apicobasal differences in mid-myocardial and subendocardial layers more than in subepicardial ones. Thus, in in situ chicken hearts, the transmural and apicobasal ARI gradients exist within the left ventricle with the shortest ARIs in the basal subepicardium and the longest ARIs in the subendocardium of the apical and middle parts of the left ventricle. Apicobasal compared to transmural heterogeneity of local repolarization properties contributes more to the total left ventricular repolarization gradient.

The comparative analysis of the contractile function of the heart left ventricle in four species of homoeothermic tetrapods (chicken, quail, rat, sheep) who differ in their spatio-temporal pattern of ventricular excitation, heart rate, and heart weight was performed. The analysis of cardiac cycle structure was performed on the basis of synchronous recording of ECG, phonocardiogram, and apex cardiogram. Indices of myocardial contractility of the left ventricle calculated on the basis of the analysis of the cardiac dynamics indicate disadvantageous contractile function of the left ventricle in rodents and non-flying birds in comparison with sheep. The functioning of the left ventricle in male rats is more strained than in female rats. One fundamental factor determining a more strained functioning of the left ventricle in birds in comparison with mammals is the heart rate. The relative weight and activation pattern of the left ventricular myocardium govern the contractile function of the left ventricle to a lesser extent.

Based on a multichannel synchronous mapping of heart electric potentials, the sequence in time of the ventricle myocardium depolarization was compared with dynamics of distribution of cardioelectric potentials on the body surface in a dog. The cardioelectric field on the dog body surface at the period of the initial ventricular activity has been shown to be characterized by the presence of two inversions of the mutual disposition of areas of positive and negative potentials. Contribution to formation of distribution of the cardioelectric potentials on the body surface at each moment of the period of initial ventricular activity was made by all myocardial layers involved by excitation.

The aim of this study was to investigate body surface potential distribution during the P wave in Wistar rats. We performed body surface potential mapping by means of a 64-channel synchronous electrocardiotopography. The positive area covered the caudal part of the thorax, and the negative one covered the cranial part of the thorax. During the P wave, we observed 1 maximum and 1 minimum on the body surface. The dynamics of the P-wave body surface potential distribution in rats was characterized by minor movement of the positive and negative areas, and a counterclockwise shift of the extrema on the ventral body surface. The obtained results are discussed in comparison with those in dogs and humans.