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Biomedical subjects

A M Pertsov

Publications and source records attributed to A M Pertsov.

34 records · Page 2Linked to original sources
PubMedDate not supplied

[Drift of vortex in the myocardium].

The behavior of a vortex in rabbit myocardium with artificial inhomogeneity was studied using mapping technique. The inhomogeneity was created by perfusion of a part of the preparation with quinidine solution. Quinidine increased the refractory period of the myocardium and diminished the conduction velocity. It has been found that the vortex drifts along the border of the inhomogeneity because of the difference of refractory periods. The drift velocity was about 4 cm/s, which was five times less than the wave velocity. The direction of the drift was determined by the vector (----omega X----delta R), where ----omega is the angular velocity of vortex rotation, and ----delta R is a gradient of the refractory period.

Animals↗
PubMedDate not supplied

[A possibility of significant lowering the defibrillation current by determining the right time for application of a defibrillating pulse. A mathematical model].

The effect of defibrillating pulses on the functionally determined re-entries (leading circles) was studied by computer simulation. Arrhythmias caused by different numbers of leading circles (from 1 to 18) were investigated. The defibrillation threshold was found to vary 2-4-fold, depending on the time of application of a pulse. At small currents the defibrillation mechanism is principally different from the commonly known one and is linked to the movement of leading circles towards each other or towards the boundary of the excitable tissue.

Arrhythmias, Cardiac↗
PubMedDate not supplied

[Interaction of spiral and flat periodic autowaves in an active medium].

Interaction between the rotating wave and a periodic external source in the model of Fitz Hugh--Nagumo type was computed. When the periods of the external source are longer than the rotation period of the spiral wave (T greater than Ts) the external source does not affect the spiral wave. At T less than Ts autowave synchronization effects are observed. The oscillation period predetermined by the external source is set in all the points of the medium except the neighbourhood of the spiral wave. The dislocation (wavebreak) persists in the medium drifting slowly at the angle to the wave vector of the flat waves. After the external source is eliminated, the spiral wave with the original period restores from this dislocation. When the dislocation reaches the interface, it disappears. In this case after the switching off of the external source the resting state is established. A theory of the drift is proposed which connects the drift velocity with the nucleus size and the rotation period of spiral wave.

Heart Rate↗
PubMedDate not supplied

[Experimental evaluation of the critical size of the myocardial reverberator].

Two independent experimental methods for estimating the minimal size of myocardium where a rotating wave could still arise (the crucial wave size) were proposed and realized. The first one was based on measuring the wavelength, the second--on the determination of the crucial size of an unexcited obstacle. The crucial rotating wave size in the myocardium without an obstacle was shown to increase under lidocaine effect.

Animals↗
PubMedDate not supplied

[Fiber interaction during impulse propagation in smooth muscle and myocardial tissues. Electrotonic interaction].

Electrotonic potential appearing in a single muscle fibre during excitation spread was calculated in the mathematical model of closely packed parallel fibres. Electrotonic depolarization values for heart and smooth muscle were shown to be 10--20 mV, that is comparable to the excitation threshold value. Tissue parameter values were estimated where the coupling coefficient was maximal. The parameter values proved to be similar to those measured in heart and smooth muscles. The data obtained indicate that the electrotonic interaction of muscle fibres should play a significant role in excitation conduction.

Cell Communication↗
PubMedDate not supplied

[Effect of specialized contacts on fiber interaction during the spread of excitation in smooth muscle and myocardial tissues].

A mathematical model of closely packed parallel muscle fibres with side by side junctions was studied. High coupling coefficient for both heart and smooth muscle fibres was shown to be available at rather low junction permeability. The coupling coefficient for heart fibers is equal to 0.5 at specific junction membrane resistance as high as 100 omega cm2. For the same coupling ratio in smooth muscle the specific junction membrane resistance should be even greater (1000 omega cm2). The role of nexuses and tight junctions in conduction of excitation is discussed.

Cell Communication↗
PubMedDate not supplied

[Instabilities of autowaves in excitable media associated with critical curvature phenomena].

While studying a two-dimensional excitable medium described by the Fitz--Hugh equation on a digital computer a new type of instabilities was discovered which had no analogy in one-dimensional systems. It has been shown that when the wave encounters upon an obstacle the front breaks, diverge, thus destroying the excitation waves. Initiation of such instabilities is associated with critical curvative phenomenon. The instabilities appear when the front curvature in the region of wave break is greater than the critical one for the given medium. The instabilities found are observed when medium excitability is suppressed. This phenomenon may be related to the processes which occur in the damage regions of the myocardium tissue.

Computers↗
PubMedDate not supplied

[Mechanism of spiral waves initiation in active media, connected with critical curvature phenomenon].

While studying on a digital computer a dimeric active medium described by Fitz-Hew, Nagumo equations a new mechanism of spiral waves initiation was observed. It has been shown that when the wave rounds the barrier where Neuman baundary conditions are set (dE/dn = 0) the wave separates from the border and the breakage of the front takes place; then it develops into a spiral. The effect is observed when the curvature of breakage is close to the critical one for the given medium. The results obtained may be of interest for explaining the mechanism of initiation of spiral waves in the damaged regions of the myocardium tissues.

Animals↗
PubMedDate not supplied

[Initiation mechanism of the first extrasystole in short-term atrial arrhythmia].

Excitation propagation during arrhythmias induced by electric stimulation into the vulnerable phase was studied on rabbit' left auricle bands by mapping (in 80-150 points). Arrhythmias were initiated under normal conditions and at acetylcholine background (0.2 mg/l). Recording of the electrical activity was realized by surface electrodes. The first extrasystole wave was shown to be conditioned as a result of the appearance of one or several point or ring-like excitation sources on the myocardium surface. There is no continuous circulation of the excitation wave on the surface of the cardiac tissue. Probable mechanisms of the appearance of such sources are discussed. Excitation circulation in the myocardium thickness (intramural re-entry) is considered as a more probable mechanism.

Animals↗
PubMedDate not supplied

[Sharp increase in refractory period induced by oxidation suppression in Fitz Hugh-Nagumo model. New mechanism of antiarrhythmic drug action].

A change in fast inward and slow outward currents and their time constants was simulated in Fitz Hugh-Nagumo model. A decrease in fast inward current was shown to increase the refractory period. The same result was observed when the slow current was increased or its time constant was decreased. These results were used to explain the antiarrhythmic drug action. The antiarrhythmic effect of drugs blocking fast inward current should be stronger in the depressed myocardial tissue than in the normal one.

Animals↗
PubMedDate not supplied

[Increase of heterogeneities at the interface of decrement conduction in Hodgkin-Huxley model].

Spatial heterogeneity was simulated by a 2-fold increase in either of gNa, gK, g1 in the central part of the fibre. The interval-dependent conduction block was not observed in the cable with normal gNa, while the uniform decrease in gNa along the fibre resulted were the block appearance. Difference in the refractory period of these parts of the fibre were the higher, the lower was gNa. The mechanism of this phenomenon was investigated. The results obtained can be used for understanding the mechanism of post infarction arrhythmias.

Animals↗
PubMedDate not supplied

[Analysis of electrophysiologic characteristics of the frog atrial trabecular membrane by ionic currents at a fixed potential].

The membrane of frog auricle trabecula was studied by the method of potential fixation. On the basis of the records of ionic currents zyro-isoclines of approximative differential equations of the 2nd order, describing the membrane studied, were plotted. The mathematical model of this membrane was analysed with the help of qualitative methods of the oscillation theory. The analysis has shown that the following phenomena which have not been observed experimentally should take place in the membrane of frog auricle trabecula: 1. absence of the minimum gradient and accomodation growth of thresholds; 2. absence of anode-disconnecting excitation; 3. coincidence of the current of repeated responses with that of the rheobase; 4. uneven depolarization.

Animals↗
PubMedDate not supplied

[Analysis of the electrophysiologic characteristics of the trabecular membrane in the atria of frogs by recording ionic currents during potential fixation. II. Accomodation. Repeated responses. Anode-breaking excitation].

Measurements were carried out by the method of double succrose gap. Accommodation was practically absent in all the preparations studied: the minimal gradient was not observed, the mean value of accommodation was 0.02 rheobasa/s, saturation current/H practically coincided with the current of rheobase IO(IH/IO = 1.0 +/- 0.1). Repeated responses were initiated in 1/3 of samples. The current of initiating the repeated responses IRR was insignificantly higher than the rheobase one (IRR/IO = 1.2 +/- 0.1). In the samples where the replated responses were absent the effect of uneven depolarization was observed. At depolarization current which was insignificantly higher than the threshold one (IO), the potential did not return to the resting potential and was settled at the level of -20 mV. Anode disconnecting excitation was absent in all the samples. The hyperpolarization level varied from -90 to -160 mV. The data obtained well agree with the results of the analysis of the mathematical model of frog auricle trabecula membrane constructed on the basis of the data on the potential fixation.

Adaptation, Physiological↗
PubMedDate not supplied

[Myocardial parameters controlling vulnerability. Analysis of mathematical models].

Vulnerability induced by application of a properly timed premature stimulus was studied on mathematical models. Two mechanisms of vulnerability 1) reentry, 2) focal reexcitation were analysed. Tissue with a region of increased refractory period Rmax was simulated on Wiener's type model. The influence of high refractoriness region dimensions and tissue parameters on the duration of vulnarable period was studied. Reentry was shown to appear on the border of high refractoriness region, which minimal length lmin being the shorter, the greater was tau (maximal latency of response) and epsilon (epsilon = deltaR/R--degree of heterogeneity). The dependence of vulnerable period duration on current strength was computed for Nobel's model. The dip-phenomenon was found in this model, the vulnerable zone was located above the minimal value of threshold.

Animals↗