Biomedical subjects
Publications and source records attributed to A B Medvinskiĭ.
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The paper describes the study of anti-arrhythmia effects of ionol. In isolated rabbit papillary muscle, ionol (a) had no effect on the depolarization-induced automaticity; (b) did not influence early afterdepolarizations: (c) delayed the onset of post-depolarizations initiated by Ca-overload and therefore inhibited the ectopic focal activity in myocardium. In isolated left auricles of rabbit, ionol suppressed the shortening of the excitation wavelength induced with adrenaline and thus protected the heart of reentry and consequent rhythm disturbances.
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An experimental model of tachy-arrhythmias due to myocardial excitation wave circulation round an unexcitable obstruction was explored. Artificial openings of various sizes and shapes in an isolated rabbit left atrium posed as obstacles. Acetylcholine, having a potent effect on the refractory period of atrial cells, was used to alter refractory characteristics. It has been demonstrated that differences in the sensitivity to the action of pharmacologic agents on both re-entry types can actually be absent. Acetylcholine is shown to shorten the period of circulation round the hole, i.e. act on such circulation in the same fashion as it does on the leading cycle, in a wide range of hole diameters, approaching the ones comparable with the size of the atrium. Sensitivity to acetylcholine only disappears when a labyrinth is set up with artificially prolonged circulation pathway. The action of acetylcholine can be attributed to the absence of tissue with fully recovered excitability between the anterior and posterior fronts of the wave circulating round the obstacle.
The mechanism of polymorphic disturbances of the heart rhythm is studied on an experimental model, isolated ventricular preparations of ground squirrel and rabbit. Polymorphic arrhythmias are identified from habitus of the isolated preparation pseudoECGs mathematically derived from electrograms registered simultaneously at 32 endocardial and 32 epicardial points. The same electrograms allow one to visualize the excitation wave propagation along each of the preparation surfaces. The comparison of excitation wave pictures and corresponding pseudoECGs enabled us to reveal the conditions necessary and sufficient for polymorphism in heart rhythm disturbances. Polymorphic arrhythmias are due to changes in wave pictures in the regions of retarded excitation propagation.
A mathematical model of two contacting cells is studied. Simple analytical formula are obtained which connect the transmission coefficient k with the parameters of contact zone (dimension of the contact region, resistence of the contact membrane, specific resistence of the interslit medium, width of intercellular slit) and with geometry of contacting cells. It is shown that in the absence of conductivity increase in the contact zone the values of transmission coefficient. k = 0.2 divided by 0.3. are available. k is evaluated for early embryonic cells. The mechanisms of electric coupling in early embryonic cells and in heart tissue are discussed.