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Biomedical subjects

V Ia Izakov

Publications and source records attributed to V Ia Izakov.

At least 19 recordsLinked to original sources
PubMed1990

[Coronary blood flow during stochastic stimulation of the canine heart].

Changes of mechanical activity and coronary blood flow induced by haphazard uncorrelated sequence of stimuli, were studied in the dog heart. The total coronary blood flow did not differ from one during determined regimen of the same mean frequency. Whereas relative contribution of systolic coronary flow increased and that of diastolic one decreased. The analysis of phasic blood flow in coronary vessels during potentiated and extrasystolic contractions, was performed.

Animals↗
PubMed1990

[The activation and mechanical determinants of the rate of isometric relaxation of the heart muscle].

In experiments with sequential loads, the relative velocity of cardiac muscle relaxation was found to be affected by the calcium ions concentration, velocity of shortening and by the terminal systolic length. Mechano-chemical dissociation played a major role, too, in the relaxation determination. The shifts in mechanical relaxation seem to be based on the cooperation phenomena in the troponine regulation of contraction and relaxation.

Animals↗
PubMed1989

[The effect of stimulation frequency on the speed of isometric myocardial relaxation in mammals].

The relaxation of tension of the rabbit and rat heart right ventricle papillary muscles was estimated by the characteristic time t30. An increase in the stimulation rate as well as an increase in extracellular concentration of Ca ions decelerated the relaxation in the rabbit myocardium, whereas in the rat myocardium a shortening of interimpulse interval accelerated isometric relaxation. Constant administration of reserpine and beta-blocking agents did not alter the effects. The mechanism of the stimulation rate effect on the velocity of relaxation are discussed.

Adrenergic beta-Antagonists↗
PubMed1989

[The relationship between rigidity and strength in the skinned fiber of rabbit skeletal muscle].

In single chemically skinned fibers of the rabbit skeletal muscle in the state of rigour and the calcium activation, the interrelationship between the strength and rigidity, in change of the sarcomeres length from 2.4 to 3.0 microns, of free calcium concentration (pCa = 6.75 +/- 5.5) and of interfilament distance, was studied. The strength-rigidity ratio under these conditions was found to be near to 1. The change in the sarcomeres length was also shown to affect the interrelationship pCa--strength, pCa--rigidity on account of the growth of the cooperation coefficient in the Hill equation.

Animals↗
PubMed1989

[The characteristics of the effect of catecholamines on the relaxation of ventricular myocardium in warm-blooded and cold-blooded animals].

The relaxation of the frog myocardium is decelerated by addition of adrenaline (10(-8)-10(-6) M) into the perfusion solution. The catecholamines in low concentrations up to 5.10(-8) M decelerate the relaxation, and in higher concentrations accelerate the drop of mechanical tension in capillary muscles of the cat ventricular myocardium. The catecholamines effects exerted upon the relaxation of myocardium seem to depend on a cooperative interaction among the calcium-troponine complexes at the actine filaments.

Animals↗
PubMed1989

[The effect of asynchronous contraction of the myocardium on its mechanical function].

The effect of asynchronous excitation of adjacent portions of intact myocardium was simulated in two parallel connected papillary muscles from the rabbit heart right ventricle. Mechanical characteristics (length-force, force-rate, final systolic length-specific time of relaxation) of each of the muscles were recorded in simultaneous and asynchronous contractions. The asynchronism was found to exert a positive inotropic effect in each of the muscles and a negative one in the duplex. The asynchronism decelerated the temporal course of relaxation both in separate muscles and in duplex. The asynchronism-related mechanochemical dissociation seems to be the crucial phenomenon underlying the whole cycle of the mechanical phenomena.

Animals↗
PubMed1988

[Myocardial contraction and relaxation in a regimen with a physiological loading sequence].

A regimen imitating the intact heart loads revealed independence of the terminal-systolic strength of the trajectory of shortening in the isolated myocardium, the strength being determined by the terminal-systolic length of the preparation, the latter being also the mechanical determinant of velocity of the relaxation isometric phase. The heterometric relaxation portion revealed within the distension phase, depended on the distension velocity, diastolic rigidity and the terminal-systolic length. The experimental possibilities of the regimen are discussed.

Animals↗
PubMed1987

[Determinants of the rate of myocardial relaxation].

The main mechanical determinant of the rate of the myocardium isometric relaxation was found to be the final-systolic length (LK.C.) in cats and frogs. Adrenaline accelerated the relaxation by shortening the LK.C. and by its "own" effect, the latter being obvious in fixed values of the LK.C. An increase in the stimulation rate shortened the LK.C. as well but decelerated the relaxation in fixed values of the LK.C. The mechanisms of control of the rate of the myocardium relaxation, are discussed.

Animals↗
PubMed1987

[Effect of initial length on the chronoinotropism of the myocardium].

Shortening di the muscle initial length was found to enhance the postextrasystolic potentiation, the Bawditch stair and other signs of chronoinotropy. A hypothesis is advanced concerning the mechanisms underlying the effect of the cardiac muscle initial length on rhythm-dependent mechanical phenomena.

Animals↗
PubMed1986

[Phasic and tonic components of mechanical tension in the myocardium of the atria and ventricle of the frog].

The complex mechanical response of the frog atria to sustained depolarizing current were divided into three components: T1--owing to slow inward calcium current; TII--related to calcium release from intracellular sources; and TIII--related to potential--dependent sodium-calcium exchange diffusion. Differences in electromechanical coupling of the frog atrium and ventricle myocardium, are discussed.

Animals↗
PubMed1984

[Comparative characteristics of the mechanical activity of atria and ventricles].

Differences between parameters of isometric and isotonic contractions of atria and ventricles were studied in warm-blooded and cold-blooded animals. The maximal shortening velocity of contractile element was determined from isometric contraction using a two-component Hill's model as well as from the strength-velocity ratio. The atrial Vmax was about twice as high as that of ventricles. The rate constant of delayed activation in atrium was 10.6 +/- 0.4 s-1, in the rabbit ventricles 4.42 +/- 0.60 s-1. The data suggest differences of ATP hydrolysis velocity with actomyosin ATP-ase of atrium and ventricles.

Adenosine Triphosphatases↗
PubMed1983

[Nature of the "length-force" relationship in mammalian heart muscle].

Alteration of myocardial contractile state (a transitional process) is shown to be associated with changes of muscle length or with 3-min pause. The drugs which block the propagation of AP along the T-tubular system, induce a less obvious response of the lengthening alone. An increase of the muscle length seems to lead to improvement of propagation along the T-tubular system and to involve "additional" functional units.

Animals↗
PubMed1983

[Effect of temperature on the myocardial chrono- and inotropism of warm-blooded animals].

The influence of temperature on interval-force characteristics of rabbit ventricular myocardium was studied in conditions of random Gaussian sequences stimulation intervals. The interval-force relationships were described with Volterra series and cross-correlation function. Decrease of temperature causes inverse influence of Tn and Tn-1 intervals of the contraction force: at 35 degrees C coefficient of cross-correlation rho (0) of Tn-Pn equals 0.1 and coefficient of cross-correlation Tn-1-Pn rho (+1) equals -0.75; at 20 degrees C rho (0) = 0.8; rho (+1) = -0.15. Index Q10 for the process responsible for extrasystolic potentiation is about 3.0 and Q10 for restitutions process equals 1.5. At high temperature calcium seems to enter the myoplasm from extracellular pool, to be absorbed by sarcoplasmic reticulum and released in next cycle contraction. At low temperature, a part of calcium entering from that pool directly activates contractions at the same cycle.

Animals↗
PubMed1983

[Chrono- and inotropic and heterometric regulation of mechanical activity in the heart of atrial fibrillation patients].

The theory of accidental functions was used in the analysis of the heart's mechanical activity. The dependence of right-ventricular pressure on R--R duration and ultimate diastolic pressure was evaluated in 10 patients, using cardiac probe. Cross-correlation and cross-variance functions were used to assess chrono-inotropic relationship and the relationship between ultimate diastolic and systolic pressure values. Poor correlation was shown between ultimate diastolic and systolic pressure in tachycardia. Evidence is presented that mechanical activity is controlled through chrono-inotropic relationship in tachysystolic arrhythmias. In cases of normosystole and bradycardia, the heterometric system makes the principal contribution to the control of the heart mechanical activity.

Adult↗