[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.

[Effect of heterogeneity of the myocardium on its mechanical function].

The influence of the mechanical heterogeneity on the myocardium contractility was evaluated. The heterogeneity was imitated by parallel connection of two papillar muscles with different mechanical properties. The rate of muscle shortening was controlled by a feed-back from tension of each of the muscles or both muscles simultaneously in the precision ergometer.

[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.

[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 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.

[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 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.

[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.

[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.

[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.

[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.

[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.

[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.