The regularity of changes in the electrical resistance of the myocardium as an indirect confirmation of the phenomenon of alternate contraction of cardiomyocyte clusters

Shevchenko Yu.L., Lychkova A.E., Ulbashev D.S.

Despite modern knowledge about the physiology of the heart, the processes of regulation of the contractile function of the myocardium in conditions of rest, physical activity and stress remain completely unexplored. The complex effect of the sympathetic and parasympathetic nervous system on the myocardium, the connection of various numerous intra- and extracardial regulatory mechanisms contributes to the possibility of alternately reducing individual associations of cardiomyocytes, which provides energetically more beneficial heart function. The study of the regulation of cardiac activity may be associated with the use of methods based on the measurement of tissue impedance, which are now widely used in various biomedical research.

Objective: to determine fluctuations in the electrical resistance of various zones of the myocardium in a state of functional rest and during stimulation of the parasympathetic and sympathetic parts of the nervous system.

Materials and methods. Chinchilla rabbits (n = 24) underwent dissection of the right and left vagus nerves, stellate ganglion. Electrodes were installed subepicardially in the myocardium of the anterior wall of the left ventricle to register the myocardial impedance. The arterial pressure in the carotid artery was measured invasively throughout the experiment. The increased load on the myocardium was created by irritation of the right stellate ganglion with current pulses of 3–7 mV, 2 ms; of the right vagus nerve — 1.5–5 mV, 2 ms.

Results. A statistically significant difference was revealed between three myocardial clusters with resistance fluctuations of high amplitude (8.0–11.0), medium (3.0–8.0) and low (less than 3.0), (p<0.05). In successive experiments, zones with different electrical resistance and alternating impedance fluctuations between these sections were determined. When the stellate ganglion was stimulated, the principle of shift change was lost — resistance increased in all clusters; when the vagus nerve was stimulated, the heart rate decreased from 150 ±11.3 to 134±10.3 in 1 min (p<0.05), while the systolic blood pressure decreased slightly from 72±5.5 to 70.5±5.1 mmHg; diastolic blood pressure with 51±6.0 to 47±5.4 mmHg. There was an asymmetric increase in the amplitude of the impedance waves in the I and II leads, a decrease in resistance in the III lead. With prolonged stimulation, there was a significant decrease in systolic blood pressure from 72±5.5 to 50.1±5.0 mmHg (p<0.05); diastolic blood pressure from 51±6.0 to 35.9±4.5 mmHg (p<0.05); heart rate from 150±11.3 to 85±7.4 in 1 min (p<0.05).

Conclusion. Based on the experimental data obtained, a conclusion was made about the simultaneous existence in the myocardium of three clusters of cardiomyocytes with alternating resistance fluctuations: high, medium and low.

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