Direct observation of the effect of hypothermia on the structures of the heart in humans is impossible, so with the help of induced experimental models, it becomes possible to analyze the morphological changes of the heart after exposure to cooling. During the research, the role of modeling the pathological condition, identifying the timing, causes, and mechanism of disorders in the morphogenesis of the heart, its wall, and structural elements or components increases. This justifies the relevance of this study and the feasibility of its implementation.
Our research aimed to study the morphological patterns of morphogenesis of the heart and structural components of the myocardium of experimental animals under conditions of hypothermiaю
The object of the study was 135 hearts of laboratory mature rats, which were divided into 5 groups; (1) control group; (2) group after exposure to general hypothermia with a duration of 10 days; (3) group after exposure to general hypothermia with a duration of 30 days; (4) group after exposure to dry cold; (5) group using the cardioplegic solution.
In the experimental group, under the conditions of modeling of general hypothermia in the early period - after cooling for 10 days, hyperemic vessels, increase in the size of cardiomyocytes, interstitial space was observed in the myocardium. This indicated the activation of the adaptive processes of the microcirculatory tract and the apparatus of energy supply of cells that arise in cardiomyocytes during general hypothermia at an early stage of action. Increased degenerative processes in the myocardium, destructive changes in muscle fibers, hyperemic endothelium of small vessels, and capillary edema were observed after exposure to general hypothermia for 30 days.
In the experimental group, under conditions of simulation of local hypothermia in dry cold conditions, irreversible damage to muscle fibers was observed in the myocardium. Dry cooling of the heart causes destructive changes in the myocardium with the development of degenerative and destructive processes in the myocardium, muscle ruptures, myofibril fibers, their destruction, and increase in intercellular spaces, indicating the depressant effect of this method on the membranes. The action of local hypothermia with the use of the cardioplegic solution to cool the heart allows you to maintain the normal structure of the myocardium while maintaining the structural organization.
The first comparative ultramicroscopic study using electron microscopy showed that after general hypothermia, with a duration of 10 days, the general structure of the mitochondrial apparatus does not change, but there is a compensatory adjustment of the energy apparatus of contractile cardiomyocytes of the left ventricle. The action of general hypothermia with a duration of 30 days destroys subsarcolemmal and paranuclear organelles, edema, and degradation of intermyofibrillar mitochondria, destructive-degenerative processes in the mitochondrial apparatus of left ventricular cardiomyocytes in the ventricles of the left ventricle and ventricles.
After a comprehensive immunohistochemical study, eNOS and LC3B expression were observed in cardiomyocytes after exposure to general hypothermia. Our study observed uneven accumulation of endothelial dysfunction marker e NOS and LC3B autophagy with the highest expression of these markers in rat myocardial vascular endothelial cells after exposure to total late-onset hypothermia with a duration of 30 days general hypothermia on the vessels of the microcirculatory tract.
After conducting a comprehensive electrophysiological study using an ECG, the effect of general hypothermia in the early and late stages on the electrophysiological parameters of the heart was noted for the first time. To conduct an electrophysiological study, action potentials were taken, ie an open-heart ECG, under which the amplitude and duration of the changing complex were measured. In addition to changes in the amplitude-temporal characteristics of the ECG, splitting of the R wave was observed on day 10 of the general hypothermic state in rats, up to 30 days of exposure to general hypothermia, these changes progressed, and additionally revealed tooth J (Osborne tooth), which appeared under hypothermia.
The results obtained on the morphogenesis of the heart after exposure to hypothermia in experimental animals give an idea of the morphological changes in the myocardium and its circulation, which we can predict and correct during general hypothermia, especially given the duration of exposure after 10 and 30 days and use the method of local hypothermia after the action of cardioplegic solution and understand the irreversible lesions that occur after exposure to dry cold.
