Influence of Factors of 21-Day Head-Down Bed Rest on the Blood Level of Myocardial Extensibility Biomarker ST2

— Head-down bed rest (HDBR) is one of the best known models of the effects of weightlessness. The responses of the cardiovascular system to thoracocranial blood redistribution continue to be studied in relation to changes in the volumes of the heart chambers and the structure of the heart muscle. The assessment of myocardial stretch, individual response of the heart muscle to HDBR, and stratification of the risk of developing heart failure according to the dynamics of a cardiomarker not dependent on the influence of such factors as gender, age, body weight, glomerular filtration rate, anemia, and hypovolemia is relevant. The aim of the study was to investigate the influence of factors of 21-day HDBR on the level of the ST2 myocardial stretch biomarker. The effect of 21-day HDBR on the level of the ST2 cardiomyocyte stretch marker was studied for the first time. The level of ST2 significantly decreased by the end of HDBR. The data obtained are of practical importance in relation to the problems of medical selection of cosmonauts and test volunteers. Background levels, variability of indicators during HDBR, and the recovery period indicate the absence of risks for the development of heart failure and cardiofibrosis in this sample of subjects in this study.