The purpose of the work is to study the time preferences of students performing daily tasks during distance learning and to determine if such preferences depend on sex and the year of study. In the absence of social regulation, the daytime and nighttime activity of students corresponded to the distribution of chronotypes that typifies a northern region, with arrhythmic and evening types prevailing but the morning bio-rhythmic stereotype having a minimal representation. With no ‘master timer’ in distance learning, students demonstrated pronounced sex differences in the daily dynamics of performance. Young females had maximum performance during the day and minimum performance at night, which corresponds to the most common type. Young males were observed to have several ascents in their performance during the 24-hour period. First-year and second-year students’ learning behavior was less synchronized with the day-night cycle. The wavelet analysis found insignificant four to five hourrhythmic fluctuations that occurred in the evening hours, during the period of students’ high educational performance.

The article presents the main characteristics of the Syndrome of undiff erentiated connective tissue dysplasia, refl ecting the essence of this problem in the system of public health, in particular children and adolescents. The mechanism of the formation of this condition and its clinical manifestations are consecrated.

Objective: to assess individual subjective chronotypic properties in residents of Khanty-Mansiysk under the influence of such biotropic and social stress factors as regular daytime and aperiodically presented shift daytime and nighttime employment. Methods. The study involved students of Khanty-Mansi Autonomous Okrug-Yugra with a daily study load, 100 girls and 53 boys, and employees of the "Ambulance" station in Khanty-Mansiysk, working in shifts, 31 women and 26 men The photoperiodic chronotype stability was studied using the computer program Photoperiodic chronotype stability calculator (registration no. 2019661664) in the form of a mobile application for Android Photoperiodic stability index. Results. The photoperiodic stability of the chronotype in women is: with regular daily employment - 3.5 (1.50-6.00) arb. units, with night shift work - 1.0 (0.00-4.00) arb. units; for men: with regular daily employment - 3.0 (1.00-4.00) arb. units, with shift night work - 1.5 (0.00-3.00) arb. units Volunteers with a regulated daytime job gravitated toward choosing to shift activities to the afternoon and refusing morning activity. In the group with shift work, the proportion of people oriented toward the morning type of work capacity was increased. In the group with shift and night work, there were no representatives of a definitely morning chronotype among women, and definitely an evening chronotype among men. In the summer season, male and female respondents, regardless of the production regime, showed an increase in the signs of the morning chronotype. Conclusion. The production and intersexual features of the chronotypological properties of the inhabitants of the North have been established. With the superposition of extreme climatic and geographical factors and social and production conditions, a general pattern of increased rigidity of the chronotype is revealed. Male and female respondents with different production regimes, when assessing subjective biorhythmic performance in the summer, demonstrate a shift towards the morning chronotype.

The parameters of central hemodynamics in young men and women, junior students of the medical faculty of the Khanty-Mansiysk State Medical Academy were analyzed in this study. Values of cardio hemodynamic indicators and vegetation index Kerdo are obtained by 24-hour monitoring. Arrhythmic type prevailed among boys and girls; the second largest type was evening type; the number of students with morning chronotype was limited. Significant differences in the average values of central hemodynamics parameters were found in groups of the young people of the same sex with different chronotype in the hours of morning rise, the diurnal activity and night's repose. Differences between the representatives of different chronotypes were evident to a greater extent in the girls' groups than in the boys' groups. In the group of youths, joined all chronotypes representatives, desynchronosis of central hemodynamic parameters was evident as ultradian rhythms. We observed more intercalated rhythms in young men with arrhythmic chronotype than in boys with evening chronotype where pulse pressure circadian rhythm also disappeared. In the group of girls, we observed disappearance of pulse pressure circadian rhythm. Girls with arrhythmic and evening chronotypes had disorders in rhythms coherence of systolic and diastolic blood pressure and heart rate that led to the absence of circadian rhythm of pulse pressure.