Risk Factors for Major Cardiovascular Diseases and Autonomic Status in Young Persons

The dissertation is devoted to the study of the main risk factors for cardiovascular diseases in young persons (aged 20-29 years) in interrelation with the features of their autonomic status. The work was carried out on the basis of the Stavropol State Medical Academy; the examined contingent consisted of senior students. The study employed a comprehensive clinical and instrumental examination, which included the collection of family history, anthropometry with phenotypic analysis of external manifestations of connective tissue dysplasia, blood pressure measurement, examination of the blood lipid profile, echocardiography with Doppler analysis of blood flow, ambulatory blood pressure monitoring, assessment of the risk of death using the SCORE system, and analysis of heart rate variability at rest and during functional tests. Percentile distributions of indicators of the blood lipid profile and heart rate variability were obtained, and a chart for assessing hereditary burden and a model for the screening assessment of the cumulative severity of risk factors were developed. A nonlinear relationship between heart rate variability and body mass index and a progressive decrease in heart rate variability with increasing hereditary burden were established, as well as the predominance of isolated office hypertension over sustained hypertension during ambulatory blood pressure monitoring. The results confirm the necessity of including in the risk group young persons not only with excess but also with deficient body weight, and propose tools for optimizing the primary prevention of cardiovascular diseases.

Relevance of the study. For many years, cardiovascular diseases (CVD) have firmly held first place among all causes of mortality in the world (Chazov E.I., 2005). At the same time, in a number of economically developed countries, thanks to successfully implemented state-level primary prevention, a steady downward trend in mortality from cardiovascular pathology has been observed in recent years, whereas Russia has demonstrated dramatic increases in such mortality (Oganov R.G., 2004; Shalnova S.A. et al., 2005; Sans S. et al., 1997). Every year in Russia more than 1 million people die from CVD, which accounts for 56% in the structure of total mortality (Oganov R.G. et al., 2002). Among CVD, coronary heart disease (CHD) and arterial hypertension (AH) occupy leading positions (WHO Materials, 2004).

In recent years, morbidity and mortality among young persons of working age have increased significantly. Thus, mortality from CVD in the age group 20-29 years in 2002 exceeded the corresponding figure for 1990 by more than three times (Chazov E.I., 2002). In all other age groups, the increase in mortality was less alarming than in young persons. The morbidity of young people can be regarded as a kind of barometer of social well-being and medical provision of the preceding period of childhood, as well as a harbinger of changes in the health of the population in subsequent years (Medik V.A., 2004). When examining young persons, attention should be focused on prenosological diagnostics (Baevsky R.M. et al., 1997; Kim V.M. et al., 2006).

The modern concept of the cardiovascular continuum implies the existence of a single mechanism of CVD development through the processes of neurohumoral dysregulation (Makolkin V.I. et al., 2002). The beginning of this process is the presence of risk factors (RF), many of which are present from the earliest period of life. Therefore, young persons appear to be the optimal contingent for studying the early features of the formation of the cardiovascular continuum. The most effective way to reduce morbidity and mortality from CVD is their primary prevention, i.e., the control of RF (Oganov R.G., 2004). The stated concept is consistent with the orientation of the Russian National Project "Health" toward the development of the preventive direction of medical care, among the priorities of which is the dispensary follow-up of risk groups. To date, the approaches to dispensary follow-up of risk groups in young persons require evidence-based scientific substantiation.

It is known that three RF for CVD — AH, smoking, and dyslipoproteinemia (DLp) — are responsible for more than 75% of all cardiovascular mortality (WHO Materials, 2002). The indicated RF are modifiable, which increases the scientific and practical interest in developing optimal approaches to their detection and correction. The study of the role of hereditary burden (HB), which is an indisputable RF for CVD (Nikitin Yu.P. et al., 2005), deserves special attention. In addition to the listed traditional RF, the study of the role of other, less well-studied factors, in particular, autonomic dysregulation, is relevant. The interrelation of various disorders of autonomic status with RF for CVD remains insufficiently studied to date (Mikhailov V.M., 2002; Standarts, 1996). The above-described relevance served as the basis for conducting the present study.

Aim of the study: to investigate the main risk factors for cardiovascular diseases in interrelation with the features of autonomic status in young persons.

Objectives of the study:

1. To conduct a comprehensive examination of persons aged 20-29 years who are senior students of the medical academy of Stavropol, in order to determine the presence and severity of the main risk factors for cardiovascular diseases in them.

2. To develop a chart for assessing the level of hereditary burden and a model for the screening assessment of the severity of the main risk factors for cardiovascular diseases in young persons.

3. To perform an in-depth analysis of heart rate variability for the quantitative assessment of autonomic status and the functional capabilities of the cardiovascular system in the examinees in interrelation with the main risk factors for cardiovascular diseases.

4. To obtain data on the percentile distribution of indicators of the blood lipid profile and heart rate variability in persons aged 20-29 years.

5. To identify young persons with elevated blood pressure and to differentiate isolated office and sustained arterial hypertension.

Scientific novelty of the study: For the first time, in persons aged 20-29 years — senior students of a medical academy — percentile distributions of heart rate variability indicators at rest, during functional tests, and of blood lipid profile indicators determined by an acoustic method have been presented. A dome-shaped dependence of heart rate variability indicators on the value of body mass index in young persons has been demonstrated. A progressive decrease in heart rate variability has been established in persons aged 20-29 years with an increase in hereditary burden with respect to major cardiovascular diseases. For the first time, autonomic status has been studied in young persons depending on the cumulative severity of the main risk factors for cardiovascular diseases. An increase in the severity of the main risk factors for cardiovascular diseases is accompanied by a decrease in heart rate variability with a change in its regulation, which manifests itself in decreased parasympathetic activity and a relative increase in the regulatory activity of the sympathetic nervous system and humoral-metabolic mechanisms.

Practical significance: The chart proposed for young persons for assessing the level of hereditary burden with respect to major cardiovascular diseases makes it possible to rank the examinees by the probability of developing the indicated pathology in the future with the aim of their timely inclusion in dispensary follow-up.

The results of the conducted study substantiate the necessity of including in the risk group for cardiovascular diseases not only young persons with excess body weight, but also those with its deficiency, which makes it possible to supplement the existing programs of dispensary follow-up of university students.

The reference values of heart rate variability indicators obtained for young persons, taking into account the severity of the main risk factors for cardiovascular diseases, can be used by other authors for comparison and interpretation of the results of their own studies.

The use of the model developed for young persons for the screening assessment of the severity of the main risk factors for cardiovascular diseases makes it possible to optimize the process of their detection in the general population and to identify high-risk groups for the purpose of carrying out effective primary prevention.

Main propositions defended:

1. The most prevalent risk factors for cardiovascular diseases in persons aged 20-29 years are hereditary burden and smoking. Modifiable risk factors for cardiovascular diseases (arterial hypertension, excess body weight, smoking, and dyslipidemia) are detected in young men more often than in young women.

2. An increase in the severity of the main risk factors for cardiovascular diseases in young persons is accompanied by a decrease in heart rate variability with a change in its regulation. This manifests itself in decreased parasympathetic activity and a relative increase in the regulatory activity of the sympathetic nervous system and humoral-metabolic mechanisms.

3. Heart rate variability in young persons has a nonlinear relationship with body mass index: it increases as body mass index rises into the range of 19-22 kg/m2, and then gradually decreases to minimal values in obese patients. The lowest heart rate variability is observed at the extreme values of body mass index (<18.5 and >30 kg/m2).

4. In persons aged 20-29 years with elevated blood pressure, during ambulatory blood pressure monitoring, isolated office hypertension is recorded significantly more often than sustained hypertension.

Implementation of the study results. The results of the dissertation research have been implemented in the practice of the physicians of the cardiological departments of the Municipal Healthcare Institution "City Clinical Hospital No. 3," the State Healthcare Institution "Regional Clinical Cardiological Dispensary," and the Municipal Healthcare Institution "City Polyclinic No. 1" of Stavropol. The theoretical propositions and practical recommendations of the dissertation research are used in the educational process at the Departments of Internal Diseases No. 2 and Internal Diseases No. 1 with a course of polyclinic therapy of the Stavropol State Medical Academy.

Publications and approbation of the work. On the topic of the dissertation, 23 scientific articles have been published, of which 9 in central press, and one monograph has been written: "The ABCs of Heart Rate Variability Analysis" (Stavropol, 2002). The materials of the study were reported at: the X, XI, and XII final scientific conferences of young scientists and students (Stavropol, 2002-2004); the Russian National Congress of Cardiologists "Russian Cardiology from the Center to the Regions" (Tomsk, 2004); the interregional scientific and practical conference "Healthy City: An Action Plan Today" (Stavropol, 2004); the Fourth Congress of Cardiologists of the Southern Federal District "From Research to Standards of Treatment" (Sochi, 2005); the conference of physicians within the framework of the 8th and 9th annual "Week of Medicine of Stavropol Krai" (Stavropol, 2004-2005); the Russian National Congress of Cardiologists "Prospects of Russian Cardiology" (Moscow, 2005); the joint meeting of the Departments of Internal Diseases No. 2, Internal Diseases No. 1 with a course of polyclinic therapy, and Clinical Laboratory Diagnostics of the Faculty of Postgraduate Education of the Stavropol State Medical Academy (Stavropol, 2006).

Scope and structure of the dissertation. The dissertation consists of an introduction, five chapters, a conclusion, conclusions, practical recommendations, appendices, and a list of used literary sources. The reference list includes 257 sources, of which 134 are domestic and 123 are foreign. The work is presented on 170 pages of typewritten text and is illustrated with 49 tables and 21 figures.