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EXERCISE TOLERANCE AND PHYSICAL ACTIVITY IN CHILDREN WITH MOST COMMON CARDIOVASCULAR DISEASES

Summary : The cardiovascular system is actively involved in the adaptive reactions of the body. The deterioration of adaptive processes decreases the functional capabilities of the heart. Arterial hypertension is often known as the main cause of fatal cardiovascular events in adults. The aim of our study was to determine the adaptive capabilities of the cardiovascular system of adolescents with non-inflammatory cardiomyopathies depending on physical activity’s level. There were examined 92 patients with arterial hypertension and connective tissue dysplasia, the mean age was 15,4 ± 1,33 years. In order to study tolerance to the minimum physical activity and its influence on the state of the cardiovascular system in children, the Ruffier test was conducted. The vegetative reactions of central nervous system were performed by the orthostatic test. The functional state of the myocardium was assessed according to the results of the ultrasonic Doppler study of the heart. As a result of the study, it was found that in connective tissue dysplasia and arterial hypertension adaptation mechanisms were affected, accompanied by a weakening of cardiac functional capabilities. This happens against the background of a decrease in the functioning of the left ventricle. These changes are accompanied by hyperactivation of the autonomic nervous system in patients in the studied groups. The physical activity and physical development of children affect the adaptive capabilities of a growing organism. This is due to the fact that the children in group with AH and CTD were less physically active than children without myocardial pathology. Adolescents who showed the reduced results of Ruffier's test and had regular sports sections need change of a mode of training and further inspection.


INTRODUCTION
Recent findings have suggested that physical inactivity worsens the general health status of children and adolescents affected by several diseases. The cardiovascular system is involved in all the adaptive reactions of the body and a decrease in functional capabilities worsens the person's adaptation to activities and stress [1]. Adaptation to physical activity implies the development of functional changes of cardiovascular system. Exercise tolerance is the ability to perform exercise at the normally expected level, and a decreased tolerance is one of the first signs of an inadequate response of the oxygen transport systems, especially the cardiovascular [2].
Among the medical problems of the cardiovascular system, the leading place is occupied by arterial hypertension and atherosclerosis, which are the main causes of mortality in the modern population [3,4]. However, current studies indicate that the atherosclerotic process starts to develop in childhood. Arterial hypertension (AH) is a fatal problem caused by widespread prevalence and a high risk of vascular complications. Multiple risk factors contributing to CVD include 91 obesity, high blood pressure, diabetes, aging, male sex, metabolic syndrome, and physical inactivity [5]. Lifestyle modifications are advocated for the prevention, treatment, and control of hypertension, with exercise being an integral component. Arrhythmiasis pathology in children could be triggered or exacerbated by exercise due to catecholamine release, increase in cardiac output, and electrolyte imbalance. Non-differentiated connective tissue dysplasia (CTD) is manifested most commonly with small abnormalities of heart development (SAHD)abnormal chords of the ventricles, which have ectopic attachment, associated with mitral valve prolapse, development of myocardial ischemia [5,6]. The presence of this pathology can lead to impaired contractile and pumping function of the heart, and therefore lead to maladaptation of the cardiovascular system.
There have been many studies in the direction of clarifying the ways of development of dysfunction and myocardial pathology, introducing new methods of research [7,8,9]. These children are characterized by the discoordination of the autonomic regulation of respiratory and cardiovascular systems, a violation of the psycho-emotional status [10,11].
Most children lead a hypodynamic lifestyle [12,13]. This is negatively affects the activity of the cardiovascular and nervous systems. Therefore, at a young age, it is necessary to study the relationship between physical activity and the reactions of the cardiovascular and autonomic nervous systems of children and adolescents in order to study the adaptive capabilities of the body.
The results of studies suggest that short-term exercise does not appear to reduce resting systolic and diastolic blood pressure in children and adolescents [14,15,16].
Significant frequency of various heart rhythm disorders, SAHD, AH which are also associated with many cases of sudden cardiac death in young people and children, myocardial dysfunction, immunological changes [17,18].
Therefore, it was necessary to study exercise tolerance as one of the components of the adaptive capacity of children with heart disease.
The aim of the study was to determine the adaptive capabilities of the cardiovascular system of adolescents with non-inflammatory cardiomyopathies depending on physical activity's level.

MATERIALS AND METHODS
There were examined 92 patients with noninflammatory myocardial diseases aged 13 to 18 years: 44 patients (18,2 % of girls and 81,8 % of boys) with diagnosed AH I and II degree-first group; 48 children (26,7 % of girls and 73,3 % of boys) with signs of CTDsecond group. There are 23 persons had cardiac arrhythmias in this groups. The control group included 20 practically healthy adolescents (6 girls and 14 boys) with the average age 15,4 ± 1,33 years.
The physical development of adolescents was assessed. Anthropometry was performed with the calculation of body mass index (BMI) [15]. The objective status was evaluated. The James-Edward Ruffier test was conducted to evaluate the functional status of the cardiovascular system. The Ruffier Squat Test is a simple cardiovascular endurance test which involves measuring heart rate before and after performing 30 squats in 45 seconds [16,19,20]. Patients were tested with the orthostatic test. Physical activity was assessed in accordance with the International Physical Activitiy Questionnaire (IPAQ) [21,22,23]. An ultrasound examination was used to study the structure and function of the heart in the «M» and «B» modes, as well as in the constant-wave and color scanning mode with a 5 MHz convex sensor on the device digital ultrasound diagnostic system SA8000 Live (firm «Medіson», Korea) according to the standard method recommended by the Ultrasound Diagnostic Association. Indicators such as diameter of aortic root (AR), left ventricular ejection fraction (EF), left ventricular stroke volume (SV), left ventricle minute volume (MV), left atrium (LA), right ventricle (RV) sizes, myocardial mass of the left ventricle (MM LV ), posterior wall of the left ventricle relative thickness (RTPW LV ), thickness of the interventricular septum (IVST), total peripheral resistance (TPR) were analyzed. All studies were conducted 2-3 days after hospitalization, under free regime, before treatment began. The collected data were stored in a database (Microsoft Excel 2003) and mean, standard deviation (SD), and correlation coefficient were calculated by using SPSS 17 to establish significance between the groups. The results were seen at 5 % level of significance and value < 0.05 was considered to be statistically significant.

RESULTS AND DISCUSSION
Children in the group with AH made complaints in 90,1 % cases, with CTDin 84,0 %. In both groups the most common complaints were cephalgia, cardialgia, fatigue and weakness. In 2,3 % of patients with CTD palpitations were increased after exercises, in 1,0 %, syncope were observed. All children in the control group did not make any complaints about their health.
ECG data showed the presence of sinus arrhythmias in 30,7 % of patients with AH and 47,0 % patients of the second group. There were tachyarrhythmia and bradyarrhythmia in equal parts. In 26,6 % of patients with CTD defined the violation of repolarization. The results of ECG in all groups were clinically insignificant for comparison.
Ultrasound examination showed that the size of the heart chambers in adolescents with AH with reduced and normal exercise tolerance did not differ significantly. Only the myocardial mass of the left ventricle in children with normal exercise tolerance was higher than the index of children with reduced tolerance (109 ± 3,5 against to 86,7 ± 2,3; p < 0,01). The pumping function of the heart (stroke volume (SV), left ventricular ejection fraction) was not different. Adolescents with AH and excess body weight had larger SV (94,9 ± 10, 1 ml; p < 0,08) and higher minute blood volume (6,2 ± 0.5 ml; p < 0,01). In both groups, the objective status was satisfactory.
Only the diameter of left atrium in children with CTD and reduced exercise tolerance signifycantly was less that of children with normal tolerance (p < 0,01). Indicators of the pumping function of the heart (stroke volume (SV), left ventricular ejection fraction (EF LV )) did not differ.
When assessing the morphometric and hemodynamic characteristics of the heart, it can be noted that the dimensions of the right ventricle, aortic root, left atrium and the thickness of the interventricular septum were larger in the children of the group with AH.
When examining hemodynamic parameters it should be noted that they were higher among children with CTDtotal peripheral resistance of the heart (TPR) -2082,0 ± 143,9) than in the comparison -1647,0 ± 135,1, indicating that in children with CTD, myocardial remodeling is compensatory.
Small structural abnormalities of the heart were found in 100,0 % cases with CTD, as signs of connective tissue dysplasia: the prolapse of mitral valve prolapse (MVP) I degree (70,2 ± 1,1 % ), which were accompanied by grade I regurgitation (5,2 ± 0,8 %) and grade II pansystolic regurgitation (3,5 ± 0,5%). In children with AH in 50,1 % cases was observed unstable and grade I prolapse of mitral valve without regurgitation. All patients with CTD and half patients with AH had false chords localized in the left ventricle.
To clarify tolerance and physical activity of the children, questionnaires were conducted and functional tests were performed.
Exercise tolerance by the Ruffier test was satisfactory in 47,2 % of children with cardiovascular disorders. In 52,8 % of them results were weak and unsatisfactory. Decreased exercise tolerance was observed in 47,6 % of children with AH, satisfactoryin 38,1 % and in single casesgood exercise tolerance (in 14,3 %). The Ruffier test in children with CTD showed unsatisfactory and weak results in 56,0 %, more frequently than in first group (p < 0,01). Satisfactory results were in 32,0 %, and good resultsin 12,0 % cases of CTD. In the control group 55,0 % of the children had satisfactory and good results, and 45,0 %weak and unsatisfactory. Tolerance for physical exercise did not correlate with anthropometric indicators, but 62,5 % of adolescents with excessive body weight had unsatisfactory results of the Ruffier test.
Patients of all groups were physically inactive assessed in accordance with the IPAQ. The low level of physical activity (0-7,5 points) was in 52,3 ± 2,9 % during the week. Children with good and satisfactory exercise tolerance had average and high level of physical activity in 81,8 %. In children with AH, both high (55,1 %) and low physical activity (44,9 %) were common. In the second group, high physical activity was observed less frequently (48,5 %), and 51,5 % had low physical activity according to the survey of IPAQ. Sports sections were attended by 25,0 % of adolescents with AH and 33,0 % of children in the second group. In control group level of physical activity was deficient in 61,1 % of children.
There were no significant differences in exercise tolerance and physical activity. Physical activity level had a direct correlation with the result of the Ruffier test. Children with low physical activity were more likely to exhibit weak and unsatisfactory exercise tolerance.
When assessing autonomic response by the orthostatic test 47,6 % of children had normal variant of vegetative response. In 29,9 % cases was unsympathetic variant, in 5,6 %hypersympathetic, in 16

CONCLUSION
Almost half of the adolescents with both AH and CTD showed a decrease in the adaptive capacity of the cardiovascular system according to the Ruffier test. The most disadvantaged was group with CTD.
The physical activity and physical development of children affect the adaptive capabilities of a growing organism. Obviously, this is due to the fact that the children in group with AH and CTD were less physically active than children without myocardial pathology. At the same time, the presence of high blood pressure in adolescents is not an indisputable factor in reducing tolerance to exercise.
There is a decrease in the adaptive capacity of the cardiovascular system in differentiated variants of CTD -Marfan-like and Elers-like, as evidenced by the low results of the Ruffier test and adaptive types of autonomic activity.
The decrease of tolerance to physical loads in most adolescents with AH and CTD occurs against the background of the deterioration of aerobic capabilities and the violation of the autonomic activity, beginning of the formation of left ventricular hypertrophy.
Adolescents who showed the reduced results of Ruffier's test and had regular sports sections need change of a mode of training and further inspection.