INTRODUCTION

The autonomic nervous system (ANS), also known as the visceral, automatic or vegetative nervous system, is part of the motor division of the peripheral nervous system and is directly related to the involuntary internal control and communication of the organism ¹ .

The activity of the various organs, devices and systems that make up the human organism are constantly influenced by the ANS, which is essential for maintaining the conditions of internal physiological balance, allowing it to perform the functions of interacting adequately with the environment around it. If there is any imbalance, organic and involuntary responses are immediate in order to reverse the ongoing process and reestablish functional balance ² . The ANS is essential for maintaining the body’s balance, defined as homeostasis ³ .

These ANS functions influence the cardiovascular system, such as heart rate (HR), blood pressure (BP), peripheral vascular resistance and cardiac output. The ANS is divided mainly into two subsystems: the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS), which function antagonistically, since while the SNS acts on the myocardium promoting an increase in HR, the PNS acts on the sinoatrial node, atrial myocardium and atrioventricular node, promoting its decrease ⁴ .

This oscillation that occurs in HR is called heart rate variability (HRV), and its analysis is mathematically based on the variation in the time elapsed between consecutive heartbeats. Changes in HRV patterns can indicate possible health problems in advance, and can also be used to assess several clinical conditions involving the cardiovascular system ⁵ .

A reduction in HRV indicates an important factor for the onset of cardiac events in apparently healthy individuals, in heart patients and also in hypertensive individuals ⁵ . In the case of hypertensive individuals, HRV presents changes, indicating greater sympathetic modulation ⁶ .

Hypertension in adolescents only became a concern in the 1960s and 1970s, a period in which several studies emerged seeking to understand the behavior of BP in this age group, its determining factors and its relationships with heart disease in the future. Studies have also shown that systemic arterial hypertension (SAH) in parents has been shown to have important implications for the development of SAH in their children ⁷ .

In this sense, the analysis of HRV can result in indicators of cardiovascular system risks, providing data on the behavior of the ANS, since individuals with a positive family history of hypertension may present an increase in sympathetic activity to the detriment of parasympathetic activity, which corresponds to a lower HRV ^8,9 . This indicates that research involving methods for early diagnosis of the risk of developing hypertension, such as the assessment of the ANS through HRV analysis, are of fundamental importance, especially among children and adolescents.

OBJECTIVE

To analyze the autonomic system through HRV in schoolchildren aged 11 to 14 years with and without a positive family history of hypertension.

METHODS

This work is the result of a cross-sectional field study, which seeks to further deepen the proposed questions rather than the distribution of the population characteristics according to certain variables. Consequently, the planning of the field study is more flexible, and its objectives may be reformulated throughout the research. This is an analytical study, as it involves a more in-depth assessment of data collection, with a quantitative nature and exploratory/descriptive objective ¹⁰ .

The research was developed in 14 schools, 12 municipal and 2 private, in which 243 students from the 6th and 7th grades, aged 11 to 14 years, of both sexes, participated, divided into 120 children of hypertensive parents (FH) and 123 children of normotensive parents (FN). Subjects with a doubtful family history of hypertension and/or individuals suffering from diseases that could cause secondary systolic arterial hypertension were not included in the research.

Initially, a questionnaire with ten closed questions was applied, which identified the name of the school, grade, class and age of the student, whether one or both parents were hypertensive and whether they used medication to control BP, whether one of the siblings or the student himself had BP, whether he was undergoing treatment, whether the student had ever measured his BP, drank alcohol, smoked, practiced physical activity and at what intensity, so that it would be possible to identify participants with or without a family history of hypertension.

BP was assessed at rest after the student remained seated for approximately five minutes. An aneroid sphygmomanometer was used, with a specific cuff for children and adolescents.

The assessment of cardiac autonomic modulation was performed using the recording of the RR interval (ms) for a period of seven minutes, based on the research by Farah et al. ⁶ , with the participant at rest and in the supine position, using a Polar brand heart rate monitor ^.model V800. The recording files were transferred to Polar Flow Sync, which allows bidirectional exchange of exercise data with a microcomputer for subsequent analysis of cardiac pulse interval variability in the different situations recorded.

After data acquisition and storage on the computer, the RR intervals from the heart rate monitor were converted into Excel files for visual inspection to identify and/or correct any incorrect recording. The data were analyzed and tabulated using the CardioSeries v.2.4 program using the fast Fourier transform (FFT). After this analysis, the absolute powers were obtained in the respective predetermined frequency bands: low frequency (LF = 0.04-0.15 Hz) and high frequency (HF = 0.15-0.4 Hz). The data were expressed in absolute values ​​and in normalized units. The LF component was used as an index of sympathetic activity, while the HF component as an index of parasympathetic activity.

According to Kawaguchi et al. ¹¹ , this analysis can be performed in two ways, in the frequency and time domains. For the present study, the frequency domain was used.

Data normality was tested using the Shapiro-Wilk test. The means were compared by analysis of variance (ANOVA). The results were presented as mean and standard error, and the significance level adopted was p<0.05.

The project is registered on the Plataforma Brasil and complied with the specificities of resolution 466/12. All individuals participating in the research and their legal guardians signed the TALE and TCLE, respectively. The project is registered under CAAE No. 55783416.2.0000.5168.

RESULTS

The results of the present study are presented in two tables. Table 1 presents the general information of the research participants, and Table 2 expresses the characteristics of the evaluation of the autonomic modulation of the FN and FH.

The percentage values ​​of BF (%BF) of the FH group showed a statistical difference (p = 0.028) compared to the BF values ​​of the FN group, demonstrating that the FH have greater sympathetic modulation in relation to the FN.

Regarding the percentage values ​​of the AF bands (%AF), the FN group showed a statistical difference (p = 0.028) compared to the FH group, thus demonstrating that the FN group has greater parasympathetic modulation than the FH group. Thus, the FN group has a higher HRV than the FH group.

DISCUSSION

When identifying the subjects according to the family history factor, it is observed that 50.62% are children of normotensive (FN) individuals (N = 123) and 49.38% children of hypertensive (FH) individuals (N = 120). The mean age was 12.4 years in both groups. When analyzing the data on systolic blood pressure, there was no statistically significant difference. However, there was a small difference between the mean FN values, which was 104 (±0.10) and the FH values, which had higher blood pressure levels, which was 105 (±0.11).

There was also a small difference in diastolic blood pressure, in which the mean blood pressure values ​​were 56 (±0.08) for FN and 59 (±0.09) for FH.

Studies indicate that family history, such as obesity, sedentary lifestyle, and environmental factors, indicate possible traits of hypertension in individuals. In addition, they indicate that children with high blood pressure measurements are more likely to become hypertensive adults ¹² .

Hypertension is one of the greatest challenges when it comes to public health, with a high prevalence especially among the younger population. This fact is worrying because the increase in blood pressure levels in adolescence extends throughout life, causing major complications in adulthood ¹³ .

Young people are at risk of developing cardiovascular diseases, whether due to hereditary or environmental factors, and many are unaware of the main risk factors for their health, such as poor eating habits and physical inactivity, as well as excessive alcohol and smoking ⁹ .

Early identification of hypertension can make an important contribution to the implementation of health programs, through the implementation of healthy eating habits and the practice of physical exercise. This change in lifestyle can contribute positively to the reduction of cases of death due to hypertension or its complications, since physical exercise has been recommended as a tool for the prevention of numerous diseases ⁶ .

In their study, Magalhães et al. ⁷pointed out a relationship between physical activity and BP levels in adults and children. In this study, it was shown that children with physical fitness below the recommended level have higher BP levels at rest and during physical exertion. The study also points out that better levels of physical fitness are accompanied by lower blood pressure levels.

In this context, school physical education can act in the prevention of health-related problems, rehabilitation and various problems related to physical activities, since the National Curricular Parameters emphasize in their objectives that the physical education teacher can ensure that the student knows and takes care of his/her own body, values ​​and adopts healthy habits as one of the aspects related to quality of life, acting responsibly in relation to his/her health and reproducing this learning to people in his/her family ¹⁴ . School physical education is able to encourage the practice of physical exercise, contributing to the prevention/control of hypertension by maintaining blood pressure levels, and thus, helps to prevent children and/or adolescents with a history of hypertension in the family from becoming hypertensive adults.

From this perspective, physical education teachers should always be concerned about developing their classes with the main objective of contributing to the student’s overall development, taking into account their motor and physiological aspects, encouraging care for the individual’s health and quality of life not only in the school context, but also outside it.

A decrease in HRV can be an important prognostic factor for cardiac events in previously healthy individuals, in whom there is an increase in sympathetic modulation and a decrease in parasympathetic modulation ⁶ .

HRV studies indicate a greater possibility of incidence of cardiovascular diseases in individuals with greater sympathetic modulation, and these diseases are the main causes of death and high public health expenditures ^5,8 .

Although the decrease in HRV and its strong relationship with heart problems, especially hypertension, is a concern, studies report that physical exercise can provide significant benefits for increasing HRV ¹⁵ . Physical exercise is capable of producing beneficial effects on the body that can be used as prevention as well as initial treatment of hypertension, in which a single session of low or high intensity exercise causes a reduction in BP, thus avoiding the use of medication and/or the reduction of its doses ^15,16 .

It is well known that physical exercise is the most recommended for preventing and controlling hypertension and maintaining blood pressure levels. Regular exercise can prevent children and/or adolescents with a family history of hypertension from becoming hypertensive adults.

In this context, physical education can provide and encourage regular physical exercise, and also intervene through content that provides information and clarification on the importance of practicing physical exercise and adopting an active and healthy lifestyle.

CONCLUSION

Considering the results found, it was possible to show that children of hypertensive parents had greater sympathetic modulation, suggesting a greater probability of developing cardiovascular diseases than children of normotensive parents, who had greater parasympathetic modulation and consequently better HRV.

It is suggested that preventive health measures be implemented in schools so that children and adolescents of hypertensive parents can reduce this risk factor. Among these preventive measures, changes in eating habits and, especially, encouragement of physical exercise stand out.