Abstract
Introduction: The fundamental aim of this study is to know the blood pressure (BP) profile of children and adolescents, and in particular the prevalence of hypertension and its main determinants.
Methods: Our sample consisted of 2285 healthy children and adolescents from the Central Region of Portugal and followed in a Sports Medicine Clinic. Of these, 503 were females, mean age 11.89 ± 3.10 years, and 1782 were male, mean age 12.79 ± 2.946 years. Mean age was 12.18 ± 3.063 years (ages 5 to 18 years) and Body Mass Index (BMI) 19.4460 ± 3.72560 kg/m2. BP and heart rate (HR) were measured three times after a rest period of 10 minutes, in the braquial artery with a clinically validated automated sphygmomanometer.
Results: The prevalence of arterial hypertension (AH) was 19.1%, with 18% of PA in the category of prehypertension. The prevalence was higher in females (24.5%) compared to males (17.6%). The overall prevalence of obesity was 8.8%, being 9.8% and 5.2% respectively for males and females. The relative proportion of AH was higher in the obese category (28.4%) compared to the overweight category (20.7%) and normal weight (17.88%), suggesting a relationship between weight the blood pressure profile. The logistic regression analysis further emphasizes this relationship, with obese subjects having 83% greater risk of hypertension. The female gender was also associated with hypertension as well as subjects with family history.
Conclusions: Preliminary results of this register revealed a significant proportion of children and adolescents with BP values above the 90th percentile, with higher expression in females and linked to obesity.

Introduction
The behavior and distribution of blood pressure (BP) in Children and Adolescents aspects remains relatively unexplored in our country, thus the need to conduct observational studies aiming to better illustrate the blood pressure profile of this particular population, this constituting the main objective of this work [1-5].

Material and Methods

Sample
Our sample consisted of 2285 healthy children and adolescents from the Central Region of Portugal and followed in a Sports Medicine Clinic. Of these, 503 were females, mean age 11.89 ± 3.10 years, and 1782 were male, mean age 12.79 ± 2.946 years. Mean age was 12.18 ± 3.063 years (ages 5 to 18 years) and Body Mass Index (BMI) 19.4460 ± 3.72560 kg/m2.

Procedure
As for BP measurement, we used a clinically validated measuring device (OMRON 705IT), with a cuff of appropriate size to the diameter of the arm, respecting the recommendations of the American Academy of Pediatrics [6]. When BP values were high, the confirmation was made with a standard mercury sphygmomanometer. For data analysis we used the average of the values and blood pressure classification was performed according to the criteria of the American Academy of Pediatrics [6], considering having hypertension when SBP and/or DBP were located above the 95th percentile for sex, age and height. Hypertension class 1 was defined for SBP and/or DBP above the 95th percentile but below the 99th percentile and high blood pressure class 2 for values at or above the 99th percentile. Pre-hypertension was defined as SBP and/or DBP located between the 90th percentile and 95th percentile. Blood pressure levels below the 90th percentile for SBP and DBP simultaneously defined the normotension.

We also calculated the BMI was classified according to their distribution by percentiles by sex and age, according to the criteria of the U.S. Center for Disease Control and Prevention [7]. Obesity was defined for the presence of a BMI above the 95th percentile and overweight for a BMI between the 85th and 95th percentile.

All participants' parents gave informed consent for the use of their data for investigation purposes.

Results
The prevalence of arterial hypertension (AH) was 19.1%, with 18% in the category of prehypertension. Of hypertensive subjects, 14.3% are in a stage 1 of hypertension and 4.9% are in stage 2. As is shown in Graphic 1, the evaluation of the gender distribution of the categories of blood pressure showed significant differences in the prevalence of HBP, which is 24.5% in females and 17.6% for males (p <0.05). On average, the values ​​of blood pressure (SBP and DBP) and HR did not differ significantly between genders (Table 1).

Graphic 1. Prevalence of HBP.

Table 1. Main quantitative characteristics of the sample. Legend: SBP - systolic blood pressure, DBP - diastolic blood pressure, BMI - Body Mass Index.

Regarding the background, 21% of individuals in our sample reported having a family history of cardiovascular disease and/or hypertension, representing 18.9% of males and 32.1% female. With regard to the individual background, these are very scarce since they are only 15 subjects (0.7%).

The relationship of BP with BMI class was also assessed, given the well documented relationship between the prevalence of obesity and HTA. As is shown in Graphic 2, the overall prevalence of obesity was 8.8%, being 9.8% and 5.2% respectively for males and females. Analysis of the distribution of categories of BP by BMI classes, expressed in Table 2, revealed that the relative proportion of AH was higher in the obese category (28.4%) compared to the overweight category (20.7%) and normal weight (17.9%), suggesting a relationship between weight profile and blood pressure levels.

Graphic 2. Prevalence of different classes of BMI.

Table 2. Prevalence of hypertension by BMI class.

The logistic regression analysis further emphasizes this relationship. In Table 3 we can see that obese subjects having 83% greater risk of hypertension (OR = 1.83, 95% CI: 0.89-1.62, p <0.001) and 61% greater risk of prehypertension (OR = 1 -61, 95% CI: 1.10 -2.36, p = 0.013). This table clearly described the linear trend of increasing prevalence of hypertension with BMI classification. The female gender was also associated with hypertension (OR = 1.51, 95% CI: 1.19 to 1.91, p = 0.001) as well as subjects with family history (OR = 1.37, 95% CI: 1.03-1.81, p = 0.028).

Table 3. Relationship between blood pressure classification with weight, sex and family history. Legend: OR - univariate odds ratio, adjusted OR - odds ratio adjusted for age and sex

In Table 4, for the male gender can see that the higher prevalence of AH is in subjects with obesity and family history (30%), followed by the group with obesity and no family history (26.2%). In females, the HBP is present in greater proportion in the group with obesity and family history (55.6%). The largest number of subjects is the group of boys with normotension, normal weight and without family history (n = 689). Although this table we can see that, contrary to expectations, in males, the prevalence of HBP in subjects without a family history is higher than in those with family history (18.9% and 12.3%, respectively).

Table 4. Prevalence of HTA by sex, family history and BMI

Discussion
The relevance of AH in children and adolescents represents a topic relatively unexplored, which is largely explained by the traditional view of this pathology as a disease of adults. However, this aspect cannot be neglected, because epidemiological studies of AH in childhood have provided consistent evidence that high blood pressure at this age is a precursor to the development of arterial hypertension in adulthood. With the body changes that young people have had, it makes sense to start at an earlier age to measure blood pressure and take early preventive measures, which will have a potentially positive long-term [3,4,6-8].

The prevalence of hypertension in younger age groups has increased, possibly due to increasing epidemic of obesity and sedentary life that children take. National and international surveys have shown that the prevalence of AH vary widely from 1% to 22% [1,3,9-13].

In this study, the prevalence of AH was 19.1%, with higher expression the female gender (24.5%) compared with male gender (17.6%). However, this difference is largely conditioned by the reduced representation of the female group (n = 503) and, according to the results of Genovesi et al, possibly by the use of hormonal contraceptives observed in the female population. This study, emphasizes a important prevalence of this disease, tended higher than that found in most of the above registers, and that is particularly relevant if we consider the particular characteristics of the sample, which is constituted by a extremely healthy subjects, with levels of physical activity above the average and with a global prevalence of obesity less than that estimated for the general population. Therefore, it is likely that the real prevalence of AH in children and adolescents in general is still higher than estimated in this study [2,13].

In our study we found an overall prevalence of overweight of 22.8%, while the prevalence of obesity was 8.8%. Compared to national studies [8,12-13], we can see that our study shows a prevalence of overweight and obesity bottom, which is possibly explained by regular physical activity present in our sample.

Arterial hypertension is highly associated with obesity and the incidence of this syndrome in the age group of our study is increasingly high, which adds interest to our work. In a recent analysis, that combined data from the Third National Health and Nutrition Examination Survey (NHANES III, conducted between 1988 and 1994) and the NHANES 1999-2000 Study, obesity represented almost 30% increase in systolic blood pressure observed in children and adolescents over a period of 12 years. In line with these results, have documented an independent association of overweight and obesity with hypertension, also looks solidly demonstrated in several studies mentioned above [15-19].

The present study has some limitations from the outset due the particular characteristics and context of evaluations, as well as not being representative of the country, since it has an essentially regional expression. The fact that the evaluation focus on young people with particular interest for sports practice limits the extrapolation of results to the general population in the age groups analyzed. On the other hand, reduced the proportion of girls significantly limits the comparisons between genders, advising caution in consideration of the differences [11, 20].

The magnitude of the studied sample does not cease to be relevant and even uncommon to our country, giving an important expression of our results. Despite these aspects, the signals extracted from these results are expressive enough to advise the representative studies with the aim of determine the true prevalence of this disease in children and adolescents in this country.

Conclusion
The results of this study should, in our opinion, to alert health officials to the need of implementing measures to try to halt the epidemic of obesity and hypertension in order to promote cardiovascular health in these age groups, which undoubtedly will bring numerous benefits over the long term.

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Publication: November 2011

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