Arterial hypertension and pulse pressure in school-age children

Materials and methods. In total 848 children in 10–17 years of age (mean age – 13.9 ± 0.06 years, 45.4 % boys and 54.6 % girls) from urban and rural areas of Chernivtsi region were examined in schools during screening for elevated blood pressure (BP). School-based ambulatory seated BP was measured by oscillometric automated recording devices with the age selection of cuffs. Elevated systolic (SAP) or diastolic (DAP) pressure was diagnosed in those children with indicators above the 95th percentile of age norms in accordance with the national normative values. In cases of elevated BP the measurements were verificated by aneroid device.

Arterial hypertension (AH) among adults remains a public health problem all over the world [1][2][3].The prevalence of hypertension is increasing at an accelerated rate not only in adult but in school-age children too.This has raised great concern about premature development of cardiovascular disease, which has important long-term health and financial implications [4][5][6].Blood pressure (BP) screening may be effective in identifying children with hypertension though evidence is limited and false-positive rates are high [7,8].
The BP wave consists of a steady and pulsatile component, mean arterial pressure and pulse arterial pressure (PAP), respectively.Current definitions of AH are primarily based on systolic arterial pressure (SAP) and diastolic blood pressure (DAP) but not on pulse pressure.Widely used mean arterial pressure is the product of cardiac output and peripheral arterial resistance.Pulse pressure -the difference between systolic and diastolic arterial pressure, depends on left ventricular ejection, the elasticity of the central arteries [6,9].Pulse pressure is an indicator of the stiffness of large arteries, especially of the aorta.More recently, increased attention has been given to PAP as a predictor of cardiovascular risk [4,5,10].In the Framingham study it was shown that the systolic blood pressure and pulse pressure reflect arterial stiffness, demonstrated that with increasing age, a gradual shift occurs from diastolic to systolic pressure and then to pulse pressure as predictors of coronary heart disease [6].The diagnostic value of PAP in children has not been studied thoroughly yet.
Unlike in adults, where a single blood pressure cutpoint is utilized for diagnostic of AH, normative BP values in children are age-, sex-, and height-dependent.The detection of children AH is generally based on blood pressure adjusted for height in the relation to national gender and age percentile standard.In addition to use of the correct normative values, repeated measurements of BP are also recommended before making a diagnosis of AH [1,8].Hypertension is diagnosed in children with readings above the 95 th percentile as results of three ambulatory BP measurements in different days.Stage I hypertension was diagnosed if a child's BP is greater than the 95 th percentile but less than or equal to the 99 th percentile plus 5 mm Hg, stage II -if a child's BP is greater than the 99 th percentile plus 5 mm Hg.There was also introduced a new category -prehypertension, which is diagnosed when a child's average BP is above the 90 th percentile but below the 95th.Although such a complex approach is aimed to avoid overdiagnosis of AH in the children, but unfortunately hypertension actually was underdiagnosed, what has been demonstrated in several recent studies [3,6,8].Early diagnostic and prevention of childhood AH therefore needs high priority and additional investigations.

Objective
The aim of this study was to determine the prevalence of arterial hypertension among school-age children and diagnostic value of pulse pressure.

Materials and мethods
In total 848 children in age of 10-17 years (mean age -13.9 ± 0.06 years, 45.4 % boys and 54.6 % girls) from urban and rural areas of region were examined in schools during screening for elevated BP.The study included assessment of resting anthropometric data, physical activity habits, structure and quality of nutrition, food preferences, family and socioeconomic data etc.Body mass index (BMI) was calculated and Z-index of BMI was estimated according to local anthropometric percentiles standards.School-based ambulatory seated blood pressure was measured by oscillometric automated recording devices.Three sequential measurements were made at least 1 minute apart were obtained and the average of the second and third measurements was recorded.Elevated SAP or DAP was diagnosed in those children with indicators above the 95 th percentile, according to the national normative values.In cases of BP elevation the measurements were verificated by aneroid device.Statistical analysis was made with the program Statistica (version 5.11, StatSoft Inc.).Data were expressed as mean ± standard error for quantitative variables and as numbers and percentages for categorical variables.Pearson correlation coefficient was used for studied variables.Statistical analysis was performed using the Student's t-test for numerical variables.All p-values were two-tailed and p < 0.05 was considered statistically significant.

Results and discussion
Because BP values in childhood are height-dependent the first step of children physical examination was stature measurements.The anthropometric data obtained during screening were presented for age groups between 10 and 17 years (Table 1).Except the stature measurements and assessments according to local percentiles standard we also analyzed the prevalence of overweight and obesity in children of age groups according to BMI.The prevalence of total overweight in our children was 19.9 % including 13.6 % of obesity.The highest prevalence of obesity was in age of 12 and 13 years -more than 20 %.The decrease in next age period correlated with puberty stage (r = -0.14, p < 0.05) and pubertal stature growth acceleration (r = -0.21,p < 0.05)the velocity of the stature increment exceeded the rate of increase in the body mass.
For BP measurements we chose cuffs which corresponded to the size of the child's arm and could vary widely.In addition, the child should be calm and rested at least 5 minutes before the BP measurements were taken.From the dataset we excluded those children who were previously treated in pediatric nephrology.The BP components measurements obtained during screening were changed with age and without significant gender difference.The average results of age subgroups are shown lower (Table 2).We identified 150 (17.7 %) hypertensive children (blood pressure >95 th percentile) and 64 (7.5 %) with prehypertension (blood pressure between 90 th and 95 th percentile).Among the 214 children with elevated BP gender proportion was nearly equal -50.7 % boys and 49.3 % girls without noticeable difference by age.The BP measurements in children in the school based screening could be inaccurate therefore it is imperative that the measurements were repeated several times before referral for further evaluation of hypertension.
When compared incidence of AH in age subgroups we found out that the highest level was in age of 16 years -29.9 % with elevated BP (21.9 % over 95 th percentile and 8.0 % between 90 th and 95 th percentiles) (Fig. 1).
Based on the health questionnaire and anthropometric measurements we tried to identify various causative factors for hypertension.The most common causes in each age group were obesity and low physical activity.The elevated SAP in our children had positive correlations with overweight (r = 0.27, p < 0.05) and negative with physical performance (r = -0.21,p < 0.05).Separately we analyzed correlation of PAP with different factors (Fig. 2).The most significant correlations of PAP were established with SAP, AH (presented by Z-index of SAP) and overweight (presented by BMI).The level of DAP was elevated in 47.3 % cases of hypertensive students and only in 4.3 % of normotensive and Original research did not associate with PAP.It gave us possibility to build up regression model (Fig. 3).
The current understanding of overweight health consequences in children is predominately based on adult studies but increasing evidence suggests that childhood obesity has a number of not only immediate but long-term health programming consequences.Overweight represents a predominance of visceral fat that usually exhibit elevated free fatty acid production, thrombogenic tendency and increasing risk of coronary heart disease [4,8].In our investigation we have established significant relationship between PAP and overweight expressed by BMI (Fig. 4) and our data closely correlated with results obtained by Polish investigators [8].
In the general pediatric population, the real prevalence of hypertension is still unknown.However, various screening studies primarily in adolescents have identified a prevalence of any hypertension (essential or secondary) between 3.2 % and 13.8 %.Our data differed from results obtained in other countries but was close to results obtained by other Ukrainian pediatricians [1].
The limitations of our investigation included observational and screening study design which did not exclude "white coat" hypertension.Certain stratified analyses performed for this study were also limited in power by the small sample size in the stratified groups.Also we were not able to make a detailed analysis of the hypertensive patients and hence did not report their clinical and the comorbid conditions.Although we had screened children in schools but we established only elevated BP stratified by level and it is not representative for real prevalence of AH in general pediatric population without following clinical examination.
In conclusion, arterial hypertension is a serious public threat in many countries worldwide including Ukraine.AH has many health and financial consequences for individuals, their families and society in general and is largely preventable.Therefore, high national priority for health protection should be given to early diagnostic and prevention of childhood AH.

Conclusions
1.The prevalence of elevated BP established by screening in our research is higher than in European countries and exceeds 20 % of child population.The elevated BP in our children has positive correlations with overweight and negative with physical performance.
2. The level of pulse pressure has significant correlations with SAP and body overweight and could be used as additional diagnostic index of AH.
Prospects of further research.To establish real pre valence of AH in general pediatric population following clinical examination must be done.The possible diagnostic role of pulse pressure could be also studied.Оригинальные исследования

Table 1 .
Anthropometric data and indexes (means) in different age subgroups

Table 2 .
Blood pressure components and pulse rate in different age subgroups (mean ± standard error)