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The
Health of Children and Young People
 8 Blood pressure
Emanuela Falaschetti and Vasant Hirani
8.1 Introduction It is well established that raised blood pressure is a risk factor for coronary heart disease (CHD) and stroke in adults.1,2,3 Evidence is now available to suggest a relationship between blood pressure levels in childhood and adulthood.4,5,6 While hypertension detected in some children may be a sign of an underlying disease, such as renal disease, in many cases an elevated blood pressure in childhood can represent the early onset of adult hypertension.7,8,9,10 It is therefore important to recognise and prevent the onset of hypertension from an early age. Body size is the major determinant of blood pressure in children. In overweight and obese children, dietary intervention to control excessive weight, and increased physical activity, can have a beneficial effect on blood pressure. Blood pressure in adults aged 16 and over has been measured in each round of the Health Survey for England (HSE) since 1991. The blood pressure of children aged 5-15 has been measured ever since children were first included in the survey in 1995. The focus of the present report is on children and young people. This chapter presents mean blood pressure and blood pressure percentiles for those aged 5-24 by age, sex and height (Section 8.3). Variations in blood pressure by socio-economic factors such as the NS-SEC classification of the household reference person, and by region, are also presented. Relationships between blood pressure and other cardiovascular risk factors such as BMI, smoke exposure and parents' raised blood pressure are also presented (Sections 8.6, 8.8 and 8.9). Comparisons between 1995-97 and 2001-02 are made to identify any time trends. Analysis of variance was carried out to show to what extent each of these factors is associated with blood pressure in young people. In addition, fruit and vegetable consumption was also included in the analysis in the light of recent evidence suggesting that an increase in fruit and vegetable intake can help lower blood pressure.11,12 8.2 Methods 8.2.1 Measuring blood pressure As in previous years of the Health Survey, blood pressure was measured in informants aged 5 and over using an automated device, the Dinamap 8100 monitor. The detailed protocol for blood pressure measurement is contained in Appendix B. After five minutes' rest, three blood pressure readings were taken on the right arm, using an appropriately sized cuff, with the informant in a seated position. The data presented here are based on the mean of the second and third measurements for informants who had all three recordings completed. Blood pressure was not measured in pregnant women or in those who had drunk alcohol, eaten or smoked in the half-hour prior to the nurse visit. Oscillometric methods (Dinamap) have advantages over auscultatory (i.e. sphygmomanometer) methods for measuring blood pressure in children. Oscillometric methods eliminate the need to detect Korotkoff sounds, which are often difficult to detect in children, and so eliminate the controversy over choosing between Korotkoff phase 4 and phase 5 for diastolic pressure. Such methods can also be used in a noisy environment. Oscillometric methods also remove observer variation and seem to produce better co-operation from children.13 The Dinamap has been extensively used for measuring blood pressure in children in surveys and studies.14,15,16,17 Blood pressure data presented here should not be directly compared with blood pressure values obtained using an auscultatory method, as the Dinamap is designed against direct intra-arterial criteria of accuracy, rather than against indirect auscultatory measurement criteria.18 The Dinamap tends to provide higher systolic and lower diastolic blood pressure levels than mercury sphygmomanometer fourth phase readings among children19,20 as is also the case among adults.21 In addition, these results should be interpreted with caution as this is a cross-sectional study in which blood pressure was measured at one single point in time, and child blood pressure is known to be more unstable than adult blood pressure. Four blood pressure measurements are presented: systolic blood pressure (SBP); diastolic blood pressure (DBP); mean arterial pressure (MAP), which is derived by adding the level of DBP to one-third of the difference between SBP and DBP; and pulse pressure, derived by subtracting DBP from SBP. 8.2.2 Blood pressure guidelines for children The levels of blood pressure that define hypertension differ in children and adults. In children, blood pressure is known to have a stronger relationship with age, height and weight than in adults.22,23,24 Therefore, reference guidelines on high blood pressure in children, published by the National High Blood Pressure Education Program Working Group, are sex, age and height specific. Consequently, children's blood pressure values in this chapter are shown by height tertiles (Tables 8.2-8.9) and adjusted by height (Tables 8.10 -8.20). 8.2.3 Response rate Age 5-15 Valid readings were obtained from 83% of boys and 84% of girls aged 5-15 who were visited by a nurse. The main reason for exclusion was that the child ate, drank or smoked in the half hour prior to the measurement (12% among boys and 11% among girls); the remainder were excluded because three valid readings were not obtained or the blood pressure measurement was refused or not attempted. Children aged 5-6 years were less likely to have a valid blood pressure reading than children aged 10-12 years. Age 16-24 Valid blood pressure readings were obtained from 80% of young men and 80% of young women aged 16-24 who were visited by a nurse. As with children, the main reason for exclusion was that the informant ate, drank or smoked in the half hour prior to the measurement (18% among young men and 16% among young women). The remainder were excluded because they were pregnant, (5% of women were excluded due to pregnancy) or because three valid readings had not been obtained or the measurement had been refused or not attempted. There was little difference in response rates between the two age groups for both young men and young women. Table 8.1 8.3 Mean blood pressure and blood pressure percentiles, by age, sex and height 8.3.1 Systolic blood pressure (SBP) Systolic blood pressure in children is known to be positively and independently associated with both age and height.11,25,26, Mean SBP generally increased with age and height in both males and females. Differences by height were less marked than those by age. Among children (age 5-15) these differences were greater between the middle and the tallest height tertiles than between the shortest and the middle height tertiles, while the opposite was true in young adults (age 16-24). In both sexes, mean SBP was 104 mmHg at age 5. It increased gradually to 109 mmHg (boys) and 110 mmHg (girls) at age 10. Thereafter the sexes diverged. From age 10 to age 12, girls' mean SBP increased more rapidly than before, whereas that of boys continued to increase at the same rate. For this short period, therefore, girls' mean SBP exceeded boys' (at age 12, boys 113 mmHg, girls 116 mmHg). Thereafter, the situation was reversed. The SBP of females increased only very slowly, reaching 119 at age 24. In males, in contrast, the rate of increase speeded up after age 12, levelling out at around age 18 (130 mmHg), and reaching 131 mmHg at age 24. SBP for males was thus markedly greater for males than females from about age 14, and was higher by 12 mmHg at age 24. Tables 8.2, 8.3, Figures 8A, 8B The table below shows mean SBP by age groups.
8.3.2 Diastolic blood pressure (DBP) In both sexes mean DBP only showed small fluctuations and was very similar in males and females up to the age of 12, then it increased in females slightly more than in males. Females' DBP exceeded males' DBP until age 17. Thereafter the increase was more rapid in males than in females, with higher mean values in males from this age onwards. The table below does not show any relationship between DBP and height, but does show an increase in DBP with age. This increase was more rapid between the two oldest groups. Figures for males and females are very similar. Tables 8.4, 8.5, Figures 8C, 8D
8.3.3 Mean arterial pressure (MAP) Mean arterial pressure (MAP) is derived by adding the level of DBP to one third of the difference between SBP and DBP. However, the Dinamap provides a direct measure of MAP, which is used in HSE. Mean MAP increased with age and slightly with height. It ranged from 76 mmHg to 91 mmHg among males and from 77 mmHg to 86 mmHg among females. Males and females had similar mean MAP up to age 14. After this age, mean MAP was higher in males than females, the gap widening with increasing age. Tables 8.6, 8.7 8.3.4 Pulse pressure Pulse pressure is derived by subtracting DBP from SBP.
Mean pulse pressure generally increased with age and height. Among males
it increased from 48 mmHg at age 5 to 8.4 Systolic blood pressure by socio-economic factors 8.4.1 Height standardisation As mean SBP is associated with height, independently of age, mean SBP has been height-adjusted for comparisons in Tables 8.10 to 8.20. 8.4.2 Systolic blood pressure (SBP) by socio-economic classification (NS-SEC) The socio-economic group of the household reference person of each participating household was defined using the new National Statistics Socio-economic Classification (NS-SEC) which was introduced for the first time in the UK Census 2001. Height-adjusted mean SBP did not show a pattern by NS-SEC for either males or females. Nevertheless females in managerial and professional occupations (other than those aged 20-24) showed a significantly lower SBP than those in semi-routine or routine occupations. No consistent difference was seen among males, although in some age groups (7-9, 13-15) the difference commented on in females was repeated. Table 8.10 8.4.3 Systolic blood pressure (SBP) by equivalised household income quintile Table 8.11 shows height-adjusted mean SBP by quintiles of equivalised household income. There did not appear to be any clear relationship between equivalised household income and mean SBP except for females aged 5-15. In this age group, adjusting by height and age, a significant inverse relationship (p=0.002) was shown, with SBP decreasing as income increased. Table 8.11 8.4.4 Systolic blood pressure (SBP)
by area deprivation (IMD, As in HSE 2001, this report based its analysis on the Indices of Deprivation 2000 (ID2000), which provide measures of deprivation for every electoral ward in England. The ID2000 combines a number of indicators that cover a range of domains (income, employment, health deprivation and disability, education skills and training, housing and geographical access to services) into a single Index of Multiple Deprivation (IMD) score for each area. The association between blood pressure and IMD quintile is shown in Table 8.12. There was no clear relationship between height-adjusted mean SBP and quintiles of IMD. Table 8.12 8.5 Systolic blood pressure by Government Office Region Although there was no clear regional pattern, mean SBP showed some significant regional differences. Among males age 16-24, compared with the national mean, mean SBP was higher in North East and Yorkshire & the Humber and lower in East Midlands and in London. Among females aged 5-15 SBP was again higher in North East and Yorkshire & the Humber, and lower in South East. Among females aged 16-24 mean SBP was highest in North East and lowest in London. Table 8.13 8.6 Systolic blood pressure by BMI Substantial evidence suggests that there is a relationship between obesity and hypertension in children, as well as in adults. This is particularly important since obese children can have increased risk of becoming hypertensive adults.28 Height-adjusted mean SBP showed a strong positive relationship with BMI for all age groups from age 7 upwards in both males and females (p<0.001). The relationship was not significant among males aged 5-6 and was less strong among females aged 5-6 (p<0.01). The difference in mean SBP between the top and the bottom BMI quintiles increased with age in both sexes. This difference ranged from 1 mmHg in males aged 5-6 to 12 mmHg in males aged 16-19 and 11 mmHg in males aged 20-24. Among females it ranged from 5 mmHg at age 5-6 to 12 mmHg at age 20-24. For all groups the biggest increase in mean SBP was between the fourth and the top BMI quintiles. Table 8.14, Figure 8E 8.7 Physical activity and blood pressure Evidence suggests that physical activity among children and adolescents can prevent or delay the development of hypertension and can reduce blood pressure in young people who already have hypertension.29 Tables 8.15 and 8.16 show mean SBP by level of physical activity. Questions on physical activities were different for children (aged 5-15) and young adults (aged 16-24) (see Chapter 4). Children aged 5-15 have been divided into two groups, those doing any kind of physical activity (for example walking, active play, sport and exercise) for 60 or minutes a day, and those doing less. Young adults aged 16-24 were divided into those who were inactive or did light activity and those who did moderate or vigorous activities. Mean SBP did not show any relationship with physical activity, either in children or in young adults, for either males or females. Tables 8.15, 8.16 8.8 Familial links in child blood pressure Studies have shown that a family history of hypertension increases the risk of high blood pressure levels in childhood.30,31 The household questionnaire collected information on the hypertensive status of parents of surveyed children aged 0-15. In some cases only one parental measurement was obtained, either because there was only one parent in the household, or because information was not obtained from the second parent, while in other cases no parental information was obtained. The analyses in this section are therefore based on sub-sets of the total sample. Among 5,637 informants aged 5-15 who had valid blood pressure readings and valid height measurements, 2,302 (41%) can be compared with their mother's hypertensive status and 1,494 (27%) with their father's hypertensive status. Results are presented for age groups 5-9 and 10-15.
Parents' hypertension, in accordance with the latest guidelines on hypertension
management,32,33,34 is defined as having any of the following:
Height-adjusted mean SBP was higher for children whose mother was hypertensive than for children whose mother was normotensive. The difference was statistically significant for all groups except for males aged 5-9. Father's hypertensive status also seemed to be associated with child's mean SBP, which was significantly higher among children whose father was hypertensive than among children whose father was normotensive. The only sex and age group in which this difference was not significant was boys aged 10-15. Table 8.17, Figure 8F 8.9 Systolic blood pressure and smoking 8.9.1 Self-reported smoking and systolic blood pressure Information on smoking behaviour was available for informants aged 18-24, who reported their answer directly to the interviewer, and for those aged 8-17, who recorded their own smoking habits in a self-administered questionnaire. The questions asked of those aged 16-17, however, were the essentially the same as for those aged 18 and over, so that the principal distinction is between those aged 8-15 and those aged 16-24. Smokers were differently defined in each group, being current cigarette smokers for informants aged 16-24 and those who reported that they had ever smoked a cigarette for informants aged 8-15. Height-adjusted mean SBP did not differ between smokers and non smokers. Table 8.18 8.9.2 Second-hand smoke exposure and systolic blood pressure Table 8.19 shows height-adjusted mean SBP by second-hand smoke exposure for males and females aged 5-24. Among informants aged 13-24, exposure to second-hand smoke was measured by asking how many hours per week each individual was exposed to other people's tobacco smoke. Six or more hours of exposure per week was considered 'exposed' while less than 6 hours per week was considered 'unexposed'. Among informants aged 5-12, exposure to second-hand smoke was measured by asking parents whether the person looking after their child for more than two hours per week smoked while doing so. Exposed and unexposed groups generally showed very similar
height-adjusted mean SBP. 8.10 Change in mean systolic blood pressure between 1997 and 2002 Table 8.20 shows the comparison over time for height-adjusted SBP using the combined years 1995-96-97 and 2001-02. Among males there was a slight decrease on SBP from 1995-97 to 2001-02 after age 15, but no change among children aged 5-15. Height-adjusted SBP was significantly lower in 2001-02 than in 1995-97 for age groups 16-19 (127 mmHg versus 128 mmHg) and 20-24 (130 mmHg versus 132 mmHg). Among females, from age 13, height-adjusted SBP was significantly lower in 2001-02 than in 1995-97 (p<0.001). Table 8.20, Figure 8G 8.11 Analysis of variance To analyse the simultaneous effects of multiple explanatory variables on blood pressure, analysis of variance was performed separately for males and females aged 5-24. The explanatory variables included in the model were: age, height tertile, BMI quintile, socio-economic classification (NS-SEC), fruit and vegetable consumption (five or more portions a day, or fewer than five), parental hypertensive status and second-hand smoke exposure. Socio-economic classification (NS-SEC) and fruit and vegetable consumption, did not show any significant association with systolic blood pressure. The model presented in this section includes age, height tertile, BMI quintile and second-hand smoke exposure as independent variables and systolic blood pressure as the outcome variable. Mean SBP increased significantly with each tertile of height and each quintile of BMI, for both males and females. The association with exposure to second-hand smoke was significant among females but not among males. When maternal and paternal hypertensive status were added to the model, they were found to be significantly associated with blood pressure, for both males and females. Systolic blood pressure was higher among children whose mother was hypertensive than among those whose mother was normotensive (p<0.05 for males and p<0.001 for females), and higher among children whose father was hypertensive than among those whose father was normotensive (p<0.01 for males and p<0.001 for females). The model is shown in Table 8.22. Tables 8.21, 8.22 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
