Blood pressure in a high school population. II. Clinical profile of the juvenile hypertensive

Elevated blood pressure among primary school children in Dar es salaam, Tanzania: prevalence and risk factors

Background

Whilst the burden of non-communicable diseases is increasing in developing countries, little data is available on blood pressure among Tanzanian children. This study aimed at determining the blood pressure profiles and risk factors associated with elevated blood pressure among primary school children in Dar es Salaam, Tanzania.

Methods

We conducted a cross sectional survey among 446 children aged 6–17 years from 9 randomly selected primary schools in Dar es Salaam. We measured blood pressure using a standardized digital blood pressure measuring machine (Omron Digital HEM-907, Tokyo, Japan). We used an average of the three blood pressure readings for analysis. Elevated blood pressure was defined as average systolic or diastolic blood pressure ≥ 90th percentile for age, gender and height.

Results

The proportion of children with elevated blood pressure was 15.2% (pre-hypertension 4.4% and hypertension 10.8%). No significant gender differences were observed in the prevalence of elevated BP. Increasing age and overweight/obese children were significantly associated with elevated BP (p = 0.0029 and p < 0.0001) respectively. Similar associations were observed for age and overweight/obesity with hypertension. (p = 0.0506 and p < 0.0001) respectively. In multivariate analysis, age above 10 years (adjusted RR = 3.63, 95% CI = 1.03–7.82) was significantly and independently associated with elevated BP in this population of school age children.

Conclusions

We observed a higher proportion of elevated BP in this population of school age children. Older age and overweight/obesity were associated with elevated BP. Assessment of BP and BMI should be incorporated in school health program in Tanzania to identify those at risk so that appropriate interventions can be instituted before development of associated complications.

Cardiovascular Risk Factors and Sequelae in Hypertensive Children Identified by Referral Versus School-Based Screening

To determine whether systematic differences exist between hypertensive children referred for evaluation by primary care providers and children identified through community-based screening, cardiovascular risk factors and surrogate markers of hypertensive injury were compared based on subject source (referral versus screening). Children referred to a hypertension clinic for persistently elevated blood pressure were compared with children identified as hypertensive during school screening of 5102 students in Houston public schools. M-mode echocardiography of the left ventricle was performed and subsequently reviewed by 2 independent sonographers blinded to identifying subject information. Subsets of subjects also underwent carotid artery ultrasound for measurement of intimal-medial thickness, overnight urine collections for microalbuminuria, and fasting serum cholesterol, triglycerides, and glucose. Ninety-seven total subjects (54 screening and 43 referral) met inclusion criteria and had technically adequate echocardiography performed. The prevalence of left ventricular hypertrophy (LVH) was 37%. Referral subjects demonstrated significantly greater left ventricular mass index (38.8 versus 34.2 g/m 2.7 ; P <0.01) and a higher prevalence of LVH (49% versus 28%; P <0.05). Among subjects who underwent carotid ultrasound (n=75), carotid intimal-medial thickness was significantly higher in referral subjects (0.61 versus 0.57, P <0.05). When controlling for BMI z score, which was significantly higher in referral subjects, systematic differences by subject source did not persist. These findings suggest that hypertensive children who are predominantly overweight, independent of the manner in which patients come to medical attention, will manifest evidence of more severe cardiovascular disease assessed by surrogate markers such as left ventricular mass index or carotid artery intimal medial thickness.

Carotid artery intimal-medial thickness and left ventricular hypertrophy in children with elevated blood pressure

OBJECTIVES

To determine the association between carotid artery intimal-medial thickness (cIMT) and left ventricular mass index (LVMI) in children with elevated blood pressure.

METHODS

Study subjects (n = 32; mean age: 13.9 +/- 2.7 years) were untreated new referrals to a pediatric hypertension clinic with confirmed elevated blood pressure. LVM was calculated from 2-dimensionally guided m-mode echocardiographic measurements of the left ventricle. LVMI was calculated as LVM (g)/height (m)2.7, and left ventricular hypertrophy (LVH) was defined as LVMI >95th percentile. Carotid artery duplex ultrasound was performed by protocol by experienced vascular sonographers who were unaware of the echocardiography results. The thickest IMT complex of the far wall of the distal common carotid artery was measured in longitudinal B-mode section using a high-resolution linear array of 8 MHz.

RESULTS

The prevalence of LVH and increased cIMT was 41% and 28%, respectively. Subjects with increased cIMT had higher LVMI (46.8 g/m2.7 vs 31.4 g/m2.7) than those with normal cIMT. The LVH prevalence was 89% (8 of 9) among subjects with increased cIMT as compared with 22% (5 of 23) in subjects with normal cIMT. cIMT was positively correlated with body mass index (r = 0.43), interventricular septal thickness (r = 0.58), posterior wall thickness (r = 0.54), and LVMI (r = 0.54). cIMT and LVMI were positively associated after accounting for age, gender, and body mass index.

CONCLUSIONS

These findings raise the possibility that carotid duplex ultrasound, by indicating the presence of early arterial wall changes, may be useful for predicting other cardiovascular sequelae in hypertensive children.

Ambulatory blood pressure and left ventricular mass index in hypertensive children

To determine whether ambulatory blood pressure is more predictive of left ventricular hypertrophy than is casual blood pressure in hypertensive children, echocardiography and ambulatory blood pressure data from 37 untreated hypertensive children were analyzed. Left ventricular mass was calculated using the Devereux equation, left ventricular mass index was calculated as left ventricular mass (in grams)/height(2.7) (in meters), and left ventricular hypertrophy was defined as left ventricular mass index >51 g/m(2.7). Average blood pressure, blood pressure load, and blood pressure index (average blood pressure divided by pediatric ambulatory blood pressure 95th percentile) were calculated. Left ventricular mass index was strongly correlated with 24-hour systolic blood pressure index (r=0.43, P=0.008) and was also correlated with 24-hour systolic blood pressure (r=0.34, P=0.037), 24-hour systolic blood pressure load (r=0.38, P=0.020), wake systolic blood pressure load (r=0.37, P=0.025), sleep systolic blood pressure (r=0.33, P=0.048), and sleep systolic blood pressure load (r=0.38, P=0.021). Left ventricular mass index did not correlate with age, weight, clinic blood pressure, or ambulatory diastolic blood pressure. The overall prevalence of left ventricular hypertrophy was 27%. The prevalence of left ventricular hypertrophy was 47% (8 of 17) in patients with both systolic blood pressure load >50% and 24-hour systolic blood pressure index >1.0, compared with 10% (2 of 20) in patients without both criteria (P=0.015). These data suggest ambulatory blood pressure monitoring may be useful for the clinical assessment of hypertensive children by identifying those at high risk for the presence of end organ injury.

Diagnosis and management of hypertension in childhood

Blood pressure measurements should be taken at intervals on all children. At the very least, blood pressure measurements should be recorded on school and hospital admission. Once obtained, the pressure should be compared to established normals. If the pressure is repeatedly high, hypertension may be diagnosed and a cause sought. Unfortunately, most hypertension is usually mild in childhood, treatment programs should be initiated using nonpharmacologic measures. If needed a number of effective antihypertensive medications are available. The step-care approach presented in this article may be helpful in guiding the pediatric practitioner in this therapy.

Hemodynamic characteristics of the early phase of primary hypertension. The Dutch Hypertension and Offspring Study

BACKGROUND

The hemodynamic characteristics of the early phase of primary hypertension are subject to debate. In particular, it remains unclear whether an increased vascular peripheral resistance or a raised cardiac output is involved as the primary hemodynamic alteration in hypertension.

METHODS AND RESULTS

We studied hemodynamic characteristics and oxygen consumption in relation to 24-hour ambulatory blood pressure measurements in three groups of normotensive children with a different familial predisposition for hypertension. Selection of participants was based on parental blood pressure levels. Mean 24-hour blood pressure was higher in the offspring of two hypertensive parents compared with the offspring of two normotensive parents; there was a difference of 4.7 mm Hg (95% confidence interval [CI], 1.8-7.6) for systolic blood pressure and a difference of 4.8 mm Hg (CI, 2.3-7.3) for diastolic blood pressure. The 24-hour blood pressure pattern was consistently at a higher level for both systolic and diastolic blood pressures in the offspring of two hypertensive parents compared with the offspring of two normotensive parents. The smallest differences in blood pressure were seen at night, and the largest differences in blood pressure between the groups of offspring were seen during periods of physical activity. Echocardiographic examination combined with registration of oxygen consumption did not show a difference in cardiac index and arteriovenous oxygen difference between the study groups. However, differences in cardiac dimensions were apparent, with an increased left ventricular mass index (8.7 g/m2; CI, 2.4-15.0) in the offspring of two hypertensive parents.

CONCLUSIONS

These findings do not support the existence of a hyperkinetic circulatory phase but may indicate the presence of an increased left ventricular mass in early primary hypertension.

New perspectives on left ventricular hypertrophy: anatomy, physiology, and significance

The advent of echocardiography has added an important and sensitive tool for assessment of left ventricular hypertrophy (increased left ventricular mass). Recent echocardiographic studies in large population-based samples suggest an epidemic of left ventricular hypertrophy. Preliminary data suggesting important prognostic importance for such left ventricular hypertrophy (independent of standard risk factors) has fueled interest in the development, determinants, and other features of the hypertrophy. Hemodynamic and neurohumoral factors are the most prominent stimuli to adaptive (physiologic) myocardial hypertrophy, which can progress to maladaptive (pathologic) hypertrophy. The overall blood pressure experience, overweight, the cardiovascular response to recurrent psychosocial stress and physical activity level are four important correlates and potential determinants of left ventricular mass in various urban-suburban populations. Determination of the relative contributions and interrelations of these and other factors (such as heredity) to various forms of left ventricular hypertrophy found in various demographic groups warrants intensive investigation.

Cardiovascular pathophysiology of essential hypertension: a clue to therapy

Arterial hypertension is by definition a haemodynamic disorder. At least 3 different subsets of cardiovascular pathophysiological features can be identified in so-called essential hypertension: The young lean patient characterised by an elevated cardiac output and renal blood flow, elevated plasma renin activity and circulating catecholamine levels, as well as symptoms and signs of hyperadrenergic hypertension. The elderly patient characterised by a low cardiac output often with left ventricular hypertrophy, elevated total peripheral resistance, nephrosclerosis, and symptoms and signs of target organ disease. The obese patient (and to a lesser degree the black patient) characterised by expanded fluid volume state, elevated cardiac output, a normal to low total peripheral resistance, and symptoms and signs of volume overload. To initiate antihypertensive therapy, the drug of choice in the young patient is a beta-adrenergic receptor blocker; in the elderly it is a haemodynamic vasodilator (anti-adrenergic drug, slow channel calcium blocker, or converting enzyme (ACE) inhibitor), and in black or obese patients it remains a thiazide diuretic. Enalapril, a new ACE inhibitor is indicated as a first-step agent in the great majority of hypertensive patients in whom the elevated arterial pressure should be reduced by a decrease in total peripheral resistance, without compromising systemic or regional blood flow. In contrast to other antihypertensive agents, enalapril will lower preload and afterload to the left ventricle while improving systemic and regional flow in elderly patients with latent or manifest congestive heart failure.

Effect of exercise training on the blood pressure and hemodynamic features of hypertensive adolescents

Twenty-five adolescents (aged 16 +/- 1 years) whose blood pressure (BP) was persistently above the 95th percentile for their age and sex were studied before and after 6 +/- 1 months of exercise training and again 9 +/- 1 months after the cessation of training. Maximal oxygen consumption (VO2) increased significantly with training. There was no change in body weight or sum of skinfolds. Both systolic and diastolic BP decreased significantly with training; however, complete BP normalization was not achieved. When the subjects were retested 9 +/- 1 months after cessation of training, systolic BP and VO2 max had returned to pretraining levels; however, diastolic BP was still below pretraining levels in the subjects who had diastolic hypertension initially. Except in subjects who initially had an elevated cardiac output, no consistent hemodynamic changes were found with training or cessation of training to account for the reductions in BP. The subjects whose resting cardiac outputs were high initially had significantly lower cardiac outputs after training as a result of decreases in both heart rate and stroke volume; however, vascular resistance remained unchanged. Sedentary control subjects with similar BP had no significant change in any of the variables measured over a similar period. These data indicate that moderate endurance exercise training can lower BP in otherwise healthy hypertensive adolescents as an initial therapeutic intervention.

Cardiac anatomy and function in juvenile hypertension. Current understanding and future concerns

Recently, several groups of investigators have independently identified subtle cardiac changes very early in the development of primary hypertension. Echocardiographic evidence for left ventricular hypertrophy has been found in 10 to 15 percent of adolescents with mild persistent hypertension. However, in individual cases and within groups, the relationship between left ventricular mass and random blood pressure measurements was not extremely strong. Factors other than blood pressure probably influence the development of left ventricular hypertrophy in teenagers. Resting left ventricular function and overall estimates of exercise capacity for hypertensive teenagers fell within normal limits. However, during upright bicycle exercise, peak exercise systolic and diastolic pressures, and peak heart rates were significantly higher in hypertensive male and female adolescents compared to normotensive controls. Myocardial oxygen consumption may be considerably higher for hypertensive teenagers at rest and during peak exercise. Juvenile onset essential hypertension and left ventricular hypertrophy may be separate but interrelated long-term cardiovascular risk factors. Uniform echocardiographic methods for assessment of left ventricular anatomy are recommended to provide the basis for systematic, longitudinal studies needed to resolve these important issues.

R-wave amplitude change during aerobic exercise in hypertensive adolescents after treatment

This study attempts to determine whether the blunted reduction in R-wave amplitude during progressive aerobic exercise observed in adolescents with systemic hypertension could be altered by pharmacologic therapy to reduce blood pressure. Twenty-nine hypertensive adolescents were randomly assigned to treatment with either a diuretic, hydrochlorothiazide, or a centrally acting agent, clonidine. After 16 weeks of therapy, casual blood pressure was significantly reduced in both groups. Repeat exercise stress testing on therapy demonstrated a significant change in R-wave response. In both treatment groups the change in R-wave amplitude during exercise corresponded with the R-wave response pattern observed in normotensive control subjects. These observations indicate that the altered R-wave amplitude response to exercise observed in young hypertensive subjects is reversible and suggest that the altered R-wave response before treatment is related to a higher vascular resistance.

Blood pressure and haemodynamics in teenagers

It has been suggested that a hyperkinetic circulatory state, with high cardiac output, causes high blood pressure in childhood and, secondarily, in adulthood. We studied blood pressure and cardiac output in 319 subjects aged 15 to 19. Blood pressure was measured with an automated device; cardiac output was estimated by M-mode echocardiography and indexed by body surface area. The distribution of cardiac output was stratified using quartiles. Mean arterial pressure was virtually constant over these strata, with boys and girls showing essentially the same pattern. Linear regression of mean arterial pressure on cardiac output yielded a coefficient which was not significantly different from zero. A history of high blood pressure in the parents was positively associated with mean arterial pressure, but unrelated to cardiac output, in the offspring. This evidence does not support the hypothesis that the hyperkinetic circulatory state causes high blood pressure in childhood; rather, raised blood pressure in adolescents appears to relate to increased peripheral vascular resistance. Therefore, our findings lend support to the view that change in blood pressure over time is caused by a gradual increase in peripheral resistance beginning early in life.

Changes in R wave amplitude during aerobic exercise stress testing in hypertensive adolescents

The change in R wave amplitude during progressive aerobic exercise was studied in hypertensive adolescent boys. A comparable control group consisted of normotensive adolescent boys matched for age, body size and race. Twenty-four normotensive and 22 hypertensive subjects exercised to exhaustion on a treadmill utilizing the Bruce protocol. Blood pressure and heart rate were monitored during exercise and recovery. The change in R wave amplitude in a lead V5 electrocardiogram was determined at each level of exercise. The normotensive group demonstrated a progressive increase in systolic pressure, heart rate and rate-pressure product (heart rate x systolic pressure) during exercise and a progressive decrease in R wave amplitude with a significant correlation of R wave change versus the cardiac response variable (p less than 0.001). Hypertensive subjects manifested a greater increase in systolic pressure, heart rate and rate-pressure product during exercise with no decrease in R wave amplitude until the exercise end point. The difference in R wave response to progressive exercise in the two groups was significant (p less than 0.01). A variation in myocardial function in hypertensive adolescents as demonstrated by a difference in R wave response to exercise may reflect a level of peripheral vascular resistance greater than that of normotensive control subjects.

Cardiac involvement in adolescent hypertension. Echocardiographic determination of myocardial hypertrophy

We measured left ventricular chamber dimension and wall thickness using M-mode echocardiography in 61 adolescents with systolic or diastolic blood pressures above the 90th percentile for age and sex and in 49 normotensive adolescents. Left ventricular posterior wall and ventricular septal thickness indexed to body surface area were significantly greater (p less than 0.001) in the hypertensive group than in the normotensive controls. Left ventricular chamber diastolic and systolic dimensions were not different in the hypertensive group when compared to normotensive adolescents with comparable body size. Left ventricular diastolic and systolic volumes as well as left ventricular function did not differ between the hypertensive and control groups. Calculated parameters of left ventricular hypertrophy, namely, the radius-to-wall-thickness ratio, cross-sectional muscle area, and left ventricular mass, in the hypertensive adolescents were all significantly different (p less than 0.001) from those in the control groups. The finding of myocardial hypertrophy in young, mildly hypertensive subjects suggests early myocardial involvement in the hypertensive process.