Adolescent Hypertension : A Challenge for the Future

Hypertension emerges from a complex interplay of genetic, environmental and behavioral factors. Hypertension in the young which is mostly undiagnosed is increasing in prevalence, with much of the increase being fuelled by the increase in obesity among them. Apart from obesity, factors that have an influence on hypertension are hereditary effects, stress, race and diet. It is well established that blood pressure during childhood and adolescence is a predictor of adult blood pressure, which in turn increases mortality from Cardiovascular, Cerebro vascular and other complications, clearly underscores the importance of identification and treatment of hypertension among them.


Introduction:
Hypertension is an iceberg disease with high morbidity & mortality and is a silent threat to the health of the people both in developed and developing countries.It plays a major role in the development of ischemic heart disease, cerebrovascular disease, cardiac and renal failure.Unlike most of the diseases hypertension mostly goes unnoticed before the development of complications.Around 1 billion people in the world were Hypertensives in the year 2000 and this is expected to increase to 1.56 billion by 2025 1 .About 54% of all stroke and 47% of all coronary artery disease are attributable to hypertension 2 .Globally, the overall prevalence of raised blood pressure (BP) in adults aged 25 and over was around 40% in 2008.The prevalence of raised BP was highest in the World Health Organization African Region, where it was 46% for males and females combined 3 .Adolescent Hypertension: Hypertension emerges from a complex interplay of genetic, environmental and behavioural factors.Owing to the hereditary component of hypertension, the disorder is considered to have its origin in the childhood.Children and adolescents with high BP tend to maintain those levels of BP in adulthood 4 .
Apart from progression of hypertension into adult life; there are other complications of childhood and adolescent hypertension.Hypertension in the young is increasing in prevalence, with much of the increase being fuelled by the increase in obesity among them.Worldwide prevalence of Hypertension among adolescents is not known.The prevalence of hypertension among children and adolescents in recently done studies in western countries ranged from 7% to 19% 5 .

Classification of Adolescent Hypertension:
According to the Fourth report on the diagnosis, evaluation and treatment of high blood pressure in children and adolescents by National High Blood Pressure Education Program Working Group 6 blood pressure is classified as follows, the prevalence of hypertension was found to be 6.4%, of which 2.7% had isolated systolic, 2% had isolated diastolic and 1.7% had both systolic and diastolic hypertension 9 .

Etiology of Hypertension among Adolescents:
Among pre adolescent children primary or essential hypertension is exceedingly rare.In these age groups secondary hypertension is common (Table 2).Among the secondary causes of hypertension renal diseases tops the list 10 .In adolescents, however, essential hypertension accounts for majority of the cases (80-90%).The secondary causes of hypertension are comparable to the list of causes in younger children.Primary hypertension in adolescents is mostly characterized by isolated systolic hypertension.On the other hand diastolic hypertension most often accompanies secondary causes of hypertension 11 .

Factors influencing Hypertension among Adolescents: a) Obesity and Hypertension
The prevalence of obesity in the children and adolescents has increased markedly in the last two decades.Primary hypertension in the adolescents is becoming increasingly common in association with obesity.Moore

5-15%
hypertension.Those with more physical activity had a less risk of incident hypertension than the less physical activity group (Hazard rate ratio=0.83;95% CI: 0.73-0.93) 21.

Consequences of Adolescent Hypertension:
The most important consequence of elevated BP among children and adolescents is that it predicts the development of adult hypertension.The long term sequelae of adult hypertension such as myocardial infarction and stroke do not occur in children.But it has been proved that persistent elevation of BP in children and adolescents can produce other target organ damages such as left ventricular hypertrophy, etc.

a) Hypertension during adulthood (Tracking of BP)
It is increasingly clear that adult hypertension have their origin in childhood itself."Tracking" is persistence of rank order of BP from childhood to adult stage.Many studies have been done to support this phenomenon.In the Bogalusa cohort, 40% of those with systolic BP and 37% of those with diastolic BP above the 80th percentile at baseline continued to have BP above the 80th percentile 15 years later 22 .Zinner SH et al found a significant relation between BP readings taken initially and follow up reading taken after 4 years.(p <0.001 for SBP and 0.14, p = 0.001 for DBP).This data proves that stratification of BP into peer groups occurs in childhood itself 23

. b) Increased Cardiovascular Disease in Adulthood
As of now there are no clear data on relationship between hypertension during young age and cardio vascular morbidity and mortality in adult life.But studies have shown that BP and cardio vascular risk factors in childhood predict the subsequent presence of Carotid intima-media thickness and arterial stiffness, both of which are accepted markers of atherosclerosis 10 .In the Cardiovascular Risk in young Finns study Juonala M et al. studied the relationship between childhood BP and endothelial dependent brachial flow mediated dilation in adulthood.They reported an inverse relationship between SBP among male adolescents and adulthood flow mediated dilation 24 .In addition studies have demonstrated that children with hypertension are at increased risk of developing metabolic syndrome during adulthood which is an important predictor of cardiovascular morbidity.

Hypertensive Target Organ Damage in Adolescents: a) Left ventricular hypertrophy (LVH)
Among the hypertensive children and adolescents the prevalence of LVH was found to be between 10-38% in various studies.This difference occurs due to variation in echo cardio graphic protocol.Sorof M J et al. in their comparative study between hypertensive children identified by school based screening and referred cases found that the prevalence of LVH was 37% among them.Referral subjects had more left ventricular mass index 25 .
McNiece K L et al. found that among hypertensive subjects those with stage 2 hypertension have increased odds for LVH.And the risk for LVH was similar among subjects with stage 1 and masked hypertension whereas the risk was same for those with white coat hypertension and normal subjects 26 .b) Carotid intimal thickening Atherosclerosis begins in childhood and the common carotid artery intima media thickness is a marker of pre clinical atherosclerosis.Carotid intima-media thickness has become a marker of hypertensive vascular damage.In a prospective cohort study conducted by Raitakari OT et al. 2229 participants were examined during young age (3-18 yrs) and re examined 21 years later.Intimal medial thickness has showed significant association with childhood SBP (P<0.001),BMI (P=0.007) and LDL cholesterol 27 .Lande MB et al. in their matched case control study found that the median carotid intima media thickness in hypertensives was greater than controls (0.67vs 0.63 mm; P=0.045) 28 .c) Impaired cognitive function Recently, impaired cognitive function has been described as one of the target organ damage due to hypertension in the children and adolescents.This finding requires confirmation, but adds value to the recommendation of starting anti hypertensive therapy in children with persistently elevated BP.Lande MB et al. compared the cognitive scores of children with elevated BP and normal BP.They found that children with elevated SBP had lower scores for digit span (p=0.01),block design (p=0.03) and mathematics (p=0.01).Children with elevated DBP had lower scores on block design (p=0.01) 29

. d) Retinal artery narrowing
In a population based study conducted in two countries-Australia and Singapore involving 1952 students by Mitchell P et al. found that children in the higher quartiles of BP were having narrow retinal arterioles than those with normal BP.They reported that for every 10 mmHg increase in SBP there was narrowing of retinal arterioles by 2.08µm 30 .

Management of Adolescent Hypertension:
The management of hypertension among children and adolescents is largely empirical in contrast to management of hypertension in adults, which is guided by many number of clinical trials.The decision as to whether a child to be started on drug therapy or not should be individualized 31 .Treatment of hypertension should start with non pharmacological measures.Although the magnitude of change in BP may be modest with the measures like weight loss, dietary changes and regular exercise, all of them have shown to reduce BP in adolescents successfully.Accepted indications for usage of anti hypertensives for treating hypertension in children and adolescents include the following: a) symptomatic hypertension; b) secondary hypertension; c) Type 1 or 2 diabetes; d) Hypertensive target organ damage or e) persistent hypertension despite of non pharmacologic measures.Pharmacologic reduction of BP in hypertensive children who fall into the above categories is likely to result in health benefits.Other indications for starting drug therapy have been proposed.For example, it is suggested that anti hypertensive therapy is initiated if the child has hyperlipidemia 6 .The anti hypertensives commonly used include Angiotensin converting enzyme inhibitors, Angiotensin Receptor Blockers, α and β adrenergic antagonists and Calcium channel blockers31.
The following table shows the classification of blood pressure among adolescents, its evaluation, life style changes for each category and also the pharmacological treatment.(Table 3)

Conclusion:
As the symptoms of childhood and adolescent hypertension are largely nonspecific, most children with hypertension are likely to be undiagnosed.But there are ample evidences proving the development of hypertensive end organ damage in hypertensive children and there are data suggesting hypertension in young may have adverse cardiovascular effects in adulthood.To conclude, blood pressure to be monitored routinely even among adolescents and those who are identified as having high blood pressure should be treated early in order to avoid progression of the disease, which may prove to be a serious health challenge in the future.

Table 1 .
Blood Pressure classification in Children and Adolescents

Table 2 .
14 et al. in their study healthyKids Project reported 28% of overweight among 769 students from Anadarco student population.They found that BMI more than 95 th percentile was strongly associated with elevated BP (RR-3.8;95%CI:2.6-5.4)12.Paradis G et al. found that BMI was associated with SBP and DBP consistently in all the ages and both the genders.BMI was 4-6 kg/ m 2 higher among those with SBP >95 th percentile13.In a study conducted in China by He Q et al. hypertension was seen in 19.4% of obese children and 7%in non obese children with P<0.000114.Estimated Causes of Hypertension in Children and Adolescents

Table 3 .
Classification and Management of Hypertension in Adolescents 10