Joseph T. Flynn
Although more than 58 million American adults, or approximately 29% of the population, have systemic hypertension, screening studies in children and adolescents have demonstrated a prevalence of persistent hypertension of between 1% and 2%. Given the impact of the obesity epidemic on the prevalence of hypertension in adolescents, more recent studies, however, have demonstrated a higher prevalence of approximately 5% in obese minority adolescents (Sorof et al., 2004). Most adolescents and adults with hypertension have primary hypertension—that is, no identifiable underlying cause can be found for their blood pressure (BP) elevation. Most hypertensive adolescents, particularly those with primary hypertension, are asymptomatic. Therefore, it is imperative that BP is measured whenever an adolescent is seen for health care. Detection and treatment of hypertension in the adolescent years may prevent later cardiovascular diseases, with their catastrophic consequences (Kavey et al., 2003).
Definition of Hypertension in Adolescence
The cardiovascular endpoints used to define hypertension in adults (myocardial infarction, stroke, etc.) do not occur in children and adolescents. Therefore, the definition of hypertension in the young is a statistical one derived from analysis of a large database of BPs obtained from healthy children (National High Blood Pressure Education Program Working Group, 2004). The most recent classification of BP in the young is summarized in Table 13.1.
Normative BP values for adolescents ≤17 years of age are listed in Tables 13.2 and 13.3. For these children, height should first be obtained and plotted on a standard growth curve to determine the child's height percentile. Then the gender-appropriate chart should be used to determine the BP percentile. For adolescents ≥18 years of age, the adult BP classification scheme issued by the Joint National Commission (Chobanian et al., 2003) should be followed (Table 13.4).
Common to both the pediatric and adult BP classification schemes is the recent concept of “prehypertension”. This refers to BPs that would have been classified as “high-normal” in prior consensus recommendations. Although the term prehypertension has proved to be controversial, it is meant to serve as a means of alerting patients and physicians alike of the potential for later development of hypertension, and of the need to make lifestyle changes that might prevent this from occurring. The same BP value of >120/80 mm Hg is used in both adolescents and adults to designate prehypertension.
Also common to both the pediatric and adult BP classification schemes is the concept of “staging” the degree of hypertension. For children and adolescents, this replaces the older terms of denoting higher levels of hypertension, such as “significant” and “severe”. As will be discussed later, the staging system also plays a role in determining how rapidly a hypertensive adolescent should be
evaluated, and when antihypertensive drug therapy should be instituted.
There are several important considerations in evaluating BP in children and adolescents of any age. They are as follows:
the adolescent should have rested for several minutes and should not have smoked or ingested caffeine within 30 minutes before measurement.
As noted in the introduction, the prevalence of hypertension in children and adolescents in screening studies is generally between 0.5% and 2%. The importance of repeated measurements is demonstrated in a study of
3,537 adolescents in New York (Kilcoyne et al., 1974). In this study, 5.4% of adolescents had systolic hypertension and 7.8% had diastolic BPs of >140/90 mm Hg on the first screening. The prevalence dropped to 1.2% and 2.4%, respectively, after a second screening. More recently, screenings conducted in Houston, Texas, public schools have also demonstrated a decreased prevalence of hypertension after repeated measurements (Sorof et al., 2004). Table 13.5 lists various prevalence studies of hypertension in children and adolescents.
Factors that Influence Blood Pressure
Height and Weight
Height has already been mentioned as part of the definition of normative BP in childhood and adolescence (Rosner et al., 1993; National High Blood Pressure Education Program Working Groups, 1996, 2004); this conclusion was based on statistical analysis of the childhood BP database. Others hold that weight is the most important factor in determining BP. Weight has long been held to have a positive relationship with BP, as demonstrated in a study of Minneapolis school children (Luepker et al., 1999). More than half of hypertensive young people are obese. Higgins et al. (1984) suggested that if weight could be reduced in young people to below-obesity levels the prevalence of hypertension would decrease by one third.
BP increases with age in a nonlinear manner through adolescence; this is likely related to growth. Beyond adolescence, BP continues to increase in a significant percentage of individuals as the result of genetic and environmental factors.
Sodium and Other Dietary Constituents
Controversy prevails over the numerous studies concerning the relationship of sodium intake to BP. For most individuals, little correlation exists. However, in certain
salt-sensitive individuals, sodium restriction appears beneficial. For example, it has been suggested (Hohn et al., 1983) that African-American children from hypertensive families may be salt sensitive. Obese adolescents also have heightened responsiveness to sodium intake (Rocchini et al., 1989).
Other studies have found a link between potassium intake and both elevated and low BP. However, efforts to correlate calcium and other divalent cations with BP have been equivocal. Similarly, correlations between BP and vitamins A, C, and E, although suggestive, remain to be proved. Falkner et al. (2000) noted that dietary modification of certain nutrients when instituted at an early age could contribute to the prevention of hypertension in urban minority adolescents at risk for hypertension.
Both physical stress and mental stress evoke changes in BP. Indeed, the degree of change has been thought by some to be useful in predicting later-life hypertension. Early studies by Falkner demonstrated that hypertensive adolescents had significantly greater increases in heart rate, systolic BP, and diastolic BP during mental stress (performance of difficult arithmetic problems) than normotensive adolescents (Falkner et al., 1981). Increased cardiovascular reactivity to the cold pressor test has also been shown to predict the subsequent development of hypertension (Menkes et al., 1989).
Although a significant determinant in adult BP, race is not a factor in teens. Hohn et al. (1983) suggested that certain subgroups of African-American youths have higher BPs than their white counterparts, and Rabinowitz et al. (1993) found a higher prevalence of hypertension among African-American females than among non-Hispanic females. However, Baron et al. (1986) found no significant differences in BP among white, black, and Mexican-American youths. Ethnicity and socioeconomic status have also been related to BP and cardiovascular reactivity (Barnes et al., 2000).
Both familial aggregation BP studies, such as those of Lascaux-Lefebvre et al. (1999), and twin studies, such as those of Schieken (1993), indicate a strong positive correlation between hereditary influences and BP measurements. Colhoun (1999) estimated that approximately one third of variations in BP among individuals are due to genetic factors most likely from several genes. Additionally, several single-gene defects have also been recently described (Lifton et al., 2001), which account for hypertension in a small number of children and adolescents, especially those with a family history of severe hypertension of early onset.
Birth Weight and Other Perinatal Factors
The so-called “fetal origins” hypothesis maintains that low birth weight is a risk factor for the subsequent development of primary hypertension in adulthood. This hypothesis is based on the findings of large population studies that demonstrate an inverse correlation between birth weight and adult BP (Barker et al., 1993; Zureik et al., 1996). Proposed explanations for this effect include deficient maternal nutrition, possibly leading to acquisition of a reduced number of nephrons in utero. Other investigators have demonstrated that maternal smoking during pregnancy and bottle-feeding of newborns also may lead to hypertension later in life (Beratis et al., 1996; Singhal et al., 2001), thereby widening the spectrum of possible influences on later BP to include postnatal factors as well. On the other hand, other epidemiological studies have found that adult BP is more closely related to early childhood growth (Falkner et al., 1998) than to birth weight. While more research is clearly needed, it is apparent that at least in some individuals, perinatal and early childhood factors may play an important role in the later development of hypertension.
The causes of hypertension vary among different age-groups. In adolescents, the prevalence of primary hypertension is increased in comparison with younger children. This is particularly true for mild hypertension. Table 13.6 shows an estimation of the causes of hypertension in adolescents from data gathered from a number of population studies. This information shows that primary hypertension is by far the most common cause of hypertension in the adolescent. As in younger children, renal parenchymal diseases are the most common secondary cause in the adolescent age-group.
At least 80% of hypertensive adolescents have no known cause for their disorder and are labeled as having primary or essential hypertension. Primary hypertension in adolescents is frequently characterized by isolated systolic BP elevation (Flynn and Alderman, 2005), whereas diastolic
BP elevation is more likely to be present in secondary hypertension. Obesity and a positive family history of hypertension are also common in adolescents with primary hypertension.
Confirmation of Hypertension
Adolescents make fewer visits per year to health care practitioners than other age-groups. However, each visit presents an opportunity to assess the BP. Approximately 10% of these young people will have a high initial BP (at or above the 95th percentile). They should be labeled as having an elevated BP, and not given a diagnosis of hypertension. Before a diagnosis of hypertension can be made, two subsequent BP determinations on different days must also show a high systolic or diastolic pressure or both (National High Blood Pressure Education Program Working Group, 2004). Only 1% to 2% of adolescents will fulfill these criteria and, by definition, have hypertension.
Additionally, determination of “out-of-office BP” to assess possible “white coat hypertension” is increasingly advocated. Recently, however, Vaindirlis et al. (2000) presented data supporting the hypothesis that such “white coat” hypertension may actually be a prelude to permanent hypertension.
Once the diagnosis of hypertension has been confirmed, a diagnostic evaluation and management plan can be initiated. The algorithm in Figure 13.1, although originally designed for children ≤17 years of age, is appropriate for all adolescents and should be followed.
FIGURE 13.1 Algorithm for the identification, diagnosis, and management of hypertension in adolescents. BMI, body mass index; BP, blood pressure; Rx, Treatment.
The diagnostic evaluation must be tailored to the individual patient, taking into account the age, sex, race, family history, and level of hypertension. For example, a 12-year-old white female with a past medical history of recurrent urinary tract infections, no family history of hypertension, and a BP of 150/115 mm Hg would be a candidate for an aggressive evaluation for secondary causes, particularly renal parenchymal disease, specifically reflux nephropathy.
In contrast, invasive studies to look for a secondary cause are unlikely to be helpful in a 17-year-old obese African-American boy with a family history of hypertension and a BP of 150/78 mm Hg. Consultation with someone knowledgeable about hypertension in young people can often be helpful to pursue the most cost-effective and safest diagnostic evaluation.
Physical examination findings suggestive of secondary causes of hypertension are listed in Table 13.8. In addition, the clinician should remember that severe hypertension in an adolescent suggests a secondary cause, particularly renal disease. Acute onset may also suggest acute renal disease.
example, plasma normetanephrine to norepinephrine ratio if pheochromocytoma is suspected, or a 24-hour urine collection for proteinuria if there is persistent proteinuria on the urinalysis.
Optimally, measures to prevent or minimize the effects of hypertension should be applied to those adolescents at risk of developing hypertension later in life. The difficulty lies in finding those at risk and deciding what measures to apply. Data from young people for this purpose are lacking, and long-term follow-up information is unavailable. Nevertheless, a starting point for such a strategy is to consider those with the findings listed in the subsequent text as being at risk. They should be counseled about nonpharmacologic approaches to maintain lower BP and should be periodically monitored:
Although the magnitude of change in BP may be modest, weight loss, aerobic exercise, and dietary modifications have all been shown to successfully reduce BP in children and adolescents, at least in research settings. Such “therapeutic lifestyle changes” should therefore be incorporated into the treatment plan for any hypertensive adolescent, whether a secondary cause has been identified, and whether there is an indication to initiate antihypertensive drug therapy (Fig. 13.1).
Rarely an adolescent will have signs of encephalopathy or heart failure at presentation and be found to have extraordinarily high BP, at levels well above stage 2 hypertension. This constitutes a true emergency and may have disastrous consequences unless efforts to lower the BP are begun at once. Assistance from an expert in hypertension should be sought. Meanwhile, the patient should be hospitalized and an intravenous line placed. Usually, a continuous infusion of either nicardipine or labetalol should be started at a low dose and then titrated up as needed to slowly reduce the BP. The initial reduction should be no more than 25% over the first 8 hours in order to prevent cerebral, cardiac, or renal ischemia from overly rapid BP reduction (Adelman et al., 2000). BP can be further lowered to the 95th percentile over the next 24 hours. When adequate pressure control has been achieved, oral antihypertensive agents can be gradually introduced and the intravenous agents discontinued. A vigorous search for the cause of the hypertension, if not known, must be made once the patient's condition has been stabilized.
As adolescents mature toward full adulthood, an increasing number will be found to have hypertension. Perhaps this progression can be delayed or avoided through the applications of the principles outlined in this chapter. At the very least, BP should be taken when adolescents are seen for health care, regardless of the complaint.
When pressures are found to be repeatedly elevated, nonpharmacologic antihypertensive measures should be started. They are good general health rules. Initially, in the absence of severe hypertension, a set of basic diagnostic studies should be obtained. Depending on the history, physical examination, and results of the initial studies, other tests may or may not be necessary.
For selected adolescents, drug therapy is indicated. The individualized stepped-care approach displayed in Figure 13.2 is recommended. When hypertension is resistant to initial drug therapies, consultation with an expert on hypertension in adolescents should be sought.
FIGURE 13.2 Stepped-care approach to antihypertensive therapy. BP, blood pressure.
For Teenagers and Parents
http://www.americanheart.org/presenter.jhtml?identifier=4609. American Heart Association site on childhood hypertension. Free.
http://pediatrichypertension.org. Home of the International Pediatric Hypertension Association. Includes links to additional patient education Web sites about hypertension. Free.
http://www.nhlbi.nih.gov/hbp/index.html. NIH patient education site on hypertension. Free.
http://www.medscape.com/pages/editorial/patiented/index/index-hypertension. WebMD/Medscape patient education site on hypertension. Requires free registration.
http://www.nlm.nih.gov/medlineplus/highbloodpressure.html. “Medline Plus” site on hypertension. Free.
http://www.mayoclinic.com/health/high-blood-pressure/DS00100. Mayo Clinic patient education site on hypertension. Free.
http://monitorbloodpressure.com/. Commercial site to buy home BP monitors.
For Health Care Professionals
http://www.nhlbi.nih.gov/health/prof/heart/hbp/hbp_ped.htm. Home of The Fourth Report on the Diagnosis, Evaluation, and Treatment of High Blood Pressure in Children and Adolescents. Includes link to downloadable PDA application. Free.
http://pediatrichypertension.org. Home of the International Pediatric Hypertension Association. Includes links to additional Web sites about hypertension for health care professionals. Free; membership available for health care professionals.
http://www.who.int/topics/cardiovascular_diseases/en/. World Health Organization site containing links to various cardiovascular disease-related WHO initiatives and resources. Free.
http://www.hdcn.com/fhh.htm. Nephrology-oriented site on hypertension. Contains links to educational lectures and other materials. Requires paid annual subscription to access all content.
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