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An elevated blood pressure level in a child is defined as a blood pressure that is above the 90th percentile for age and sex. Although the finding of an elevated blood pressure on physical examination constitutes an abnormal sign, it does not mean that hypertension (i.e., sustained blood pressure elevation) is persistent. Most pediatricians recommend that for a child to be diagnosed with hypertension the blood pressure must be abnormal (above the 95th percentile rank of age and sex) on at least 3 separate examinations over a 6- to 12-month interval (see table). The only exception is if at the time of the initial examination the child has signs and/or symptoms commonly found with severe hypertension (e.g., heart muscle enlargement, headache, dizziness, seizures, eye and vision damage).19 Obese children are at approximately a 3-fold higher risk for hypertension than nonobese children. In addition, the risk of hypertension in children increases across the entire range of body mass index (BMI) values and is not defined by a simple threshold effect.13  The link between obesity and hypertension may be mediated in part by sympathetic nervous system (SNS) hyperactivity. This state of hyperactivity may include cardiovascular manifestations such as increased heart rate and blood pressure variability, neurohumeral manifestations such as increased levels of plasma catecholamines, and neural manifestations such as increased peripheral sympathetic nerve traffic. Obese children are also reported to have increased heart rate variability and blood pressure variability compared with nonobese children. 13 |
Evidence suggests that the increased heart rate variability in obese children may be due to an altered balance between parasympathetic and sympathetic activity and not due exclusively to increased sympathetic activity. Altered vascular structure and function may also contribute to the pathogenesis of obesity hypertension. 13  This association between obesity and hypertension in children has been reported in numerous studies among a variety of ethnic and racial groups, with virtually all studies finding higher blood pressures and/or higher prevalences of hypertension in obese compared with lean children. 13  A major problem is that many health care providers underdiagnose hypertension in children. Unlike in adults, in whom the definition and severity of hypertension are defined by straightforward threshold values based on the risk of outcomes, children require a separate threshold of blood pressure normality at each stage of physical maturity because of the normal age and height-related rise in blood pressure throughout childhood. The accurate measurement of blood pressure in obese children may be particularly challenging because of the absence of blood pressure cuffs that are of appropriate length and width for the upper arm of a small obese patient. Larger-than-appropriate cuff size can give falsely low measurements, whereas a smaller one can give falsely high readings.13 |