Prevalence

With 35 million office visits annually, hypertension is the most common primary diagnosis in America.¹ Before 1990, the prevalence of hypertension was steadily declining; however, recent evidence indicates that the trend has reversed, and hypertension is once again on the rise.³ According to National Health and Nutrition Examination Survey (NHANES) data for the period 1999 to 2000, at least 65 million adults in the United States have high blood pressure (HBP) or are taking antihypertensive medication.⁴ This estimate equals about one fourth of the population and represents a 30% increase from 1988 to 1994.⁵ In a typical practice population of 2000 patients, therefore, around 500 will have hypertension. This marked increase is attributed to aging of the population and to the epidemic increase in obesity. The National High Blood Pressure Education Program was begun in 1972, and in a little more than 3 decades, it has had significant success.¹ The number of people with HBP who are aware of their condition has increased from 51% to 70%, and the percentage of those receiving treatment for HBP has increased from 31% to 59%. The proportion of patients taking medication whose blood pressure is controlled to 140/90 increased from 10% to 34% during the same period. Concomitant with increased awareness and treatment has been a significant decline in number of deaths from coronary heart disease (50%) and from stroke (57%), although this decline has slowed in recent years.¹ Although these trends are encouraging, 30% of patients with HBP remain unaware of their disease, 40% of patients with HBP are not being treated, and more than 60% of hypertensive patients are taking medications but have not achieved adequate control of the condition.

Diagnosis and treatment of hypertension were once based largely on diastolic blood pressure; with growing recognition of the importance of systolic blood pressure, however, this is no longer the case. Isolated systolic hypertension gradually increases with age such that among patients older than 50 years of age, it is the most prevalent form of hypertension.

The prevalence of high blood pressure increases with aging, such that more than half of all Americans aged 65 and older have hypertension.⁶ If people live long enough, more than 90% will develop hypertension.⁷ Systolic blood pressure continues to rise throughout life, but diastolic blood pressure rises until around age 50 and then levels off or falls; as a result, after the age of 50, isolated systolic hypertension becomes the more prevalent pattern. In one study, isolated systolic hypertension was identified in 87% of inadequately controlled patients older than 60 years of age.⁸ Isolated diastolic hypertension most commonly is seen before age 50. Diastolic blood pressure is a more potent cardiovascular risk factor than is systolic blood pressure until age 50; thereafter, systolic blood pressure is more important.⁹

Prevalence varies with race as well and is highest among African Americans. In general, it is lower among Hispanics than among whites; however, variation has been noted among racial subgroups. For example, the prevalence of hypertension among Mexican Americans is lower than among non-Hispanic whites, although among Puerto Rican Americans, it is higher.¹⁰ Prevalence generally is higher in Asian Americans, Native Americans, and Native Alaskans than in whites; however, again, variation is seen among subgroups.¹¹

Etiology

About 90% of patients have no readily identifiable cause for their disease, which is referred to as primary (essential) hypertension. In the remaining 10% of patients, an underlying cause or condition may be identified; for these patients, the term secondary hypertension is applied. Box 3-1 is a listing of the most common identifiable causes of secondary hypertension. Lifestyle can play an important role in the severity and progression of hypertension; obesity, excessive alcohol intake, excessive dietary sodium, and physical inactivity are significant contributing factors.

Pathophysiology and Complications

In primary hypertension, the basic underlying defect is a failure in the regulation of vascular resistance. The pulsating force is modified by the degree of elasticity of the walls of larger arteries and the resistance of the arteriolar bed. Control of vascular resistance is multifactorial, and abnormalities may exist in one or more areas. Mechanisms of control include neural reflexes and ongoing maintenance of sympathetic vasomotor tone and other effects mediated by neurotransmitters such as norepinephrine, extracellular fluid, and sodium stores; the renin-angiotensin-aldosterone pressor system; and locally active hormones and substances such as prostaglandins, kinins, adenosine, and hydrogen ions (H⁺). In isolated systolic hypertension, which commonly is seen in elderly persons, the underlying problem is one of central arterial stiffness and loss of elasticity.⁷

Many physiologic factors may have an effect on blood pressure. Increased viscosity of the blood (e.g., polycythemia) may cause an elevation in blood pressure resulting from an increase in resistance to flow. A decrease in blood volume or tissue fluid volume (e.g., anemia, hemorrhage) reduces blood pressure. Conversely, an increase in blood volume or tissue fluid volume (e.g., sodium/fluid retention) increases blood pressure. Increases in cardiac output associated with exercise, fever, or thyrotoxicosis also may increase blood pressure.

A linear relationship exists between blood pressures at any level above normal and an increase in morbidity and mortality rates from stroke and coronary heart disease. Blood pressures above 115 mm Hg systolic and 75 mm Hg diastolic are associated with increased risk of cardiovascular disease.¹² It is estimated that about 15% of all blood pressure–related deaths from coronary heart disease occur in persons with blood pressure in the prehypertensive range.¹³ However, the higher the blood pressure, the greater the chances of heart attack, heart failure, stroke, and kidney disease. For every increase in blood pressure of 20 mm Hg systolic and 10 mm Hg diastolic, a doubling of mortality related to ischemic heart disease and stroke occurs.¹ Hypertension precedes the onset of vascular changes in the kidney, heart, brain, and retina that lead to such clinical complications as renal failure, stroke, coronary insufficiency, MI, congestive heart failure, dementia, encephalopathy, and blindness. If the condition goes untreated, about 50% of hypertensive patients die of coronary heart disease or congestive heart failure, about 33% of stroke, and 10% to 15% of renal failure.¹⁴

Signs and Symptoms

Hypertension may remain an asymptomatic disease for many years, with the only sign being an elevated blood pressure. Blood pressure is measured with the use of a sphygmomanometer (Figure 3-1). Pressure at the peak of ventricular contraction is the systolic pressure. Diastolic pressure represents the total resting resistance in the arterial system after passage of the pulsating force produced by contraction of the left ventricle. The difference between diastolic and systolic pressures is called pulse pressure. Mean arterial pressure is roughly defined as the sum of the diastolic pressure plus one-third the pulse pressure. Patients commonly are found to have significant variability in blood pressures. Labile hypertension is the term that was previously used to describe the status of a subgroup of patients with wide variability in blood pressure readings; however, this term has fallen into disuse because it is now recognized that variability in blood pressure is the norm rather than the exception. About 15% to 20% of patients with untreated stage 1 hypertension have what is called white coat hypertension, which is defined as persistently elevated blood pressure only in the presence of a health care worker but not elsewhere.⁶ In these patients, accurate blood pressure readings may require self-measurement at home or 24-hour ambulatory monitoring. Persons with blood pressure elevation in this setting are at lower risk for hypertensive complications than are those with sustained hypertension.

FIGURE 3-1 Standard blood pressure cuff (sphygmomanometer) and stethoscope.

Before the age of 50, hypertension typically is characterized by an elevation in both diastolic and systolic pressures. Isolated diastolic hypertension, defined as a systolic pressure of 140 or less and a diastolic pressure of 90 or greater, is uncommon and most often is found in younger adults. Although the prognostic significance of this condition remains unclear and controversial, it appears that it may be relatively benign.¹⁵ Isolated systolic hypertension is defined as a systolic pressure of 140 or higher and a diastolic blood pressure of 90 or less; it generally is found in older patients and constitutes an important risk factor for cardiovascular disease. Occasionally, isolated systolic blood pressure elevation is found in older children and young adults, often male. In these age groups, this form of hypertension is due to the combination of rapid growth in height and very elastic arteries, which accentuate the normal amplification of the pressure wave between the aorta and the brachial artery, resulting in high systolic pressure in the brachial artery but normal systolic pressure in the aorta.⁶

The earliest sign of hypertension is an elevated blood pressure reading; however, funduscopic examination of the retina may show early changes of hypertension consisting of narrowed arterioles with sclerosis. As indicated earlier, hypertension may remain an asymptomatic disease for many years, but when symptoms do occur, they include headache, tinnitus, and dizziness. These symptoms are not specific for hypertension, however, and may be experienced just as commonly by normotensive persons.¹⁴

Late signs and symptoms are related to involvement of various target organs, including kidney, brain, heart, or eye (Box 3-2). In advanced cases, retinal vessel hemorrhage, exudate, and papilledema may occur and are indicative of accelerated malignant hypertension, which is a medical emergency and requires immediate intervention. Hypertensive encephalopathy is characterized by headache, irritability, alterations in consciousness, and other signs of central nervous system (CNS) dysfunction. Other findings in advanced cases may include enlargement of the left ventricle with impairment of cardiac function, leading to congestive heart failure. Renal involvement can result in hematuria, proteinuria, and renal failure. Persons with hypertension may report fatigue and coldness in the legs, resulting from the peripheral arterial changes that may occur in advanced hypertension. Patients with hypertension often demonstrate an accelerated cognitive decline with aging.¹⁶ Although these changes may be seen in patients with both primary and secondary hypertension, additional signs or symptoms may be present in secondary hypertension associated with underlying disease.

Laboratory Findings

The JNC 7¹ recommends that patients who have sustained hypertension be screened through routine laboratory tests, including 12-lead electrocardiogram, urinalysis, blood glucose, hematocrit, and a serum potassium, creatinine, calcium, and lipid profile. Results of these tests serve as baseline laboratory values that the physician should obtain before initiating therapy. Additional tests should be ordered if clinical and laboratory findings suggest the presence of an underlying cause for hypertension.