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Arterial Hypertension Health Article

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Epidemiology

Affecting one fourth of the adult population (50 million in the United States and 1 billion people worldwide), arterial hypertension is the most common cause for a visit to a physician and the most widely recognized treatable risk factor for stroke, myocardial infarction, heart failure, peripheral vascular disease, aortic dissection and chronic renal failure. Despite this knowledge and unequivocal scientific proof that treating hypertension dramatically reduces its attendant morbidity and mortality, hypertension remains untreated or poorly treated in the majority of affected individuals in all countries, including those with the most advanced health care (Fig. 63-2). Inadequate treatment of hypertension is a major factor contributing to some of the adverse secular trends in the last decade, including an increased incidence of stroke, heart failure, and renal failure plus a leveling off of the decline in coronary heart disease mortality.

AGING AND PULSE PRESSURE.

Patients often ask what is more important: systolic or diastolic blood pressure? The answer depends on the age of the patient. In industrialized societies, systolic pressure rises progressively with age; if individuals live long enough, almost all develop systolic hypertension. This age-dependent rise in blood pressure is not an essential part of human biology, because in less industrialized societies, where the consumption of calories and salt is low, blood pressures remain low and do not rise with age. In industrialized societies, diastolic pressure rises until age 50 and decreases thereafter, producing a dramatic rise in pulse pressure (systolic pressure minus diastolic pressure) (Fig. 63-3).

Different hemodynamic faults underlie hypertension in younger and older individuals. The minority of patients who develop hypertension before the age of 50 typically have combined systolic and diastolic hypertension : systolic pressure greater than 140 mm Hg and diastolic pressure greater than 90 mm Hg. The risks of coronary heart disease and stroke increase curvilinearly with either systolic or diastolic blood pressure. The main hemodynamic fault is vasoconstriction at the level of the resistance arterioles. In contrast, the majority of patients who develop hypertension after the age of 50 have isolated systolic hypertension : systolic pressure greater than 140 mm Hg but diastolic pressure less than 90 mm Hg. In these older patients, cardiovascular risk increases curvilinearly with increasing systolic pressure but is inversely related to diastolic pressure. A blood pressure of 170/70 mm Hg carries twice the risk of coronary heart disease as a blood pressure of 170/110 mm Hg! (see Fig. 63-4.)

In isolated systolic hypertension, the main hemodynamic fault is decreased distensibility of the large conduit arteries. This problem is caused by the replacement of elastin by collagen and fibrous tissue in the elastic lamina of the aorta, an age-dependent process that is accelerated by atherosclerosis and hypertension. The cardiovascular risk associated with isolated systolic hypertension is related to pulsatility, the repetitive pounding of the blood vessels with each cardiac cycle and a more rapid return of the arterial pulse wave from the periphery, both begetting more systolic hypertension. The importance of these findings for patients and physicians is that the prior clinical emphasis on diastolic blood pressure was misplaced. In the United States, the majority of uncontrolled hypertension occurs in older patients with isolated systolic hypertension, a problem perpetuated by a persistent focus on lowering diastolic blood pressure, a fear of lowering blood pressure excessively in older patients, and an inherently greater difficulty in achieving systolic blood pressure goals with available medications.

GENDER AND ETHNICITY.

Before age 50, the prevalence of hypertension is lower in women than in men, suggesting a protective effect of estrogen. After menopause, the prevalence of hypertension increases rapidly in women and exceeds that in men.

Within the United States, the prevalence of hypertension varies widely by ethnicity, being most prevalent in African Americans. Hypertension is present in one in three African American adults compared with one in four or five white or Mexican American adults. Compared with all other ethnic groups, hypertension in African Americans is not only more prevalent but also starts at a younger age and causes much more target organ damage, leading to excessive and premature disability and death. In the Bogalusa Heart Study, higher blood pressures in black than in white children were already evident by grade school. Gene-environment interactions have been postulated, as the prevalence of hypertension is low in Africans living in Africa and intermediate in African-Caribbeans.

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