Hypertension

Hypertension, present in 50 million Americans, is one of the most powerful contributors to cardiovascular morbidity and mortality: the 600,000 annual cases of stroke, 1.1 million annual heart attacks, 400,000 annual new cases of CHF, and most of the nearly 1 million annual deaths from cardiovascular and kidney diseases.2,4

Prevalence

In a 1988-1994 national survey of persons aged 20 to 74 years, the prevalence of hypertension, i.e., systolic blood pressure of 140 mmHg or greater or diastolic blood pressure of 90 mmHg or greater or on antihypertensive medication, was 24 per- cent in white men, 19 percent in white women, 35 percent in black men, and 34 percent in black women.24 Prevalence in- creases with age and is highest among blacks and the elderly (Fig. 1-8). Isolated systolic hypertension is a common and distinctly hazardous condition in the elderly. There is evidence from the Systemic Hypertension in the Elderly Program (SHEP) and the Syst-Eur trial that treatment of this form of hypertension in the elderly is distinctly efficacious not only against stroke but also against coronary disease.25,26 Persons with hypertension face serious excess risks of cardiovascular sequelae, and since much of this excess risk is attributable to mild hypertension, there is need for intervention through preventive lifestyle modification, if not through drug treatment. Because of the higher prevalence of milder hypertension, almost 60 percent of the excess mortality attributable to hypertension comes from this blood pressure range. The risks of cardiovascular sequelae are proportional to the blood pressure level at any age and in both sexes and are increased whether the elevation is systolic or diastolic. Approximately one-half of persons who suffer a first heart attack and two-thirds who suffer a first stroke have blood pressures greater than 160/95 mmHg.

Figure 1-8: Prevalence of hypertension by age, race, and sex; United States, 1988-1994 (hypertension: 140/90 mmHg or greater or on antihypertensive medication). (From the National Health and Nutrition Examination Survey, National Center for Health Statistics.)

Although there is a rise in blood pressure with age in both sexes, in most affluent populations this is not universal, and it does not imply that blood pressure inevitably must rise with age or that in those whose pressures do rise it reflects a normal aging process. In the United States, there is about a 20 mmHg systolic and 10 mmHg diastolic rise in mean pressures from age 30 to age 64. Systolic pressures continue to rise in women into their eighties and in men into their seventies. Diastolic pressures level off earlier and in men decline beyond age 55. The pressures start lower in young-adult women and rise more steeply in middle age (50 and over), and they equal those of men in their fifties and then progressively exceed those of men in later life; this crossover is observed for both systolic and diastolic pressures. In some populations in the world, blood pressure does not rise with age.

For the following discussion, hypertension means that a patient has blood pressure of 160/95 mmHg or greater or is on antihypertensive medication; undercontrol means that a patient is on antihypertensive medication and has blood pressure of less than 160/95 mmHg. Between the periods 1971-1972 and 1988-1994, there have been large improvements in the percentage of hypertensive patients who (1) are aware of their hypertension (from 51-88 percent), (2) are on antihypertensive medication (from 36-79 percent), and (3) are under control (from 16-65 percent).! Although an improving trend is also seen at the 140/90 mmHg and greater level of control, using this definition, 46 percent still do not have medication prescribed for their hypertension.2

Incidence

Longitudinal observation of blood pressures as people age reveals a different pattern than cross-sectional prevalence data. The reason for this difference is obscure. Diastolic pressures are essentially parallel in both sexes, with women's pressures consistently below those of men at all ages. In women, systolic pressures are initially lower than in men but subsequently rise more steeply with age. They converge at age0 with those of men but never exceed them. With advancing age in both genders, a progressive and disproportionate rise in systolic pressure occurs that is presumed to result from loss of arterial elasticity. Blacks have higher blood pressures than whites in most Western cultures.

Determinants

While genetic susceptibility plays a large role in hypertension, this may be only permissive, requiring one or more environmental cofactors such as salt intake, alcohol, or weight gain to bring on hypertension. Of all the identifiable determinants of hypertension, weight gain and adiposity, particularly abdominal in distribution, seem to be predominant. New underlying causes of hypertension are discovered every decade, but the causes of the vast majority of cases remain undetermined. Of the identifiable causes, chronic renal diseases, renovascular disease, and oral contraceptives head the list. Routine search for underlying causes not suggested by signs or symptoms is usually unrewarding and often counterproductive. Recent research suggests that insulin resistance occurring in association with obesity may play a fundamental role 27 (see also Chaps. 41 and 56).

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