Hypertension is one of the most serious concerns of modern medical practice. It is estimated that in the United States, as many as 60 million people are hyper-tensive or are being treated with antihypertensive drugs. Among the growing population of elderly Americans, some 15 million have high blood pressure. The level of blood pressure in itself is not a chief con-cern, since individuals with high blood pressure may be asymptomatic for many years. What is of prime signifi-cance is that hypertension has been shown convincingly to be the single most important contributing factor to car-diovascular disease, the leading cause of morbidity and untimely death in the United States.
The actual level of pressure that can be considered hypertensive is difficult to define; it depends on a num-ber of factors, including the patient’s age, sex, race, and lifestyle. As a working definition, many cardiovascular treatment centers consider that a diastolic pressure of 90 mm Hg or higher or a systolic pressure of 140 mm Hg or higher represents hypertension. Hypertension is consid-ered to be stage I, or mild, if diastolic pressure is 90 to 99 mm Hg and/or systolic pressure is 140 to 159 mm Hg. Stage II, or moderate, hypertension is diastolic pressure of l00 to 109 mm Hg and/or systolic pressure of 160 to 179 mm Hg. Stage III, or severe, hypertension exists when diastolic pressure is 110 mm Hg or greater and/or systolic pressure is 180 mm Hg or greater.
These values should not be considered as absolutes but rather as indicators for facilitating discussion, par-ticularly in relation to the indications for use of specific drugs. Since in general terms hypertension can be de-fined as the level of blood pressure at which there is risk, the ultimate judgment concerning the severity of hypertension in any given individual must also include a consideration of factors other than diastolic or systolic pressure.
The aim of therapy is straightforward: reduction of blood pressure to within the normal range. When hyper-tension is secondary to a known organic disease, such as renovascular disease or pheochromocytoma, therapy is directed toward correction of the underlying malady. Unfortunately, about 90% of cases of hypertension are of unknown etiology. The therapy of primary, or essen-tial hypertension, as these cases are generally called, is often empirical.
There are three general approaches to the pharma-cological treatment of primary hypertension. The first involves the use of diuretics to reduce blood volume. The second employs drugs that interfere with the renin–angiotensin system, and the third is aimed at a drug-induced reduction in peripheral vascular resist-ance, cardiac output, or both. A reduction in peripheral vascular resistance can be achieved directly by relaxing vascular smooth muscle with drugs known as vasodila-tors or indirectly by modifying the activity of the sym-pathetic nervous system.