Hypertension
From Encyclopædia
Hypertension is the medical term for abnormally high BLOOD
pressure. It is not synonymous with nervous tension,
anxiety, or overactivity. High blood
pressure results from either an increased output of blood from the HEART or an increased resistance to its flow through tiny branches of the arteries, called arterioles (see
arteriosclerosis), or both. Blood
pressure is measured in millimeters of mercury (mm Hg) and is expressed as systolic
pressure over diastolic
pressure. The systolic blood
pressure is recorded during the instant that the heart
contracts (systole) to force blood into the circulation; it is always higher than the diastolic blood
pressure, which is recorded when the heart relaxes between beats (diastole). Thus, blood
pressure of 120/80 mm Hg means that the systolic
pressure is 120 and the diastolic
pressure is 80. Blood
pressure is measured by an inflatable cuff (sphygmomanometer) that is wrapped around the arm.Blood
pressure fluctuates considerably even in normal individuals. It tends to increase with physical activity, excitement,
fear, or emotional
stress, but such elevations are usually transient. The term hypertension indicates that blood
pressure exceeds the upper limits most of the time, not just for short periods. Most physicians would not make the diagnosis of hypertension unless the
pressure was high on at least three separate occasions.High systolic blood
pressure with normal diastolic blood
pressure--for example, 160/80 mm Hg--is known as isolated systolic hypertension. It occurs more commonly in elderly people than in young or middle-aged populations.PrevalenceIt has been estimated that in the
United States at least 30 million people have hypertension. (This can mean a systolic
pressure greater than 160, or a diastolic
pressure of 95, or both.) It is more frequent and more severe in black than in white U.S. populations and is uncommon but not unheard of in children and adolescents. It usually appears after the age of 30 and is slightly more common in women than in men after the age of 50. It occurs throughout the
world and is most prevalent in Japan. In societies that consume little or no salt the incidence of hypertension is extremely low, and the blood
pressure does not tend to rise with age as it does among people in other societies.Causative FactorsHypertension can be primary or secondary, depending on whether a cause can be identified for it. Some of the recognized causes for secondary hypertension include diseases of the kidney or adrenal gland, narrowing of the
artery that supplies the kidney (renal
artery), congenital narrowing of the aorta (coarctation), and the use of birth
Control pills.In more than 90 percent of patients with hypertension, an underlying cause cannot be identified. This type is called primary or essential hypertension. It is believed that genetic as well as environmental factors are responsible for the development of essential hypertension. The nature of the genetic factors is unknown, but environmental factors include excessive salt in the diet, obesity, and emotional
stress, among others. It is unlikely that environmental influences alone can produce hypertension in the absence of genetic predisposition.The
kidneys contain an enzyme called renin that operates in response to deprivation of blood supply. Renin reacts with a blood protein to produce angiotensin, which causes constriction of the arterioles and thus increases resistance to the flow of blood, raising blood
pressure. Although an increased amount of renin is probably responsible for the hypertension associated with some types of kidney or kidney
artery disease, it cannot be implicated in most
cases of essential hypertension because more than 80 percent of all patients with essential hypertension have normal or low levels of renin in the blood (see
kidney disease).Overactivity of the sympathetic (adrenergic)
nervous system, which
Controls the rate and force of the heart beat and the
tone of the arterioles and veins, has been demonstrated in many hypertensive persons, sometimes before blood
pressure is consistently elevated.EffectsHypertension rarely causes symptoms until complications occur. Contrary to popular belief, a florid complexion and hyperactive behavior are not attributes of the hypertensive patient.
headaches, nosebleeds, dizziness, fatigue, and an inward feeling of
anxiety are not more common in people with high blood
pressure than in people with normal blood
pressure.Hypertension accelerates the process of
atherosclerosis, or hardening of the arteries, which is a factor contributing to
strokeS and HEART ATTACKS. Damage to the arterioles
leads to brain hemorrhage or kidney failure. The arterioles can be visualized in the retina, thus permitting the physician to evaluate the severity of the disease and to estimate the prognosis by examining the eyes. Hypertension overworks the heart muscle, and this may result in enlargement of the heart and ultimately in
heart failure. Thus the brain, the heart, the
kidneys, and the eyes are especially vulnerable to the effects of hypertension and are therefore called the target
organs of hypertension. Women are more resistant to the deleterious effects of hypertension than are men.The course of essential hypertension is variable. The blood
pressure tends to get higher as the disease progresses, but often 20 years or more may elapse before sustained hypertension causes enough damage to produce symptoms or complications in one or more of the target
organs. Occasionally, for no apparent reason, there is an abrupt worsening, or acceleration, of hypertension when blood-
pressure levels become exceedingly high, leading rapidly to heart or kidney failure or to brain hemorrhage (malignant hypertension). On the other
hand, some patients have mild elevations of blood
pressure intermittently throughout life without progression and with little or no damage to target
organs. Untreated, most hypertensive patients die at an earlier age than healthy individuals. The most frequent causes of death are
heart failure, heart attack (myocardial infarction), and
stroke.TreatmentProbably no more than 3 percent of all hypertensive patients can be cured by surgical means--removal of a diseased kidney or a tumor of the adrenal gland, surgical repair of a diseased kidney
artery, or coarctation of the aorta. For the others, treatment consists of dietary measures (see
DIET, HUMAN) to reduce salt intake and--if the patient is obese--weight, as well as relaxation techniques. For
cases ?f more severe hypertension, usually one or more
drugs are also required. The desirability of
drugs for mild hypertension is debated, because they can have side effects that exceed their usefulness. Antihypertensive
drugs include diuretic
agents, which promote the loss of water and salt from the body; vasodilator
drugs, which relax and dilate the arterioles and thus decrease the resistance to the flow of blood; adrenergic blockers, which affect the sympathetic
nervous system and its
Control of the rate and force of the heartbeat and the
tone of the arterioles; angiotensin converting enzyme (ACE) inhibitors, which prevent the formation of angiotensin; and the calcium antagonists, which keep calcium ions from reaching the interior of smooth muscle
cells, so that the arteries and arterioles are dilated.Many studies have demonstrated that if blood
pressure is maintained within normal or nearly normal limits with appropriate medication, the fatal and nonfatal complications of hypertension are significantly reduced. Because hypertension seldom disappears spontaneously, treatment can be a lifelong process.Ray W. Gifford, M.D.
bibliography: Gasner, Douglas, and McCleary, E.H., The
American Medical Association Straight-Talk No-Nonsense Guide to Heartcare, rev. ed. (1984); Langford, H.G., and Watson, R., Preventing Hypertension (1990); O'Brien, E., et al., eds., ABC of Hypertension, 2d ed. (1987).
