HYPERTENSION

also called High Blood Pressure, condition in which the blood pressure in either arteries or veins is abnormally high. Blood pressure is the force exerted by the blood against the walls of the blood vessels. Normally, the pumping of the heart creates a rhythmic pulsing of blood along and against the walls of the blood vessels, which are flexible enough to dilate or contract and thus keep the pressure constant. Most physicians consider the blood pressure of a healthy adult to be in the neighbourhood of 120/80i.e., equivalent to the pressure exerted by a column of mercury 120 mm high during contraction of the heart (systole) and 80 mm high during relaxation (diastole). Sometimes, however, for a variety of reasons, the blood vessels may lose their flexibility, or the muscles surrounding them may force them to contract. As a result, the heart must pump more forcefully to move the same amount of blood through the narrowed vessels into the capillaries, thereby increasing the blood pressure. Over time, this higher pressure, or hypertension, can damage the arterioles (the small terminal twigs of an artery that end in capillaries) in such organs as the liver, kidney, or brain and can also weaken the overworked heart. The increased risk of death from congestive heart failure, kidney failure, or stroke is the chief danger of hypertension. Known as the silent killer because it may be present for years with no perceptible symptoms, hypertension is usually detected by a routine blood-pressure test. In urbanized societies it can be quite common among the elderly. Despite its fatal consequences if untreated, the condition responds well to medical and other therapeutic measures. Hypertension is generally classified by cause either as essential (of unknown origin) or as secondary (the result of a specific disease, disorder, or other condition). Secondary hypertension may result from a wide range of causes. Renal (kidney) hypertension affects the entire systemic circulation and arises from hypertension within the renal arteries, which branch from the aorta to supply blood to the kidneys. The underlying cause is disease of the kidneys or narrowing or blocking of the arteries, as by arteriosclerosis. Hypertension may also result from the excess hormones that are secreted during abnormal functioning of the outer substance, or cortex, of the adrenal glands (Cushing's syndrome; aldosteronism); from the excess hormones resulting from pheochromocytoma, which is a tumour of the inner substance (medulla) of the adrenal glands; or from the excess hormones secreted by pituitary tumours. Other causes of secondary hypertension are coarctationlocalized narrowingof the aorta, pregnancy, and the use of oral contraceptives. In all secondary cases, the hypertension is relieved by treating the underlying condition or cause. By far the most common form of hypertension (90 percent of cases) is essential, or idiopathic, hypertension. Although no specific cause can be determined in such cases, studies have pointed out several contributing factors. Included among these are a family history of hypertension, obesity, high salt intake, smoking, and, most importantly, emotional and physical stress. In its milder forms, essential hypertension is usually treated with a self-help regimen that includes a no-salt diet and perhaps a weight-reducing diet, a decrease in or cessation of smoking, mild exercise, and the avoidance of or more successful coping with stressful situations. If a self-help program does not help lower the patient's blood pressure, the physician will usually prescribe diuretics or sympathetic-nerve blockers. The diuretics increase sodium excretion and thereby decrease the volume of body water. Since diuretics may act to deplete the body of potassium, supplements or potassium-saving drugs may be used with the diuretic. The nerve blockers generally act by decreasing heart output and peripheral resistance to blood flow. Beta blockers are the most commonly used of these drugs and include metoprolol, nadolol, and propranolol. More severe hypertension often requires the use of drugs called vasodilators, which dilate the arteries, thus lowering the blood pressure. Oral vasodilators, which include hydralazine and minoxidil, are often used in conjunction with a diuretic and a sympathetic nerve blocker to inhibit the body's natural tendency to increase fluid retention and increase blood flow in response to the arterial dilation. Once medical therapy for essential hypertension begins, it must continue for the rest of the patient's life. Severe and immediately life-threatening hypertension, either secondary or essential, is called malignant hypertension and usually requires hospitalization and acute medical care. Treatment includes the intravenous administration of vasodilators such as diazoxide.