When there is no
demonstrable underlying cause of hypertension, the condition is classified as
essential hypertension. Essential hypertension is also called primary or
idiopathic hypertension. This is by far the most common type of high blood
pressure, occurring in 90 to 95 percent of patients. Genetic factors appear to
play a major role in the occurrence of essential hypertension. Secondary
hypertension is associated with an underlying disease, which may be renal,
neurologic, or endocrine in origin; examples of such diseases include Bright
disease (glomerulonephritis; inflammation of the urine-producing
structures in the kidney), atherosclerosis of blood vessels in the
brain and Cushing syndrome (hyperactivity of the adrenal glands). In cases
of secondary hypertension, correction of the underlying cause may cure
hypertension. Various external agents also can raise blood pressure. These
include cocaine, amphetamines, cold remedies, thyroid supplements,
corticosteroids, nonsteroidal anti-inflammatory drugs (NSAIDs), and oral
contraceptives.
Malignant hypertension is present when there is a
sustained or sudden rise in diastolic blood pressure exceeding 120 mmHg, with
accompanying evidence of damage to organs such as the eyes, brain, heart, and
kidneys. Malignant hypertension is a medical emergency and requires immediate
therapy and hospitalisation.
Epidemiology
Elevated arterial
pressure is one of the most important public health problems in developed
countries. In the United States, for instance, nearly 30 percent of the adult
population is hypertensive. High blood pressure is significantly more prevalent
and serious among Asians. Age, race, sex, smoking, alcohol intake, elevated
serum cholesterol, salt intake, glucose intolerance, obesity and
stress all may contribute to the degree and prognosis of the disease. In both
men and women, the risk of developing high blood pressure increases with age.
Hypertension
has been called the “silent killer” because it usually produces no symptoms. It
is important, therefore, for anyone with risk factors to have their blood
pressure checked regularly and to make appropriate lifestyle changes.
Complications
The most common immediate cause of
hypertension-related death is heart disease, but death from
stroke or renal (kidney) failure is also frequent. Complications result
directly from the increased pressure (cerebral hemorrhage, retinopathy, left
ventricular hypertrophy, congestive heart failure, arterial aneurysm and
vascular rupture), from atherosclerosis (increased coronary, cerebral, and renal vascular
resistance), and from decreased blood flow and ischemia (myocardial infarction,
cerebral thrombosis and renal nephrosclerosis). The risk of developing
many of these complications is greatly elevated when hypertension is diagnosed
in young adulthood.
Treatment
Effective treatment
will reduce overall cardiovascular morbidity and mortality.
Non-drug therapy
consists of: (1) relief of stress, (2) dietary management (restricted intake of
salt, calories, cholesterol, and saturated fats; sufficient intake of
potassium, magnesium, calcium and vitamin C), (3) regular aerobic
exercise, (4) weight reduction, (5) smoking cessation and (6) reduced intake of
alcohol and caffeine.
Mild to moderate hypertension may be controlled by a single-drug regimen, although more severe cases often require a combination of two or more drugs. Diuretics are a common medication; these agents lower blood pressure primarily by reducing body fluids and thereby reducing peripheral resistance to blood flow. However, they deplete the body’s supply of potassium, so it is recommended that potassium supplements be added or that potassium-sparing diuretics be used. Beta-adrenergic blockers block the effects of epinephrine (adrenaline), thus easing the heart’s pumping action and widening blood vessels. Vasodilators act by relaxing the smooth muscle in the walls of blood vessels, allowing small arteries to dilate and thereby decreasing total peripheral resistance. Calcium channel blockers promote peripheral vasodilation and reduce vascular resistance. Angiotensin-converting enzyme (ACE) inhibitors inhibit the generation of a potent vasoconstriction agent and they also may retard the degradation of a potent vasodilator (bradykinin) and involve the synthesis of vasodilatory prostaglandins. Angiotensin receptor antagonists are similar to ACE inhibitors in utility and tolerability but instead of blocking the production of angiotensin II, they completely inhibit its binding to the angiotensin II receptor. Statin, best known for its use as a cholesterol-lowering agent, has shown promise as an antihypertensive drug because of its ability to lower both diastolic and systolic blood pressure. The mechanism by which statins act to reduce blood pressure is unknown; however, scientists suspect that these drugs activate substances involved in vasodilation.
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