What Causes Hypertension?
Hypertension is a condition in which the blood pressure is abnormally high. Hypertension may be due to a variety of disorders, and it is present in about 10% of the adult population of the United States. In all individuals the pressure of the blood on the walls of the arteries rises when the heart contracts, and falls when the heart relaxes. The pressure of the blood is measured at both periods. In normal adults, the pressure when the heart contracts, the systolic pressure, is usually about 130 mm of mercury as measured by a sphygmomanometer.
The pressure when the heart is relaxed, the diastolic pressure, usually ranges between 70 and 85 mm of mercury. In people with hypertension, the diastolic pressure may be over 90 mm of mercury, sometimes as high as 150 mm, and the systolic pressure may exceed the diastolic pressure by 50 to 150 mm of mercury. Often both the systolic and diastolic pressures are elevated, but sometimes only the systolic pressure is abnormally high.
Causes of Hypertension
When only the systolic pressure is elevated, it is often the result of atherosclerosis, a disorder in which the artery walls lose their elasticity. A high systolic pressure may also result from any condition that increases the output of the heart. Among the disorders that may produce increases in both the systolic and diastolic pressures are diseases of the kidney, the adrenal gland, and the sympathetic nervous system.
Hypertension may also occur in pregnant women or overweight persons. In some cases it is caused by psychological factors.
In disorders of the kidney as well as in disorders that reduce the blood supply to the kidney, the kidney produces a protein, renin, which acts on a blood globulin to produce angiotensin, a substance that constricts the small arteries and tllUl) raises the pressure within the arterial system. In certain disorders of the adrenal glands and sympathetic nervous system, hypertension may result from the excessive production of adrenaline (epinephrine) or noradrenaline (norepinephrine). These substances also operate by constricting the small arteries.
The form of hypertension that sometimes occurs in pregnant women results from an impairment in the body's handling of water and sodium. Water accumulates in all the body tissues, including the brain, causing swelling and sometimes leading to convulsions. In obese people, the mechanism causing hypertension is not known.
Treatment of Hypertension
The treatment of hypertension depends largely on the underlying cause. In many cases it may be treated with sedatives, drugs that block the release or action of adrenaline or noradrenaline, or by the surgical removal of a diseased kidney or adrenal gland. Surgery may also be needed to remove a tumor of the sympathetic nervous system or an adrenal gland, or to correct narrowings Or obstructions of the arteries leading to the kidneys.
The hypertension of pregnancy is treated with sedatives, a low salt diet, diuretics (drugs that increase the output of urine), and, :if necessary, the termination of the pregnancy through abortion. The hypertension that occurs in obese individuals may be relieved by the patient's losing weight.
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