To many people, the word hypertension suggests excessive tension, nervousness, or stress. In medical terms, however, hypertension refers to a condition of elevated blood pressure, regardless of the cause. It has been called "the silent killer" because it usually doesn't cause symptoms for many years--until a vital organ is damaged.

The number of Americans who have high blood pressure is estimated to be more than 50 million. It occurs more often in blacks--38 percent of black adults have high blood pressure, compared with 29 percent of whites. At any given blood pressure level, the consequences of high blood pressure are worse in blacks.

In the United States, only an estimated two out of three people with high blood pressure have been diagnosed. Of these people, about 75 percent receive drug treatment, and of these, about 45 percent receive adequate treatment.

When blood pressure is checked, two values are recorded. The higher one occurs when the heart contracts (systole); the lower occurs when the heart relaxes between beats (diastole). Blood pressure is written as the systolic pressure followed by a slash followed by the diastolic pressure--for example, 120/80 mm Hg (millimeters of mercury). This reading would be referred to as "one-twenty over eighty."

High blood pressure is defined as a systolic pressure at rest that averages 140 mm Hg or more, a diastolic pressure at rest that averages 90 mm Hg or more, or both. In high blood pressure, usually both the systolic and the diastolic pressures are elevated.

In isolated systolic hypertension, the systolic pressure is 140 mm Hg or more, but the diastolic pressure is less than 90 mm Hg--that is, the diastolic pressure is in the normal range. Isolated systolic hypertension is increasingly common with advancing age. In almost everyone, blood pressure increases with age, with systolic pressure increasing until at least age 80 and diastolic pressure increasing until age 55 to 60, then leveling off or even falling.

Malignant hypertension is a particularly severe form of high blood pressure that, if left untreated, usually leads to death in 3 to 6 months. It's fairly rare, occurring in only about 1 in every 200 people who have high blood pressure, but it's several times more common in blacks than in whites, in men than in women, and in people of lower socioeconomic status than in those of higher socioeconomic status. Malignant hypertension is a medical emergency.

Control of Blood Pressure

The pressure in the arteries can be increased in various ways. For one, the heart can pump with more force, putting out more fluid each second. Another possibility is that the large arteries can lose their normal flexibility and become stiff, so that they can't expand when the heart pumps blood through them. Thus, the blood from each heartbeat is forced through less space than normal, and the pressure increases. That's what happens in elderly people whose arterial walls become thickened and stiff because of arteriosclerosis. Blood pressure is similarly increased in vasoconstriction--when the tiny arteries (arterioles) are temporarily constricted as a result of stimulation by nerves or by hormones in the blood. A third way in which the pressure in the arteries can be increased is for more fluid to be added to the system. This happens when the kidneys malfunction and aren't able to remove enough salt and water from the body. The volume of blood in the body increases, so the blood pressure increases.

Conversely, if the heart's pumping activity diminishes, if the arteries are dilated, or if fluid is removed from the system, the pressure falls. Adjustments of these factors are governed by changes in kidney function and in the autonomic nervous system--the part of the nervous system that regulates many body functions automatically.

The sympathetic nervous system, which is part of the autonomic nervous system, temporarily increases blood pressure during the fight-or-flight response (the body's physical reaction to a threat). The sympathetic nervous system increases both the speed and force of the heartbeats. It also narrows most arterioles, but it expands those in certain areas, such as in skeletal muscle, where an increased blood supply is needed. In addition, the sympathetic nervous system decreases the kidney's excretion of salt and water, thereby increasing the body's blood volume. The sympathetic nervous system also releases the hormones epinephrine (adrenaline) and norepinephrine (noradrenaline), which stimulate the heart and blood vessels.

The kidneys control blood pressure in several ways. If blood pressure rises, they increase their excretion of salt and water, which lowers blood volume and brings the blood pressure back down to normal. Conversely, if blood pressure falls, the kidneys decrease their excretion of salt and water, so that blood volume increases and blood pressure returns to normal. The kidneys also can increase blood pressure by secreting an enzyme called renin, which triggers the production of a hormone called angiotensin, which in turn triggers the release of a hormone called aldosterone.

Because the kidneys are important in controlling blood pressure, many kidney diseases and abnormalities can cause high blood pressure. For example, a narrowing of the artery supplying one of the kidneys (renal artery stenosis) can cause hypertension. Kidney inflammation of various types and injury to one or both kidneys can also cause blood pressure to rise.

Whenever a change causes an increase in blood pressure, a compensatory mechanism is triggered to counteract it and keep the pressure at normal levels. So an increase in the volume of blood pumped out by the heart, which tends to increase blood pressure, causes the blood vessels to dilate and the kidneys to increase their excretion of salt and water, which tends to reduce blood pressure. However, the presence of arteriosclerosis makes arteries stiff and prevents the dilation that would otherwise lower blood pressure back to normal. Arteriosclerotic changes in the kidney can impair the kidneys' ability to excrete salt and water, which tends to increase blood pressure.

Selected Causes of Secondary Hypertension

Kidney disease Renal artery stenosis Pyelonephritis Glomerulonephritis Kidney tumors Polycystic kidney disease (usually inherited) Injury to the kidney Radiation therapy affecting the kidney Hormonal disorders Hyperaldosteronism Cushing's syndrome Pheochromocytoma Drugs Oral contraceptives Corticosteroids Cyclosporine Erythropoietin Cocaine Alcohol abuse Licorice (excessive amounts) Other causes Coarctation of the aorta Pregnancy complicated by preeclampsia Acute intermittent porphyria Acute lead poisoning

Causes

In about 90 percent of people with high blood pressure, the cause isn't known and the condition is referred to as essential or primary hypertension. Essential hypertension probably has more than one cause. Several changes in the heart and blood vessels probably combine to elevate the blood pressure.

When the cause is known, the condition is called secondary hypertension. In 5 to 10 percent of the people with high blood pressure, the cause is kidney disease. In 1 to 2 percent, the cause is a condition such as a hormonal disorder or the use of certain drugs such as oral contraceptives (birth control pills). A rare cause of high blood pressure, pheochromocytoma is a tumor of the adrenal gland that produces the hormones epinephrine (adrenaline) and norepinephrine (noradrenaline).

Obesity, a sedentary lifestyle, stress, and excessive amounts of alcohol or salt in food all can play a role in the development of high blood pressure in people who have an inherited sensitivity. Stress tends to cause the blood pressure to increase temporarily, but blood pressure usually returns to normal once the stress is over. This explains "white coat hypertension," in which the stress of visiting a doctor's office causes the blood pressure to rise high enough to be diagnosed as high blood pressure in someone who, at other times, has normal blood pressure. In susceptible people, these brief increases in blood pressure are thought to cause damage that eventually results in permanently high blood pressure, even though the stress may no longer be present. This theory that temporary high blood pressure can give rise to permanent high blood pressure hasn't been proved.

Symptoms

In most people, high blood pressure causes no symptoms, despite the coincidental occurrence of certain symptoms that are widely--but erroneously--believed to be associated with high blood pressure: headaches, nosebleeds, dizziness, flushed face, and tiredness. Although people with high blood pressure may have these symptoms, they occur just as frequently in those with normal blood pressure.

If a person has high blood pressure that's severe or long-standing and untreated, symptoms such as headache, fatigue, nausea, vomiting, shortness of breath, restlessness, and blurred vision occur because of damage to the brain, eyes, heart, and kidneys. Occasionally, people with severe high blood pressure develop drowsiness and even coma caused by brain swelling. This condition, called hypertensive encephalopathy, requires emergency treatment.

Diagnosis

Blood pressure is measured after the person sits or lies for 5 minutes. A reading of 140/90 mm Hg or more is considered high, but a diagnosis can't be based on a single high reading. Sometimes, even several high readings aren't enough to make the diagnosis. If a person has an initial high reading, the blood pressure is measured again and then measured twice on at least two other days to make sure that the high blood pressure persists. The readings not only determine the presence of high blood pressure but also are used to classify its severity.

After high blood pressure has been diagnosed, its effects on key organs, especially the blood vessels, heart, brain, and kidneys, are usually evaluated. The retina (the light-sensitive membrane on the inner surface of the back of the eye) is the only place where a doctor can directly view the effects of high blood pressure on arterioles. The assumption is that the changes in the retina are similar to changes in blood vessels elsewhere in the body, such as the kidneys. To examine the retina, a doctor uses an ophthalmoscope (an instrument that provides a view of the inside of the eye). By determining the degree of damage to the retina (retinopathy), a doctor can classify the seriousness of the high blood pressure.

Changes in the heart--particularly enlargement because of the increased work required to pump blood at the increased pressure--can be detected by electrocardiography (see page 73 in Chapter 15, Diagnosis of Heart Disease) and chest x-rays. In the early stages, such changes are best detected by echocardiography (a test that uses ultrasound waves to create an image of the heart). (see page 76 in Chapter 15, Diagnosis of Heart Disease) An abnormal heart sound, called the fourth heart sound, which can be heard with a stethoscope, is one of the earliest heart changes caused by high blood pressure.

Early indications of kidney damage are detected primarily by examining the person's urine. The presence of blood cells and albumin (a type of protein) in the urine, for example, can indicate such damage.

A doctor also looks for the cause of the high blood pressure, especially in a younger person, even though a cause is identified in less than 10 percent of people. The higher the blood pressure and the younger the patient, the more extensive the search for a cause is likely to be. The evaluation may include x-ray and radioisotope studies of the kidney, a chest x-ray, and examinations of blood and urine for certain hormones.

To detect a kidney problem, a doctor first takes a medical history, asking about previous kidney problems. Then during the physical examination, the area of the abdomen over the kidneys is checked for tenderness. A stethoscope is placed over the abdomen to listen for a bruit (the sound caused by blood rushing through a narrowing in the artery supplying the kidney). A urine specimen may be sent to the laboratory for analysis, and x-rays or ultrasound scans of the kidney's blood supply and other tests of the kidneys are performed, if necessary.

When pheochromocytoma is the cause, breakdown products of the hormones epinephrine (adrenaline) and norepinephrine (noradrenaline) show up in the urine. Usually, these hormones also produce various combinations of severe headache, anxiety, an awareness of a rapid or irregular heart rate (palpitations), excessive perspiration, tremor, and paleness.

Other rare causes of high blood pressure may be detected by certain routine tests. For example, measuring the potassium level in the blood can help detect hyperaldosteronism, (see page 715 in Chapter 146, Adrenal Gland Disorders) and measuring the blood pressure in both arms and legs can help detect coarctation of the aorta.

Prognosis

Untreated high blood pressure increases a person's risk of developing heart disease (such as heart failure or heart attack), kidney failure, and stroke at an early age. High blood pressure is the most important risk factor for stroke. It's also one of the three major risk factors for heart attack (myocardial infarction) that a person can do something about; the other two are smoking and high blood cholesterol levels. Treatment that lowers high blood pressure greatly decreases the risk of stroke and heart failure. Such treatment may also decrease the risk of heart attack, although not as dramatically. Without treatment, fewer than 5 percent of people with malignant hypertension survive for a year.

Treatment

Essential hypertension can't be cured, but it can be treated to prevent complications. Because high blood pressure itself has no symptoms, doctors try to avoid treatments that make people feel bad or interfere with their lifestyle. Before any drugs are prescribed, alternative measures are usually tried.

Overweight people with high blood pressure are advised to reduce their weight to ideal levels. Changes in diet for those with diabetes, obesity, or high blood cholesterol levels also are important for overall cardiovascular health. Cutting down to less than 2.3 grams of sodium or 6 grams of sodium chloride a day (while maintaining an adequate intake of calcium, magnesium, and potassium) and reducing daily alcohol intake to less than 24 ounces of beer, 8 ounces of wine, or 2 ounces of 100-proof whiskey may make drug therapy for high blood pressure unnecessary. Moderate aerobic exercise is helpful. People with essential hypertension don't have to restrict their activities as long as their blood pressure is controlled. Smokers should stop smoking.

Often, doctors recommend that people with high blood pressure should monitor their blood pressure at home. Those who monitor their own blood pressure are probably more likely to follow a doctor's recommendations regarding treatment.

Drug Therapy

Virtually any person with high blood pressure can get it under control with the wide variety of drugs available, but treatment has to be tailored to the individual. Treatment is most effective when patients and doctors communicate well and collaborate on the treatment program.

Experts don't agree on how much blood pressure should be lowered during treatment or on when and how stage 1 (mild) high blood pressure should be treated. But there is agreement that the higher the blood pressure, the greater the risks--even within the normal blood pressure range. So some experts point out that any elevation, however small, should be treated and that the more the blood pressure is lowered, the better. Other experts say that treatment of blood pressures below a certain level may actually increase the risks of heart attack and sudden death rather than reduce them, particularly in people with coronary artery disease.

Different types of drugs reduce blood pressure by different mechanisms. Some doctors use a stepped approach to drug therapy: They start with one type of drug and add others as necessary. Other doctors prefer a sequential approach: They prescribe one drug; if it's ineffective, they discontinue it and prescribe another type of drug. In choosing a drug, a doctor considers such factors as the person's age, sex, and race; the severity of the high blood pressure; the presence of other conditions, such as diabetes or high blood cholesterol levels; the potential side effects, which vary from drug to drug; and the costs of the drugs and of tests needed to monitor their safety.

Most people tolerate their prescribed antihypertensive drugs without problems. But any antihypertensive drug can cause side effects. So if side effects do develop, a person should tell the doctor, who can adjust the dose or switch to another drug.

A thiazide diuretic is commonly the first drug given to treat high blood pressure. Diuretics help the kidneys eliminate salt and water, which decreases fluid volume throughout the body, thus lowering blood pressure. Diuretics also cause blood vessels to dilate. Because diuretics cause a loss of potassium in the urine, potassium supplements or potassium-retaining drugs sometimes must be taken along with the diuretics. Diuretics are particularly useful in blacks, the elderly, obese people, and people with heart failure or chronic kidney failure.

Adrenergic blockers--a group of drugs that includes the alpha-blockers, beta-blockers, and the alpha-beta blocker labetalol--block the effects of the sympathetic nervous system, the system that may rapidly respond to stress by raising blood pressure. The most commonly used adrenergic blockers, the beta-blockers are particularly useful in whites, young people, and people who have had a heart attack or who have rapid heart rates, angina pectoris (chest pain), or migraine headaches.

Angiotensin converting enzyme inhibitors lower blood pressure by dilating arteries. They are particularly useful in whites, young people, people with heart failure, people with protein in their urine because of chronic kidney disease or diabetic kidney disease, and men who are impotent as a side effect of taking another drug.

Angiotensin II blockers lower blood pressure by a mechanism similar to--but more direct than--the one used by angiotensin converting enzyme inhibitors. Because of the way they work, angiotensin II blockers appear to cause fewer side effects.

Calcium antagonists cause blood vessels to dilate by a completely different mechanism. They are particularly useful in blacks, the elderly, and people with angina pectoris (chest pain), certain types of rapid heart rates, or migraine headaches. Recent reports suggest that people using short-acting calcium antagonists may have an increased risk of death from heart attacks, but there are no reports suggesting such effects for long-acting calcium antagonists.

Direct vasodilators dilate blood vessels by yet another mechanism. A drug of this class is almost never used alone; rather, it's added as a second drug when another drug alone doesn't lower blood pressure sufficiently.

Hypertensive emergencies--for example, malignant hypertension--require rapid lowering of the blood pressure. Several drugs can lower blood pressure quickly; most of them are given intravenously. These drugs include diazoxide, nitroprusside, nitroglycerin, and labetalol. Nifedipine, a calcium antagonist, is very fast acting and can be given orally; however, it can cause hypotension, so the patient must be monitored closely.

Secondary Hypertension Treatment

Treatment of secondary hypertension depends on the underlying cause of the high blood pressure. Treating kidney disease can sometimes normalize the blood pressure or at least lower it, so that drug therapy is more effective. A narrowed artery to the kidney may be dilated by inserting a balloon-tipped catheter and inflating the balloon. Or the narrowed part of the artery supplying the kidney can be bypassed; often such surgery cures the high blood pressure. Tumors that cause high blood pressure, such as pheochromocytoma, usually can be removed surgically.

After high blood pressure has been diagnosed, its effects on key organs, especially the blood vessels, heart, brain, and kidneys, are usually evaluated. The retina (the light-sensitive membrane on the inner surface of the back of the eye) is the only place where a doctor can directly view the effects of high blood pressure on arterioles. The assumption is that the changes in the retina are similar to changes in blood vessels elsewhere in the body, such as the kidneys. To examine the retina, a doctor uses an ophthalmoscope (an instrument that provides a view of the inside of the eye). By determining the degree of damage to the retina (retinopathy), a doctor can classify the seriousness of the high blood pressure.

Changes in the heart--particularly enlargement because of the increased work required to pump blood at the increased pressure--can be detected by electrocardiography (see page 73 in Chapter 15, Diagnosis of Heart Disease) and chest x-rays. In the early stages, such changes are best detected by echocardiography (a test that uses ultrasound waves to create an image of the heart). (see page 76 in Chapter 15, Diagnosis of Heart Disease) An abnormal heart sound, called the fourth heart sound, which can be heard with a stethoscope, is one of the earliest heart changes caused by high blood pressure.

Early indications of kidney damage are detected primarily by examining the person's urine. The presence of blood cells and albumin (a type of protein) in the urine, for example, can indicate such damage.

A doctor also looks for the cause of the high blood pressure, especially in a younger person, even though a cause is identified in less than 10 percent of people. The higher the blood pressure and the younger the patient, the more extensive the search for a cause is likely to be. The evaluation may include x-ray and radioisotope studies of the kidney, a chest x-ray, and examinations of blood and urine for certain hormones.

To detect a kidney problem, a doctor first takes a medical history, asking about previous kidney problems. Then during the physical examination, the area of the abdomen over the kidneys is checked for tenderness. A stethoscope is placed over the abdomen to listen for a bruit (the sound caused by blood rushing through a narrowing in the artery supplying the kidney). A urine specimen may be sent to the laboratory for analysis, and x-rays or ultrasound scans of the kidney's blood supply and other tests of the kidneys are performed, if necessary.

When pheochromocytoma is the cause, breakdown products of the hormones epinephrine (adrenaline) and norepinephrine (noradrenaline) show up in the urine. Usually, these hormones also produce various combinations of severe headache, anxiety, an awareness of a rapid or irregular heart rate (palpitations), excessive perspiration, tremor, and paleness.

Other rare causes of high blood pressure may be detected by certain routine tests. For example, measuring the potassium level in the blood can help detect hyperaldosteronism, (see page 715 in Chapter 146, Adrenal Gland Disorders) and measuring the blood pressure in both arms and legs can help detect coarctation of the aorta.

Prognosis

Untreated high blood pressure increases a person's risk of developing heart disease (such as heart failure or heart attack), kidney failure, and stroke at an early age. High blood pressure is the most important risk factor for stroke. It's also one of the three major risk factors for heart attack (myocardial infarction) that a person can do something about; the other two are smoking and high blood cholesterol levels. Treatment that lowers high blood pressure greatly decreases the risk of stroke and heart failure. Such treatment may also decrease the risk of heart attack, although not as dramatically. Without treatment, fewer than 5 percent of people with malignant hypertension survive for a year.

Treatment

Essential hypertension can't be cured, but it can be treated to prevent complications. Because high blood pressure itself has no symptoms, doctors try to avoid treatments that make people feel bad or interfere with their lifestyle. Before any drugs are prescribed, alternative measures are usually tried.

Overweight people with high blood pressure are advised to reduce their weight to ideal levels. Changes in diet for those with diabetes, obesity, or high blood cholesterol levels also are important for overall cardiovascular health. Cutting down to less than 2.3 grams of sodium or 6 grams of sodium chloride a day (while maintaining an adequate intake of calcium, magnesium, and potassium) and reducing daily alcohol intake to less than 24 ounces of beer, 8 ounces of wine, or 2 ounces of 100-proof whiskey may make drug therapy for high blood pressure unnecessary. Moderate aerobic exercise is helpful. People with essential hypertension don't have to restrict their activities as long as their blood pressure is controlled. Smokers should stop smoking.

Often, doctors recommend that people with high blood pressure should monitor their blood pressure at home. Those who monitor their own blood pressure are probably more likely to follow a doctor's recommendations regarding treatment.

Drug Therapy

Virtually any person with high blood pressure can get it under control with the wide variety of drugs available, but treatment has to be tailored to the individual. Treatment is most effective when patients and doctors communicate well and collaborate on the treatment program.

Experts don't agree on how much blood pressure should be lowered during treatment or on when and how stage 1 (mild) high blood pressure should be treated. But there is agreement that the higher the blood pressure, the greater the risks--even within the normal blood pressure range. So some experts point out that any elevation, however small, should be treated and that the more the blood pressure is lowered, the better. Other experts say that treatment of blood pressures below a certain level may actually increase the risks of heart attack and sudden death rather than reduce them, particularly in people with coronary artery disease.

Different types of drugs reduce blood pressure by different mechanisms. Some doctors use a stepped approach to drug therapy: They start with one type of drug and add others as necessary. Other doctors prefer a sequential approach: They prescribe one drug; if it's ineffective, they discontinue it and prescribe another type of drug. In choosing a drug, a doctor considers such factors as the person's age, sex, and race; the severity of the high blood pressure; the presence of other conditions, such as diabetes or high blood cholesterol levels; the potential side effects, which vary from drug to drug; and the costs of the drugs and of tests needed to monitor their safety.

Most people tolerate their prescribed antihypertensive drugs without problems. But any antihypertensive drug can cause side effects. So if side effects do develop, a person should tell the doctor, who can adjust the dose or switch to another drug.

A thiazide diuretic is commonly the first drug given to treat high blood pressure. Diuretics help the kidneys eliminate salt and water, which decreases fluid volume throughout the body, thus lowering blood pressure. Diuretics also cause blood vessels to dilate. Because diuretics cause a loss of potassium in the urine, potassium supplements or potassium-retaining drugs sometimes must be taken along with the diuretics. Diuretics are particularly useful in blacks, the elderly, obese people, and people with heart failure or chronic kidney failure.

Adrenergic blockers--a group of drugs that includes the alpha-blockers, beta-blockers, and the alpha-beta blocker labetalol--block the effects of the sympathetic nervous system, the system that may rapidly respond to stress by raising blood pressure. The most commonly used adrenergic blockers, the beta-blockers are particularly useful in whites, young people, and people who have had a heart attack or who have rapid heart rates, angina pectoris (chest pain), or migraine headaches.

Angiotensin converting enzyme inhibitors lower blood pressure by dilating arteries. They are particularly useful in whites, young people, people with heart failure, people with protein in their urine because of chronic kidney disease or diabetic kidney disease, and men who are impotent as a side effect of taking another drug.

Angiotensin II blockers lower blood pressure by a mechanism similar to--but more direct than--the one used by angiotensin converting enzyme inhibitors. Because of the way they work, angiotensin II blockers appear to cause fewer side effects.

Calcium antagonists cause blood vessels to dilate by a completely different mechanism. They are particularly useful in blacks, the elderly, and people with angina pectoris (chest pain), certain types of rapid heart rates, or migraine headaches. Recent reports suggest that people using short-acting calcium antagonists may have an increased risk of death from heart attacks, but there are no reports suggesting such effects for long-acting calcium antagonists.

Direct vasodilators dilate blood vessels by yet another mechanism. A drug of this class is almost never used alone; rather, it's added as a second drug when another drug alone doesn't lower blood pressure sufficiently.

Hypertensive emergencies--for example, malignant hypertension--require rapid lowering of the blood pressure. Several drugs can lower blood pressure quickly; most of them are given intravenously. These drugs include diazoxide, nitroprusside, nitroglycerin, and labetalol. Nifedipine, a calcium antagonist, is very fast acting and can be given orally; however, it can cause hypotension, so the patient must be monitored closely.

Secondary Hypertension Treatment

Treatment of secondary hypertension depends on the underlying cause of the high blood pressure. Treating kidney disease can sometimes normalize the blood pressure or at least lower it, so that drug therapy is more effective. A narrowed artery to the kidney may be dilated by inserting a balloon-tipped catheter and inflating the balloon. Or the narrowed part of the artery supplying the kidney can be bypassed; often such surgery cures the high blood pressure. Tumors that cause high blood pressure, such as pheochromocytoma, usually can be removed surgically.