High Blood Pressure
High blood pressure (hypertension) is abnormally high pressure in the arteries.
To many people, the word hypertension suggests excessive tension, nervousness, or stress. In medical terms, hypertension refers to high blood pressure, regardless of the cause. Because it usually does not cause symptoms for many years--until a vital organ is damaged--it has been called "the silent killer." Uncontrolled high blood pressure increases the risk of problems such as stroke, aneurysm, heart failure, heart attack, and kidney damage.
More than 50 million Americans are estimated to have high blood pressure. High blood pressure occurs more often in blacks--in 32% of black adults compared with 23% of whites and 23% of Mexican Americans. Also, the consequences of high blood pressure are worse for blacks. High blood pressure occurs more often in older people--in about three fourths of women and almost two thirds of men aged 75 or older, compared with only about one fourth of people aged 20 to 74. High blood pressure is twice as common among people who are obese as among those who are not.
In the United States, only an estimated two of three people with high blood pressure have been diagnosed. Of these people, about 75% receive drug treatment, and of these, about 45% receive adequate treatment.
When blood pressure is checked, two values are recorded. The higher value reflects the highest pressure in the arteries, which is reached when the heart contracts (during systole). The lower value reflects the lowest pressure in the arteries, which is reached just before the heart begins to contract again (during diastole). Blood pressure is written as systolic pressure/diastolic pressure--for example, 120/80 mm Hg (millimeters of mercury). This reading is referred to as "120 over 80."
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. However, the higher the blood pressure, the greater the risks--even within the normal blood pressure range--so these limits are somewhat arbitrary. The limits were established because people with blood pressure above these levels are at increasing risk of complications. In most people with high blood pressure, both systolic and diastolic pressures are high. The exception is older people who commonly have high systolic pressure (140 mm Hg or more) with normal or low diastolic pressure (less than 90 mm Hg). This disorder is called isolated systolic hypertension.
Blood pressure that is more than 180/110 mm Hg and does not produce any symptoms is a hypertensive urgency.
Malignant hypertension, a particularly severe form of high blood pressure, is a hypertensive emergency. Blood pressure is at least 210/120 mm Hg. It occurs in only about 1 of 200 people who have high blood pressure. However, it is several times more common among blacks than among whites, among men than among women, and among people in lower socioeconomic groups than among those in higher socioeconomic groups. Unlike a hypertensive urgency, malignant hypertension may produce a variety of severe symptoms. If untreated, malignant hypertension usually leads to death in 3 to 6 months.
The Body's Control of Blood Pressure
The body has many mechanisms that control blood pressure: The body can change the amount of blood the heart pumps, the diameter of arteries, and the volume of blood in the bloodstream. To increase blood pressure, the heart can pump more blood by pumping more forcefully or more rapidly. Small arteries (arterioles) can narrow (constrict), forcing the blood from each heartbeat through a narrower space than normal. Because the space in the arteries is narrower, the same amount of blood passing through them increases the blood pressure. Veins can constrict to reduce their capacity to hold blood, forcing more blood into the arteries. As a result, blood pressure increases. Fluid can be added to the bloodstream to increase blood volume and thus increase blood pressure. Conversely, to decrease blood pressure, the heart can pump less forcefully or rapidly, arterioles and veins can widen (dilate), and fluid can be removed from the bloodstream.
These mechanisms are controlled by the sympathetic division of the autonomic nervous system (the part of the nervous system that regulates internal body processes requiring no conscious effort) and by the kidneys. The sympathetic division uses several means to temporarily increase blood pressure during the fight-or-flight response (the body's physical reaction to a threat). The sympathetic division stimulates the adrenal glands to release the hormones epinephrine (adrenaline) and norepinephrine (noradrenaline). These hormones stimulate the heart to beat faster and more forcefully, most arterioles to constrict, and some arterioles to dilate. The arterioles that dilate are those in areas where an increased blood supply is needed (such as in skeletal muscle--the muscles controlled by conscious effort). The sympathetic division also stimulates the kidneys to decrease their excretion of salt and water, thereby increasing blood volume.
The kidneys also respond directly to changes in blood pressure. If blood pressure increases, the kidneys increase their excretion of salt and water, so that blood volume decreases and blood pressure returns to normal. Conversely, if blood pressure decreases, the kidneys decrease their excretion of salt and water, so that blood volume increases and blood pressure returns to normal. The kidneys can increase blood pressure by secreting the enzyme renin, which eventually results in the production of the hormone angiotensin II. Angiotensin II helps increase blood pressure by causing the arterioles to constrict and by triggering the release of another hormone, aldosterone, which causes the kidneys to increase the retention of salt and water.
 See the figure Regulating Blood Pressure: The Renin-Angiotensin-Aldosterone System.
Normally, whenever a change (for example, increased activity or a strong emotion) causes a transient increase in blood pressure, one of the body's compensatory mechanisms is triggered to counteract the change and keep blood pressure at normal levels. For example, an increase in the amount of blood pumped out by the heart--which tends to increase blood pressure--causes dilation of blood vessels and an increase in the kidneys' excretion of salt and water--which tend to reduce blood pressure.
 See the sidebar Ups and Downs of Blood Pressure.
Causes
High blood pressure with no known cause is called primary or essential hypertension. Between 85% and 90% of people with high blood pressure have primary hypertension. Several changes in the heart and blood vessels probably combine to increase blood pressure. For instance, the amount of blood pumped per minute (cardiac output) may be increased, and the resistance to blood flow may be increased because blood vessels are constricted. Blood volume may be increased also. The reasons for such changes are not fully understood but appear to involve an inherited abnormality affecting the constriction of arterioles, which help control blood pressure.
High blood pressure with a known cause is called secondary hypertension. Between 10% and 15% of people with high blood pressure have secondary hypertension. Many kidney disorders can cause high blood pressure, because the kidneys are important in controlling blood pressure. For example, damage to the kidneys may impair their ability to remove enough salt and water from the body, increasing blood volume and blood pressure. In 5 to 10% of people with high blood pressure, the cause is a kidney disorder. Such disorders include renal artery stenosis (narrowing of the artery supplying one of the kidneys), kidney inflammation, and injury.
In 1 to 2%, secondary hypertension is caused by another disorder, such as a hormonal disorder, or by the use of certain drugs, such as birth control pills (oral contraceptives). Hormonal disorders that cause high blood pressure include Cushing's syndrome (a disorder characterized by high levels of cortisol); hyperthyroidism (an overactive thyroid gland); hyperaldosteronism (overproduction of aldosterone, often by a tumor in one of the adrenal glands); and, rarely, a pheochromocytoma (a tumor that is located in an adrenal gland and that produces the hormones epinephrine and norepinephrine).
Arteriosclerosis interferes with the body's control of blood pressure, increasing the risk of high blood pressure. Arteriosclerosis makes arteries stiff, preventing the dilation that would otherwise return blood pressure to normal (see Section 3, Chapter 32).
Obesity, a sedentary lifestyle, stress, smoking, and excessive amounts of alcohol or salt in the diet all can play a role in the development of high blood pressure in people who have an inherited tendency to develop it. Stress tends to cause blood pressure to increase temporarily, but blood pressure usually returns to normal once the stress is over. An example is "white coat hypertension," in which the stress of visiting a doctor's office causes blood pressure to increase enough to be diagnosed as high blood pressure in someone who has normal blood pressure at other times. In susceptible people, these brief increases in blood pressure are thought to cause damage that eventually results in permanent high blood pressure, even when no stress is present. This theory has not been proved.
See the sidebar Some Causes of Secondary Hypertension.
Symptoms
In most people, high blood pressure causes no symptoms, despite the coincidental occurrence of certain symptoms that are widely, but erroneously, associated with high blood pressure: headaches, nosebleeds, dizziness, a flushed face, and fatigue. People with high blood pressure may have these symptoms, but the symptoms occur just as frequently in people with normal blood pressure.
Severe or long-standing high blood pressure that is untreated (especially malignant hypertension) can produce symptoms because it can damage the brain, eyes, heart, and kidneys. Symptoms include headache, fatigue, nausea, vomiting, shortness of breath, restlessness, and blurred vision. Occasionally, severe high blood pressure causes the brain to swell, resulting in nausea, vomiting, worsening headache, drowsiness, confusion, seizures, sleepiness, and even coma. This condition, called hypertensive encephalopathy, requires emergency treatment.
If high blood pressure is due to a pheochromocytoma (an adrenal gland tumor), symptoms may include severe headache, anxiety, an awareness of a rapid or irregular heart rate (palpitations), excessive perspiration, tremor, and paleness. These symptoms result from high levels of the hormones epinephrine and norepinephrine, which are secreted by the pheochromocytoma.
When pressure in the arteries is increased above 140/90 mm Hg, the heart enlarges and the heart's walls thicken because the heart has to work harder to pump blood. The thickened walls are stiffer than they normally are. Consequently, the heart's chambers do not expand normally and are harder to fill with blood, further increasing the heart's workload. These changes in the heart may result in abnormal heart rhythms (see Section 3, Chapter 27) and heart failure (see Section 3, Chapter 25).
Diagnosis
Blood pressure is measured after a person sits or lies down for 5 minutes. It should be measured again after the person stands for a few minutes, especially if the person is older or has diabetes. A reading of 140/90 mm Hg or more is considered high, but a diagnosis cannot be based on a single high reading. Sometimes, even several high readings are not enough to make the diagnosis--because for example, the readings may vary too much. If a person has an initial high reading, blood pressure is measured again during the same visit and then measured twice on at least two other days to make sure that the high blood pressure persists.
 See the figure Measuring Blood Pressure.
If there is still doubt, a 24-hour blood pressure monitor may be used. It is a portable battery-operated device, worn on the hip, connected to a blood pressure cuff, worn on the arm. This monitor repeatedly records blood pressure throughout the day and night over a 24-hour or 48-hour period. The readings determine not only whether high blood pressure is present but also how severe it is.
In people with very stiff arteries (most commonly, in older people), blood pressure may be measured as high when it is not. This phenomenon is called pseudohypertension. It occurs when the artery in the arm is too stiff to be compressed by the blood pressure cuff, and as a result, blood pressure cannot be measured accurately.
After high blood pressure has been diagnosed, its effects on key organs, especially the blood vessels, heart, brain, and kidneys, are usually evaluated. Doctors also look for the cause of high blood pressure. The number and type of tests that are performed to look for organ damage and to determine the cause of high blood pressure vary from person to person. In general, routine evaluation for all people with high blood pressure involves a medical history, a physical examination, electrocardiography (ECG), blood tests (including a complete blood cell count), and urine tests.
The physical examination includes checking the area of the abdomen over the kidneys for tenderness and placing a stethoscope over the abdomen to listen for a bruit (the sound caused by blood rushing through a narrowed artery) in the artery supplying each kidney.
The retina (the light-sensitive membrane on the inner surface of the back of the eye) is examined with an ophthalmoscope (see Section 20, Chapter 225). The retina is the only place doctors can directly view the effects of high blood pressure on arterioles. The assumption is that the changes in the arterioles of the retina are similar to changes in arterioles and other blood vessels elsewhere in the body, such as in the kidneys. By determining the degree of damage to the retina (retinopathy (see Section 20, Chapter 234)), doctors can classify the severity of high blood pressure.
A stethoscope is used to detect heart sounds. An abnormal heart sound, called the fourth heart sound, is one of the earliest changes in the heart caused by high blood pressure. This sound develops because the left atrium of the heart has to contract harder to fill the enlarged, stiff left ventricle, which pumps blood to all of the body except the lungs.
Electrocardiography (ECG) (see Section 3, Chapter 21) can detect changes in the heart--particularly enlargement. However, in the early stages, such changes are best detected by echocardiography (see Section 3, Chapter 21).
Kidney damage can be detected by urine and blood tests. Urine tests can detect early evidence of kidney damage. The presence of blood cells and albumin (the most abundant protein in blood) in the urine may indicate such damage. Symptoms of kidney damage (such as lethargy, poor appetite, and fatigue) do not usually develop until 70 to 80% of kidney function is lost.
The higher the blood pressure and the younger the person, the more extensive the search for a cause is likely to be, even though a cause is identified in less than 10% of people. A more extensive evaluation may include x-ray, ultrasonography, and radionuclide imaging of the kidneys and their blood supply; a chest x-ray; and blood and urine tests to detect certain hormones, such as epinephrine, aldosterone, and cortisol.
The cause may be suggested by abnormal results of a physical examination or by the symptoms. For example, a bruit in the artery to a kidney may suggest renal artery stenosis (narrowing of the artery supplying a kidney). Various combinations of symptoms may suggest high levels of the hormones epinephrine and norepinephrine, produced by a pheochromocytoma. The presence of a pheochromocytoma is confirmed when the breakdown products of these hormones are detected in the urine. 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 Section 13, Chapter 164).
 See the table Classifying Blood Pressure in Adults.
Treatment
Primary hypertension cannot be cured, but it can be controlled to prevent complications. Because high blood pressure itself has no symptoms, doctors try to avoid treatments that cause side effects or interfere with a person's lifestyle. Before any drugs are prescribed, alternative measures are usually tried.
Overweight people with high blood pressure are advised to lose weight. Losing as few as 10 pounds can lower blood pressure. For people who are obese or who have diabetes or high cholesterol levels, changes in diet are important for reducing the risk of heart and blood vessel disease. Smokers should stop smoking.
Reducing the intake of alcohol and sodium (while maintaining an adequate intake of calcium, magnesium, and potassium) may make drug therapy for high blood pressure unnecessary. Daily alcohol intake should be reduced to no more than 2 drinks (a daily total of 24 ounces of beer, 8 ounces of wine, or 2 ounces of 100-proof whiskey or other liquor). Daily sodium intake should be reduced to less than 2 grams, or sodium chloride intake, to 5 grams.
Moderate aerobic exercise is helpful. People with primary hypertension do not have to restrict their physical activity as long as their blood pressure is controlled. Regular exercise helps reduce blood pressure and weight and improves the functioning of the heart and overall health (see Section 1, Chapter 6).
Doctors often recommend that people with high blood pressure monitor their blood pressure at home. Monitoring their own blood pressure probably helps motivate people to follow a doctor's recommendations regarding treatment.
Drug Therapy: Drugs that are used in the treatment of high blood pressure are called antihypertensives. With the wide variety of antihypertensives available, high blood pressure can be controlled in almost anyone, but treatment has to be tailored to the individual. Treatment is most effective when patient and doctor communicate well and collaborate on the treatment program.
The blood pressure goals for antihypertensive therapy vary depending on what other disorders are present. For most people, lowering diastolic blood pressure to 70 mm Hg is safe. For people with coronary artery disease or angina, diastolic blood pressure should not go below 80 mm Hg. For people with diabetes, the target is below 130/80 mm Hg. For older people, the target is below 140/90 mm Hg.
Different types of antihypertensives reduce blood pressure by different mechanisms; therefore, many different treatment strategies are possible. For some people, doctors use a stepped approach to drug therapy: They start with one type of antihypertensive and add others as necessary. For other people, doctors find a sequential approach is preferable: They prescribe one antihypertensive; if it is ineffective, they discontinue it and prescribe another type. In choosing an antihypertensive, doctors consider such factors as the person's age, sex, and race; the severity of high blood pressure; the presence of other conditions, such as diabetes or high blood cholesterol levels; potential side effects, which vary from drug to drug; and the costs of the drugs and of tests needed to check for certain side effects.
Most people tolerate their prescribed antihypertensive drugs without problems. But any antihypertensive drug can cause side effects. So if side effects develop, a person should tell the doctor, who can adjust the dose or substitute another drug. Usually, an antihypertensive drug must be taken indefinitely to control blood pressure.
A thiazide diuretic is often the first drug given to treat high blood pressure. Diuretics cause blood vessels to dilate. Diuretics also help the kidneys eliminate salt and water, decreasing fluid volume throughout the body and thus lowering blood pressure. Because thiazide diuretics cause potassium to be excreted in the urine, potassium supplements or a diuretic that does not cause potassium loss or that causes potassium levels to increase (a potassium-sparing diuretic) sometimes must be taken with a thiazide diuretic. Usually, potassium-sparing diuretics are not used alone because they do not control blood pressure as well as thiazide diuretics do; however, the potassium-sparing diuretic spironolactone is sometimes used alone. Diuretics are particularly useful for blacks, older people, obese people, and people with heart failure or chronic kidney failure.
Adrenergic blockers include alpha-blockers, beta-blockers, alpha-beta blockers, and peripherally acting adrenergic blockers. These drugs block the effects of the sympathetic division, the part of the nervous system that can rapidly respond to stress by increasing blood pressure. The most commonly used adrenergic blockers, the beta-blockers, are particularly useful for whites, young people, people who have had a heart attack, and people who have a rapid heart rate, angina pectoris (chest pain due to inadequate blood supply to the heart muscle), or migraine headaches. The risk of side effects is higher for older people.
Centrally acting alpha-agonists lower blood pressure through a mechanism that somewhat resembles that of adrenergic blockers. By stimulating certain receptors in the brain stem, these agonists inhibit the effects of the sympathetic division of the nervous system. These drugs are rarely used now.
Angiotensin-converting enzyme (ACE) inhibitors lower blood pressure in part by dilating arterioles. They dilate arterioles by preventing the formation of angiotensin II, which causes arterioles to constrict; specifically, they block the action of angiotensin-converting enzyme, which converts angiotensin I to angiotensin II (see Section 3, Chapter 22). These drugs are particularly useful for people with coronary artery disease or heart failure, whites, young people, people with protein in their urine because of chronic kidney disease or diabetic kidney disease, and men who develop sexual dysfunction as a side effect of another antihypertensive drug.
Angiotensin II blockers lower blood pressure by a mechanism similar to the one used by angiotensin-converting enzyme inhibitors: They directly block the action of angiotensin II, which causes arterioles to constrict. Because the mechanism is more direct, angiotensin II blockers may cause fewer side effects.
Calcium channel blockers cause arterioles to dilate by a completely different mechanism. They are particularly useful for blacks; older people; and people who have angina pectoris, certain types of rapid heart rate, or migraine headaches. Calcium channel blockers may be short-acting or long-acting. Reports suggest that people using short-acting calcium channel blockers may have an increased risk of death due to heart attack, but no reports suggest such effects for long-acting calcium channel blockers.
Direct vasodilators dilate blood vessels by another mechanism. A drug of this type is almost never used alone; rather, it is added as a second drug when another drug alone does not lower blood pressure sufficiently.
 See the drug table Antihypertensive Drugs.
Treatment of Secondary Hypertension
The cause of the high blood pressure is treated if possible. Treating kidney disease can sometimes return blood pressure to normal or at least lower it, so that antihypertensive therapy is more effective. A narrowed artery to the kidney may be dilated by inserting a balloon-tipped catheter and inflating the balloon (angioplasty (see Section 3, Chapter 33)). Or the narrowed part of the artery supplying the kidney can be bypassed; often such surgery cures high blood pressure. Tumors that cause high blood pressure, such as a pheochromocytoma, usually can be removed surgically (see Section 13, Chapter 164).
Treatment of Hypertensive Urgencies and Emergencies
Hypertensive urgencies are treated with clonidine, an adrenergic blocker, given by mouth. The calcium channel blocker nifedipine, given under the tongue (sublingually), has been used but is less safe.
In hypertensive emergencies, such as malignant hypertension and hypertensive encephalopathy, blood pressure must be lowered rapidly. Most drugs used to rapidly lower blood pressure, such as nitroprusside or labetalol, are given intravenously. If an aneurysm is suspected, labetalol is preferred.
Prognosis
Untreated high blood pressure increases a person's risk of developing heart disease (such as heart failure, heart attack, or sudden cardiac death), kidney failure, or stroke at an early age. High blood pressure is the most important risk factor for stroke. It is also one of the three most important risk factors for heart attack that a person can modify (the other two are smoking and high cholesterol levels in the blood). Treatment that lowers high blood pressure greatly decreases the risk of stroke and heart failure. Such treatment may also decrease the risk of a heart attack, although not as dramatically. Without treatment, fewer than 5% of people with malignant hypertension survive for a year.
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