- The Body's Control of Blood Pressure
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High Blood Pressure
High blood pressure (hypertension) is persistently high pressure in the arteries.
Often no cause for high blood pressure can be identified, but sometimes it occurs as a result of an underlying disorder of the kidneys or a hormonal disorder.
Obesity, a sedentary lifestyle, stress, smoking, and excessive amounts of alcohol or sodium (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.
In most people, high blood pressure causes no symptoms.
Doctors make the diagnosis after measuring blood pressure on two or more occasions.
People are advised to lose weight, stop smoking, and decrease the amounts of sodium and fats in their diet.
Antihypertensive drugs are given.
To many people, the word hypertension suggests excessive tension, nervousness, or stress. In medical terms, hypertension refers to persistently high blood pressure, regardless of the cause. Because it usually does not cause symptoms for many years—until a vital organ is damaged—high blood pressure 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.
About 75 million Americans are estimated to have high blood pressure. High blood pressure occurs more often in blacks—in 41% of black adults compared with 28% of whites and 28% of Mexican Americans. It also occurs with high frequency in people whose ancestors are from China, Japan, and other East Asian or Pacific areas (such as Koreans,Thais, Polynesians, Micronesians, Filipinos, and Maori). The consequences of high blood pressure are worse for blacks and those of Asian descent. High blood pressure occurs more often in older people—in about two thirds of people aged 65 or older, compared with only about one fourth of people aged 20 to 74. People who have normal blood pressure at age 55 have a 90% risk of developing high blood pressure at some point in their life. 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 81% of people with high blood pressure have been diagnosed. Of people with a diagnosis of high blood pressure, about 73% receive treatment, and of the people receiving treatment, about 51% have adequately controlled blood pressure.
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 risk of complications—even within the normal blood pressure range—so these limits are somewhat arbitrary. In most young people with high blood pressure, both systolic and diastolic pressures are high. In contrast, many older people with high blood pressure 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.
A hypertensive urgency is blood pressure that is more than 180/120 mm Hg but has not yet caused any organ damage that is apparent to people or their doctors. A hypertensive urgency usually does not cause symptoms.
A hypertensive emergency is a particularly severe form of high blood pressure. Blood pressure is at least 180/120 mm Hg, and there is evidence of progressive damage in one or more vital organs (typically the brain, heart, and kidneys), often accompanied by a variety of symptoms. Hypertensive emergencies are uncommon, but they are 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. If untreated, a hypertensive emergency can be fatal.
The body has many mechanisms to control blood pressure. The body can change the
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.
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 sodium and water, thereby increasing blood volume. The body controls the movement of sodium in and out of cells, to prevent an excess of sodium inside cells. Excessive amounts of sodium inside cells can cause the body to become overly sensitive to stimulation by the sympathetic division.
The kidneys also respond directly to changes in blood pressure. If blood pressure increases, the kidneys increase their excretion of sodium and water, so that blood volume decreases and blood pressure returns to normal. Conversely, if blood pressure decreases, the kidneys decrease their excretion of sodium 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, by triggering the sympathetic division of the autonomic nervous system, and by triggering the release of two other hormones, aldosterone and vasopressin (also called antidiuretic hormone), which cause the kidneys to increase the retention of sodium and water. The kidneys normally produce substances that cause arterioles within the kidney to dilate. This helps balance the effects of hormones that cause constriction of arterioles.
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 sodium and water—which tend to reduce blood pressure.
High blood pressure may be
High blood pressure with no known cause is called primary (formerly called essential) hypertension. Between 85% and 95% 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. Other changes may contribute to increases in blood pressure, including accumulation of excessive amounts of sodium inside cells and decreased production of substances that dilate arterioles.
High blood pressure with a known cause is called secondary hypertension. Between 5% and 15% of people with high blood pressure have secondary hypertension. In many of these people, high blood pressure results from a kidney disorder. Many kidney disorders can cause high blood pressure because the kidneys are important in controlling blood pressure. For example, damage to the kidneys from inflammation or other disorders may impair their ability to remove enough sodium and water from the body, increasing blood volume and blood pressure. Other kidney disorders that cause high blood pressure include renal artery stenosis (narrowing of the artery supplying one of the kidneys), which may be due to atherosclerosis, injury, or other disorders.
In a few people, 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 hyperaldosteronism (overproduction of aldosterone, often by a noncancerous tumor in one of the adrenal glands), Cushing syndrome (a disorder characterized by high levels of cortisol), hyperthyroidism (an overactive thyroid gland), 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 Arteriosclerosis).
Obesity, a sedentary lifestyle, stress, smoking, and excessive amounts of alcohol or sodium 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. Additionally, sleep apnea can contribute to or aggravate existing high blood pressure.
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.
In most people, high blood pressure causes no symptoms, despite the coincidental occurrence of certain symptoms that are widely, but erroneously, attributed to 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 can cause symptoms because it can damage the brain, eyes, heart, and kidneys. Symptoms include headache, fatigue, nausea, vomiting, shortness of breath, and restlessness. 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 is called hypertensive encephalopathy.
Severe high blood pressure increases the workload of the heart and may cause chest pain and/or shortness of breath. Sometimes very high blood pressure causes the large artery that carries blood from the heart (the aorta) to tear, causing chest or abdominal pain. People who have such symptoms have hypertensive emergencies and, as such, require emergency treatment.
If high blood pressure is due to a pheochromocytoma, 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.
Long-standing high blood pressure can damage the heart and blood vessels and increase the risk of
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 normal. 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 or heart failure.
High blood pressure causes thickening of the walls of blood vessels and also makes them more likely to develop hardening of the arteries (atherosclerosis). People with thickened blood vessel walls and atherosclerosis are at higher risk of stroke, heart attack, and kidney failure.
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.
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.
In some people, blood pressure may also be measured as normal when it is high. This is called masked hypertension. Masked hypertension affects up to 10% of people who have high blood pressure. Recognizing this type of high blood pressure may be impossible unless blood presssure is measured at home or if a complication (for example, heart failure) is suspected to have been caused by high blood pressure.
After high blood pressure has been diagnosed, its effects on key organs, especially the blood vessels, heart, brain, eyes, and kidneys, are usually evaluated. Doctors also look for the cause of high blood pressure. The number and type of tests that are done 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 the hematocrit level [the portion of total blood volume made up of red blood cells], potassium and sodium levels, and tests of kidney function), 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 in each eye is examined with an ophthalmoscope (see What Is an Ophthalmoscope?). 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 (hypertensive retinopathy), 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) is usually done to detect changes in the heart—particularly thickening (hypertrophy) of the heart muscle or heart enlargement. If enlargement is suspected, the person may undergo echocardiography.
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 as well as a chest x-ray. Blood and urine tests are done to measure the levels of 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.
Classifying Blood Pressure in Adults
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. Alternative measures are usually tried before any drugs are prescribed. However, drug therapy is usually started at the same time as alternative measures in all people with blood pressure at or above 160/100 mm Hg and in people with blood pressure at or above 140/90 mm Hg who also have diabetes, a kidney disorder, evidence of damage to a vital organ, or other risk factors for coronary artery disease.
The goal for antihypertensive therapy is to decrease blood pressure to below 140/90 mm Hg in most people. However, if a person is 60 or older and decreasing their blood pressure to less than 140/90 mmHg causes problems, such as fainting, light headedness, memory loss or dizziness, , blood pressure should be decreased to less than 150/90 mm Hg. These problems are usually seen in people with very low diastolic BPs <70 when starting therapy. For some people, for example, those at high risk of heart disease, a lower systolic goal of 125 to 130 may be appropriate.
Overweight people with high blood pressure are advised to lose weight. Losing as few as 10 pounds (4.5 kilograms) can lower blood pressure. For people who are obese or who have diabetes or high cholesterol levels, changes in diet (one rich in fruits, vegetables, and low-fat dairy products, with reduced saturated and total fat content) 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 [about 1 liter] of beer, 8 ounces [about 240 milliliters] of wine, or 2 ounces [about 60 milliliters] of 100-proof whiskey or other liquor) in men and 1 drink in women. Daily sodium intake should be reduced to less than 2½ grams, or sodium chloride (salt) intake, to 6 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 Benefits of Exercise).
Doctors often recommend that people with high blood pressure monitor their own blood pressure at home. Self-monitoring probably helps motivate people to follow a doctor's recommendations regarding treatment.
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 the person and doctor communicate well and collaborate on the treatment program.
Different types of antihypertensives reduce blood pressure by different mechanisms, so 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, and if it is ineffective, they stop it and prescribe another type. For people with blood pressure at or above 160/100 mm Hg, usually two drugs are started at the same time. In choosing an antihypertensive, doctors consider such factors as
A majority of people (more than 74%) ultimately require two or more drugs to reach their blood pressure goal.
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-like diuretic such as chlorthalidone or indapamide may be the first drug given to treat high blood pressure. Diuretics cause blood vessels to dilate. Diuretics also help the kidneys eliminate sodium and water, decreasing fluid volume throughout the body and thus lowering blood pressure. Because thiazide-like 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-like diuretic. Usually, potassium-sparing diuretics are not used alone because they do not control blood pressure as well as thiazide-like 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 disease.
Adrenergic blockersinclude 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, and people who have had a heart attack. They are also useful for 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. Alpha-blockers are no longer used as the main therapy because they do not decrease the risk of death. Peripherally acting adrenergic blockers are usually only used if a third or fourth type of drug is needed to control blood pressure.
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, these inhibitors block the action of angiotensin-converting enzyme, which converts angiotensin I to angiotensin II (see Figure: Regulating Blood Pressure: The Renin-Angiotensin-Aldosterone System). 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 receptor blockers (ARBs) 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 receptor blockers may cause fewer side effects.
Calcium channel blockers cause arterioles to dilate by a completely different mechanism. They are particularly useful for blacks and older people. Calcium channel blockers are also useful for people who have angina pectoris, certain types of rapid heart rate, or migraine headaches. Calcium channel blockers may be short-acting or long-acting. Short-acting calcium channel blockers are not used to treat high blood pressure. 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.
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). 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.
If people still have high blood pressure despite taking three different drugs, doctors in Europe sometimes insert a catheter into the artery to each kidney. The catheter produces radio waves that destroy the sympathetic nerves along the renal arteries. The first studies on this procedure appeared to show that it lowered blood pressure. However, a recent, much larger and more complete study did not show that the procedure worked. This treatment is not available in the US.
Another treatment for high blood pressure is called pacemaker therapy. An electrode is implanted in the neck, where it stimulates certain nerve endings that help regulate blood pressure. This treatment, although effective, is not yet available in the US, but it is available in Europe and Canada.
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.