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Hypertension

Definition

Hypertension is high blood pressure. Blood pressure is the force of blood pushing against the walls of arteries as it flows through them.

Description

As blood flows through arteries it pushes against the inside of the artery walls. The more pressure the blood exerts on the artery walls, the higher the blood pressure will be. The size of small arteries also affects the blood pressure. When the muscular walls of arteries are relaxed, or dilated, the pressure of the blood flowing through them is lower than when the artery walls narrow, or constrict.

Blood pressure is highest when the heart beats to pump blood out into the arteries. Between beats, when the heart relaxes to refill with blood, the pressure drops to its lowest point. The blood pressure peak, when the heart pumps, is called systolic pressure. The blood pressure trough, when the heart is filling, is called diastolic pressure. When blood pressure is measured, the systolic pressure is stated first and the diastolic pressure second. Blood pressure is measured in millimeters of mercury (mm Hg). For example, if a person's systolic pressure is 120 and diastolic pressure is 80, it is written as 120/80 mm Hg. The American Heart Association considers systolic blood pressure less than 140 and diastolic blood pressure less than 90 normal for adults.

Hypertension is a significant public health problem. Since it has no symptoms, many people are unaware that they have hypertension. In the United States, about 50 million people age six and older have high blood pressure. Hypertension occurs more frequently in men than women and in people over the age of 65 than in younger persons. More than half of all Americans over the age of 65 have hypertension. It is also more prevalent in African Americans than in white Americans.

Hypertension is serious because it places patients at higher risk for heart disease and other medical problems than people with normal blood pressure. Serious complications may be prevented by encouraging patients to check their blood pressure regularly, and by treating hypertension once it is diagnosed.

If left untreated, hypertension can lead to the following medical conditions:

• arteriosclerosis, also called atherosclerosis
• myocardial infarction (heart attack)
• cerebrovascular accident (stroke)
• left ventricular hypertrophy leading to congestive heart failure
• chronic renal failure (kidney damage)

Arteriosclerosis is hardening of the arteries. The walls of arteries have a layer of muscle and elastic tissue that makes them flexible and able to dilate and constrict as needed. High blood pressure can cause artery walls to thicken and harden. When artery walls thicken, the lumen (hollow center of the blood vessel) narrows. Cholesterol and fatty plaques are more likely to build up on the walls of damaged arteries, further narrowing them. Blood clots can also become trapped in narrowed arteries, blocking the flow of blood.

Arteries narrowed by arteriosclerosis may restrict blood flow to organs and other tissues. Reduced or blocked blood flow to the heart can cause myocardial infarction (a heart attack). Similarly, if an artery to the brain is blocked, a stroke can result.

Hypertension forces the heart muscle to work harder to pump blood through the body. The extra workload can cause the heart muscle to thicken and stretch. When the heart becomes too enlarged, it cannot pump enough blood. If hypertension continues and is not treated, the heart may fail.

The kidneys remove waste from the blood. Chronic hypertension thickens the arteries to the kidneys and impairs renal (kidney) function. As the condition progresses, the kidneys eventually fail and hemodialysis or kidney transplant will be needed. About 25% of people who receive hemodialysis have kidney failure caused by hypertension.

Causes and symptoms

Blood pressure varies in response to physical and emotional stimuli. Many different actions or situations normally raise blood pressure. Physical activity can temporarily raise blood pressure. Emotionally stressful situations also can increase blood pressure. When the stress subsides or disappears, blood pressure usually returns to normal. These temporary increases in blood pressure are not considered hypertension. A diagnosis of hypertension is made only when a patient has multiple high blood pressure readings over a period of time.

For 90-95% of patients with hypertension, the cause is unknown. Hypertension without a known cause is called primary or essential hypertension.

When a patient has hypertension caused by another medical condition, it is considered secondary hypertension. Secondary hypertension may be caused by a variety of disorders. Many patients with kidney diseases have secondary hypertension because the kidneys regulate the balance of salt and water in the body. If the kidneys cannot rid the body of excess salt and water, blood pressure rises. Chronic pyelonephritis (kidney infections), renal artery stenosis, and glomerulonephritis are examples of kidney diseases that may cause secondary hypertension.

Cushing's syndrome and tumors of the pituitary and adrenal glands often increase levels of the adrenal gland hormones—cortisol, adrenaline and aldosterone—which can cause hypertension. Other conditions that may cause secondary hypertension are vasculitis, thyroid disorders, some prescription and over-the-counter medications, alcoholism, and pregnancy.

Although the cause of most hypertension is not known, some individuals have greater risk of developing hypertension. Many lifestyle-associated risk factors may be modified or eliminated to reduce the chance of developing hypertension or to reduce blood pressure in patients with hypertension.

Risk factors for hypertension include:

• Age; persons over 60 are at greater risk.
• Gender; males are more often affected.
• Race; African Americans are more often affected.
• Heredity; persons with a family history of hypertension are at greater risk.
• Salt sensitivity.
• Obesity.
• Inactive, sedentary lifestyle.
• Heavy alcohol consumption.
• Use of oral contraceptives.

Some risk factors for getting hypertension can be changed, while others cannot. Age, gender, heredity, and race are risk factors that cannot be influenced. An individual with any of these non-modifiable risk factors should avoid or eliminate other, controllable risk factors to reduce the chance of developing hypertension.

Diagnosis

Since hypertension is asymptomatic (does not cause symptoms), it is important for patients to have regular blood pressure checks. Conventionally, blood pressure is measured with an instrument called a sphygmomanometer. When the cuff is inflated, an artery in the arm is squeezed to momentarily stop the flow of blood. Then, the air is let out of the cuff while a stethoscope placed over the artery is used to detect the sound of the blood spurting back through the artery. This first sound is the systolic pressure, the pressure when the heart beats. The last sound heard as the air is being released is the diastolic blood pressure.

Normal blood pressure is defined by a range of values. Systolic blood pressure lower than 140 mm Hg and diastolic blood pressure lower than 90 mm Hg is considered normal. A number of factors such as pain, stress, or anxiety can cause a temporary increase in blood pressure. For this reason, hypertension is not diagnosed on the basis of a single elevated blood pressure reading. If a blood pressure reading is 140/90 or higher, the physician or mid-level practitioner (physician assistant or nurse practitioner) will have the patient return for another blood pressure check or instruct the patient to check their blood pressure at home using an inexpensive, automated device. Diagnosis of hypertension usually is made based on two or more readings after the first visit.

Isolated systolic hypertension is common among older adults and is diagnosed when diastolic pressure is normal or low, but the systolic is elevated, e.g., 170/70 mm Hg. This condition usually co-exists with atherosclerosis (hardening of the arteries).

Blood pressure measurements are classified in stages, according to severity:

• Normal blood pressure: less than 130/85 mm Hg.
• High normal: 130-139/85-89 mm Hg.
• Mild hypertension: 140-159/90-99 mm Hg.
• Moderate hypertension: 160-179/100-109 mm Hg.
• Severe hypertension: 180-209/110-119 mm Hg.
• Very severe hypertension: 210/120 mm Hg or higher.

A typical physical examination to evaluate hypertension includes:

• medical and family history
• physical examination
• ophthalmoscopy: examination of the blood vessels in the eye
• chest x ray
• electrocardiogram (ECG)
• blood and urine tests, including electrolytes, creatinine, protein, calcium, random blood sugar, thyroid stimulating hormone (TSH), routine and microscopic urinalysis, and urine for culture and sensitivity

The medical and family history help the physician or mid-level practitioner to determine if the patient has any conditions or disorders that might contribute to or cause the hypertension. A family history of hypertension may suggest a genetic predisposition for hypertension.

The physical exam may include several blood pressure readings at different times and in different postural positions. The physician or mid-level practitioner uses a stethoscope to listen to sounds made by the heart and for abdominal bruits (blood flowing through partially obstructed arteries). The pulse, reflexes, and height and weight are checked and recorded. Internal organs are palpated to determine if they are enlarged.

Since hypertension may cause damage to the blood vessels in the eyes, the eyes may be examined with an ophthalmoscope to detect thickening, narrowing, or hemorrhages in the blood vessels.

A chest x ray can detect an enlarged heart, other vascular abnormalities, or pulmonary (lung) disease.

An electrocardiogram (ECG) measures the electrical activity of the heart. It can detect if the heart muscle is enlarged and if there is damage to the heart muscle from blocked arteries.

Urine and blood tests may be performed to determine whether the hypertension has already caused kidney damage and to detect the presence of disorders that might cause secondary hypertension.

Treatment

There is no cure for primary hypertension, but blood pressure can almost always be lowered with appropriate treatment. The goal of treatment is to lower blood pressure to levels that will prevent heart disease and other complications of hypertension. In secondary hypertension, the underlying disease responsible for the hypertension is treated along with the hypertension itself. Successful treatment of the underlying disorder may entirely eliminate the secondary hypertension.

Treatment to lower blood pressure usually includes changes in diet, regular exercise, and antihypertensive medications. Patients with mild or moderate hypertension who do not have damage to the heart or kidneys may initially be treated with lifestyle changes.

Lifestyle changes that may reduce blood pressure by about 5-10 mm Hg include:

• Reduce salt intake.
• Reduce fat intake.
• Lose weight.
• Get regular exercise.
• Quit smoking.
• Reduce alcohol consumption.
• Manage stress.

Patients whose blood pressure remains higher than 139/89 will most likely be advised to take antihypertensive medication. Numerous drugs have been developed to treat hypertension. The choice of medication will depend on the stage of hypertension, side effects, other medical conditions the patient may have, and other medicines the patient is taking.

Patients with mild or moderate hypertension are initially treated with monotherapy, a single antihypertensive medicine. If treatment with a single medicine fails to lower blood pressure sufficiently, a different medicine may be tried or another medicine may be added to the first. Patients with more severe hypertension may initially be given a combination of drugs to control hypertension. Combining antihypertensive medicines with different mechanisms of action often controls blood pressure with smaller doses of each drug than would be needed for monotherapy. It is not uncommon to treat a patient with hypertension with three or more different anti-hypertensive drugs.

Antihypertensive medicines include several classes of drugs:

• diuretics
• beta-adrenergic blockers
• calcium channel blockers
• angiotensin converting enzyme inhibitors (ACE inhibitors)
• angiotensin receptor antagonists
• alpha-adrenergic blockers
• alpha-beta adrenergic blockers
• vasodilators
• selective alpha-adrenergic antagonists
• centrally acting adrenergic agonists

Diuretics, such as hydrochlorthiazide, help the kidneys eliminate excess salt and water, thereby reducing intravascular volume. This results in dilatation of arteries and lower blood pressure.

Beta-adrenergic blockers, such as metoprolol or atenolol, lower blood pressure by blocking the effects of adrenaline thereby slowing the heart rate and reducing the force of the heart's contraction. They are used with caution in patients with heart failure, asthma, diabetes, or peripheral arterial disease.

Calcium channel blockers, such as diltiazem, nifedipine, or verapamil, block the entry of calcium into muscle cells in artery walls. Muscle cells need calcium to contract, so reducing their calcium keeps them more relaxed and the arteries dilated. This action lowers blood pressure.

ACE inhibitors, such as lisinopril or captopril, block the effects of angiotensin converting enzyme, thus reducing the production of aldosterone. They are also used for treating congestive heart failure or diabetic nephropathy. ACE inhibitors may be used together with diuretics.

Angiotensin receptor antagonists, such as losartan or candesartin, block angiotensin II receptors in many tissues, allowing blood vessels to dilate and the kidneys to eliminate excess sodium and water.

Alpha-adrenergic blockers, such as phentolamine, act on the nervous system to dilate arteries and reduce the force of the heart's contractions.

Alpha-beta andrenergic blockers, such as labetlol, combine the actions of alpha and beta blockers.

Vasodilators, such as hydralazine, act directly on arteries to relax their walls so blood can move more easily through them. They lower blood pressure rapidly and are injected in hypertensive emergencies when patients have dangerously high blood pressure.

Selective alpha-adrenergic antagonists, such as prazosin or terazosin, act on the nervous system to relax arteries and reduce the force of the heart's contractions. They usually are prescribed together with a diuretic. Selective alpha-adrenergic antagonists may cause slowed mental function and lethargy.

Centrally acting adrenergic agonists, such as clonidine or methyldopa, also act on the nervous system to relax arteries and slow the heart rate. They are usually used with other antihypertensive medicines.

Health care team roles

The diagnosis of hypertension may be made by a primary care physician, mid-level practitioner, or nurse. Often, hypertension is identified during a routine medical visit or during screening at events such as health fairs. Laboratory technologists perform needed blood work and urinalysis; radiologic technologists conduct any ordered x rays, ECG, or imaging studies. Patients returning for follow-up blood pressure checks may be seen by nurses and may receive nutrition education from dieticians.

Patient education

Nurses, health educators, dieticians, physicians, mid-level practitioners, and other health professionals are involved in educating the community-at-large about the risks associated with untreated hypertension. Screening programs to detect hypertension also aim to identify individuals with hypertension and encourage them to seek treatment.

Since the condition is asymptomatic, many patients mistakenly believe that they can safely stop treating their hypertension. Health professionals should not only emphasize the importance of adherence, but also should educate patients about the long-term health risks and consequences of untreated hypertension.

Prognosis

There is no known cure for hypertension. However, it can be effectively controlled with proper treatment. Therapy with a combination of lifestyle changes and antihypertensive medicines usually can maintain blood pressure at levels that will not cause damage to the heart or other organs. The key to avoiding serious complications of hypertension is to detect and treat it before damage occurs. Because antihypertensive medicines control blood pressure, but do not cure it, patients must continue taking the medications to maintain reduced blood pressure levels and avoid complications.

Prevention

Prevention of hypertension centers on avoiding or eliminating known risk factors. Even persons at risk because of age, race, or gender or those who have an inherited risk can lower their chance of developing hypertension.

The risk of developing hypertension can be reduced by making the same changes recommended for treating hypertension:

• Reduce salt intake.
• Reduce fat intake.
• Lose weight.
• Get regular exercise.
• Quit smoking.
• Reduce alcohol consumption.
• Manage stress.

KEY TERMS

Arteries—Blood vessels that carry blood to organs and other tissues of the body.

Arteriosclerosis (atherosclerosis)—Hardening and thickening of artery walls.

Cushing's syndrome—A disorder in which too much of the adrenal hormone, cortisol, is produced; it may be caused by a pituitary or adrenal gland tumor.

Diastolic blood pressure—Blood pressure when the heart is resting between beats.

Hypertension—High blood pressure.

Renal artery stenosis—Disorder in which the arteries that supply blood to the kidneys constrict.

Sphygmomanometer—An instrument used to measure blood pressure.

Systolic blood pressure—Blood pressure when the heart contracts (beats).

Vasodilator—Any drug that relaxes blood vessel walls.

Ventricle—One of the two lower chambers of the heart.

Resources

BOOKS

Ahya, Shubhada N., Kellie Flood, and Subramanian Paranjothi. The Washington Manual of Medical Therapeutics, 30th ed. Philadelphia: Lippincott Williams & Wilkins, 2001, pp. 76-85.

Bellenir, Karen, and Peter D. Dresser, eds. Cardiovascular Diseases and Disorders Sourcebook. Detroit: Omnigraphics, 1995.

Texas Heart Institute. Heart Owner's Handbook. New York: John Wiley and Sons, 1996.

PERIODICALS

"Pulmonary Hypertension." American Family Physician (May 1, 2001).

Woods, Anne Dabrow. "Managing Hypertension." Nursing Library (March 1999).

ORGANIZATIONS

American Heart Association. 7272 Greenview Avenue, Dallas, TX 75231-4596. (800) AHS-USA1. 〈http://www.amhrt.org/〉.

National Heart, Lung, and Blood Institute. Information Center. PO Box 30105, Bethesda, MD 20824-0105. (301) 251-1222.

Texas Heart Institute. Heart Information Service, PO Box 20345, Houston, TX 77225-0345. (800) 292-2221.