HYPERTENSION


DEFINITION

Hypertension is the medical name for high blood pressure.

DESCRIPTION

The circulatory system is the network of organs and blood vessels through which blood travels in the body. Blood is pumped out of the heart into blood vessels known as arteries. After passing through the body, blood returns to the heart by way of blood vessels known as veins.

As blood flows through arteries and veins, it pushes on their walls. Blood pressure is defined as the force exerted by blood inside arteries.

Blood does not flow steadily through the circulatory system. At one moment, the heart muscle squeezes blood out of the heart into the arteries. At this point, the blood pressure is high because of the force exerted by the heart. At the next moment, the heart muscle relaxes to let fresh blood into the heart. At this point, the blood pressure is lower because of reduced force by the heart muscle.

Hypertension: Words to Know

Arteries:
Blood vessels that carry blood from the heart to organs and tissues of the body.
Arteriosclerosis:
Hardening and thickening of artery walls.
Diastolic blood pressure:
Blood pressure exerted by the heart when it is resting between beats.
Sphygmomanometer:
An instrument used to measure blood pressure.
Systolic blood pressure:
Blood pressure exerted by the heart when it contracts (beats).
Vasodilator:
Any drug that causes a blood vessel to relax.

The two stages of high and low blood pressure have special names. The highest pressure reached by blood in the arteries is called the systolic pressure. The lowest pressure reached by blood in the arteries is known as the diastolic pressure.

When a doctor or nurse takes a person's blood pressure, he or she records two readings: the systolic (highest) and the diastolic (lowest) pressure. For example, a patient's blood pressure might be recorded as 140/80, which is read as "140 over 80." That reading means that the patient's highest blood pressure is 140 and the lowest blood pressure is 80.

The numbers 140 and 80 are measured in units called "millimeters of mercury" or "mm Hg." This unit is commonly used by scientists to measure pressure.

The American Heart Association considers blood pressure less than 140 and greater than 90 to be normal for adults. A person whose diastolic pressure is less than 90 is said to have low blood pressure. Someone with a systolic pressure of more than 140 is said to have high blood pressure—or hypertension.

Hypertension is a serious problem because people with the condition have a higher risk for heart disease and other medical problems than people with normal blood pressure. If left untreated, hypertension can lead to a number of medical conditions, including:

  • Arteriosclerosis
  • Heart attack (see heart attack entry)
  • Stroke (see stroke entry)
  • Enlarged heart
  • Kidney damage

Arteriosclerosis is also called hardening of the arteries. The arteries are normally flexible. They expand and contract to adjust to the flow of blood through them. High blood pressure can cause artery walls to become thick and tough. The arteries themselves may become narrower. Blood cannot flow as easily through them.

When that happens, certain substances in the blood can begin to build up inside the arteries. These substances make the openings even narrower. Eventually, an artery may close completely. When that happens, blood can no longer flow through the circulatory system. A blocked artery can result in a heart attack or a stroke.

Hypertension can also damage the heart itself because the heart has to work harder to push blood through the circulatory system. It grows larger to keep up with this job. If the heart becomes too large, it may no longer be able to pump enough blood through the body. The heart may fail.

Kidneys can also be damaged by hypertension. The kidneys filter waste products from the blood. If blood vessels to the kidneys become clogged, fewer wastes are removed from the blood. The kidneys may fail and wastes may build up in the blood. About 25 percent of the people who are treated for failed kidneys have hypertension.

Blood pressure is measured using a sphygmomanometer. (© 1994 CMSP. Reproduced by permission of Custom Medical Stock Photo.)
Blood pressure is measured using a sphygmomanometer. (© 1994
CMSP
. Reproduced by permission of
Custom Medical Stock Photo
.)

CAUSES

High blood pressure can be caused by certain events in a person's life. For example, strenuous physical activity or stress can cause blood pressure to rise. However, high blood pressure is usually temporary in such cases. When the activity ceases or the stress goes away, the blood pressure returns to normal. This form of high blood pressure is not regarded as a form of hypertension.

True hypertension exists only when a person has high blood pressure readings on a number of different occasions. If a doctor suspects hypertension, he or she will take a number of blood pressure readings over a period of weeks. If those readings are consistently high, the patient may have hypertension.

The cause of hypertension in 90 to 95 percent of all cases is not known. One important factor may be heredity. People who have family members with hypertension are more likely to develop the condition than people whose family members have no hypertension. Hypertension with no known cause is called primary hypertension.

Hypertension can also be caused by a variety of medical conditions. For example, people with kidney disorders may develop hypertension. The kidneys regulate the balance of water and salt in the body. If the kidneys do not function normally, the amount of salt and water in the body may increase. This increase can cause high blood pressure.

Other conditions that can cause hypertension include blood vessel diseases, disorders of the thyroid or other glands, alcoholism (see alcoholism entry), pregnancy, and the use of certain prescription drugs. Hypertension caused by some other medical problem is known as secondary hypertension.

Certain factors are known to increase a person's risk for hypertension. These factors include:

  • Age over sixty
  • Male sex
  • Heredity
  • Sensitivity to table salt
  • Obesity (see obesity entry)
  • Inactive lifestyle
  • Heavy alcohol consumption
  • Use of oral contraceptives (birth control pills)

SYMPTOMS

Hypertension is a major health problem, especially because it has no symptoms. Many people have hypertension without knowing it. In the United States, about fifty million people age six and older have high blood pressure. Hypertension is more common in men than women and in people over the age of sixty-five than in younger persons.

DIAGNOSIS

Because hypertension does not produce symptoms it is important to have regular checkups. Taking a person's blood pressure is simple and painless. A doctor or nurse uses an instrument called a sphygmomanometer. A sphygmomanometer (pronounced SFIG-moh-muh-nahm-et-er) consists of a cloth-covered rubber cuff and a pressure valve. The cuff is wrapped around the patient's arm, and air is pumped into the cuff. As the air is slowly released, the doctor or nurse listens through a stethoscope to the sound of the blood rushing through the artery. He or she reads the pressure at which he or she hears distinctive heart sounds (the "lubb" and "dubb" made when a heart beats). These readings provide the patient's systolic and diastolic blood pressures.

MEASURING BLOOD PRESSURE

Blood exerts pressure. Anyone who has ever cut an artery knows that fact. When that happens, blood gushes out of the artery with surprising force. That fact was first discovered by the English physician William Harvey (1578–1657) in the 1600s.

No one actually tried to measure blood pressure, however, until nearly a century later. Then, the English clergyman and physiologist Stephen Hales devised the first blood pressure measuring device. He cut open the blood vessel in various animals and inserted a metal pipe into the vessel. He then connected the pipe to a long glass tube. Blood was pushed out of the vessel into the glass tube. The blood rose to different levels in the tube for different animals.

It took another century for physicians to find a way to take blood pressure without actually cutting into a blood vessel. In 1876, the German physician Samuel Siegried von Basch (1837–1905) invented the first sphygmo-manometer (pronounced SFIG-moh-muh-nahmet-er). That tongue-twisting name describes the type of blood pressure measuring device used today. It consists of a rubber tube placed around the patient's upper arm. Air is pumped into the tube. Pressure from the air briefly cuts off the flow of blood in the patient's arm.

As the air is released from the tube, the medical worker listens to the patient's arm through a stethoscope. As blood starts flowing in the arm again, the sound produced by systolic pressure can be heard. A few moments later, the sound produced by the diastolic pressure can be heard. The worker notes the amount of pressure observed in a gauge on the arm band at each sound. These two pressures make up the patient's blood pressure reading.

There is no single point at which a person is said to have hypertension. Instead, certain levels of the condition are set depending on the person's blood pressure. These levels are as follows:

  • Normal blood pressure: In the range 130/85
  • High normal: In the ranges 130–140/85–90
  • Mild hypertension: In the ranges 140–160/90–100
  • Moderate hypertension: In the ranges 160–180/100–110
  • Severe hypertension: In the ranges 180–210/110–120
  • Very severe hypertension: Higher than 210/120

Patients with higher-than-normal blood pressure may then be given other tests. These include:

  • Medical and family histories. These help a doctor find out if the patient has risk factors in his or her family. If hypertension is common in the family, the patient is likely to be at higher risk for the condition.
  • Physical examination. Sometimes other health problems may be discovered during a physical examination that explain the patient's high blood pressure.
  • Examination of the blood vessels in the eyes. High blood pressure may cause blood vessels in the eyes to become thick or narrow. Bleeding in the eyes may also be visible.
  • Chest X ray. This is used to check for an enlarged heart, other heart disorders, and lung disease.
  • Electrocardiograph (ECG). This test measures the electrical activity of the heart. It can determine whether the heart muscle is functioning normally.
  • Blood and urine tests. These help determine the general health of the patient.

TREATMENT

There is no cure for primary hypertension, but blood pressure can almost always be reduced with the correct treatment. The goal of this treatment is to prevent the complications of hypertension.

In cases of secondary hypertension, one approach is to treat the medical condition that causes hypertension. Efforts may be made at the same time to reduce the patient's blood pressure.

A program designed to reduce blood pressure usually has three parts: changes in diet, a plan of regular exercise, and antihypertensive medications. Some changes in lifestyle that can reduce blood pressure include the following:

The effects of hypertension on the heart and kidney. Hypertension has caused atrophy and scarring of the kidney (left) and left ventricular hypertrophy in the sectioned heart (right). (Photograph by Dr. E. Walker. Reproduced by permission of Photo Researchers, Inc.)
The effects of hypertension on the heart and kidney. Hypertension has caused atrophy and scarring of the kidney (left) and left ventricular hypertrophy in the sectioned heart (right). (Photograph by
Dr. E. Walker
. Reproduced by permission of
Photo Researchers, Inc.
)

  • Reducing salt intake
  • Reducing fat intake
  • Losing weight
  • Getting regular exercise
  • Quitting smoking
  • Reducing alcohol consumption
  • Learning how to manage stress

For patients with mild or moderate hypertension, these steps may be enough to bring their blood pressure into the normal or high normal range. For patients with more serious hypertension, medications may be prescribed. A variety of medications are available for the treatment of hypertension. They fall into the following categories:

  • Diuretics help the kidneys eliminate excess salt and water. The loss of fluid from the kidneys causes arteries to expand and blood pressure to become lower.
  • Beta-blockers cause the heart to beat more slowly and with less force.
  • Calcium channel blockers help relax muscle cells, reducing the force with which they pump blood.
  • Angiotensin converting enzyme (ACE) inhibitors are chemicals that prevent blood vessels from tightening up. As a result, the pressure exerted by blood in the blood vessels is reduced.
  • Alpha-blockers act on the nervous system, causing arteries to expand and reduce the pressure exerted by the heart on blood flow.
  • Vasodilators are chemicals that act directly on arteries, causing them to relax (dilate) so that blood can move more easily through them.
  • Nervous system antagonists and agonists act on the nerves that control the size of arteries. They cause arteries to open and allow blood to flow through them more easily.

PROGNOSIS

There is no cure for hypertension, but it can be controlled by changes in one's lifestyle and the use of medications. The major goal of treatment is to avoid the most serious complications of hypertension, such as heart disease and strokes.

PREVENTION

Some risk factors of hypertension cannot be eliminated. For example, a person may inherit a tendency for the disorder. But many risk factors can be prevented or reduced. Some of the most important changes a person can make in his or her life to prevent hypertension include the following:

  • Reduce salt intake.
  • Reduce fat intake.
  • Lose weight.
  • Get regular exercise.
  • Quit smoking.
  • Reduce alcohol consumption.
  • Learn how to manage stress.

FOR MORE INFORMATION

Books

Murray, Michael T. Heart Disease and High Blood Pressure: How You Can Benefit from Diet, Vitamins, Minerals, Herbs, Exercise, and Other Natural Methods. Rocklin, CA: Prima Publishing, 1997.

Pickering, Thomas. Good News About High Blood Pressure: Everything You Need to Know to Take Control of Hypertension—And Your Life. New York: Simon and Schuster, 1996.

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

Wood, Stephen, and George Wood. Conquering High Blood Pressure: The Complete Guide to Managing Hypertension. New York: Insight Books, 1997.

Organizations

American Heart Association. 7272 Greenview Ave., 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.

Web sites

"Ask NOAH About: Heart Disease and Stroke." NOAH: New York Online Access to Health. [Online] http://www.noah.cuny.edu/heart_disease/heartdisease.html#H. (accessed on October 25, 1999).