Blood pressure is a measure of the force of blood inside an artery. If the pressure of blood is higher than normal on two or more occasions, you may have high blood pressure (hypertension). The measurement is taken by temporarily stopping the flow of blood in an artery, usually by inflating a cuff around the upper arm, and then listening for the sound of the blood beginning to flow through the artery again as air is released from the cuff. As blood flows through the artery, it can be heard through a stethoscope placed on the skin over the artery inside the elbow.

Blood pressure is recorded as two measurements.

• The reading on the gauge when blood flow is first heard is called the systolic pressure. Systolic pressure represents the peak blood pressure that occurs when the heart contracts.
• The reading on the gauge when blood flow can no longer be heard is the diastolic pressure. Diastolic pressure represents the lowest blood pressure that occurs when the heart relaxes between beats.

These two pressures are expressed in millimeters of mercury (mm Hg). Systolic pressure, the higher of the two readings, is measured first. Diastolic pressure is the lower reading. These blood pressure measurements are recorded as systolic/diastolic. For example, if your systolic pressure is 120 mm Hg and your diastolic pressure is 80 mm Hg, your blood pressure is recorded as 120/80 and read as "120 over 80."

Home blood pressure monitoring provides a measurement of a person's blood pressure at different times and in different environments, such as at home and at work, throughout the day. It may be done to:

• Help establish the diagnosis of high blood pressure.
• Monitor the effects of medicine taken to lower blood pressure.
• Help people with high blood pressure to see the effects of medicines or lifestyle changes on their blood pressure. Home monitoring can help people feel more involved in and more in control of their own health care.
• Help diagnose low blood pressure that may be caused by irregular heart rhythms (arrhythmias), certain medicines, or other medical conditions.
• Monitor the blood pressure of people who are taking medicines, such as monoamine oxidase inhibitors (MAOIs), that can cause episodes of high pressure.

Blood pressure normally fluctuates from day to day and even from minute to minute depending on activity, posture, temperature, diet, medicines, and emotional and physical state.

Home blood pressure monitoring is most effective when the person also records in a diary his or her daily activities, such as the time when medicine is taken or when a stressful event occurs. This record of activities can help explain an unusual blood pressure reading and help the doctor adjust medicine dosages accurately.

Some people experience a significant rise in blood pressure only when they are in a doctor's office. This is called "white-coat hypertension," and it probably is caused by anxiety about the doctor visit. By monitoring blood pressure at home, these people can often find out whether their blood pressure readings generally are lower when they are not in the doctor's office. In some cases, ambulatory blood pressure monitoring (ABPM) also may be done to help diagnose white-coat hypertension.

You should not eat, use tobacco products, use medicines known to raise blood pressure (such as certain nasal decongestant sprays), or exercise (for at least 30 minutes) before taking your blood pressure.

Avoid taking your blood pressure if you are nervous or upset. Rest at least 15 minutes before taking a reading.

When you first obtain a blood pressure device, check its accuracy by comparing readings from it with readings obtained by a doctor or nurse taken in the doctor's office. Ask your doctor or nurse to observe your technique to make sure that you are using the device correctly and that it works right. It is a good idea to have your device checked every year.

The size and position of the blood pressure cuff can greatly affect the accuracy of blood pressure readings. If the cuff is too small or too large, the blood pressure results will be inaccurate. As a general rule, the inflatable part of the cuff needs to be at least as long as the widest measurement around your upper arm. Hospital and medical supply stores generally carry a variety of cuff sizes.

Take your blood pressure while you are seated in a comfortable, relaxed position. Try not to move or talk while you are measuring your blood pressure. Be aware that the blood pressure readings may be 10 to 20 mm Hg different between your right arm and your left arm. For this reason, you may want to use the same arm for every reading. Blood pressure readings also vary throughout the day. They usually are highest in the morning after you wake up and move around, decrease throughout the day, and are lowest in the evening.

Record your blood pressure reading. Your doctor may give you a form to use, or you can use this home blood pressure log(What is a PDF document?).

The instructions for using blood pressure monitors vary depending on the specific device you choose. Here are the basic principles.

Manual blood pressure monitors: Sit with your arm slightly bent and resting comfortably on a table so that your upper arm is on the same level as your heart. Expose your upper arm by rolling up your sleeve but not so tightly as to constrict blood flow. If you are not able to roll up your sleeve, remove your arm from the sleeve or take off your shirt. Wrap the blood pressure cuff snugly around your upper arm so that the lower edge of the cuff is about 1in. above the bend of your elbow. See an illustration of blood pressure cuff placement.

A large artery, the brachial artery, is located slightly above the inside of your elbow. You can check its location by feeling for a pulse in the artery with the fingers of your other hand. If you are using a stethoscope, place the earpieces in your ears and the bell of the stethoscope over the artery, just below the cuff. The stethoscope should not rub on the cuff or your clothing, since this may cause noises that can make your pulse hard to hear. If you are using a cuff with a built-in stethoscope bell, be sure the part of the cuff with the stethoscope is positioned just over the artery. The accuracy of a blood pressure recording depends on the correct positioning of the stethoscope over the artery. You may want to have another person help you take your blood pressure-someone who knows how to use a stethoscope properly.

Close the valve on the rubber inflating bulb. Squeeze the bulb rapidly with your opposite hand to inflate the cuff until the dial or column of mercury reads about 30 mm Hg higher than your usual systolic pressure. (If you don't know your usual pressure, inflate the cuff to 210 mm Hg.) The pressure in the cuff will stop all blood flow within the artery temporarily.

Now, open the pressure valve just slightly by twisting or pressing the valve on the bulb. The pressure should fall gradually at about 2 to 3 mm Hg per second. Some blood pressure devices have a valve that automatically controls the fall at this rate. As you watch the pressure slowly fall, note the level on the dial or mercury tube at which you first start to hear a pulsing or tapping sound through the stethoscope. The sound is caused by the blood starting to move through the closed artery. This is your systolic blood pressure.

Continue letting the air out slowly. The sounds will become muffled and finally will disappear. Note the pressure when the sounds completely disappear. Record this as your diastolic blood pressure. Finally, let out all the remaining air to relieve the pressure on your arm.

Electronic blood pressure monitors: For electronic models, press the on/off button on the electronic monitor and wait until the ready-to-measure "heart" symbol appears next to zero in the display window. Then press the start button. The cuff will inflate automatically to approximately 180 mm Hg (unless the monitor determines that you require a higher value). It then begins to deflate automatically, and the numbers on the screen will begin to drop. When the measurement is complete, the heart symbol stops flashing and your blood pressure and pulse readings are displayed alternately.

All blood pressure monitors: Repeat the same procedure two more times, for a total of three readings. Wait 5 to 10 minutes between recordings while the blood flows unimpeded in your arm. Record your systolic and diastolic pressures, the date and time, which arm you used (left or right), and your position (sitting, standing, lying). After you get used to taking your own blood pressure, you probably will need to take it only one or two times.

Inspect your blood pressure cuff frequently to see whether the rubber tubing, bulb, valves, and cuff are in good condition. Even a small hole or crack in the tubing can lead to inaccurate results.

You may feel some discomfort when the blood pressure cuff inflates, squeezing your arm.

If you have poor hearing or eyesight or limited manual dexterity, you may not be able to use a manual blood pressure monitor well enough to get accurate results. For people with these limitations, an electronic arm- or wrist-cuff model is a better choice.

Talk with your health professional

If you have questions about this information, take it with you when you visit your doctor. You may want to use a highlighter to mark areas or make notes in the margins of the pages where you have questions.

Organizations

National Heart, Lung, and Blood Institute (NHLBI)
P.O. Box 30105
Bethesda, MD  20824-0105
Phone:	(301) 592-8573
Fax:	(240) 629-3246
TDD:	(240) 629-3255
E-mail:	nhlbiinfo@nhlbi.nih.gov
Web Address:	www.nhlbi.nih.gov
The U.S. National Heart, Lung, and Blood Institute (NHLBI) information center offers information and publications about preventing and treating heart, lung, and blood diseases.
American Heart Association (AHA)
7272 Greenville Avenue
Dallas, TX  75231
Phone:	1-800-AHA-USA1 (1-800-242-8721)
Web Address:	www.americanheart.org
Call the American Heart Association (AHA) to find your nearest local or state AHA group. The AHA can provide brochures and information on support groups and community programs, including Mended Hearts, a nationwide organization whose members visit heart patients and provide information and support. AHA's Web site also has health information on various heart-related conditions.