Blood pressure is a measure of the force of blood inside an artery. If your blood pressure is higher than normal on two or more occasions after an initial screening, you may have high blood pressure (hypertension). A blood pressure 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) because the original devices that measured blood pressure used a column of mercury. 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."

High blood pressure is defined as a systolic blood pressure of 140 mm Hg or higher or a diastolic blood pressure of 90 mm Hg or higher. High blood pressure means that the heart must work harder to pump blood throughout the body. Uncontrolled high blood pressure increases the risk of stroke, heart failure, kidney failure, and heart attack. As blood pressure increases, the risk of it causing these problems also increases.

High blood pressure is often referred to as the "silent killer," because it usually has no obvious symptoms and most people cannot tell if their own blood pressure is high unless it is measured.

Home blood pressure monitors make it easy to measure your blood pressure at home. If you are concerned that you might have high blood pressure, or if your family has a history of high blood pressure, you may want to consider getting a home blood pressure monitor.

The two general types of blood pressure monitors commonly available are manual and automatic. (Automatic types may also be called electronic or digital).

Manual blood pressure monitors

Manual models are similar to those that your doctor or nurse might use to take your blood pressure. Called a sphygmomanometer, these devices usually include an arm cuff, a squeeze bulb for inflation, a stethoscope or microphone, and a mechanical gauge or column of mercury to measure the blood pressure. Manual blood pressure monitors require good eyesight and hearing to use them correctly. There are two basic styles of manual blood pressure devices.

• Mercury column blood pressure devices. A column of mercury rises and falls in a clear tube with the units of measure marked along the side. As the cuff pressure increases, the mercury rises. As the cuff pressure falls, so does the mercury column. A stethoscope is required to listen for the sound of blood flowing through the artery. Mercury column blood pressure monitors are the most accurate of the blood pressure devices, but they are bulky, easily broken, and may be difficult to read. It takes practice to learn to use them properly.
• Aneroid blood pressure devices. These display the blood pressure on a circular dial with a needle. As the pressure in the cuff rises, the needle moves clockwise on the dial. As the cuff pressure falls, the needle moves counterclockwise. Again, a stethoscope is required; some models have the stethoscope head permanently attached to the cuff. The aneroid devices are compact and inexpensive but somewhat difficult to use. Also, the dial gauges may need to be recalibrated from time to time to maintain their accuracy.

Automatic (also called electronic or digital) blood pressure monitors

Electronic battery-operated monitors use a microphone to detect blood pulsing in the artery instead of having to listen with a stethoscope. The cuff, which is attached to your wrist or upper arm, is connected to an electronic monitor that automatically inflates and deflates the cuff when you press the start button. First you place your wrist or upper arm inside the cuff. Then press the start button on the monitor and wait for a reading to display. The monitor records your pulse as well as your blood pressure.

The electronic devices are by far the easiest to use, but they are also the most expensive. Generally, the electronic models that use an arm cuff are more accurate than those that use a wrist cuff.

The type of blood pressure monitor typically found in supermarkets, pharmacies, and shopping malls is an electronic device.

Ambulatory blood pressure monitoring (ABPM)

Another method of measuring blood pressure, called ambulatory blood pressure monitoring (ABPM), may be ordered by your doctor to provide a more accurate picture of your blood pressure over time. ABPM may be done if a manual or an electronic method of measurement yields inconsistent results.

ABPM automatically records blood pressure over a period of a few hours to an entire day. The device generally consists of a cuff worn on one arm and a monitor worn around the waist. Your doctor's office will fit you with the monitor and provide instructions on its use.

Home Blood Pressure Monitoring
Results

The Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNCVI) provides recommended blood pressure measurements for adults over age 18.

JNCVI recommends regular blood pressure checks by a health professional based on a person's initial blood pressure reading.

A diagnosis of hypertension is based on the average of 2 or more blood pressure readings taken at each of 2 or more visits after an initial screening. The 1997 JNCVI defines three stages of high blood pressure (hypertension).

The blood pressure goal for people with diabetes is a systolic (upper) value of 130 mm Hg or lower and a diastolic (lower) value of 85 mm Hg or lower.

Generally, as long as you don't have symptoms such as lightheadedness or faintness, the lower your blood pressure the better. If your blood pressure is usually below 90/60 mm Hg and you feel well, don't worry. However, if your blood pressure normally runs higher than your most recent blood pressure reading, consult a health professional.