Blood Pressure Facts

Posted: Nov. 1, 2005

Blood pressure is the force of blood against the walls of arteries. Blood pressure rises and falls during the day. When blood pressure stays elevated over time, it is called high blood pressure.

The medical term for high blood pressure is hypertension. High blood pressure is dangerous because it makes the heart work too hard and contributes to atherosclerosis (hardening of the arteries). It increases the risk of heart disease and stroke, which are the first- and third-leading causes of death among Americans. High blood pressure also can result in other conditions, such as congestive heart failure, kidney disease, and blindness.

A blood pressure level of 140/90 mmHg or higher is considered high. About two-thirds of people over age 65 have high blood pressure.

If your blood pressure is between 120/80 mmHg and 139/89 mmHg, then you have prehypertension. This means that you don't have high blood pressure now but are likely to develop it in the future. You can take steps to prevent high blood pressure by adopting a healthy lifestyle.

What is systolic blood pressure?
Systolic pressure is the force of blood in the arteries as the heart beats. It is shown as the top number in a blood pressure reading. High blood pressure is 140 and higher for systolic pressure.

Diastolic pressure, shown as the bottom number in a blood pressure reading, does not need to be high for you to have high blood pressure. The condition is called "isolated systolic hypertension," or ISH.

ISH is the most common form of high blood pressure for older Americans. For most Americans, systolic blood pressure increases with age, while diastolic increases until about age 55 and then declines.

You may have ISH and feel fine. As with other types of high blood pressure, ISH often causes no symptoms. To find out if you have ISH — or any type of high blood pressure — see your doctor and have a blood pressure test. The test is quick and painless.

Any form of high blood pressure is dangerous if not properly treated. Both numbers in a blood pressure test are important, but, for some, the systolic is especially meaningful. That's because, for those persons middle aged and older, systolic pressure gives a better diagnosis of high blood pressure.

What is diastolic blood pressure?
Diastolic pressure is the force of blood in the arteries as the heart relaxes between beats. It's shown as the bottom number in a blood pressure reading.

The diastolic blood pressure remains, especially for younger people, an important hypertension number. The higher the diastolic blood pressure, the greater the risk for heart attacks, strokes and kidney failure.

As people become older, the diastolic pressure will begin to decrease and the systolic blood pressure begins to rise and becomes more important.

Your physician will use both the systolic and the diastolic blood pressure to determine your blood pressure category and appropriate prevention and treatment activities.

Source: National Heart, Lung and Blood Institute

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