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What is blood pressure and how is it measured?

Most often, you hear blood pressure described as two numbers, called the systolic (top) and diastolic (bottom) readings. These readings are often recorded as a fraction, with systolic over diastolic. For example: 120/70. Blood pressure is measured as millimeters of mercury (mm Hg), but few people directly refer to these units.

The systolic reading measures the force created when the heart contracts and pushes blood through the aorta and into the circulatory system.

The diastolic reading measures the force exerted by the walls of the arteries when the heart relaxes between contractions.

Blood pressure measurements vary during the course of the day, depending on your activity level and even your emotional state. Blood pressure is lower during periods of sleep and usually rises in response to exercise.

How do I know if I have high blood pressure?

In most instances, high blood pressure (hypertension) has no warning signs. So the best way to detect it is to have your blood pressure checked regularly.

High blood pressure is usually diagnosed after more than one high reading is recorded. High blood pressure is classified as follows:

Category

• Normal: Systolic less than 120 and diastolic less than 80
• Prehypertension: Systolic 120 to 139 or diastolic 80 to 89
• Hypertension Stage 1: Systolic 140 to 159 or diastolic 90 to 99
• Hypertension Stage 2: Systolic greater than 160 or diastolic greater than 100

What causes high blood pressure and how prevalent is it?

In most cases, high blood pressure has no known cause. This type of high blood pressure is known as essential hypertension. Less often, high blood pressure can result from other illnesses like kidney or adrenal gland problems. That type of high blood pressure is called secondary hypertension.

High blood pressure increases the risk for heart disease and stroke. These are leading causes of death in this country. About one in three American adults has high blood pressure. Among African Americans, two in five have high blood pressure, and high blood pressure affects one in five Hispanics and Native Americans, and one in six Asians, according to the Centers for Disease Control and Prevention.

Sources: Centers for Disease Control and Prevention. High blood pressure fact sheet. Accessed May 29, 2008. National Heart, Lung and Blood Institute. Seventh report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure. Accessed May 29, 2008.

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