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What Is High Blood Pressure?

Blood pressure is the force in the arteries when the heart beats (systolic pressure) and when the heart is at rest (diastolic pressure). It's measured in millimeters of mercury (mm Hg). High blood pressure (or hypertension) is defined in an adult as a blood pressure greater than or equal to 140 mm Hg systolic pressure or greater than or equal to 90 mm Hg diastolic pressure.
High blood pressure directly increases the risk of coronary heart disease (which leads to heart attack) and stroke, especially when it's present with other risk factors.

High blood pressure can occur in children or adults, but it's more common among people over age 35. It's particularly prevalent in African Americans, middle-aged and elderly people, obese people, heavy drinkers and women taking birth control pills. It may run in families, but many people with a strong family history of high blood pressure never have it. People with diabetes mellitus, gout or kidney disease are more likely to have high blood pressure, too.

American Heart Association recommended blood pressure levels

Blood Pressure Category Systolic
(mm Hg) Diastolic
(mm Hg)
Normal less than 120 and less than 80
Prehypertension 120–139 or 80–89

High
Stage 1 140–159 or 90–99
Stage 2 160 or higher or 100 or higher
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What Causes High Blood Pressure?

In 90 to 95 percent of high blood pressure cases, the cause is unknown. In fact, you can have high blood pressure for years without knowing it. That's why it's the “silent killer” — it creeps up on you. When the cause is unknown, you have what's called essential or primary hypertension. Factors that may lead to high blood pressure in the remaining 5–10 percent of cases, which are known as secondary hypertension, include:
Kidney abnormality
A structural abnormality of the aorta (large blood vessel leaving the heart) existing since birth
Narrowing of certain arteries
These problems can usually be corrected. For example, doctors can repair a narrowed artery that supplies blood to a kidney. Most of these problems can be ruled out by a careful history, a physical examination and a few tests. Special tests are sometimes needed, but you don't usually have to stay in the hospital.

How does high blood pressure develop?

Your heart pumps blood through the body's arteries. The large arteries that leave your heart taper into smaller arteries called arterioles. The arterioles then taper into smaller vessels called capillaries, which supply oxygen and nutrients to all the organs of your body. The blood then returns to your heart through the veins.
Certain nerve impulses cause your arteries to dilate (become larger) or contract (become smaller). If these vessels are wide open, blood can flow through easily. If they're narrow, it's harder for the blood to flow through them, and the pressure inside them increases. Then high blood pressure may occur. When this happens, your heart becomes strained and blood vessels may become damaged. Changes in the vessels that supply blood to your kidneys and brain may cause these organs to be affected.

Your heart, brain and kidneys can handle increased pressure for a long time. That's why you can live for years without any symptoms or ill effects. But that doesn't mean it's not hurting you. High blood pressure is a major risk factor for stroke, heart attack, heart failure and kidney failure.

What does high blood pressure do to your body?

High blood pressure adds to the workload of your heart and arteries. Your heart must pump harder, and the arteries carry blood that's moving under greater pressure. If high blood pressure continues for a long time, your heart and arteries may not work as well as they should. Other body organs may also be affected. There is increased risk of stroke, congestive heart failure, kidney failure and heart attack. When high blood pressure exists with obesity, smoking, high blood cholesterol or diabetes, the risk of heart attack or stroke increases several times.

What about low blood pressure?

Within certain limits, the lower your blood pressure reading is, the better. In most people, blood pressure isn't too low until it produces symptoms, such as lightheadedness or fainting. In certain disease states, it's possible for blood pressure to be too low. Examples include:

Certain nerve or endocrine disorders
Prolonged bed rest
Decreases in blood volume due to severe bleeding (hemorrhage) or dehydration
Blood pressure less than 120/80 mm Hg is generally considered ideal. Levels higher than this increase your risk for cardiovascular disease. If you have unusually low blood pressure, have it evaluated.

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How Do I Know If I Have High Blood Pressure?

High blood pressure usually has no symptoms. In fact, many people have this disease for years without knowing it. Having high blood pressure (hypertension) doesn't mean you're tense, nervous or hyperactive. You can be a calm, relaxed person and still have hypertension. The only way to find out if you have this disease is to have your blood pressure checked! A blood pressure test is quick and painless. It can be done in a doctor's office, hospital clinic, school, nurse's office, company clinic or at a health fair.
A single high reading doesn't mean you have high blood pressure, but it's a sign that you need to watch your blood pressure carefully. If your blood pressure is normal, get it checked at least every two years. If you have prehypertension, or if you have a family history of high blood pressure, you're at higher risk. Your doctor will tell you how often to have it checked.

How is blood pressure checked?
Blood pressure is measured using a medical instrument called a sphygmomanometer. A rubber cuff is wrapped around your upper arm and inflated. When the cuff is inflated, it compresses a large artery in your arm, momentarily stopping the blood flow.

Next, air in the cuff is released, and the person measuring the blood pressure listens with a stethoscope. When the blood starts to pulse through the artery, it makes a sound. Sounds continue to be heard until pressure in the artery exceeds the pressure in the cuff.

The person listens and watches the gauge, then records two measurements. Systolic pressure is the pressure of the blood flow when the heart beats (the pressure when the first sound is heard). Diastolic pressure is the pressure between heartbeats (the pressure when the last sound is heard). Blood pressure is measured in millimeters of mercury, which is abbreviated mm Hg.

Do blood pressure cuffs come in different sizes?
Yes. Children and adults with smaller or larger than average-sized arms may need special-sized cuffs. These are available in some pharmacies and from medical supply companies. They may also be ordered directly from companies that sell blood pressure cuffs. Ask your doctor or pharmacist for help.