What is high blood pressure?

Think of your heart as a pump. Every time your heart beats, it pumps blood through the blood vessels in your body. The pressure of the blood against the inside walls of these blood vessels is called "blood pressure." When this pressure is higher than it should be, it is called "high blood pressure." When your blood pressure is too high for a long period of time, your blood vessels get thicker and lose their elasticity, making them smaller and harder. This makes it more difficult for your heart to pump blood through these vessels to your body. This creates a great strain on your heart. Untreated high blood pressure can persist without symptoms for many years, damaging your heart, brain, kidneys and other organs.

A doctor or nurse measures your blood pressure with a sphygmomanometer, a pressure gauge and a rubber cuff that wraps around your upper arm. The cuff inflates, tightening around your arm, then deflates. This produces a blood pressure reading on the gauge. This reading consists of two numbers, such as 120/80. The first (systolic) number is the pressure of the blood pushing against the wall of the blood vessel when the heart is beating. The second (diastolic) number is the pressure when your heart is at rest (between beats).

What until recently was considered normal blood pressure has changed. Normal blood pressure is defined as systolic pressure less than 120 and diastolic pressure less than 80. New guidelines define a class of blood pressure called prehypertension. People with a systolic pressure of 120-139 or a diastolic pressure of 80-89 are prehypertensive. People with prehypertension have an increased risk of developing hypertension and cardiovascular disease. If you have prehypertension, you should take measures to reduce your blood pressure. Be more active, lose some weight, and eat a healthy diet. For more suggestions about things you can do to lower your blood pressure, see
How is high blood pressure treated or prevented with lifestyle changes?

Blood Pressure Classification Systolic Blood Pressure Diastolic Blood Pressure Lifestyle Modification
Normal less than 120 and less than 80 Encourage
Prehypertension 120 - 139 or 80 - 89 Yes
Hypertension 140 or greater 90 or greater Yes

High blood pressure is medically defined as a systolic pressure at rest that averages 140 or more, a diastolic pressure at rest that averages 90 or more, or both. In most cases of high blood pressure, both the systolic and the diastolic pressures are too high. In many cases, the younger you are, the lower your blood pressure should be. Your physician usually will not decide you have high blood pressure with a single reading. Several above-normal readings are required to make this determination. Remember that your blood pressure can change throughout the day in response to smoking, drinking alcohol, stress, excitement, or heavy exercise. There are many things to consider before deciding if your pressure is too high.

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Written by: Janice C. May, M.P.A.
Reviewed by: Jeffrey G. Schultze, M.D.
Last Modified: Thursday September 26, 2019 9:09 AM