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What is Blood Pressure?
Blood is
carried from the heart to all parts of your body in vessels called arteries.
Blood pressure is the force of the blood pushing against the walls of the
arteries. Each time the heart beats (about 60-70 times a minute at rest), it
pumps out blood into the arteries. Your blood pressure is at its highest when
the heart beats, pumping the blood. This is called systolic pressure. When the
heart is at rest, between beats, your blood pressure falls. This is the
diastolic pressure.
Blood pressure is always given as these two numbers, the systolic and diastolic
pressures. Both are important. Usually they are written one above or before the
other, such as 120/80 mmHg. The top number is the systolic and the bottom the
diastolic. When the two measurements are written down, the systolic pressure is
the first or top number, and the diastolic pressure is the second or bottom
number (for example, 120/80). If your blood pressure is 120/80, you say that it
is "120 over 80."
Blood pressure changes during the day. It is lowest as you sleep and rises when
you get up. It also can rise when you are excited, nervous, or active.
Still, for most of your waking hours, your blood pressure stays pretty much the
same when you are sitting or standing still. That level should be lower than
120/80. When the level stays high, 140/90 or higher, you have high blood
pressure. With high blood pressure, the heart works harder, your arteries take
a beating, and your chances of a stroke, heart attack, and kidney problems are
greater.
What causes it?
In many people with high blood pressure, a single specific cause is not known.
This is called essential or primary high blood pressure. Research is continuing
to find causes.
In some people, high blood pressure is the result of another medical problem or
medication. When the cause is known, this is called secondary high blood
pressure.
This section ©
National Heart, Lung, and Blood Institute
What is high blood pressure?
A blood pressure of 140/90 or higher is considered high blood pressure. Both
numbers are important. If one or both numbers are usually high, you have high
blood pressure. If you are being treated for high blood pressure, you still
have high blood pressure even if you have repeated readings in the normal
range.
There are two levels of high blood pressure: Stage 1 and Stage 2 (see the chart
below).
Categories for Blood Pressure Levels in Adults*
(In mmHg, millimeters of mercury)
| Category |
Systolic
(Top number) |
Diastolic
(Bottom number) |
| Normal
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Less than 120 |
Less than 80 |
| Prehypertension |
120-139 |
80-89 |
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| High Blood Pressure |
Systolic |
Diastolic |
| Stage 1 |
140-159 |
90-99 |
| Stage 2 |
160 or higher |
100 or higher |
* For adults 18 and older who:
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Are not on medicine for high blood pressure
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Are not having a short-term serious illness
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Do not have other conditions such as diabetes and kidney disease
Note: When systolic and diastolic blood pressures fall into different
categories, the higher category should be used to classify blood pressure
level. For example, 160/80 would be stage 2 high blood pressure.
There is an exception to the above definition of high blood pressure. A blood
pressure of 130/80 or higher is considered high blood pressure in persons with
diabetes and chronic kidney disease.
Hypertension & Women
Symptoms of High Blood Pressure
Headaches & High Blood Pressure
Measuring High Blood Pressure
Stress & High Blood Pressure
Miscellaneous
Related Diseases
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