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What Is Blood Pressure?

Blood pressure is the force of blood against the walls of arteries. Blood pressure is recorded as two numbers the systolic pressure (as the heart beats) over the diastolic pressure (as the heart relaxes between beats). The measurement is written one above or before the other, with the systolic number on top and the diastolic number on the bottom. For example, a blood pressure measurement of 120/80 mmHg (millimeters of mercury) is expressed verbally as "120 over 80."

Categories for Blood Pressure Levels in Adults (in mmHg, or millimeters of mercury):

Category Systolic
(top number)
  Diastolic
(bottom number)
Normal Less than 120 And Less than 80
Prehypertension 120139 Or 8089
High blood pressure      
Stage 1 140159 Or 9099
Stage 1 160 or higher Or 100 or higher

In about 10 percent of patients, high blood pressure, also known as hypertension, can be traced to specific causes: heredity, kidney abnormalities, adrenal gland tumors, diabetes, chronic kidney disease, hormone abnormalities, use of birth control pills, pregnancy or a congenital narrowing of the aorta. This is called secondary hypertension. In the other 90 percent of patients, the cause is unknown and is referred to essential hypertension.

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