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Blood pressure is the force of the blood pushing against the artery walls. The force is generated with each heartbeat as blood is pumped from the heart into the blood vessels. The size and elasticity of the artery walls also affect blood pressure. Each time the heart beats (contracts and relaxes), pressure is created inside the arteries.
The pressure is greatest when blood is pumped out of the heart into the arteries or systole. When the heart relaxes between beats (blood is not moving out of the heart), the pressure falls in the arteries or diastole.
Two numbers are recorded when measuring blood pressure. The top number, or systolic pressure, refers to the pressure inside the artery when the heart contracts and pumps blood through the body. The bottom number, or diastolic pressure, refers to the pressure inside the artery when the heart is at rest and is filling with blood. Both the systolic and diastolic pressures are recorded as "mm Hg" (millimeters of mercury). This recording represents how high the mercury column is raised by the pressure of the blood.
Blood pressure is measured with a blood pressure cuff and stethoscope by a nurse or other healthcare provider. A person cannot take his or her own blood pressure unless an electronic blood pressure monitoring device is used.
Levels of high blood pressure
The National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health (NIH) has determined two levels of high blood pressure for adults:
140 mm Hg to 159 mm Hg systolic pressure—higher number
90 mm Hg to 99 mm Hg diastolic pressure—lower number
160 mm Hg or higher systolic pressure
100 mm Hg or higher diastolic pressure
What is chronic hypertension?
High blood pressure, or hypertension, directly increases the risk of coronary heart disease (heart attack) and stroke (brain attack). With high blood pressure, the arteries may have an increased resistance against the flow of blood, causing the heart to pump harder to circulate the blood. Usually, high blood pressure has no signs or symptoms. However, you can know if your blood pressure is high by having it checked regularly by your health care provider.
How does blood pressure increase?
The following conditions are known to contribute to high blood pressure:
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