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.
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 healthcare provider.
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
The NHLBI defines prehypertension as:
120 mm Hg - 139 mm Hg systolic pressure
80 mm Hg - 89 mm Hg diastolic pressure
The NHLBI guidelines define normal blood pressure as follows:
Less than 120 mm Hg systolic pressure
Less than 80 mm Hg diastolic pressure
These numbers should be used as a guide only. A single elevated blood pressure measurement is not necessarily an indication of a problem. Your physician will want to see multiple blood pressure measurements over several days or weeks before making a diagnosis of hypertension (high blood pressure) and initiating treatment. A person who normally runs a lower-than-usual blood pressure may be considered hypertensive with lower blood pressure measurements than 140/90.
Nearly one-third of all Americans have high blood pressure, but it is particularly prevalent in:
persons with diabetes mellitus, gout, or kidney disease.
African-Americans (particularly those who live in the southeastern United States).
persons in their early to middle adult years; men in this age group have higher blood pressure more often than women in this age group.
persons in their middle to later adult years; women in this age group have higher blood pressure more often than men in this age group (more women have high blood pressure after menopause than men of the same age).
middle-aged and elderly people - more than half of all Americans age 60 and older have high blood pressure.
persons whose parents or grandparents have/had high blood pressure.
heavy drinkers of alcohol.
women who are taking oral contraceptives.
The following may contribute to an increase in blood pressure:
excessive sodium intake
a lack of exercise and physical activity
Many people can control high blood pressure by:
choosing foods that are low in sodium (salt).
choosing foods low in calories and fat.
choosing foods high in starch and fiber.
maintaining a healthy weight, or losing weight if overweight.
limiting serving sizes.
increasing physical activity.
reducing or omitting alcoholic beverages.
However, other people must take daily medication to control hypertension. People with hypertension should routinely have their blood pressure checked and be under the care of a physician.