What do the blood pressure numbers mean?

Blood pressure measurements contain two numbers—the systolic (top) number and the diastolic (bottom) number. The systolic number is a measurement of the pressure when the heart pumps blood out to the body. The diastolic number measures the pressure in the arteries between heart beats, while the heart is filling up with blood.

Blood pressure is recorded as systolic pressure over diastolic pressure. Systolic pressure is created during the contraction of the heart, while diastolic pressure is created during relaxation. A normal blood pressure is less than 120 systolic and less than 80 diastolic, or 120/80.

Blood pressure is typically expressed as two numbers, one over the other, and is measured in millimeters of mercury (noted as mm Hg). The first number is the systolic blood pressure, the pressure used when the heart beats. The second number, diastolic blood pressure, is the pressure that exists in the arteries between heartbeats.Depending on your activities, your blood pressure may increase or decrease throughout the day. If you are not acutely ill, are over 18 years of age and are not taking antihypertensive drugs, a blood pressure reading of 119 mm Hg or below systolic and/or 79 mm Hg or below diastolic (119/79) is considered normal. If your systolic blood pressure is 120 to 139 mm Hg systolic and/or your diastolic pressure is 80 to 89 mm Hg, you have prehypertension. This means that you don't have high blood pressure now but are more likely to develop it in the future, and you have increased risk factors for cardiovascular disease and other conditions related to hypertension.

A blood pressure level of 140/90 mm Hg or higher is considered high. You have stage 1 hypertension if your systolic pressure is 140 to 159 and/or diastolic is between 90 and 99. If your systolic pressure is 160 or above and/or your diastolic is100 or more, you have stage 2 hypertension. Only one of the numbers needs to be above normal for a diagnosis of high blood pressure; that is, you can have isolated systolic or diastolic hypertension. Isolated systolic hypertension (ISH) is the most common form of high blood pressure in older Americans. The National Heart, Lung, and Blood Institute (NHLBI) estimates that 65 percent of people with hypertension over age 60 have ISH. The cause of approximately 90 to 95 percent of all hypertension isn't known. This type of hypertension is called primary or essential high blood pressure. Secondary hypertension is somewhat different because it represents all of the specific diseases that cause elevated blood pressure. It is important to diagnose this type of hypertension because the treatment differs from primary hypertension.

You should have your blood pressure checked whenever you see a healthcare professional. Because blood pressure can be variable, it should be checked on several different days before a high blood pressure diagnosis is made. One elevated blood pressure reading doesn't necessarily mean you have high blood pressure, but it does warrant repeated measurements and means you have to watch your blood pressure carefully.