Health Library

Health Library

What Those Blood Pressure Numbers Mean

A quick, painless test measures blood pressure: A rubber cuff is wrapped around your arm and inflated, which compresses an artery in your arm and momentarily stops your blood flow. The pressure in the cuff is slowly released and, as blood begins to flow, your blood pressure can be measured either with a stethoscope or a device that recognizes the sound made by the flow of blood.

Blood pressure readings are a double measurement of the force of the blood against arterial walls. The two measurements indicate how much pressure builds up in the arteries as the heart beats and between beats. The first, higher number is the systolic pressure, which indicates the heart's pumping force. The second, lower number is the diastolic pressure, which indicates the amount of stretchability, which is worse when the arteries stiffen due to age or cholesterol buildup.

The higher the blood pressure, the more resistance there is to blood flow. A blood pressure level with the systolic less than 120 and the diastolic less than 80 is considered optimal. If the systolic is 120 to 139 or the diastolic is 80 to 89, this is called prehypertension regardless if one of them is normal. If the systolic is 140 or higher or the diastolic is 90 or higher, this is called hypertension (high blood pressure) regardless of whether one of the readings is normal or in the prehypertensive range.

To make a diagnosis of prehypertension or hypertension, your doctor will measure your blood pressure over several visits, or you may take your blood pressure at home. If the pressure is usually above 140/90, then the diagnosis of hypertension is made. If the majority of the readings are between 120/80 and 139/89, then the diagnosis of prehypertension is made. Hypertension is a sign that the heart is working too hard to pump blood through the circulatory system because of narrow and/or inflexible arteries.