# How is blood pressure determined?

Blood pressure is measured by a quick, painless test using a medical instrument called a sphygmomanometer. A rubber cuff is wrapped around a person’s upper arm and inflated. It compresses a large artery in the arm, momentarily stopping the blood flow. Then the air in the cuff is released and the person measuring the blood pressure listens with a stethoscope. When the blood starts to pulse through the artery, it makes a sound. The person listening and watching the sphygmomanometer gauge records two measurements.

+ Systolic pressure (the higher number) is the pressure of the blood flow when the heart beats (the pressure when the first sound is heard).+ Diastolic pressure is the pressure between heartbeats (the pressure when the last sound is heard).

Blood pressure is measured in millimeters of mercury, which is abbreviated mm Hg. The harder it is for blood to flow, the higher the numbers will be.