MODEL RELEASED. Doctor taking blood pressure of a young girl. Blood pressure is measured using a sphygmomanometer. It consists of an arm cuff (girl's right arm), which is inflated by a pump (doctor's left hand) until the blood flow stops. The cuff is deflated until some blood flow resumes. The reading on the blood pressure gauge (left) shows the systolic pressure (pumping heart). The cuff is further deflated until the blood flow is smooth and the gauge shows the diastolic pressure (relaxed heart). Blood pressure is expressed as the difference between these two values, in millimetres of mercury (mm Hg).