Blood pressure is measured with a sphygmomanometer, an inflatable rubber cuff with a pressure gauge. Blood flow through the brachial artery is monitored by listening at the radial artery with a stethoscope. Cuff pressure is applied to the upper arm to stop blood flow in brachial artery. Then, the pressure is gradually released.
No sounds are heard when blood flow stops (above systolic pressure) or is completely open (below diastolic pressure). In-between these two pressures Korotkoff sounds are heard. These are due to pulsatile, turbulent flow. As pressure is released, sounds are first heard when the pressure is just below systolic, so this pressure reading is recorded as systolic pressure. As the pressure continues to be decreased, the point when no sounds are heard is recorded as diastolic pressure.
The blood pressure measurement is written as (systolic pressure)/(diastolic pressure). Typically, BP = 120/80. Pulse pressure is the difference between systolic pressure and diastolic pressure. Mean arterial pressure (MAP) is the average blood pressure: MAP = diastolic pressure + 1/3 of pulse pressure.
Making a Difference in the World 