Measurement of Blood Pressure

Blood pressure is commonly measured in the brachial artery of the left arm using a sphygmomanometer. It includes a rubber cuff, a rubber bulb for inflating the cuff, and a meter that records the cuff pressure.

First, the cuff is wrapped around the arm, just above the elbow, and inflated. This pressure, approximately 30 mm Hg above the typical systolic pressure, temporarily stops the blood flow in the brachial artery.

A stethoscope is then placed below the cuff on the brachial artery, and the cuff is slowly deflated. This opens the artery to let a blood spurt pass through, creating an audible sound detected in the stethoscope.

The pressure measured at this first audible sound corresponds to the systolic blood pressure.

Further deflation of the cuff causes the sounds to become faint until they are inaudible. The pressure measured at this point is the diastolic blood pressure.

These sounds heard during blood pressure measurement are known as Korotkoff sounds.

The difference between systolic and diastolic pressure, known as pulse pressure, usually around 40 mm Hg, is also clinically significant.