1. Arterial Blood Pressure Taking a person’s Blood Pressure with a sphygmomanometer

2. Measurement: A Sphygmomanometer  A sphygmomanometer is the inflatable cuff connected by tubing to a compressible bulb and pressure gauge used to take blood pressure.  Today blood pressure is, usually, taken electronically. However, all medical professionals have to learn the hand held procedure, initially.

3. The Bulb Is Used to Pump  The Bulb is used to pump air into the cuff, and a rise in pressure is indicated on the pressure gauge.  The pressure on the cuff is measured in mm Hg (millimeters of mercury) based on earlier equipment using a glass tube containing a column of mercury … similar to a thermometer … in place of a pressure gauge.

4. Wrapped around the arm, surrounding the brachial artery  Wrapped around the arm, surrounding the brachial artery; air is pumped into the cuff until the cuff pressure exceeds the pressure of that artery.  As a result, the vessel is squeezed closed, and its blood flow is stopped!  At this time if the diaphragm of a stethoscope is placed over the brachial artery at the distal border of the cuff, no sounds will be heard because the blood flow is interrupted.

5. As Air Is Slowly Released  As air is slowly released from the cuff, the air pressure inside it d-e-c-r-e-a-s-e-s.  When the cuff pressure is approximately equal to the systolic blood pressure within the brachial artery, the artery opens enough for a small amount of blood to spurt through. This movement produces a sharp sound called Korotkoff’s sound that can be heard through the stethoscope.  The height of the mercury column when this first tapping sound is heard represents the arterial systolic pressure (SP).

6. Cuff Pressure Continues to Drop  As the cuff pressure continues to drop, a series of increasingly louder sounds can be heard.  When the cuff pressure is equal to that within the fully opened artery, the sounds become abruptly muffled, and disappear.  The height of the mercury column when this happens represents the arterial diastolic pressure (DP). This sound results from turbulence occurring when the artery narrows.

7. The Results of Blood Pressure  The results of blood pressure are reported as a fraction, such as 120/80.  The upper number represents the systolic pressure in mm Hg, and the lower number represents the diastolic pressure in mm Hg.  The difference between the systolic and diastolic pressures (SP-DP) is called the pulse pressure; and should be, generally, about 40 mm Hg.

8. Average Pressure & Mean Arterial Pressure  The average pressure in the arterial system represents the force that is effective throughout the cardiac cycle for driving blood into the tissues.  This Force, called the mean arterial pressure, is approximated by adding the diastolic pressure and one third of the pulse pressure. (DP + 1/3 PP).