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

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.

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.

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.

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).

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.

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.

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).