The McGill Physiology Virtual Lab

Cardiovascular Laboratory

 Blood Pressure> Palpatory Method
  The relaxed subject sits on a chair.  The cuff of the sphygmomanometer is wrapped firmly around the right arm above the elbow. The lower arm should be resting on a table-top or bench. 

The radial pulse (the pulse at the radial artery in the wrist) is palpated with the fingers of the left hand.  The number of beats in 30 seconds is counted, and the heart rate in beats per minute is recorded.

 

 The valve on the inflating bulb of the sphygmomanometer is turned fully clockwise so that it is closed.  The cuff is inflated slowly (10 mm Hg/sec) by pumping the inflating bulb until the radial pulse is no longer felt.  The cuff is inflated further until the pressure is about 30 mm Hg higher. 
The valve on the inflating bulb is opened slightly by turning it in the counterclockwise direction, allowing the pressure to drop slowly by about 5 mm Hg/sec.  At some point, one will be able to feel the radial pulse once again.  The pressure indicated on the gauge when the pulse reappears is noted.  This is the systolic pressure.  Now the pressure in the cuff is quickly released, so as not to cause undue discomfort to the subject.
The determination of blood pressure is repeated two more times for the right arm, and then repeated again using the left arm instead of the right arm.
Explanatory Notes
 

The cuff pressure's constriction of the artery is opposed by the blood pressure.  Therefore, in order to completely constrict the artery, the cuff pressure must be greater than the highest blood pressure, the systolic pressure.

The cuff pressure is gradually decreased. At the point where the cuff pressure drops below the systolic pressure of the blood, blood can pass through the constricted opening of the artery and the pulse will be felt.  In other words, the systolic pressure, the highest blood pressure, will be the point at which the cuff pressure is first overcome.
The pulse will continue to be felt as the pressure in the cuff falls from systolic all the way down to zero.
  Note that the although the radial pulse is palpated, the systolic blood pressure actually recorded is that in the brachial artery, where the actual cuff constriction occurs.
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