The indirect measurement of blood pressure by the sphygmomanometer involves the application of a controlled lateral pressure by an inflatable cuff to occlude the artery by compression, thereby stopping the flow. The detection of the resumption of flow during slow deflation allows the determination of the pressure. The cuff is normally applied to the arm over the brachial artery. When the cuff pressure exceeds the systolic pressure, the brachial artery is fully occluded and the flow ceases. When the cuff is deflated to pressures just below the systolic peak, the flow begins to resume with each cardiac systole. The jet of blood coming through the partially occluded vessel is associated with tapping-type sounds, which can be recognized using a stethoscope placed over the brachial artery just distal to the cuff. These sounds, termed the Korotkoff sounds, help in identifying the systolic and the diastolic pressures in the artery. The detection ofthe first appearance of Korotkoff sounds (Phase I) as the cuff is being deflated corresponds to the systolic pressure, and the disappearance of Korotkoff sounds with further deflation ofthe cuff corresponds to the diastolic pressure. Korotkoff sounds generally become muffled first when the cuff is being deflated before they totally disappear. It is always advisable to take the diastolic pressure to the level at which the sounds disappear because it is less likely to introduce errors (1).
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