The auscultatory method of measuring arterial blood pressure involves first increasing the air pressure in a broad cloth or plastic cuff placed around the arm (sometimes the leg) (Figure 11). The cuff pressure is then gradually allowed to decrease, as one listens with the bell of a stethoscope placed over the brachial artery at a point immediately below the cuff.
A sharp slapping sound is initially heard. This is called the appearance. Then follows the loudening phase which is heard as an increase in sound intensity, then a muffling phase, and finally a disappearance of all sound.
These Korotkow or Korotkoff sounds are produced by turbulence resulting from high blood flow velocity in the vessel, as the cuff pressure is decreased below the systolic pressure. Blood flows at high velocity through the small opening which forms for an instant; the increased velocity prediposes to turbulence. It is the turbulence which is heard through the stethoscope. Systolic blood pressure is most closely correlated with the appearance.
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