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Measuring Blood Pressure
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Measuring blood pressure
The Korotkoff method typically includes the occlusion of the brachial artery by a cuff placed on the upper arm and inflated to a pressure above systolic pressure. When the cuff is inflated above systolic pressure, blood flow in the artery is completely occluded or stopped. The pressure is then gradually lowered at 2-3 mmHg per second until pulsatile blood flow occurs. This will cause intra-arterial sounds during auscultation over the brachial artery secondary to turbulent flow and oscillations of the arterial wall. The sounds are described to have five phases, which are as follows:
  • Phase I is the appearance of tapping sounds corresponding to the appearance of a palpable pulse
  • Phase II sounds become softer and longer
  • Phase III sounds become crisper and louder
  • Phase IV sounds become muffled and softer
  • Phase V sounds disappear completely

The fifth phase is the recorded value of the last audible sound. There is agreement among researchers that phase I corresponds to systolic pressure but tends to underestimate the systolic pressure recorded by intra-arterial measurement.

There has been some debate in the past as to whether phase IV or V is the accepted value for diastolic pressure, but both are felt to occur before diastolic pressure is determined by intra-arterial recordings. Therefore, it is now accepted that phase V should be used, except when the disappearance of the sounds cannot be reliably determined because the sounds are audible even after complete deflation of the cuff. This situation can occur in pregnant women, patients with arteriovenous fistulas, and patients with aortic insufficiency. 

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Section: Measuring Blood Pressure
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