A student measures blood pressure by auscultation. As cuff pressure falls just below systolic pressure, sounds first appear. At what point do the Korotkoff sounds disappear, marking the diastolic reading?

• A When cuff pressure equals mean arterial pressure
• B When cuff pressure reaches central venous pressure
• C When cuff pressure exceeds systolic pressure and flow stops completely
• D When the artery remains open throughout the cardiac cycle and turbulent flow ceases ✓

Explanation

Korotkoff sounds arise from turbulent flow produced when the artery opens partially during systole and snaps shut during diastole under the cuff. Once cuff pressure falls below diastolic pressure, the vessel stays patent throughout the cycle, flow becomes laminar again and the sounds disappear, which defines phase five as diastolic pressure. Sounds begin when cuff pressure crosses below systolic pressure, not at mean arterial pressure, and complete silence above systolic pressure precedes any sound.

Reference: Ganong's Review of Medical Physiology, 26th ed.

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