What do Korotkoff sounds I and V represent?

• A. Phase I is mean arterial pressure; Phase V is pulse pressure.
• B. Phase I is systolic pressure; Phase V is diastolic pressure.
• C. Phase I is diastolic pressure; Phase V is systolic pressure.
• D. Phase I and V both indicate systolic pressure.

Answer: (B)

Korotkoff sounds are the clues we use when measuring blood pressure with a cuff and stethoscope. As the cuff deflates, the first tapping sound you hear marks the moment the artery starts to open and blood begins to flow again under partial obstruction. That first sound corresponds to the systolic pressure—the pressure in the arteries when the heart contracts.

As deflation continues, the sounds change and eventually fade away. The point at which all sounds disappear is taken as the diastolic pressure—the pressure in the arteries when the heart is relaxed and the artery is no longer turbulent. In adults, this disappearance (Phase V) is used to denote diastolic pressure. (Sometimes Phase IV muffling is noted in practice, but Phase V is the standard indicator for diastolic pressure.)

So, Phase I equals systolic pressure, and Phase V equals diastolic pressure.