Phase IV Korotkoff sounds for diastolic blood pressure

Phase IV Korotkoff sounds for diastolic blood pressure

What are the situations in which phase IV of Korotkoff’s sounds are used to measure the diastolic blood pressure?

Phase IV diastolic pressure is measured in all hyperdynamic circulatory states which include pregnancy, children, aortic regurgitation, thyrotoxicosis, anemia and beriberi.

Korotkoff’s sounds are divided into five phases (I to V). Usually Phase V is taken for measurement of the diastolic pressure. These sounds were named after Nikolai Korotkoff. They were discovered in 1905, while he was working at Imperial Medical Academy in St. Petersburg. Phase IV is muffling of the Korotkoff’s sounds and Phase V is disappearance. Systolic blood pressure is taken at Phase I. In some cases of severe aortic regurgitation, if you go for phase V diastolic blood pressure, we may get it as zero. There is also a method of recording diastolic pressures at both phase IV and phase V.

A study evaluated the inter observer variability of blood pressure measurements in pregnancy. They found that variability was more when calculating the phase IV diastolic pressure which it was not so with phase V diastolic pressure. Hence the authors of that study recommended using phase V for better accuracy and reliability [1].

Reference

1. S G Blank, G Helseth, T G Pickering, J E West, P August. How Should Diastolic Blood Pressure Be Defined During Pregnancy? Hypertension. 1994 Aug;24(2):234-40.