Korotkoff Sounds: Definition & Phases

Instructor: Tracey Stoeckel

Tracey teaches college courses in medical assisting and is pursuing a master's degree in education.

In this lesson you will learn about the five different phases of Korotkoff sounds that can be heard during the process of blood pressure measurement. We will discuss how to identify Korotkoff sounds and how health care professionals use them.

What Are Korotkoff Sounds?

Have you ever wondered what the medical assistant or doctor at your clinic was listening to when they put the stethoscope on your arm and inflate the blood pressure cuff? Does it seem like they listen to a voice inside your arm that is giving them a set of random numbers to declare? Well that number is definitely not random, but what are they listening to, and where does that number it come from?

In 1905 Dr. Nikolai Korotkoff discovered that there are a series of sounds made by the blood pumping through your arteries during blood pressure measurement. He further determined that the changes in these sounds make up several distinct phases that allow healthcare providers to determine your blood pressure and play an important role to cardiac health. This series of sounds is referred to as Korotkoff sounds (sometimes called K sounds), after the doctor who discovered them.

To accurately measure blood pressure using the auscultatory (listening) method, a stethoscope is placed over an artery that has been closed off by an inflated blood pressure cuff, called a sphygmomanometer. The brachial artery, the one on the inside of your arm, opposite your elbow, is the one most commonly used.

The pressure applied by the cuff on the arm forces the blood to push against the walls of the artery. As the blood pressure cuff is slowly deflated, the pressure in the cuff is decreased and the artery is allowed to open. At this point blood rushes with a greater than normal force through the artery, and a series of sounds can be heard through a stethoscope. As the blood pressure cuff continues to deflate, these sounds can be heard to change and make up five distinct phases. It is these five phases that make up the Korotkoff sounds.

The Five Phases

The first sound you hear as the blood pressure cuff deflates, Phase I is a clear, sometimes sharp, tapping sound. This first 'tap' denotes your systolic blood pressure. For most of us, we know this as 'the top number' in your blood pressure reading. The blood pressure cuff must be initially inflated to a pressure that is higher than the patient's systolic blood pressure reading.

The sound changes in Phase II, to a swishing sound or a soft murmur.

Next comes Phase III where the sound changes to a knocking or a slapping sound that are rhythmic and usually quite distinct.

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