Tracey teaches college courses in medical assisting and is pursuing a master's degree in education.
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.
Phase IV is denoted by a sudden muffling of the sounds that become faint. And then suddenly, there is Phase V.
The Phase V sound isn't a sound at all, but rather an absence of sound. At the exact point where the sounds stop and silence begins is where we measure the diastolic pressure. The silence heard means that the cuff pressure now equals the diastolic pressure reading or 'the bottom number' of your blood pressure reading and the flow of blood inside your brachial artery has returned to normal.
In summary, Korotkoff sounds is the name given to the series of sounds that are made by the blood rushing through an artery as it is allowed to slowly open by the deflation of a blood pressure cuff or sphygmomanometer. The sounds are characterized by five distinct phases. The most important Korotkoff phases are Phase 1 and Phase 5 which determine the systolic and diastolic number that make up your total blood pressure reading.
Medical Disclaimer: The information on this site is for your information only and is not a substitute for professional medical advice.
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