Korotkoff sounds are distinctive sounds that can be distinguished when a blood pressure cuff is applied and adjusted. They were first described in 1905 by Russian physician Nikolai Korotkoff. Listening for these sounds with a stethoscope while using a blood pressure cuff allows a health practitioner to take a blood pressure reading. Many people are familiar with the process of manually taking blood pressure in clinical settings, as blood pressure is a vital sign commonly tested at doctor visits.
Under normal conditions, the movement of blood through the artery in the arm is not audible. This is because the flow of blood is not turbulent. In people with artery disease, sounds can be heard as the flow is disrupted. When a blood pressure cuff is applied, it disrupts the flow of blood in a stable and predictable fashion, and this can be used to generate information about the patient's blood pressure.
When a blood pressure cuff is inflated above the systolic blood pressure, no sounds can be heard. The flow of blood is occluded and thus it is not moving through the artery in the arm at all. As pressure is lowered, the first phase of the Korotkoff sounds, a sharp tapping noise, is heard as the blood starts to woosh back into the artery. The reading on the cuff at this point is equal to the systolic blood pressure. As the pressure falls, the blood moves into the second stage, a swishing noise, followed by the third stage, characterized by pounding as blood moves through the vessel.
The fourth phase in the Korotkoff sounds is a blowing noise, followed by silence in the fifth phase as the pressure equals that of the diastolic pressure. The flow of blood returns to normal without the pressure of the blood pressure cuff, and silence resumes. A skilled practitioner can get an accurate blood pressure reading with one session, while others may take a second reading to confirm. Completely electronic blood pressure reading machines are programmed to listen for the Korotkoff sounds and take readings as appropriate.
Things which can interfere with the Korotkoff sounds can include placing the stethoscope improperly or being in a noisy environment. Patients also need to follow directives from the health care provider, including staying still and relaxed to avoid accidentally increasing their blood pressure. Talking or moving during the test can disrupt the readings and force the health care provider to repeat the test.