Korotkoff sounds are the sounds that medical personnel listen for when they are taking blood pressure using a non-invasive procedure. They're named after Dr. Nikolai Korotkoff, a Russian physician who discovered them in 1905, when he was working at the Imperial Medical Academy in St. Petersburg, Russian.

Korotkoff sounds

If the cuff of a sphygmomanometer is placed around a patient's upper arm and inflated to a pressure above the patient's systolic blood pressure, there will be no sound audible. This is because the pressure in the cuff is high enough such that it completely occludes the blood flow.

If the pressure is dropped to a level equal to that of the patient's systolic blood pressure, the first Korotkoff sound will be heard. As the pressure in the cuff is the same as the pressure produced by the heart, some blood will be able to pass through the upper arm when the pressure in the artery rises during systole. This blood flows in spurts as the pressure in the artery rises above the pressure in the cuff and then drops back down beyond the cuffed region, resulting in turbulence that produces an audible sound.

Eventually, as the pressure in the cuff drops further, the sounds change in quality, then become muted, and finally disappear altogether. This occurs because, as the pressure in the cuff drops below the diastolic blood pressure.

There're five Korotkoff sounds:

• Phase I—The first appearance of faint, repetitive, clear tapping sounds which gradually increase in intensity for at least two consecutive beats is the systolic blood pressure.
• Phase II—A brief period may follow during which the sounds soften and acquire a swishing quality.
• Phase III—The return of sharper sounds, which become crisper to regain, or even exceed, the intensity of phase I sounds.
• Phase IV—The distinct abrupt muffling of sounds, which become soft and blowing in quality.
• Phase V—The point at which all sounds finally disappear completely is the diastolic pressure.