Korotkoff sounds are the specific sounds heard while measuring blood pressure using a sphygmomanometer, typically with a stethoscope or a Doppler device. They are named after Russian physician Nikolai Korotkov, who first described them in 1905. These sounds correspond to turbulent blood flow in the artery as the blood pressure cuff is gradually released after inflation.

During blood pressure assessment, inflating the cuff 30 millimeters of mercury above the patient's systolic blood pressure leads to the absence of Korotkoff sounds due to complete blood flow occlusion. These sounds appear when the cuff pressure equals the patient's systolic blood pressure and are audible through a stethoscope, or Doppler positioned distal to the cuff. Korotkoff sounds have five distinct phases:

1. Phase One (Appearance of faint tapping sounds): As the cuff's pressure is released, the first faint tapping sounds become audible. This initial appearance marks the systolic pressure reading, with the intensity gradually increasing.
2. Phase Two (Softer tapping sounds with swishing): The tapping sounds become softer, accompanied by a swishing sound as the cuff deflates. The characteristics of these sounds provide additional information about blood flow.
3. Phase Three (Crisp, intense tapping sounds): As the cuff pressure continues to fall, phase three features crisp and intense tapping sounds, softer than in phase one. These sounds indicate increased blood flow through the artery.
4. Phase Four (Softer and muffled sounds): With further decrease in cuff pressure, phase four comprises softer and muffled sounds. The transition from tapping to muffled sounds during this phase signifies the first diastolic reading.
5. Phase Five (Total disappearance of sounds): The final phase is characterized by the total disappearance of all Korotkoff sounds, indicating complete cuff deflation and normal blood flow, representing diastolic blood pressure.

Understanding the progression of Korotkoff sounds through these five phases is essential for healthcare professionals to obtain accurate blood pressure readings and assess cardiovascular health.