Korotkoff sounds are generated when a blood pressure cuff changes the flow of blood through the artery. These sounds are heard through either a stethoscope or a doppler that is placed distal to the blood pressure cuff.
There are five distinct phases of Korotkoff sounds:
Phase 1: A sharp tapping.
This is the first sound heard as the cuff pressure is released. This sound provides the systolic pressure reading.
Phase 2: A swishing/whooshing sound.
Swishing sounds as the blood flows through blood vessels as the cuff is deflated.
Phase 3: A thump (softer than phase 1).
Intense thumping sounds that are softer than phase 1 as the blood flows through the artery but the cuff pressure is still inflated to occlude flow during diastole.
Phase 4: A softer, blowing, muffled sound that fades.
Softer and muffled sounds as the cuff pressure is released. The change from the thump of phase 3 to the muffled sound of phase 4 is known as the first diastolic reading.
Phase 5: Silence.
Silence that occurs when the cuff pressure is released enough to allow normal blood flow. This is known as the second diastolic reading.
Learn more about blood pressure here: https://www.ausmed.com.au/cpd/articles/how-to-take-blood-pressure.