Answer:
The first Korotkoff sound is the first audible sound heard during blood pressure measurement using a sphygmomanometer (blood pressure cuff) and a stethoscope. It is an important sound because it indicates the systolic blood pressure.
The first Korotkoff sound is a tapping or knocking sound that is heard as the cuff pressure is released and the blood begins to flow through the constricted artery. This sound is produced when the force of the blood flow through the artery overcomes the force of the cuff pressure on the artery. The first Korotkoff sound is heard at the point where the blood pressure in the artery is sufficient to cause blood flow, and it is an indication that the heart is contracting and pushing blood out into the arteries.
The appearance of the first Korotkoff sound is important in determining the systolic blood pressure, which is the pressure in the arteries when the heart is contracting. The sound is also used to determine the diastolic blood pressure, which is the pressure in the arteries when the heart is at rest between beats.