Final answer:
The 5th Korotkoff sound represents the diastolic pressure.
Step-by-step explanation:
The 5th Korotkoff sound represents the diastolic pressure. When measuring blood pressure using a sphygmomanometer, the first sound heard (1st Korotkoff sound) corresponds to the systolic pressure, while the last sound heard (5th Korotkoff sound) represents the diastolic pressure. The diastolic pressure is the pressure in the arteries when the heart is at rest between beats. The 5th Korotkoff sound represents the pressure at which there is uninterrupted blood flow through the brachial artery, indicating the diastolic pressure. This is the point where the Korotkoff sounds disappear completely when taking a blood pressure measurement. During a blood pressure reading, initially no Korotkoff sounds are heard because the cuff's pressure stops the blood flow. As the pressure is slowly released from the cuff, the first sound heard through the stethoscope is the first Korotkoff sound, which represents the systolic pressure. Ultimately, as the pressure drops further and blood can flow freely and silently through the artery, the disappearance of Korotkoff sounds heralds the diastolic pressure.