Which Korotkoff sound indicates systolic pressure?

The first Korotkoff sound is the correct choice for indicating systolic pressure during blood pressure measurement. This sound is the initial thumping noise that is heard through a stethoscope when the healthcare provider releases the pressure in a sphygmomanometer cuff. It occurs when the pressure in the cuff drops just below the systolic pressure in the brachial artery, allowing blood to flow partially and create turbulence. This turbulence produces the distinctive sound that signifies the point at which the heart's ventricles contract and force blood into circulation, marking the systolic pressure.

The other Korotkoff sounds, such as the second, third, and fourth, relate to other phases of blood pressure measurement but do not denote the systolic pressure. The second sound suggests the flow of blood becomes more continuous, while the third sound indicates more distinct, clearer sounds. The fourth sound refers to the eventual cessation of sound as the cuff pressure drops to diastolic levels, thus representing the diastolic pressure. Understanding these sounds is essential for properly interpreting blood pressure readings and ensuring accurate assessment of cardiovascular health.