Final answer:
Systolic pressure is recorded when the first Korotkoff sounds begin during the deflation of the sphygmomanometer cuff, indicating blood flow starting as the cuff pressure equals the systolic arterial pressure.
Step-by-step explanation:
When taking blood pressure, you would record systolic pressure when Korotkoff sounds begin. The Korotkoff sounds are audible noises that are heard using a stethoscope during the measurement of blood pressure with a sphygmomanometer.
As the cuff pressure is slowly reduced, the first Korotkoff sound indicates the moment the pressure in the cuff is equal to the systolic pressure in the arteries, indicating blood is beginning to spurt through the brachial artery. This initial sound is what should be recorded as the systolic pressure. Conversely, diastolic pressure is noted when these sounds can no longer be heard, indicating blood flow is uninterrupted and free from any obstruction due to the cuff's pressure.