Next, the observer should proceed to carry out the first BP reading. The systolic value (1st phase Korotkoff) can be identified as the pressure level where the first of 2 or more sounds are heard in the appropriate rhythm. The diastolic value (5th phase Korotkoff) can be identified as the pressure level where the last of these rhythmic sounds is heard.
NOTE: A single sound heard in isolation (i.e., not in rhythmic sequence) before the first of the rhythmic sounds (systolic) or following the last of the rhythmic sounds (diastolic) does not meet these criteria for the systolic or diastolic endpoints. If the sounds are heard all the way to 0 mm Hg, record the 4th phase DBP. The measurement should be recorded as Korotkoff 1/Korotkoff 4/ Korotoff 5 (e.g., 122/60/0) on the X FORM
The American Heart Association (1980) defines the K-sounds as follows. (American Heart Association. Recommendation for Human Blood Pressure Determination by Sphygmomanometer. Dallas, American Heart Association, 1980).