In what situation should a medical assistant read the diastolic pressure while deflating a blood pressure cuff?

Reading the diastolic pressure while deflating a blood pressure cuff is crucial for accurately assessing a patient's blood pressure. The diastolic pressure is the point at which blood flow resumes in the arteries, which is indicated by the disappearance of the Korotkoff sounds during deflation. This sound corresponds to the heart's relaxation phase, and detecting when it fades allows the medical assistant to determine the diastolic measurement accurately.

The other scenarios don't provide a reliable indication of the diastolic pressure. For example, fully deflating the cuff or allowing the pressure to reach zero does not correlate with the physiological events of the heartbeat and can lead to inaccuracies in measurement. Similarly, waiting for a patient to express discomfort is not a standardized or reliable practice for measuring blood pressure and could introduce variability or influence in the reading based on the patient's anxiety or discomfort rather than the actual physiological measurements. Thus, identifying the diastolic pressure based on the disappearance of the sound during deflation is the correct and most accurate method.