On the flow-time scalar illustrated below, identify the component of the tracing labeled "b."

A. point of end-inspiration
B. point of beginning of expiration
C. expiratory hold maneuver
D. inspiratory hold maneuver

?ANS: D
A. Incorrect response: See explanation D.
B. Incorrect response: See explanation D.
C. Incorrect response: See explanation D.
D. Correct response:
The scalar presented here is a square wave (rectangular) flow-time tracing frequently seen during volume-control ventilation. Label "a" reflects the constant flow delivered throughout the time the tidal volume is being delivered by the ventilator to the patient.?Label "b" represents an inspiratory pause, which prolongs inspiratory time, but does not involve any additional tidal volume delivery. In fact, the flow during the inspiratory pause is zero. ?Once the inspiratory pause concludes, the flow descends below the baseline signifying the onset of expiration (end-inspiration). The expiration continues as the flow tracing changes direction, and moves upward toward the baseline, as shown by label "c." When the flow tracing returns to the baseline (assuming no expiratory hold maneuver is initiated), expiration ends