The therapist is preparing to calculate the expiratory airway resistance of a mechanically ventilated patient. Based on the pressure-time scalar displayed here, which pressure or pressure gradient does the therapist need to use in the calculation?

A. "g" minus "h"
B. "f" minus "g"
C. "f"
D. "g"

?ANS: A
A. Correct response: The pressure difference between "g" and "h" represents the pressure gradient developed to overcome airway resistance during expiration. Specifically, the gradient is the difference between the plateau pressure and PEEP. Dividing this pressure gradient by the peak expiratory flow enables the calculation of expiratory airway resistance.
B. Incorrect response: The pressure gradient between "f" and "g" signifies the pressure difference between the peak inspiratory pressure and the plateau pressure.
C. Incorrect response: The pressure associated with label "f" is the peak inspiratory pressure, which is used for the calculation of the dynamic compliance.
D. Incorrect response: The label "g" is the plateau pressure, which is the value used when calculating the static compliance.