Based on the pressure-time waveform depicted below, what is the value of the transairway pressure gradient during the inspiratory pause?
A. 40 cm H2O
B. 30 cm H2O
C. 10 cm H2O
D. 0 cm H2O
?ANS: D
A. Incorrect response: See explanation D.
B. Incorrect response: See explanation D.
C. Incorrect response: See explanation D.
D. Correct response: The transairway pressure gradient is the difference between the airway pressure and the atmospheric pressure. This is the gradient responsible for the flow of air into and out of the lungs during both spontaneous and mandatory ventilation.
When an inspiratory pause is instituted, both the airway pressure and the atmospheric pressure are in equilibrium. Therefore, during an inspiratory pause, the transairway pressure is zero. Because no pressure gradient exists at this time, no gas flows. Furthermore, because no gas flows at this time, no airway resistance is present. An inspiratory pause is a static measurement.
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