Which of the following statements about the equal pressure point (EPP) is true?

a. As gas travels from the EPP to the mouth, greater expiratory effort increases flow.
b. At the EPP, pressure inside the airway exceeds Ppl.
c. The EPP normally occurs at volumes greatly below the FRC.
d. Upstream from the EPP (toward the alve-oli), Ppl exceeds pressure in the airway.

ANS: C
At some point along the airway, the pressure inside equals the pressure outside in the pleural space. This point is referred to as the EPP. Downstream from this point, pleural pressure exceeds the airway pressure. The resulting positive transmural pressure gradient causes airway compres-sion and can lead to actual collapse. Airway compression increases expiratory airway resistance and limits flow. At the EPP, greater expiratory effort only increases pleural pressure, further re-stricting flow. In airways of healthy subjects, the EPP occurs only with forced exhalation and at low lung volumes.