Intrapleural pressure at end expiration during passive breathing is which value?

• A. 0 cm H2O
• B. -5 cm H2O
• C. 10 cm H2O
• D. -10 cm H2O

Answer: (B)

Intrapleural pressure is kept subatmospheric, which creates the transpulmonary pressure that keeps the lungs inflated. At the end of a quiet, passive breath, the system is at functional residual capacity with no air flow, and the intrapleural pressure is typically around −5 cm H2O. This negative pressure is what prevents the lungs from collapsing and allows for easy opening of the alveoli on the next inspiratory effort.

Zero intrapleural pressure would eliminate the distending force on the lungs, making collapse more likely, and a positive value would occur only with stronger, non-passive efforts. The value of −10 cm H2O is more negative than typical end-expiration during quiet breathing, while +10 cm H2O is not seen in passive breathing. Therefore, −5 cm H2O best describes intrapleural pressure at end expiration during passive breathing.