At functional residual capacity, the inward elastic recoil of the lung is 5 cm H2O. What is the intrapleural pressure relative to atmospheric pressure, assuming chest wall recoil is negligible at this volume?

• A +5 cm H2O
• B +10 cm H2O
• C -5 cm H2O ✓
• D 0 cm H2O

Explanation

Transpulmonary pressure is the difference between alveolar pressure and intrapleural pressure. At functional residual capacity, alveolar pressure is zero relative to the atmosphere. The lung's inward elastic recoil of 5 cm H2O must be balanced by a transpulmonary pressure of 5 cm H2O. Solving the equation, intrapleural pressure must be -5 cm H2O. This negative pressure prevents the lung from collapsing at its resting volume.

Reference: West's Respiratory Physiology, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.