If surfactant is deficient, what is the most likely consequence in the alveoli?

• A. Decreased alveolar surface tension leading to overinflation.
• B. Increased surface tension causing alveolar collapse.
• C. Increased compliance.
• D. Decreased airway resistance.

Answer: (B)

Surfactant’s job is to lower surface tension at the air–liquid interface inside the alveoli, which makes them easier to inflate and prevents collapse during exhalation. When surfactant is deficient, surface tension rises, especially in the smaller alveoli, so the collapsing pressure increases (per Laplace’s law, P = 2T/r). This leads to alveolar collapse or atelectasis, reducing gas exchange and lowering lung compliance, with the patient experiencing increased work of breathing and hypoxemia.

The other options describe effects that don’t fit surfactant deficiency. Decreasing surface tension would promote overinflation, not collapse. Increased compliance would occur with adequate surfactant; deficiency actually lowers compliance. Decreased airway resistance is not a direct consequence of surfactant status and isn’t the primary outcome of its deficiency.