Respiratory Mechanics and Gas Exchange · USMLE Step 1

Why does surfactant deficiency lead to decreased lung compliance in neonates with respiratory distress syndrome?

  1. Because surfactant raises airway resistance to airflow
  2. Because surfactant lowers surface tension, easing expansion
  3. Because surfactant thickens the alveolar–capillary membrane
  4. Because surfactant blocks perfusion of alveolar capillaries
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Correct answer: Because surfactant lowers surface tension, easing expansion

Surfactant reduces surface tension at the alveolar air–liquid interface, lowering the pressure needed to expand alveoli; deficiency raises surface tension, increasing the work of expansion and reducing compliance.

Difficulty: Medium Question 16 of 20

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