Respiratory Mechanics and Gas Exchange · USMLE Step 1

Which of the following changes would you expect in a diffusion-limited gas exchange scenario (e.g., thickened alveolar membrane)?

  1. Equilibration achieved rapidly despite membrane thickening
  2. Blood flow becomes the limiting factor for gas transfer
  3. Slower O₂ and CO₂ transfer across the membrane
  4. Perfusion increases to overcome diffusion limitation
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Correct answer: Slower O₂ and CO₂ transfer across the membrane

Thickening of the alveolar–capillary membrane slows diffusion across it, reducing the rate of O₂ uptake and CO₂ elimination, characteristic of diffusion-limited exchange.

Difficulty: Medium Question 18 of 20

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