A patient with pulmonary fibrosis has thickened alveolar membranes. Which mechanism explains why their blood oxygen saturation decreases even with supplemental oxygen?

💡 Explanation

Reduced blood oxygen saturation in pulmonary fibrosis results from impaired alveolar gas exchange. Thicker membranes increase diffusion distance, reducing diffusion capacity, because Fick's Law dictates that gas transfer rate is inversely proportional to membrane thickness; therefore, less oxygen enters the blood, rather than increased affinity or shunting bypassing the alveoli.

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