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PVR Lowest at FRC — FRCA Primary MCQ

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HardPhysiology - RespiratoryPVR Lowest at FRCFRCA Primary

A ventilated patient is moved from functional residual capacity to very high lung volume. Which pair of pulmonary-vessel changes best explains the rise in pulmonary vascular resistance?

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Correct answer: E — Alveolar vessels are compressed while extra-alveolar vessels are relatively distended

The best answer is “Alveolar vessels are compressed while extra-alveolar vessels are relatively distended”. At high lung volume, expanding alveoli compress capillaries in their walls, increasing alveolar-vessel resistance. Radial traction tends to distend extra-alveolar vessels, but this does not offset alveolar compression, so total PVR rises. At low volumes, the converse extra-alveolar-vessel narrowing dominates. The minimum PVR lies near functional residual capacity.

Reference: RCoA, Primary FRCA syllabus: https://www.rcoa.ac.uk/sites/default/files/documents/2026-01/Primary-FRCA-Syllabus.pdf; Lung circulation review: https://pmc.ncbi.nlm.nih.gov/articles/PMC7432532/