Pulmonary vascular resistance (PVR) is lowest at which lung volume, and what dual mechanism explains this relationship?

• A At total lung capacity (TLC); maximum stretch of alveolar vessels reduces their resistance
• B At residual volume (RV); extra-alveolar vessels are fully expanded by elastic recoil
• C At FRC; hypoxic vasoconstriction is minimised at the optimal alveolar PO2
• D At functional residual capacity (FRC); alveolar vessels are not over-distended and extra-alveolar vessels are not compressed ✓

Explanation

Pulmonary resistance is the sum of alveolar vessel resistance and extra-alveolar vessel resistance. Alveolar vessels (capillaries) are compressed at high lung volumes (high TLC) by alveolar distension, increasing their resistance. Extra-alveolar vessels (arteries, veins) are pulled open by radial traction from lung parenchyma and are most compressed at low lung volumes (near RV). At FRC (the natural resting volume), neither component is at its extreme — the combined PVR is minimal. This U-shaped relationship between lung volume and PVR is a key concept in mechanical ventilation management.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.