PVR increases when lung volume rises above FRC due to which mechanism?

PVR increases when lung volume rises above FRC due to which mechanism?

• A. Alveolar compression of small intra-alveolar vessels
• B. Alveolar edema
• C. Vasodilation of pulmonary arteries
• D. Increased cardiac output

Answer: (A)

When lung volume climbs above the functional residual capacity, the alveolar spaces expand and mechanically squeeze the small intra-alveolar vessels and capillaries. This compression narrows their lumens, increasing the resistance to blood flow through the pulmonary circulation. That is why PVR rises with volumes above FRC. Alveolar edema would not explain this compression mechanism; vasodilation would reduce resistance, and increased cardiac output affects flow rather than causing the capillary compression that raises PVR.

When lung volume climbs above the functional residual capacity, the alveolar spaces expand and mechanically squeeze the small intra-alveolar vessels and capillaries. This compression narrows their lumens, increasing the resistance to blood flow through the pulmonary circulation. That is why PVR rises with volumes above FRC. Alveolar edema would not explain this compression mechanism; vasodilation would reduce resistance, and increased cardiac output affects flow rather than causing the capillary compression that raises PVR.