Which mechanism leads to pleural effusion via decreased intrapleural pressure (atelectasis)?

Which mechanism leads to pleural effusion via decreased intrapleural pressure (atelectasis)?

• A. Decreased intrapleural pressure
• B. Increased hydrostatic pressure
• C. Increased capillary permeability
• D. Rupture of vessels

Answer: (A)

When pleural effusion forms through this route, the key idea is that fluid balance in the pleural space is tipped by changes in pleural pressure and lymphatic drainage. If intrapleural pressure drops (becomes less negative), the lung loses volume and portions of the pleura can collapse. This atelectasis impairs the parietal pleural lymphatics’ ability to clear pleural fluid. With continued capillary filtration and reduced drainage, fluid accumulates in the pleural space, producing an effusion. The other mechanisms describe different paths to effusion: higher hydrostatic pressure drives fluid out of capillaries, increased capillary permeability (inflammation) raises fluid leakage, and rupture of vessels can release blood into the space.

When pleural effusion forms through this route, the key idea is that fluid balance in the pleural space is tipped by changes in pleural pressure and lymphatic drainage. If intrapleural pressure drops (becomes less negative), the lung loses volume and portions of the pleura can collapse. This atelectasis impairs the parietal pleural lymphatics’ ability to clear pleural fluid. With continued capillary filtration and reduced drainage, fluid accumulates in the pleural space, producing an effusion.

The other mechanisms describe different paths to effusion: higher hydrostatic pressure drives fluid out of capillaries, increased capillary permeability (inflammation) raises fluid leakage, and rupture of vessels can release blood into the space.