Which mechanism contributes to pleural effusion by decreasing intrapleural pressure?

Which mechanism contributes to pleural effusion by decreasing intrapleural pressure?

• A. Increased pulmonary vascular hydrostatic pressure
• B. Decreased intrapleural pressure
• C. Decreased lymphatic drainage
• D. Rupture of vascular or lymphatic structures

Answer: (B)

The main idea is that pleural fluid movement depends on the pressure gradient across the pleural membranes. The intrapleural space is normally kept at a slight negative pressure, which helps keep the lung expanded. If this intrapleural pressure becomes more negative (decreases), the transmural pressure difference across the pleural surfaces increases. That larger gradient drives more fluid from the capillaries into the pleural space, contributing to a pleural effusion. This mechanism is distinct from increased hydrostatic pressure in the vessels (which pushes fluid into the space via higher capillary pressure), impaired lymphatic drainage (which slows removal of fluid), or rupture of vascular or lymphatic structures (which leaks fluid directly).

The main idea is that pleural fluid movement depends on the pressure gradient across the pleural membranes. The intrapleural space is normally kept at a slight negative pressure, which helps keep the lung expanded. If this intrapleural pressure becomes more negative (decreases), the transmural pressure difference across the pleural surfaces increases. That larger gradient drives more fluid from the capillaries into the pleural space, contributing to a pleural effusion. This mechanism is distinct from increased hydrostatic pressure in the vessels (which pushes fluid into the space via higher capillary pressure), impaired lymphatic drainage (which slows removal of fluid), or rupture of vascular or lymphatic structures (which leaks fluid directly).