Which pressure helps maintain alveolar inflation?

• A. Transrespiratory Pressure
• B. Transthoracic Pressure
• C. Transairway Pressure
• D. Transpulmonary Pressure

Answer: (D)

Transpulmonary pressure is the distending force that keeps alveoli open. It’s the difference between airway pressure and pleural pressure, so P_L = Paw − Ppl. This positive gradient across the lung tissue is what prevents alveolar collapse and maintains inflation during the breath. In practice, increasing this gradient (for example with PEEP) helps keep alveoli open at end expiration. Other pressure definitions describe drops or differences across the chest wall or airways and don’t directly determine alveolar stability, so they don’t control alveolar inflation the way transpulmonary pressure does.