During which process does the pleural pressure change?

• A. Coughing
• B. Breathing/Respiration
• C. Sleeping
• D. Digestion

Answer: (B)

Pleural pressure changes with the ventilatory cycle because the intrapleural space is kept negative to help keep the lungs expanded. During inspiration, the chest wall expands and the intrapleural pressure becomes more negative, pulling the lungs outward and allowing air to flow in. During expiration, the chest wall and lungs recoil, the intrapleural pressure becomes less negative, and air is pushed out as the lungs recoil. This pattern of pressure fluctuation is the hallmark of breathing/respiration. Coughing involves rapid, transient intrathoracic pressure shifts but is not the ongoing cycle that characterizes pleural pressure changes; sleeping is just a state during which breathing occurs, and digestion is unrelated to pleural space pressures.