Intrapulmonary pressure is defined as the pressure inside which anatomical region?

• A. The pleural cavity
• B. The respiratory tract, at the alveoli
• C. Atmospheric pressure
• D. The chest wall

Answer: (B)

Intrapulmonary pressure is the pressure inside the lungs, specifically within the alveolar spaces of the respiratory tract. This alveolar (lung) pressure changes as you breathe: it drops slightly below atmospheric pressure during inspiration to draw air in, then rises above atmospheric pressure during expiration to push air out. At the end of each breath, it roughly equals atmospheric pressure, so there’s no net airflow. This is different from intrapleural pressure, which is the negative pressure in the pleural cavity that helps keep the lungs inflated, and it’s not a pressure of the chest wall itself.