Intrapulmonary pressure is defined as which of the following?

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

Answer: (B)

Intrapulmonary pressure is the pressure inside the lungs, specifically in the respiratory tract at the level of the alveoli. This is the pressure that fluctuates as you breathe and drives air in and out of the lungs: it becomes slightly lower than atmospheric during inspiration to pull air in, then slightly higher than atmospheric during expiration to push air out, and it is equal to atmospheric pressure at the end of each breath. This is distinct from intrapleural pressure, which is the pressure in the pleural cavity, and from atmospheric pressure, which is the outside air.