Pulmonary ventilation is defined as

• A. Gas exchange between alveoli and blood.
• B. The diffusion of oxygen into the blood.
• C. Inflow and outflow of air within the lungs.
• D. The inflow and outflow of air between the atmosphere and lungs.

Answer: (D)

Pulmonary ventilation is the bulk movement of air into and out of the lungs, meaning the inflow and outflow of air between the atmosphere and the lungs. This breathing process happens as the chest expands and contracts, changing the pressure inside the thoracic cavity so air rushes in during inspiration and out during expiration. It sets up the fresh air that reaches the alveoli for gas exchange but is not itself the gas exchange step. The other descriptions refer to what happens after air reaches the lungs: gas exchange between the alveoli and blood, or the diffusion of oxygen into the blood, which occur across the alveolar–capillary membrane rather than the bulk movement of air.