Alveolar ventilation is defined as which of the following?

• A. The total air entering the lungs per minute
• B. The volume of air that reaches the alveoli; determined by subtracting dead space air from tidal volume
• C. The maximum volume of air exhaled in one breath
• D. The oxygen content in the alveoli

Answer: (B)

Alveolar ventilation is the amount of air per unit time that actually reaches the gas-exchanging areas of the lungs. Per breath, this is the portion of tidal volume that makes it to the alveoli, which means subtracting the air that fills the conducting airways (dead space) from the total tidal volume. So the air reaching the alveoli per breath is tidal volume minus dead space, and to get the per-minute value you multiply by the breathing rate.

This is why the best description is the volume of air that reaches the alveoli, determined by subtracting dead space air from tidal volume. If you know tidal volume and dead space, you can estimate alveolar ventilation, and you’d multiply by the respiratory rate to get per-minute alveolar ventilation (VT − VD) × f.

Understanding helps you see why the other ideas aren’t alveolar ventilation: total air entering the lungs per minute is minute ventilation, not all of which reaches the alveoli; the maximum volume exhaled in one breath describes a different lung volume measure; and oxygen content in the alveoli describes gas composition, not the amount of air reaching the alveoli for gas exchange.