Which statement describes the formula for alveolar minute volume?

• A. Tidal volume times respiratory rate
• B. (Tidal volume minus dead space) times respiratory rate
• C. Dead space times respiratory rate
• D. Tidal volume minus respiratory rate

Answer: (B)

Alveolar minute volume is the air that actually reaches the gas-exchanging parts of the lungs each minute. It is found by taking the air per breath that reaches the alveoli (tidal volume minus dead space) and multiplying by how many breaths you take per minute. So the correct expression is (tidal volume − dead space) × respiratory rate. This matters because a portion of each breath fills the dead space and doesn’t participate in gas exchange, so only the alveolar portion contributes to ventilation. The total air moved per minute (tidal volume × respiratory rate) includes dead space air and is larger—this is called minute ventilation, not alveolar ventilation. Dead space times respiratory rate equals the volume that doesn’t reach the alveoli, not the alveolar portion. Subtracting respiratory rate from tidal volume isn’t a valid calculation.