If tidal volume is 750 mL, dead space is 150 mL, and respiratory rate is 12 breaths per minute, alveolar ventilation is:

• A. 6,000 mL
• B. 5,400 mL
• C. 8,400 mL
• D. 7,200 mL

Answer: (D)

Alveolar ventilation is the amount of air per minute that actually reaches the gas-exchanging units of the lungs. To get this, remove the dead space from each breath and then multiply by the breathing rate. Here, the air reaching the alveoli per breath is 750 mL minus 150 mL, which equals 600 mL. With a respiratory rate of 12 breaths per minute, alveolar ventilation = 600 mL per breath × 12 breaths per minute = 7,200 mL per minute. This is lower than total minute ventilation (which would be 750 mL × 12 = 9,000 mL/min) because some air fills dead space and does not participate in gas exchange. The other options arise from using the full tidal volume without subtracting dead space or from a different breathing rate.