If tidal volume is 500 mL, dead space is 150 mL, and respiratory rate is 12 breaths per minute, what is the alveolar ventilation rate?

If tidal volume is 500 mL, dead space is 150 mL, and respiratory rate is 12 breaths per minute, what is the alveolar ventilation rate?

• A. 4200 mL/min
• B. 6000 mL/min
• C. 3150 mL/min
• D. 2400 mL/min

Answer: (A)

Alveolar ventilation rate is the amount of air that actually reaches the alveoli for gas exchange each minute. To find it, subtract dead space from the tidal volume to get the effective volume per breath, then multiply by the respiratory rate. Here, that’s 500 mL minus 150 mL equals 350 mL per breath. At 12 breaths per minute, the alveolar ventilation is 350 × 12 = 4200 mL per minute. So the alveolar ventilation rate is 4200 mL/min. This differs from total ventilation, which would use the full tidal volume, not accounting for the portion that doesn’t participate in gas exchange.

Alveolar ventilation rate is the amount of air that actually reaches the alveoli for gas exchange each minute. To find it, subtract dead space from the tidal volume to get the effective volume per breath, then multiply by the respiratory rate. Here, that’s 500 mL minus 150 mL equals 350 mL per breath. At 12 breaths per minute, the alveolar ventilation is 350 × 12 = 4200 mL per minute. So the alveolar ventilation rate is 4200 mL/min. This differs from total ventilation, which would use the full tidal volume, not accounting for the portion that doesn’t participate in gas exchange.