Which expression correctly defines alveolar ventilation?

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Multiple Choice

Which expression correctly defines alveolar ventilation?

Alveolar ventilation is the portion of air per minute that actually reaches the gas-exchanging units of the lungs. It’s found by removing the air that fills the dead space from each breath, then multiplying by how many breaths you take per minute: VA = (VT − VD) × f. This is why the correct expression uses the difference between tidal volume and physiologic dead space, then scales by the breathing rate. For example, with a tidal volume of 500 mL, dead space of 150 mL, and a rate of 12 breaths per minute, alveolar ventilation is (500 − 150) × 12 = 350 × 12 = 4200 mL/min. Total minute ventilation, VT × f, includes the air that fills dead space and doesn’t participate in gas exchange, which is why it’s larger than alveolar ventilation in most cases. The other expressions either count dead space air alone or produce nonsensical results.

Alveolar ventilation is the portion of air per minute that actually reaches the gas-exchanging units of the lungs. It’s found by removing the air that fills the dead space from each breath, then multiplying by how many breaths you take per minute: VA = (VT − VD) × f.

This is why the correct expression uses the difference between tidal volume and physiologic dead space, then scales by the breathing rate. For example, with a tidal volume of 500 mL, dead space of 150 mL, and a rate of 12 breaths per minute, alveolar ventilation is (500 − 150) × 12 = 350 × 12 = 4200 mL/min.

Total minute ventilation, VT × f, includes the air that fills dead space and doesn’t participate in gas exchange, which is why it’s larger than alveolar ventilation in most cases. The other expressions either count dead space air alone or produce nonsensical results.

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