Which definition correctly expresses minute ventilation?

• A. Gas flow rate X Inspiratory time
• B. Peak inspiratory pressure minus peak end expiratory pressure
• C. Tidal volume X frequency
• D. Alveolar ventilation index

Answer: (C)

Minute ventilation is the total volume of air moved in and out of the lungs each minute. It depends on how much air is moved with each breath (tidal volume) and how many breaths occur per minute (respiratory rate). So, minute ventilation = tidal volume × respiratory rate. This is different from alveolar ventilation, which is (tidal volume − dead space) × respiratory rate, because some air fills dead space and doesn’t participate in gas exchange.

The other expressions don’t describe the amount of air moved per minute: one describes the volume during inspiration (which would approximate tidal volume under a constant flow assumption but not minute ventilation), a pressure difference measures pressure rather than volume per time, and the alveolar ventilation index is a different calculation that accounts for dead space.