An adult weighing 70 kg has a tidal volume of $0.5 L$ , a dead space volume of $0.1 L$ and breathes at $12$ breaths per minute. Calculate the alveolar ventilation per minute.

medium 3 marks Class 11 · Biology · Breathing and Exchange of Gases

Answer

4.8 L / min

The correct answer is $4.8 L / min$ — 5. This value represents the volume of fresh air reaching alveoli per minute.

Step-by-step solution

1. Alveolar ventilation per breath is $V_{T} - V_{D}$ .
2. Compute $V_{T} - V_{D} = 0.5 L - 0.1 L = 0.4 L$ per breath.
3. Multiply by breathing frequency $f = 12$ breaths/min: $0.4 L \times 12 = 4.8 L / min$ .
4. So alveolar ventilation is $4.8 L / min$ .
5. This value represents the volume of fresh air reaching alveoli per minute.

Common mistake: Using tidal volume directly without subtracting dead space

Concept tested: Alveolar ventilation calculation