Which lung capacity includes residual volume?

• A. Vital capacity
• B. Functional residual capacity
• C. Total lung capacity
• D. Expiratory reserve volume

Answer: (C)

The correct answer is total lung capacity, which encompasses all the air in the lungs after a maximum inhalation. It includes several components, specifically tidal volume, inspiratory reserve volume, expiratory reserve volume, and importantly, residual volume. Residual volume is the amount of air that remains in the lungs after a complete exhalation and cannot be voluntarily expelled.

By definition, total lung capacity is the sum of these volumes, ensuring that even after one exhales completely, the lungs still contain this residual air to prevent lung collapse and facilitate gas exchange. This distinguishes total lung capacity from other lung capacities and volumes, such as vital capacity, which measures the maximum amount of air that can be exhaled after a maximum inhalation and does not account for any residual volume. Thus, total lung capacity is the broadest measure regarding lung volume, incorporating all aspects of lung function, including residual air.