Total Lung Capacity (TLC) is defined as

• A. The sum of vital capacity and residual volume.
• B. The sum of tidal volume and inspiratory reserve volume.
• C. The sum of tidal volume and residual volume.
• D. The sum of residual volume and inspiratory reserve volume.

Answer: (A)

Total Lung Capacity is the total amount of air in the lungs after a maximal inhalation. This full capacity combines the air you can actively move in and out (vital capacity) with the air that stays in the lungs even after a full exhale (residual volume). So TLC = vital capacity + residual volume.

Vital capacity is the maximum air you can exhale following a deep breath, and residual volume is the air remaining in the lungs after a maximum exhalation. Add those together and you get the total air the lungs can hold at full inflation.

The other options mix volumes that don’t sum to TLC: tidal volume with inspiratory reserve is related to inspiratory capacity, not TLC; tidal volume with residual volume isn’t a standard lung capacity; and residual volume with inspiratory reserve doesn’t correspond to a named total lung capacity.