Which formula correctly defines Total Lung Capacity (TLC)?

Which formula correctly defines Total Lung Capacity (TLC)?

• A. RV + ERV
• B. RV + VC
• C. TV + IRV
• D. RV + TV

Answer: (B)

Total Lung Capacity is the maximum amount of air the lungs can hold after a full, deep inspiration. It combines the air that remains in the lungs after a complete exhale (residual volume) with the total amount you can move in and out of the lungs during a full breath (vital capacity). So the correct way to express TLC is RV plus VC. Why this fits: TLC must account for all the air in the lungs, which is the sum of what’s left after exhaling as much as you can (RV) and the amount you can actively move in and out during a full range of breathing (VC). If you add RV to VC, you’re capturing both components, giving the total capacity. In the alternatives: RV plus ERV would give the amount left after a normal exhale (functional residual capacity), not TLC. TV plus IRV gives inspiratory capacity, the amount you can inhale after a normal exhale. RV plus TV isn’t a standard measure for any common lung capacity. For a quick example, if RV is 1.5 L and VC is 4.5 L, TLC would be 6.0 L.

Total Lung Capacity is the maximum amount of air the lungs can hold after a full, deep inspiration. It combines the air that remains in the lungs after a complete exhale (residual volume) with the total amount you can move in and out of the lungs during a full breath (vital capacity). So the correct way to express TLC is RV plus VC.

Why this fits: TLC must account for all the air in the lungs, which is the sum of what’s left after exhaling as much as you can (RV) and the amount you can actively move in and out during a full range of breathing (VC). If you add RV to VC, you’re capturing both components, giving the total capacity.

In the alternatives: RV plus ERV would give the amount left after a normal exhale (functional residual capacity), not TLC. TV plus IRV gives inspiratory capacity, the amount you can inhale after a normal exhale. RV plus TV isn’t a standard measure for any common lung capacity.

For a quick example, if RV is 1.5 L and VC is 4.5 L, TLC would be 6.0 L.