What is the formula to calculate total lung capacity?

The total lung capacity (TLC) is the maximum amount of air the lungs can hold after taking the deepest breath possible. To understand the correct formula for calculating TLC, it's essential to recognize the components involved.

The total lung capacity is calculated by adding the following volumes:

• Residual Volume (RV): the amount of air remaining in the lungs after a full exhalation.

• Expiratory Reserve Volume (ERV): the volume of air that can be forcibly exhaled after the expiration of a normal tidal volume.

• Tidal Volume (TV): the amount of air inhaled or exhaled during normal breathing.

• Inspiratory Reserve Volume (IRV): the amount of air that can be forcibly inhaled after the inspiration of a normal tidal volume.

Therefore, the formula for total lung capacity indeed combines all four of these key volumes: RV, ERV, TV, and IRV. This comprehensive summation accounts for all the air that can fill the lungs completely. Hence, the correct formula for total lung capacity is RV + ERV + TV + IRV.