What is the equation for total lung capacity (TLC)?

Total lung capacity (TLC) is defined as the maximum amount of air that the lungs can hold. This includes all the volumes of air in the lungs when they are fully inflated. The key components that make up total lung capacity are vital capacity (VC) and residual volume (RV).

Vital capacity (VC) refers to the maximum amount of air that can be exhaled after a maximum inhalation, which includes the inspiratory reserve volume (IRV), tidal volume (TV), and expiratory reserve volume (ERV). Residual volume (RV) is the amount of air that remains in the lungs after a complete exhalation and cannot be voluntarily expelled.

Therefore, the relationship can be expressed as:

TLC = VC + RV

This equation accurately reflects the total lung capacity as it quantifies both the air that can be actively exchanged during breathing (via VC) and the air that remains in the lungs at all times (RV).

The other options do not correctly encapsulate the definition of total lung capacity with the required components. For example, attempts to include combinations of FRC (functional residual capacity) or arrangements of IRV, ERV, and others do not provide the comprehensive capacity of the lungs when entirely inflated