What is the Difference Between Lung Volume and Lung Capacity?

Lung volumes and lung capacities are measures used to assess the function of the respiratory system. They are typically measured using a spirometer and can provide valuable information for diagnosing and managing respiratory diseases. The key differences between lung volumes and lung capacities are:

Lung Volumes: These refer to the volume of gas in the lungs at a given time during the respiratory cycle. There are four standard lung volumes: tidal volume (TV), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), and residual volume (RV). Tidal volume measures the amount of air inspired and expired during a normal breath, while inspiratory and expiratory reserve volumes represent the additional air that can be inhaled or exhaled, respectively, following a normal breath. Residual volume is the amount of air left in the lungs after a maximal exhalation and cannot be measured directly but can be calculated.
Lung Capacities: These are derived from the sum of two or more lung volumes. The four standard lung capacities are inspiratory capacity (IC), functional residual capacity (FRC), vital capacity (VC), and total lung capacity (TLC). Inspiratory capacity is the maximum volume of air that can be inhaled following a maximal exhalation, while vital capacity represents the maximum volume of air that can be inhaled or exhaled from the end of a maximal exhalation. Functional residual capacity and total lung capacity are derived from the sum of other lung volumes and represent the volume of air left in the lungs after a maximal exhalation and the total volume of air in the lungs upon the maximum effort of inspiration, respectively.

In summary, lung volumes measure the amount of air for a specific function, such as inhalation or exhalation, while lung capacities represent the sum of two or more lung volumes and provide an overview of the respiratory system's overall function.