Lung Volumes and Capacities
We show a of couple rounds of normal, quiet breathing, followed by maximal inspiration, maximal expiration, and, then, a couple more rounds of normal breathing.
Tidal Volume: Quiet breathing comprises inspiration and expiration of so-called "tidal volume" (TV), approximately 500 mL of air.
Inspiratory Reserve Volume: The volume of air above tidal volume that was inspired during maximal inspiration comprises Inspiratory Reserve Volume (IRV) (approximately 3000 mL).
Inspiratory Capacity: Tidal volume plus the inspiratory reserve volume comprise the Inspiratory Capacity – this is how much the individual can inspire in one intake.
Expiratory Reserve Volume: The volume of air below tidal volume that was expired during maximal expiration is the Expiratory Reserve Volume.
Residual Volume: Even at maximal expiration, we do not expire all of the air in our respiratory system; indicate that the remaining air volume is the Residual Volume.
Functional Residual Capacity: The expiratory reserve volume plus the residual volume comprises the Functional Residual Capacity.
– As we'll soon see, changes in functional residual capacity differentiate obstructive and restrictive lung diseases.
Vital Capacity: Vital capacity comprises the inspiratory reserve volume, tidal volume, and the expiratory reserve volume (in other words, all volumes except residual volume).
Total Lung Capacity: Total lung capacity comprises all air in the respiratory system.
Forced Expiratory Volume: Forced expiratory volume (FEV) is the volume of air that can be forcibly expired following maximal inspiration; we measure how much air can be forcibly expired in 1, 2, and 3 seconds to determine expiratory rate.
– For example, patients with obstructive lung disease have lower values of forced expiration volume in 1 second because expiration is impaired.
