Tidal volume is the volume of air inhaled or exhaled during one normal breath. Vital capacity is the maximum volume of air that can be exhaled after the deepest possible inhalation; both can be measured using a spirometer.
Lung-volume definitions
This content is required at both SL and HL in subtopic B3.1 Gas exchange.
| Lung volume | Meaning | How it appears on a spirometer trace |
|---|---|---|
| Tidal volume | Air moved into or out of the lungs in one normal breath | Vertical difference between a normal peak and the following trough |
| Inspiratory reserve volume | Additional air inhaled after a normal inhalation | From the normal inhalation peak to the maximum inhalation level |
| Expiratory reserve volume | Additional air exhaled after a normal exhalation | From the normal exhalation trough to the maximum exhalation level |
| Vital capacity | Maximum air exhaled after maximum inhalation | Difference between the maximum inhalation and maximum exhalation levels |
Therefore: