List I | List II | ||
A | Expiratory capacity | I | Expiratory reserve volume + Tidal volume + Inspiratory reserve volume |
B | Functional residual capacity | II | Tidal volume + Expiratory reserve volume |
C | Vital capacity | III | Tidal volume + Inspiratory reserve volume |
D | Inspiratory capacity | IV | Expiratory reserve volume + Residual volume |
The air that we breathe in and breathe out of the lungs varies in its pressure. So basically when there is a fall down in air pressure the alveolar spaces drop down and the air enters the lungs (inspiration) as the pressure of the alveoli surpasses the atmospheric pressure, the air that is blown from the lungs (expiration). The rate of flow of air is in proportion to the magnitude of the pressure difference.
Read More: Mechanism of Breathing