A spirometer measures the volumes in the lung during different patterns of respiration.

In Fig 1, the spirometry trace indicates quiet breathing interrupted by one maximal inspiration and expiration (approximate values for a fit young male).

The following measures are shown:

V_T Tidal volume (500 mL)

IRV Inspiratory reserve volume (3000 mL)

ERV Expiratory reserve volume (1500 mL)

RV Residual volume (1000 mL)

TLC Total lung capacity (6000 mL)

VC Vital capacity (5000 mL)

FRC Functional residual capacity (2500 mL)