Spirometry is the most commonly employed lung function test and can measure the amount (volume) and speed (flow) of air that can be inhaled and exhaled during both normal and forced breaths.
Common measurements obtained by spirometry include (see figure below),
- Vital capacity (VC) or forced vital capacity (FVC) – the maximum amount of air that can be expelled from the lungs after a full inhalation
- Forced expiratory volume in 1 second (FEV1) – volume of air which can be forcibly exhaled in one second
- Tidal volume (TV) – the volume of air inhaled and exhaled during restful breathing
- The inspiratory and expiratory reserve volumes (IRV and ERV) – the volume of additional air that can be forcible inhaled (IRV) or exhaled (ERV) outside of a normal tidal breath.
Spirometry diagram with lung volumes and capacities marked.
Spirometry cannot, however, be used to measure the residual volume (the volume of air present in the lungs after a forced expiration) or any capacities which incorporate the residual volume such as functional residual capacity (FRC) and total lung capacity (TLC). Volumes and capacities which include the RV are estimated using alternative techniques such as whole body plethysmography or helium dilution.