- Lung Volumes and Capacities
|
Term |
Meaning (approx. value) |
|
Tidal Volume (TV) |
Air in/out during normal breathing (~500 mL) |
|
Inspiratory Reserve Volume (IRV) |
Extra air forcibly inhaled after a normal breath (~3,100 mL) |
|
Expiratory Reserve Volume (ERV) |
Extra air forcibly exhaled after a normal breath (~1,200 mL) |
|
Residual Volume (RV) |
Air remaining after forced exhalation (~1,200 mL) |
|
Vital Capacity (VC) |
TV + IRV + ERV — max air expired after full inhalation |
|
Total Lung Capacity (TLC) |
VC + RV — maximum air the lungs can hold |
|
Dead space air |
Air in airways that never reaches the alveoli |
Lung volumes are measured with a spirometer (a water-filled chamber with a counterweighted lid, connected by a mouthpiece, recording a trace on a rotating kymograph; soda lime absorbs COâ‚‚).