Body plethysmography is required to measure:
|A||Inspiratory reserve volume|
|B||Expiratory reserve volume|
|D||Functional residual capacity (FRC)|
Functional residual capacity (FRC)
Spirometry cannot measure residual volume so FRC and total lung capacity (TLC) can not be measured with spirometry.
They are measured by helium dilution, nitrogen washout and body plethysmography.