Parameter | Spirometry | FOT/IOS |
Main principle | Flow sensor/volume displacement helps measure flow rates and lung volumes | Forced oscillations of single frequency sound waves (FOT) or impulses of multiple frequency sound waves (IOS) are pushed into the lungs as pressure waves to measure respiratory resistance and reactance |
Main parameters | Volumes: FEV1, FVC | Zrs, Rrs, Xrs, Fres, Ax |
Flows: PEFR, FEF25–75% |
Patient co-operation required | +++ | + |
Type of breathing manoeuvre | Forced exhalation | Tidal breathing |
Variability (intra-subject) | 3–5% | 5–15% |
Sensitivity to airway location | | |
Central | + | +++ |
Peripheral | ++ | +++ |
Cut off for bronchodilator response | 12–15% for FEV1 | 40% for R5 or X5 |
Cut off for bronchoconstrictor response | 20% for FEV1 | 50% for R5 |
Insight into lung mechanics | + | +++ |
Standardised methodology | +++ | ++ |
Availability of robust reference values | +++ | + |