Figures
- Figure 1
Type of sound waves in FOT and IOS and distances travelled by sound waves of different frequencies.
- Figure 2
Respiratory resistance versus frequency.
- Figure 3
Reactance values in a healthy subject showing the “C” (compliance) and “I” (inertance) portions of reactance, area of reactance (AX) and resonant frequency (Fres).
- Figure 4
Position of the patient while performing IOS. Note how the cheeks are held firmly.
- Figure 5
Mean a) ΔAX and b) ΔX5 values in healthy subjects, and patients with asthma, COPD and ILD. Adapted from [28] with permission from the publisher.
Tables
- Table 1
Differences between spirometry and FOT/IOS
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 +++ + FEV1: forced expiratory volume in 1 s; FVC: forced vital capacity; PEFR: peak expiratory flow rate; FEF25–75%: forced expiratory flow at 25–75% of FVC; Zrs: respiratory impedance; Rrs: respiratory resistance; Xrs: respiratory reactance; Fres: resonant frequency; Ax: reactance area; R5: respiratory resistance at 5 Hz; X5: respiratory reactance at 5 Hz.
