Forced oscillation technique (FOT) has led to an increased understanding of respiratory mechanics. Several FOT devices are commercially available. There remain uncertainties about the comparability across different FOT devices.
This study assessed the agreement between two FOT devices, Impuls Oscillometry (IOS) and TremoFlo (AOS), in patients with asthma (n=53) and chronic obstructive pulmonary disease (COPD) (n=52).
All patients underwent routine pulmonary function tests, IOS and AOS. IOS/AOS parameters included resistance at 5 Hz (R5), at 20 Hz (R20), the fall in resistance from 5 to 20 Hz (R5-20), reactance at 5 Hz (X5), reactance area (AX), and resonant frequency (Fres). Spearman correlation determined the relationship between IOS/AOS parameters. Agreement between the FOT devices was assessed using Bland-Altman plots.
Analysis showed a strong correlation between the two devices with regard to resistance (R5, R20, R5-20, ρ = 0.812, 0.845, 0.821, p<0.01) and reactance variables (X5, AX and Fres, ρ = 0.855, 0.895, 0.905, p<0.01). Although Bland-Altman plots demonstrated good agreement for resistance variables, they suggested a bias for reactance variables (figure 1).
In conclusion, results from IOS and AOS show a high correlation both for resistance and reactance variables. Agreement between the two devices is seen for resistance variables only.