Background: The use of commercialised forced oscillation techniques to assess impedance in obstructive diseases such as asthma has gained popularity. However, it has yet to be fully established whether resistance and reactance measurements are comparable across different FOT devices.
Methods: We compared two commercially available FOT devices: Impulse Oscillometry System (IOS) and TremoFlo FOT (Thorasys) in a) clinical adult population of healthy controls (n=14), asymptomatic smokers (n=17) and individuals with asthma (n=73) and b) a 3D printed CT-based airway model resistance, as well as a 3 litre standardised volume reactance.
Results: Resistance measurements were higher with FOT compared to IOS, however there was no evidence of systematic bias. In contrast, significant bias was demonstrated with reactance (primarily elastance) measurements across the devices. The TremoFlo device recorded smaller (more negative) reactances at 5Hz and 20Hz (numerically smaller) when compared to IOS. The printed airway resistance and standardised volume reactance confirmed the observations in patients.
Discussion: We have demonstrated that the impulse oscillation system and Tremoflo FOT generate comparable measurements of airways resistance. In contrast, FOT appeared to be more sensitive at probing airway elastance properties when compared to IOS. Our results highlight the need for further standardisation across FOT measurement devices.