Abstract
The use of commercialised forced oscillation (FOT) devices 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, particularly in disease. We compared two commercially available FOT devices: Impulse Oscillometry (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-derived airway tree model resistance, as well as a 3 L standardised volume reactance. Bland-Altman Plots and linear regressions were used to evaluate bias between the devices. Resistance measurements at both 5 and 20 Hz were numerically higher with IOS compared to FOT, with evidence of small and statistically significant proportional systematic bias and a positive Bland-Altman regression slope at both 5 and 20 Hz. In contrast, the IOS device recorded reactances that were less negative at both 5 Hz and 20 Hz and significantly smaller reactance areas when compared to TremoFlo. Larger statistically significant proportional systematic biases were demonstrated with both reactance at 5 Hz and reactance area (AX) between the devices with a negative Bland-Altman regression slope. The printed airway resistance and standardised volume reactance confirmed the observations seen in patients. We have demonstrated that the impulse oscillation system and TremoFlo FOT demonstrate comparative bias, particularly when comparing airway reactance in patients. Our results highlight the need for further standardisation across FOT measurement devices, specifically using variable test loads for reactance standardisation.
Highlights
A number of studies have evaluated the utility of FOT, most commonly IOS in both adults and children
Age differed numerically across groups (p = 0.018, one way ANOVA), statistically significant differences were not seen between groups
The asthmatic individuals were primarily Global Initiative for Asthma (GINA8) treatment steps II to IV, with sub optimal control of symptoms, Asthma Control Questionnaire [ACQ-6: 1.07, 1.05)]. Both Forced Expiratory Volume in the first second (FEV1) (L) and FEV1 standardised residual (SR) were significantly different across the three groups, with significantly more expiratory flow limitation in the asthmatic group when compared with healthy controls
Summary
A number of studies have evaluated the utility of FOT, most commonly IOS in both adults and children. The purpose of this study was to evaluate and compare the impedance (resistance and reactance) between these two commercial devices using (i) a clinical population study of adults with asthma, aged matched healthy volunteers and asymptomatic smokers and (ii) using a three dimensional printed airway resistance phantom and standardised volume (reactance only) phantoms. We hypothesised that both devices would yield comparable resistance and reactance without evidence of systematic measurement bias between the two devices
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