Discrepancy between airwave and impulse oscillometry measurements of impedance in healthy children

Introduction: Respiratory oscillometry (OSC) is a pulmonary function test that measures respiratory system impedance and is well-suited for young children. Previous studies have suggested that there may be differences between impedance values obtained on different instruments, however, no studies comparing instruments have been done in healthy children. Methods: We performed both impulse oscillometry (IOS) and airwave oscillometry (AOS), in random order, in a cohort of healthy children with no history of cardiopulmonary disease or recent illness. We used linear regression analysis and Bland Altman plots to compare results. Results: Eighty children ages 4 – 18 years completed study visits. Compared with AOS, the IOS mean and median values for resistance at 5 Hz (R5) were higher (p < 0.001), reactance at 5 Hz (X5) mean and median values were less negative (p < 0.001), and both the area under the reactance curve (AX) and resonant frequency (Fres) were lower (p < 0.001). Bland Altman analysis revealed proportional bias between the two systems. Conclusions: Our results in healthy children show differences between results obtained on different OSC instruments. This may be due to differences in the type of pressure signal produced by the instrument, or, in the case of IOS, may be related to a stress-relaxation response. Our results suggest that normal values obtained on one instrument may not be comparable to results obtained on another.