I Say IOS You Say AOS: Comparative Bias in Respiratory Impedance Measurements

Abstract

Background The forced oscillation technique (FOT) measures respiratory impedance during normal tidal breathing and requires minimal patient cooperation. Objective To compare IOS and AOS devices in patients with asthma and COPD. Methods We compared two different FOT devices, namely impulse oscillometry using a loudspeaker (IOS: Jaeger Masterscreen) and airwave oscillometry using a vibrating mesh (AOS: Thorasys Tremoflo) for pre- and post-bronchodilator measurements in 84 patients with asthma and COPD. Results The overall pattern of measurement bias was for higher resistance with IOS and higher reactance with AOS, this being the case in asthma and COPD separately. There were small but significantly higher values using IOS for resistance at 5 Hz (R5) and 20(19) Hz (R20(19)). In converse, values for reactance at 5 Hz (X5), reactance area (AX) and resonant frequency (Fres) were significantly higher using AOS but to a much larger extent. The difference in AX between devices was more pronounced in COPD than in asthma. Salbutamol reversibility as % change was greater in asthma than COPD patients with AX but not FEV1. Conclusion Our study showed evidence of better agreement for resistance than reactance when comparing IOS and AOS, perhaps inferring that AOS may be more sensitive at measuring reactance in patients with airflow obstruction. Electronic supplementary material The online version of this article (10.1007/s00408-019-00247-y) contains supplementary material, which is available to authorised users.

Comparison of oscillometry devices using active mechanical test loads

“…with and without simulated breathing with any of the devices) (figure S1a-f). Device performances were also characterised in terms of commonly employed Z rs measures, such as f res , A X and R 5-20 (19) ( figure 5). The theoretical values of f res were nicely recovered by some devices (Wave Tube, TremoFlo and Resmon Pro), while they were markedly mis-estimated or even undetected by the rest of the devices (figure 5a).…”

“…While almost all devices were relatively accurate in measuring reactance at the lower frequencies, poor performance at higher frequencies resulted in widely variable values in f res and A X , which are common indices to describe the elasticity of the respiratory system and the inhomogeneity of the lung periphery [5,28,29]. Smaller differences were seen in the courses of R m ; however, these were magnified in the scattering values of R 5-20 (19) , a popular measure suggested to characterise peripheral airway obstruction [29]. Although the physiological validity of these oscillometry measures has yet to be confirmed, the huge biases due to the different performances of the oscillometry devices reduce their utility in clinical practice; indeed, interdevice comparisons [16][17][18][19] have raised concerns about systematic differences in these measures.…”

“…Smaller differences were seen in the courses of R m ; however, these were magnified in the scattering values of R 5-20 (19) , a popular measure suggested to characterise peripheral airway obstruction [29]. Although the physiological validity of these oscillometry measures has yet to be confirmed, the huge biases due to the different performances of the oscillometry devices reduce their utility in clinical practice; indeed, interdevice comparisons [16][17][18][19] have raised concerns about systematic differences in these measures. These findings also emphasise that standardisation criteria [5] based on single values of Z rs (or R rs , X rs and |Z rs |) alone are insufficient because of the growing importance of the derived indices mentioned above.…”

“…If f res was beyond the measurement frequencies, integration was truncated at the highest frequency. A commonly used measure of peripheral respiratory mechanics, the difference in R rs between 5 and 20 or 19 Hz (whichever is available) was also characterised by the R 5-20 (19) values. Two devices (MostGraph-02 and Resmon Pro) each offered two different spectral signal types (table 2), and the tests were accomplished with both versions.…”

“…The importance of device compatibility has long been recognised, and initial studies comparing the performance of two or more oscillometry devices have been conducted in the same subjects [11][12][13][14][15][16][17][18][19], different study populations [20], or known mechanical test loads [14, 16-18, 21, 22]. However, to our knowledge, reports comparing outputs of all five of the currently marketed oscillometry devices have not been published.…”