Relationship Between Intra-breath Oscillometry and Pulmonary Function Testing in Patients With COPD: A Cross-sectional Study

Abstract Rationale A complete pulmonary function test (PFT) includes plethysmography and diffusion capacity testing, which are considered the reference measurements for assessing hyperinflation, gas trapping, and lung diffusing capacity. However, conducting full PFTs can be challenging due to the significant time and staff resources required, and can be difficult to access. In contrast, oscillometry is increasingly being used in daily clinical practice as a non-invasive method to characterize the mechanical properties of the respiratory system. Intra-breath oscillometry measurements have emerged as a highly sensitive technique through the detection of patterns which are not reflected by standard spectral analysis. The present study aimed to evaluate the capability of intra-breath oscillometry parameters and their correlations with hyperinflation, gas trapping, and lung diffusion capacity as an alternative to a full PFT. Methods Data from a cross-sectional observational study (ClinicalTrials.govNCT05913323), which included adult participants with spirometry-confirmed “mild” (GOLD 1) or “very severe” (GOLD 4) COPD, was used. Intra-breath oscillometry parameters, i.e., the mean difference in lung reactance between inspiration and expiration cycles (ΔXrs) and reactance-volume loop area (AXV), were calculated from testing performed at a frequency of 10 Hz. Each participant also underwent a full PFT, which included measurements of total lung capacity (TLC) as a marker of hyperinflation, the ratio of residual volume (RV) to TLC (RV/TLC) as a marker of gas trapping, and the Diffusing Capacity of the Lung for Carbon Monoxide (DLco) as a marker of gas transfer. Spearman correlation analysis, adjusted for age, sex, and FEV1, was conducted to estimate the association between the intra-breath parameters and PFT measurements. Results In 17 participants, 9 had mild and 8 had very severe COPD. Of these participants, 52.94% were female, with mean age of 66.4±8.3 years, and mean FEV1 of 1.5L (57.84% predicted). The strongest correlation coefficient observed was between ΔXrs and RV/TLC (0.75 [0.46,0.9] p<0.001), while ΔXrs was inversely correlated with DLco (-0.72 [-0.84,-0.41] p<0.001). AXV showed a weaker correlation with RV/TLC (0.69 [0.38,0.85] p<0.001) and a weaker inverse correlation with DLco (-0.50 [-0.87,-0.01] p<0.001). The correlation coefficients of ΔXrs and AXV with TLC were less than 0.5 (see Figure 1). Conclusions These results confirm that intra-breath oscillometry parameters can potentially be used to assess gas trapping and gas transfer in patients with COPD, serving as a possible complement and/or alternative to full PFTs.

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