Respiratory oscillometry identifies disease progression in interstitial lung disease

Background Respiratory oscillometry is an effort-independent method of evaluating lung function. Its role in the monitoring of interstitial lung disease (ILD) is unclear. This observational longitudinal study assessed the relationship between oscillometry and pulmonary function test (PFT) parameters in ILD over time and determined whether oscillometry can detect disease progression. Methods Participants underwent PFT and oscillometry within the same visit at two time points. Oscillometry parameters of interest included resistance at 5 Hz (R 5 ), reactance at 5 Hz (X 5 ), resonant frequency (F res ) and area under the reactance curve (AX). Oscillometry and PFT parameters were compared using Spearman correlation and linear mixed-effects models. Participants were categorised as having progressed if they had interval symptomatic worsening, radiographic progression or treatment escalation. Temporal changes in lung function were evaluated using repeated measures analysis of variance. Results Of the 43 participants enrolled, 17 (40%) demonstrated interval clinical worsening over a median follow-up of 384 days. Spirometry parameters displayed moderate-to-strong correlations with all oscillometry parameters, especially the reactance measures AX and X 5 , at both time points, without a significant time interaction. When stratified by disease progression, AX, F res and X 5 displayed significant time-by-outcome interactions. PFT parameters did not significantly differ between progressors and non-progressors. Conclusion Reactance measures of oscillometry remained correlated with traditional lung function tests over time. Oscillometry parameters also showed significant temporal differences between participants with and without evidence of clinical worsening, unlike spirometry measures, which did not capture progression. These findings suggest that oscillometry may hold value in the longitudinal monitoring of ILD.