Oscillometry Assesses Small Airway Disease and Reveals Peripheral Lung Pathology in Early Pulmonary Fibrosis: A Cross-Sectional Study

<b>Background/Objectives:</b> Small airway disease/dysfunction (SAD) is crucial in obstructive airway diseases but is less investigated in interstitial lung disease (ILD). There are only a few physiological studies investigating SAD in the context of pulmonary fibrosis. Oscillometry is a simple technique that assesses SAD with minimal patient effort. In this study, we investigated the role of oscillometry in patients with mild pulmonary fibrosis without evident obstructive disorder, focusing on small airways. <b>Methods:</b> Oscillometry and pulmonary function test (PFT) data of consecutive patients newly diagnosed with pulmonary fibrosis of unknown etiology in a university hospital ILD clinic were collected and analyzed. <b>Results:</b> Data from 34 patients with mild pulmonary fibrosis were collected in 6 months. Disease severity, as evaluated by FVC, presented strong correlations with the oscillometry parameters: resistance (R5: r = -0.588, <i>p</i> < 0.001), reactance (X5: r = 0.671, <i>p</i> < 0.001), resonant frequency (Fres: r = -0.562, <i>p</i> = 0.001), and the area of reactance (AX: r = -0.515, <i>p</i> = 0.002). The oscillometry parameter R5-19-expressing was abnormal in 27% of patients, correlated with FEF25-75% (r = -0.370, <i>p</i> = 0.021) and was a predictor of a FEF25-75% < 60% pred. with AUC 0.738 (95%Cl 0.519-0.956). R5-19 correlated with FVC (r = -0.481, <i>p</i> = 0.004) and was the only SAD parameter that correlated with the composite physiologic index (CPI, r = 0.338, <i>p</i> = 0.04), while FEF 25-75% and RV/TLC% did not. <b>Conclusions:</b> Oscillometry is an easy to perform technique that may reveal early mechanical alterations caused by pulmonary fibrosis. Peripheral resistance, as expressed by R5-19, which identifies small airway dysfunction as a marker of peripheral lung pathology, may be complementary to pulmonary function testing and may also have prognostic implications for ILD patients.