Assessing small airways in interstitial lung diseases: The use of oscillometry

<bold>Introduction:</bold> Small airways disease (SAD) is increasingly recognized in patients with interstitial lung diseases (ILDs). Spirometry cannot reliably assess airflow through peripheral airways. Forced oscillation technique (FOT) has been reliably applied in the evaluation of SAD. <bold>Aim:</bold> To investigate the frequency of SAD in different forms of ILDs using both functional (FOT) and imaging (HRCT) modalities. <bold>Methods:</bold> Patients with ILD were prospectively enrolled in the study between 1/9/2023 and 1/2/2024. FOT was performed using Resmon Pro Full device. <bold>Results:</bold> Eighty-seven(n=87) patients were analyzed [females:43, median age (95%CI): 71.0(69 to 75), mean baseline FVC%pred ±SD: 79.3±18.9, connective tissue disease-ILD:21, idiopathic pulmonary fibrosis:20, hypersensitivity pneumonitis:8, non-specific interstitial pneumonia:8]. The frequency of small airways abnormalities based on the difference between resistance at 5 and 20Hz (R5-20) >0,7cmH2O was 30%(n=26). Thirteen patients(50%) were on bronchodilators and twelve(46%) on antifibrotics at the time of FOT. Imaging features indicative of SAD were only detected in ten patients(38%). The difference between expiratory and inspiratory reactance at 5Hz(DX5) was significantly higher and the area under reactance curve (AX) was increased in SAD group compared to patients without SAD [(0.58, 95%CI: -0.01 to 0.99, vs. -0.22, 95%CI: -0.35 to -0.1, p<0.001) and (7.43, 95%CI: 4.97 to 7.29, vs. 7.43, 95%CI: 6.18 to 10.53, p=0.02)]. <bold>Conclusion:</bold> FOT can play a significant role in the early detection of SAD in ILDs. Larger cohorts are needed to establish cut-offs points, to improve reproducibility and to explore more applications of this clinician’s and patients’ friendly modality.