Detection of Idiopathic Pulmonary Fibrosis Disease Progression using Respiratory Oscillometry

<bold>Background:</bold> The prognosis of idiopathic pulmonary fibrosis (<bold>IPF</bold>) is poor, with mean survival of 3-5 years. Common measures of disease progression are pulmonary function tests (<bold>PFTs</bold>) and six-minute walk distance (<bold>6MWD</bold>). However, these tests require access to healthcare facilities with qualified personnel. This is not always feasible for patients in smaller communities. Respiratory oscillometry is a different PFT modality; its metrics of lung stiffness, reactance at 5Hz during inspiration (<bold>X5in</bold>.) and end-inspiration reactance (<bold>XeI</bold>) have been found to correlate with IPF severity. <bold>Objective:</bold> To evaluate whether changes in X5in. and XeI can detect IPF progression. <bold>Methods:</bold> From September 2019 to December 2022, 230 subjects with IPF diagnosed according to international guidelines were enrolled for paired spectral (5-37Hz) and monofrequency (10Hz) oscillometry before every clinically-indicated routine PFTs and 6MWT. <bold>Results:</bold> Of the 230 subjects enrolled, 87 (58M/29F; mean±SD age=71.2±7.7 years) exhibited a decline in forced vital capacity (<bold>FVC</bold>) of ≥10% in on follow-up (mean±SD = 524 ± 260 days). In these 87 patients, we observed significant decline in the diffusing capacity (DLCO: median [IQR] = 11.8 [9.0, 15.1] vs 9.9 [7.9, 13.2] ml/min/mmHg, p=0.016), 6MWD (mean±SD = 465.4±105.6 vs 421.2±112.3 m, p=0.009). Oscillometry revealed significant worsening of both X5in and XeI (median [IQR]) = -2.1 [−2.9, -1.6] vs -2.5 [−3.4, -1.9] cmH₂O s/L and -0.6 [−1.0, -0.3] vs -0.8 [−1.3, -0.5] cmH₂O s/L, respectively, p<0.05 for both). <bold>Conclusion:</bold> X5in. and Xel can detect IPF progression and should be used when patients cannot access or perform standard PFTs.