Characterization of Idiopathic Pulmonary Fibrosis (IPF) and Combined Pulmonary Fibrosis and Emphysema (CPFE) using Respiratory Oscillometry

Introduction: Idiopathic pulmonary fibrosis (IPF) is one of the most common forms of interstitial lung diseases (ILD), while combined pulmonary fibrosis and emphysema (CPFE) is a distinct entity with upper lobe emphysema and lower lobe fibrosis, occurring mostly in men with > 40 pack years of smoking. While pulmonary function tests (PFTs) are used to determine the severity and monitor disease progression, they are a poor measure of lung elastance and compliance, and do not readily distinguish between IPF and CPFE. Respiratory oscillometry (Osc) performed during tidal breathing, is exquisitely sensitive respiratory mechanics but has not been well studied in ILD. Objective: To characterize IPF and CPFE using Osc. Methods: Patients with IPF and CPFE diagnosed according to ATS/ETS guidelines, were prospectively enrolled for paired PFTs-Osc and six-minute walk test (6MWT). Comparisons between IPF and CPFE were performed using the Student’s T-test. Results: 201 IPF (70F, 131M; median age=65.2) and 26 CPFE (7F, 19M; median age=73.1) patients were enrolled from Sept 2019-Dec 2021. Osc was significantly different between IPF and CPFE, particularly in the reactance (X) measurements (p<0.05 for all) of X5in (mean inspiratory X at 5Hz) and the intrabreath metrics, XeI (X at end inspiration) and AXV (area of X-volume loop). In contrast, %predicted diffusing capacity was the only standard PFT parameter that was significantly different between the 2 groups. CPFE patients also had lower absolute and % predicted 6MWT (p<0.01). Conclusion: These findings suggest that Osc can provide information to distinguish IPF from CPFE that is not available with standard PFTs.