Role of Impulse Oscillometry within Multimodal Testing in Muco-Obstructive Lung Disease

Background Evidence in clinical utility of impulse oscillometry (IOS) in muco-obstructive lung disease is limited. We compared IOS with nitrogen-multiple-breath washout (N 2 MBW), spirometry, and body plethysmography in cystic fibrosis (CF), primary ciliary dyskinesia (PCD), and humoral immunodeficiencies (HID). Method At routine follow-up, 111 patients (median age 19.7 years; 42.3% male) underwent same-day IOS, N 2 MBW, spirometry, body plethysmography. We evaluated feasibility, abnormality detection, cross-test associations in the total cohort and by disease group, and modelled predictors of elevated lung clearance index (LCI). Results IOS showed excellent feasibility (100.0%), followed by N 2 MBW (99.1%); body plethysmography and spirometry were less feasible, mainly due to poor cooperation in children and effort limits in advanced disease. IOS indices indicated air trapping and ventilation inhomogeneity. Reactance (Xrs5) and resonance frequency (Fres) achieved area under the curve (AUC)≥0.70 for predicting elevated LCI, with Fres demonstrating the highest specificity and negative predictive value, while reactance area (AX) showed the greatest sensitivity. IOS correlated with both, LCI and the body plethysmographic air-trapping marker residual volume/total lung capacity (RV/TLC). In PCD and HID, IOS-LCI correlations exceeded IOS-spirometry correlations and IOS related closely to RV and RV/TLC, indicating sensitivity to small-airway dysfunction when spirometry may be normal; CF showed similar but weaker patterns. Conclusion Across ages and diagnoses, IOS aligns with N 2 MBW and body plethysmography and complements spirometry. Given its low effort and minimal need for cooperation, IOS can complement existing methods for detecting and monitoring small airway disease in muco-obstructive lung disease, where evidence and child-friendly tools remain limited.