Role of Impulse oscillometry(IOS)in diagnosing small airway dysfunction in patients with ILD-A prospective observational study

Abstract

Background: ILDs are known to cause structural alterations in peripheral airways. Conventional tests like spirometry and HRCT chest are not very sensitive to diagnose small airway dysfunction(SAD) in ILD. IOS can be used as non-invasive, easy to perform method to reliably detect and measure early onset SAD in ILD patients thus offering potential pharmaceutical benefits. Objective: To assess the frequency of SAD in ILD patients using IOS and correlate its findings with spirometric parameters Methods: This prospective observational study enrolled 123 consecutive patients, aged>20years, diagnosed as ILD(clinical, radiological or histopathological basis as per ATS/ERS criteria) between 2016-2017. Cardiac patients and acutely ill patients were excluded from study. All patients underwent spirometry, IOS and HRCT chest; outcome parameters were recorded in a prestructured Performa and correlated statistically. Results: Out of total, 26%(n=32) were found to have SAD on IOS with mean age 60.91±8.7years and female predominance(75%). Majority had symptom duration between 3-7 years(n=21) and etiology as hypersensitivity pneumonitis(n=10), sarcoidosis(n=9) and CTD-ILD(n=8). FEV1, FVC, FEV1/FVC ratio and FEF25% were significantly negatively correlated with R5, R5-20, D5-20%, AX and significantly positively correlated with X5. On ROC curve, X5(AUC=77.8%) and AX(AUC=77.9%) had highest diagnostic ability to detect SAD on IOS. Conclusion: IOS is a good modality to detect small airway dysfunction in early stages and certain occupational ILD where spirometry may remain normal and can be used as an adjunct to spirometry both for diagnosis and follow up of therapeutic outcomes in ILD.