Respiratory reactance in forced oscillation technique reflects disease stage and predicts lung physiology deterioration in idiopathic pulmonary fibrosis

Background: Idiopathic pulmonary fibrosis (IPF) is a chronic progressive disease. Although pulmonary function test (PFT) is useful for evaluating the progression of IPF, obtaining adequate results in advanced cases can be challenging. Conversely, the forced oscillation technique (FOT) can be noninvasively performed, even in patients with severely deteriorated lung function. In this study, the usefulness of FOT for the evaluation of IPF disease status was investigated. Methods: We analyzed the PFT and FOT data of 97 patients with IPF. Results: The respiratory reactance (Xrs) components of FOT, especially in the inspiratory phase, correlated with the PFT values. Patients with advanced disease had significantly lower reactance at 5 Hz (X5), higher resonant frequency (Fres) and low-frequency reactance area (ALX). The longitudinal deterioration of Xrs was also observed. Moreover, X5 in the inspiratory phase predicted subsequent lung capacity deterioration. Conclusion: The Xrs components of FOT, especially in the inspiratory phase, reflected restrictive ventilatory impairment and disease severity in patients with IPF.