Clinical Significance of Forced Oscillation Technique for Evaluation of Small Airway Disease in Interstitial Lung Diseases

Small airway disease (SAWD) in patients with interstitial lung disease (ILD) is often assessed by high-resolution computed tomography (HRCT). However, frequent HRCT examinations result in a high level of radiographic exposure. This study investigated the utility of the forced oscillation technique (FOT) to evaluate SAWD in patients with ILD. Broadband FOT using a commercially available device (MostGraph-01) and pulmonary function tests (PFT) were performed in 90 patients with ILD. HRCT images taken within 3 months were reviewed. The patients were divided into two groups according to the presence or absence of SAWD findings detected by HRCT. Clinical characteristics, PFT, and FOT between the two groups were compared. Of the 90 patients with ILD, 19 were classified as having SAWD findings (the presence group) and 71 as not having SAWD findings (the absence group). There were no significant differences in parameters of PFT between the two groups. The presence group had higher absolute values of reactance at 5 Hz (X5), resonant frequency (Fres), and low-frequency reactance area (ALX) than did the absence group. A within-breath change analysis demonstrated that the change in X5, Fres, and ALX between expiration and inspiration (Delta X5, Delta Fres, Delta ALX, respectively) was significantly different between the groups. A univariate analysis revealed that X5, Fres, ALX, Delta X5, Delta Fres, Delta ALX were significantly associated with the presence of SAWD findings. Multivariate analysis validated that Fres was related to the presence of SAWD findings. The FOT may be useful in detecting and evaluating SAWD in patients with ILD. Trial registration: UMIN 000020733.