Forced oscillation technique in veterans with preserved spirometry and chronic respiratory symptoms

Purpose: To evaluate the utility of the forced oscillation technique (FOT) among military veterans with preserved spirometry and chronic unexplained respiratory symptoms. Methods: 178 veterans referred for evaluation of unexplained respiratory symptoms completed pulmonary function testing and FOT. Preserved spirometry was defined as FEV1/FVC, FEV1 and FVC >= 5th percentile. Frequency dependence of resistance (R4-R20) and reactance area (AX) were assessed via FOT, and R4-R20 >= 20% and AX >= 95th percentile were considered abnormal. Results: Spirometry was preserved in 71.3%, of whom 124 had acceptable FOT data. 93 of 124 (75.0%) veterans with preserved spirometry had one or more abnormal findings on FOT. Veterans with abnormal R4-R20 and/or AX had reduced FVC, FEV1, FEF25-75, and diffusing capacity (% predicted) in comparison to those with Normal FOT (p = 0.030 top < 0.001). Conclusions: In our referral sample, distal airway dysfunction in the presence of preserved spirometry appears common and may represent an at-risk group requiring closer surveillance.