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 FEV/FVC, FEV 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, FEV, FEF, and diffusing capacity (% predicted) in comparison to those with Normal FOT (p = 0.030 to p <  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.