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 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.