Longitudinal changes of respiratory impedance-based phenotypes in COPD

Background: Forced oscillation technique (FOT) has been applied to chronic obstructive pulmonary disease (COPD) as a useful method to assess respiratory resistance and reactance. We hypothesized that the FOT data could reflect the pathophysiological change and the progression of COPD. Methods: One hundred eighteen COPD patients and 28 non-COPD smokers were enrolled. Chest CT scan, pulmonary function tests and FOT were performed annually. For the quantification of emphysematous lesions and airway lesions, the percentage of low attenuation volume (LAV%) and the square root of airway wall area of the hypothetical airway with an internal perimeter of 10 mm (√Aaw at Pi10) were measured by chest CT scan. Results: The COPD patients were divided into four phenotypes based on R5 and X5 of the non-COPD smokers: the normal like group (NL), the resistance dominant group (RD), the reactance dominant group (XD), and the mixed group (MIX).Relationship between severity of airflow limitation and the phenotypes revealed that the ratio of NL tended to be decreased and the ratio of MIX tended to be increased when the airflow limitation worsened. RD were limited in mild and moderate airflow limitation, while XD can be observed from mild to very sever groups. These tendency was also observed in a longitudinal analysis (after 1 year and 2 years). Among NL and RD at baseline, 10 patients whose X5 worsened after 1 year follow-up were significantly older and had lower FEV1 at baseline. On the other hand, among MIX at baseline, the 9 patients whose R5 and/or X5 improved had significantly lower √Aaw at Pi10 at baseline. Conclusion: The FOT-based phenotypes might give us a new aspect for the assessment of COPD progression.