Visualized changes in respiratory resistance and reactance along a time axis in smokers: a cross-sectional study.

BACKGROUND

Early detection of changes in respiratory function in smokers is important for the prevention of chronic obstructive pulmonary disease (COPD). The objective of this study was to investigate any changes in the respiratory impedance of smokers with normal FEV1/FVC.

METHODS

We assessed and compared the impedance components, respiratory resistance, and reactance in both the inspiratory and expiratory phases of nonsmokers, smokers, and COPD patients.

RESULTS

Approximately 60% of smokers showed elevated resistance and a negative shift in reactance, mainly in the expiratory phase, as observed in COPD patients. Smokers showed an increased gap between the maximum and minimum R5 and X5 values (R5sub, X5sub) in comparison with nonsmokers. Furthermore, R5-R20 was significantly higher in smokers than in nonsmokers. The expiratory-inspiratory gaps in resistance and reactance were also significantly higher in smokers than in nonsmokers. In smokers and COPD patients, the magnitude of expiratory X5 was more negative than that in nonsmokers. In smokers with V·50/V·25≥3, R5-R20 was significantly higher than those in smokers with V·50/V·25<3.

CONCLUSIONS

Approximately 60% of smokers were shown to exhibit apparent impedance changes despite having normal FEV1/FVC values. Smoking-induced early remodeling of the small airways may be responsible for the observed changes in airway function of smokers. Further studies are necessary to determine if the change in respiratory impedance observed in smokers is an early indicator of COPD.