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Respir Investig. 2013 Sep;51(3):166-74. doi: 10.1016/j.resinv.2013.02.006. Epub 2013 May 4.

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

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  • 1Division of Respiratory Medicine, Department of Internal Medicine, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe, Hyogo, Japan.



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.


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


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.


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.

© 2013 The Japanese Respiratory Society. Published by Elsevier B.V. All rights reserved.


3-dimensional; 3D; COPD; Chronic obstructive pulmonary disease; FEV(1); FOT; Forced oscillation technique; Fres; ICS; LABA; LAMA; PFT; R20; R5; R5sub; R5–R20 sub; Respiratory impedance; Rrs; Rrs at 20Hz; Rrs at 5Hz; Small airway disease; Smoker; X5; X5sub; Xrs; Xrs at 5Hz; Zrs; chronic obstructive pulmonary disease; difference of R5 between maximum and minimum value; difference of X5 between maximum and minimum value; forced expiratory volume in 1s; forced oscillation technique; frequency of resonance; inhaled corticosteroids; inhaled long-acting muscarinic antagonist; long-acting beta-agonist; pulmonary function test; respiratory impedance; respiratory reactance; respiratory resistance

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