Detection of small airway dysfunction in asymptomatic smokers with preserved spirometry: The value of the impulse oscillometry system

Purpose: Smoking-induced bronchiolitis with progressive small airway dysfunction (SAD) is a leading cause of chronic obstructive pulmonary disease. We investigated the value of using the impulse oscillometry system (IOS) to detect SAD in asymptomatic smokers with preserved spirometry. Patients and Methods: We included 75 asymptomatic smokers (37 females, mean age 47 ±12 years, 26±17 pack/year) with preserved spirometry [forced expiratory volume at 1st second (FEV1)/forced vital capacity (FVC) ≥0.70 and normal FVC] and 34 never-smokers (19 females, mean age 42±15 years). Results: In smokers, pack/years were significantly related to spirometry and IOS parameters (p < 0.05). The values of the fall in resistance from 5 Hz to 20 Hz (R5 – R20) were significantly and inversely related to the values of the ratio of forced expiratory volume in 3 and in 6 seconds (FEV3/FEV6) (p < 0.05). In addition, the percentage of heavy smokers (≥30 pack/year) with R5 – R20 >0.07 kPa·s·L−1, considered as IOS index of SAD, but not with FEV3/FEV6 less than a lower limit of normal, a spirometry index of SAD, was significantly higher than that of mild smokers (<30 pack/year) and never-smokers (p < 0.05). Conclusion: This study demonstrates that IOS has the potential to detect SAD in asympto-matic heavy smokers with preserved spirometry and with FEV3/FEV6 values in the normal range. We confirm that IOS provides parameters which can complement traditional measure-ments of pulmonary function.