Background : Impulse oscillometry(IOS) is a method to characterize the mechanical properties of respiratory system over wide range of frequency. It's most important advantage is to require minimal cooperations from subject. Therefore it is used to estimate pulmonary function of young children and to study epidemiology of occupational asthma. This study was performed to evaluate the usefulness for the clinical applications of IOS in bronchial asthmatics by estimating the associations between asthma severity and IOS parameters, and the relationships between IOS parameters and conventional spirometry. Methods : 216 subjects with bronchial asthma were enrolled in this study. Subjects were grouped to 3 different groups according to their symptoms and pulmonary functions. Respiratory impedance, resistance (at 5Hz, 20Hz, 35Hz) and resonant frequency were measured by IOS. FEV1, FVC and MMEF were measured with conventional spirometry. Results : There were significant difference of resonant frequency, resistance at 5Hz and 20Hz, resistance difference at 5Hz and 20Hz according to asthma severity(p<0.05, respectively). Resonant frequency, resistance at 5Hz, impedance were significantly correlated with FEV1 (r= -0.55, 0.48, 0.49, p<0.05, respectively). And resistance at 5Hz had similar reproducibility compared to FEV1 (resistance at 5Hz, r= 0.78 vs FEV1, r= 0.79). Conclusion : IOS is an useful and alternative method to evaluate clinical status of brnochial asthmatics. And further studies will be needed to clarify its values for wide range of clinical applications.(Korean J Med 59:522-528, 2000)ope
