Clinical Applications of Forced Oscillation Techniques (FOT) in Patients with Bronchial Asthma

BACKGROUND: Forced oscillation technique (FOT) is a method to characterize the mechanical properties of the respiratory system over a wide range of frequencies. Its’ most important advantage is to require minimal cooperation from the subject. This study was performed to evaluate the usefulness of the FOT applications in patients with bronchial asthma by estimating the associations between asthma severity and FOT parameters, and the relationships between FOT and spirometry parameters. METHODS: 216 patients with asthma were enrolled in this study. Patients were classified into 3 different groups according to their symptoms and pulmonary functions. Respiratory impedance, resistance (at 5 Hz, 20 Hz, 35 Hz) and resonant frequency were measured by FOT. FEV(1), FVC and MMEF were measured with conventional spirometry. RESULTS: There were significant differences of resonant frequency, resistance at 5 Hz and 20 Hz, resistance difference at 5 Hz and 20 Hz according to asthma severity (p<0.05, respectively). Resonant frequency, resistance at 5 Hz, and impedance were significantly correlated with FEV(1) (r = −0.55, −0.48, −0.49, p<0.05, respectively), and with MMEF in patients with normal pulmonary function (r = −0.37, −0.35, −0.34, p<0.05, respectively). Resistance at 5 Hz had similar reproducibility compared to FEV(1) (resistance at 5 Hz, r = 0.78 vs FEV(1), r = 0.79). CONCLUSION: FOT is a useful and alternative method to evaluate the clinical status of bronchial asthma. Further studies will be needed to clarify its value for a wide range of clinical applications.