The diagnostic value of total respiratory impedance by impulse oscillometry in chronic obstructive lung disease.

Abstract

To investigate the diagnostic significance of total respiratory impedance for chronic obstructive lung disease. The impedance of respiratory system was measured by impulse oscillometry method and compared with parameter values of routine pulmonary function in 57 patients with chronic obstructive pulmonary disease (COPD). It significantly increased in viscous resistance ranging from 5 Hz and 35 Hz and resonant frequency in COPD group than that in healthy group. Reactance from 5 Hz and 35 Hz in COPD group was marked lower than that in healthy group. There were marked frequency dependence of viscous resistance and reactance in COPD patients. Resonant frequency was markedly and negatively correlated with parameters of pulmonary ventilation indices; X5 was positively correlated with parameters of pulmonary ventilation indices. But no statistical correlation was showed between R20 and parameters of pulmonary ventilation indices. Correlation was found between resonance frequency and FEV1, resonance frequency and Vmax. The correlation coefficient values were -0.671 and -0.666 respectively. The sensitivity of resonant frequency, R5 and X5 for diagnosing COPD were 94.74%, 59.65% and 54.38%, respectively. The specificity of them were 86.66%, 96.66% and 90%, respectively. Resonant frequency was the most sensitive index in the parameters measured by IOS for diagnosing COPD. Since impedance measurement was a non-invasive method and only passive co-operation of the patient was needed. This technique could therefore be applied in COPD patients with acute attack for dynamic examination.