Oscillatory respiratory impedance and lung tissue compliance

The respiratory impedance was measured by means of the forced oscillation technique (Landser et al.) and the lung tissue compliance was measured with an oesophageal balloon in 30 patients with a wide range of values of lung tissue compliance. According to the model of respiratory impedance of Nagels et al. it is unlikely that the impedance data are markedly affected by the lung tissue compliance. This hypothesis has not been clinically tested yet. The semistatic compliance (Css) or specific compliance (Cspec) were not statistically correlated with any of the impedance data. Consequently the oscillatory respiratory measurements are not systematically influenced by the compliance of the lung tissue during quiet breathing. However, the dynamic compliance and the frequency dependence of the compliance showed a low but significant correlation with the reactance and resonant frequency (varying from r = 0.41, P < 0.05 to r = -0.54, P < 0.01). A significant correlation was found between the frequency dependence of the lung tissue compliance and the frequency dependence of the oscillatory resistance, both being indicative of peripheral airway obstruction (varying from r = -0.54, P < 0.01 for the whole group, to r = -0.75, P < 0.001 for 15 patients with severe peripheral airway obstruction: mean (SD) FEV1 59.5 (24.8)% pred, mean (SD) MEF50 30.9 (25.8)% pred.