RESPIRATORY MECHANICS IN VENTILATED COPD PATIENTS - FORCED OSCILLATION VERSUS OCCLUSION TECHNIQUES

The respiratory mechanics of artificially ventilated chronic obstructi ve pulmonary disease (COPD) patients mere investigated by moans of the forced oscillation (FOT) and the end-inspiratory airway occlusion (AO T) techniques. FOT was applied to measure respiratory resistance (Rrs) and reactance (Xrs) from 0.25-16 Hz. Maximum (Rmax) and minimum (Rmin ) resistances, static elastance (Est) and time constant (tau) mere com puted by AOT. FOT and AOT data were interpreted with models featuring airway wall shunt, tissue viscoelasticity and parallel inhomogeneity. Rrs and Xrs*, predicted from the AOT data, were computed and compared with Rrs and Xrs measured by FOT. Rrs and Xrs (hPa . s . L-1) decreas ed from 31.2+/-10.3 to 5.9+/-4.6 and increased from -20.3+/-7.1 to -8. 0+/-4.4 from 0.25-16 Hz, respectively. Central resistance (Rc) and per ipheral resistance (Xp) tin hPa . s. L-1), and shunt elastance (Esh) a nd tissue elastance (Et) (in hPa . L-1) were 4.4+/-5.4, 28.4+/-15.3, 7 23+/-393 and 31.8+/-10.1, respectively. Rmin, Rmax and Est were 18.4+/ -5.9, 28.4+/-12.8 and 18.1+/-4.2 respectively, and tau=0.76+/-0.25 s. The frequency dependence of predicted Rrs and Xrs* differed markedly from that of measured Rrs and Xrs. The use of different models to inte rpret the measured data suggests that both airway and tissue propertie s determined the frequency dependence of respiratory resistance and re spiratory reactance in ventilated chronic obstructive pulmonary diseas e patients at the investigated frequencies 10.25-16 Hz).