PARTITIONING OF PULMONARY IMPEDANCE - MODELING VS ALVEOLAR CAPSULE APPROACH

Pulmonary input impedance (ZL), transfer tissue impedances (Ztti), and transfer airway impedances (Ztaw) were measured in open-chest dogs an d isolated canine lungs by means of small-amplitude pseudorandom oscil lations between 0.2 and 21.1 Hz. In the determination of Ztti and Ztaw , local alveolar pressures (PA) sensed in alveolar capsules were used. The global impedances of the airways (Zaw) and tissues (Zti) were est imated by fitting to the ZL data between 0.2 and 4.9 Hz (open-chest do gs) and between 0.2 and 5.9 Hz (isolated lungs) two models based on Hi ldebrandt's formulations (Bull. Math. Biophys. 31: 651-667, 1969), the parameters of which included airway resistance (Raw) and inertance (l aw) and tissue damping (GL) and elastance (HL). The tissue parameters of Ztti (Gti and Hti) were also obtained from model fitting, whereas t he Ztaw data were evaluated in terms of resistance (Rtaw) and inertanc e (Itaw). Excellent agreement was found between HL and Hti in both exp erimental groups and between GL and Gti in the isolated lungs (r great er-than-or-equal-to 0.999). The damping coefficients were also closely related in the open-chest dogs (r = 0.95), but Gti overestimated GL s lightly (by 9%). Raw was underestimated by Rtaw (by 3-33%) and law by Itaw (by 2-16%), depending on the model type and, in the excised lungs , the number of punctures in the capsules. In the case of the airway p arameters, the systematic differences were accompanied by lower r valu es (0.535-0.935), which are explained primarily by the regional variat ions in PA. Because of the inevitable undersampling of the PA distribu tion, the model-based partitioning Of ZL is advocated as a technically easier and more reliable method for the separation of global tissue a nd airway parameters.