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 and isolated canine lungs by means of small-amplitude pseudorandom oscillations 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 estimated by fitting to the ZL data between 0.2 and 4.9 Hz (open-chest dogs) and between 0.2 and 5.9 Hz (isolated lungs) two models based on Hildebrandt's formulations (Bull. Math. Biophys. 31: 651-667, 1969), the parameters of which included airway resistance (Raw) and inertance (Iaw) and tissue damping (GL) and elastance (HL). The tissue parameters of Ztti (Gti and Hti) were also obtained from model fitting, whereas the Ztaw data were evaluated in terms of resistance (Rtaw) and inertance (Itaw). Excellent agreement was found between HL and Hti in both experimental groups and between GL and Gti in the isolated lungs (r > or = 0.999). The damping coefficients were also closely related in the open-chest dogs (r = 0.95), but Gti overestimated GL slightly (by 9%). Raw was underestimated by Rtaw (by 3-33%) and Iaw 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 parameters, the systematic differences were accompanied by lower r values (0.535-0.935), which are explained primarily by the regional variations in PA.(ABSTRACT TRUNCATED AT 250 WORDS)