Characterization of pulmonary arterial input impedance with lumped parameter models

The purpose of this study is to evaluate systematically the ability of lumped parameter models to approximate pulmonary arterial input impedance (Z(in)) and estimate characteristic impedance (Z(c)) and pulmonary arterial compliance (C(art)). To assess goodness of fit, the parameters of each model were adjusted so that the model's impedance approximates the Z(in) measured in anesthetized cats. To assess the ability of the model to estimate Z(c) and C(art), the lumped parameter models were fitted to Z(in) calculated from a distributed parameter model of the feline pulmonary vasculature. In addition, we assessed the concordance between the lumped parameter model estimates of Z(c) and C(art). The results indicate that no one model was superior; any of four models would be reasonable choice. A four-element model was used to compare Z(in) measured at different phases of the respiratory cycle. Small differences in the impedance spectra were found that have not been previously reported. We conclude that lumped parameter models can be used 1) to provide close approximations to Z(in), 2) to estimate Z(c) and C(art), and 3) to provide a useful approach for statistical comparisons of impedance spectra.