Characterization of embryonic aortic impedance with lumped parameter models

Abstract

We systematically constructed and analyzed 18 analog circuit models to characterize embryonic arterial impedance. We measured simultaneous dorsal aortic pressure and flow, and we calculated experimental impedance in stage 24 chick embryos (n = 15). Cycle length was altered with thermal probes to improve frequency resolution of the impedance spectrum. Models were categorized according to the framework and the location of inductance and resistance terms. Models were excluded if they failed to reproduce the fundamental characteristics of the experimental impedance spectrum. We used weighted least-square parameter optimization to fit the model impedance curves to the experimental impedance data. Models that failed to converge parameters or revealed overparameterization were also excluded. We assessed goodness of fit in the frequency domain with the F-test, Akaike information criterion, and Schwarz criterion to determine the best-fit model. The addition of a serial inductance term to the traditional three-element windkessel model improved fit by reproducing modulus fluctuation and phase zero crossing (P < 0.001). Thus, despite dramatic differences in scale and geometry, the embryonic and mature vascular systems can be described using lumped parameter circuit models.