CHARACTERIZATION OF EMBRYONIC AORTIC IMPEDANCE WITH LUMPED-PARAMETER MODELS

We systematically constructed and analyzed 18 analog circuit models to characterize embryonic arterial impedance. We measured simultaneous d orsal aortic pressure and flow, and we calculated experimental impedan ce in stage 24 chick embryos (n = 15). Cycle length was altered with t hermal probes to improve frequency resolution of the impedance spectru m. Models were categorized according to the framework and the location of inductance and resistance terms. Models were excluded if they fail ed to reproduce the fundamental characteristics of the experimental im pedance 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 overparameteriz ation were also excluded. We assessed goodness of fit in the frequency domain with the F-test, Akaike information criterion, and Schwarz cri terion to determine the best-fit model. The addition of a serial induc tance 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 em bryonic and mature vascular systems can be described using lumped para meter circuit models.