Quantitative evaluation of the systemic arterial bed by parameter estimation of a simple model

The parameters of a simple model (r-L-C-R) of the systemic circulation are estimated from aortic root pressure and flow, which are either simulated by a complex model of the systemic circulation or measured in dogs. This model contains one additional parameter (inductance L) as compared with the r-C-R model proposed by Westerhof; it allows for a better representation of the input impedance of the complex model and of the systemic circulation in dog, resulting in meaningful values for the parameters r, C, R. Because there is a good relation between C and the sum of the compliances of the complex model, and because C varies in the direction of the expected changes in compliance following angiotensin and sodium nitroprusside administration in dogs, C appears to be a valid estimate of the total systemic arterial compliance. The good relation between r and the characteristic impedance in the complex model or in the upper thoracic aorta of the dog indicates that r is a good measure of the characteristic impedance. The r-L-C-R model therefore appears to provide a better characterisation of the left ventricular afterload than the r-C-R model. The identification of this r-L-C-R model also permits a more convenient quantification of the afterload than the classical computation of input impedance.