On quantification of arterial compliance by a third-order lumped model

The aim was to test the validity of a third-order lumped model to evaluate systemic arterial compliance. The model consists of two compliances, C₁ and C₂, an inertance, L, and a resistance, R. Fundamental to the use of this model has been the assumption that its parameter estimates are independent of the arterial pressure measurement site. In three anaesthetised open-chest dogs the authors measured pulsatile pressure and flow in the ascending aorta and pulsatile pressure in the terminal aorta, under basal and vasoconstricted conditions. The ratio between mean pressure and cardiac output yielded values of R. The other model parameters were estimated by fitting experimental and model predicted diastolic portions of ascending aortic pressure (P_ad) and terminal aortic pressure (P_td ). The parameter estimates were nor always independent of the pressure measurement site. Vasoconstrictor-induced changes in C₁ and C₂ obtained from fitting Pad or P_td were in contradiction