Parameter Estimation in the Stenosed Coronary Circulatory System
In a stenosed coronary circulation, the following parameters were estimated from pressure measurements: coronary vascular resistances, transmural blood flow, and endocardial to epicardial (ENDO: EPI) flow ratio. This was done by modeling the hemodynamics of the coronary system with an analogous electrical circuit. The circuit topology consists of a nonlinear stenosis resistance and an endocardial branch in parallel with an epicardial branch. The unknown, linear endocardial and epicardial resistances were determined by a least-squares estimation method with three inputs: the left ventricular pressure (LVP), the aortic pressure (AP), and the distal coronary arterial pressure (DP). In this paper, computer simulations also show that the input DP may be replaced by a phasic arterial coronary flow synthesized from its mean systolic and diastolic values. In animal studies, DP may be measured directly while such pressure measurements are difficult to obtain clinically since it requires passing a catheter distal to a stenosis. However, mean systolic and diastolic coronary arterial flow have been obtained in humans via video densitometry. Thus, this method may potentially be useful in clinical situations. Validity of the method was tested with 23 animal studies using swine under a variety of physiological conditions. Linear regression analyses were made between the ENDO: EPI flow ratios estimated by the model and those measured by use of the radiolabeled microsphere technique.