Macromolecular Transport in the Arterial Wall: Alternative Models for Estimating Barriers

Early atherosclerosis, or atherogenesis, is characterized by the abnormal accumulation of plasma-borne macromolecules (e.g., LDL) in the arterial intima. The change of barrier characteristics of tissue in the arterial wall requires evaluation of macromolecular transport across the endothelial cell layer (ECL) and internal elastic lamina (IEL), the luminal and abluminal boundaries of the arterial intima, respectively. In this study, alternative mathematical models are derived from dynamic mass balances to describe macromolecular transport across the arterial wall. One model considers each medial layer as a spatially lumped compartment, whereas another model consists of a spatially lumped intima and spatially distributed media. Model simulations of a tracer concentration distribution in the arterial wall are compared with concentration distributions of horseradish peroxidase (HRP) after i.v. injection in mice. For each model, optimal parameter values are obtained that yield model outputs matching the data well for two different HRP circulation times. The model parameter estimates show that the ECL is the major barrier for macromolecular transport across the normal arterial wall. Sensitivity analysis indicates that the parameter estimates of the transport coefficients of the ECL and IEL are well determined. Optimal circulation times are determined and expected to yield improved precision of parameter estimates in future experiments to reflect disease progression.     

脉象图的参数模型及其应用研究

作者采用双弹性腔模型，将心脏作为模型的输入信号，实验得到的桡动脉脉搏波作为模型的输出，利用系统辩识技术对脉象图进行客观化研究，从而估计出模型中有生理意义的参数；并用这些参数作为脉搏波的特征值。通过对运动前后参数变化的比较，得到有益的结果。     

Pulse Pressure Method and the Area Method for the Estimation of Total Arterial Compliance in Dogs: Sensitivity to Wave Reflection Intensity

We estimated total arterial compliance (C) in eight anesthetized mongrel dogs with (i) the area method (AM), (ii) the pulse pressure method (PPM), and (iii) the stroke volume-to-pulse pressure ratio (SV/PP). Average compliance was C__AM=1.11 ± 0.7 ml mm Hg¹ using AM; C_PPM=0.60 ± 0.31 ml mm Hg_-1 using PPM and C_SV/PP=0.87 ± 0.49 ml mm Hg^-1 using SV/PP. Mean aortic pressure was 64 ± 23 mm Hg. The overall agreement between C_AM and C_PPM was relatively poor (C_AM=0.15+1.61 C_PPM; r²=0.48), with a consistent overestimation of the area method with respect to the pulse pressure method. There was a significant correlation (r= -0.78) between the relative difference between PPM and AM, and the modulus of the first harmonic of the wave reflection coefficient || which was low in our dog population (0.37 ± 0.18). SV/PP overestimated PPM, but both methods were highly correlated (C_SV/PP=0.06+1.60 C_PPM; r²=0.97). C_SV/PP and C_AM were similar only for || > 0.4. The effect of isolated changes of || on PPM, AM, and SV/PP was studied using the linear wave separation technique. The area method appeared very sensitive to the wave reflection intensity. For low reflection coefficients, the diastolic wave profile was flattened and compliance was overestimated. PPM and SV/PP were relatively independent of || and remained even applicable for || = 0. We believe that the pulse pressure method is the most consistent method for the estimation of total arterial compliance in hemodynamic conditions characterized by a low wave reflection intensity. © 1999 Biomedical Engineering Society. PAC99: 8719Uv, 8719Hh