Structured-tree Modeling Of Distal Arterioles And Its Application To Hemodynamic Studies On Hypertension And Tetralogy Of Fallot

One-dimensional(1D)hemodynamic models have been widely applied to study wave propagation and reflection phenomena in the arterial system.Windkessel model(WK)is a classical approach to account for the biomechanical properties of distal vessels,which is featured mainly by convenient parameter setting and low computational cost and hence has been frequently employed to provide distal boundary conditions for 1D models of the arterial tree.However,a Windkessel model is inherently deficient in describing wave propagation and reflection phenomena,which may cause problems in the simulations of more complex hemodynamic phenomena.For instance,the morphological and mechanical properties of small arteries,which cannot be reasonably represented by a simple WK model,have significant influence on arterial blood pressure under hypertensive conditions.Moreover,hemodynamic characteristics in pulmonary arteries are a major subject of studies focusing on pediatric congenital heart disease.The specific anatomy of the pulmonary circulation highlights the need of constructing models capable of reasonably predicting wave propagation phenomena.In the context,researchers have proposed the structured-tree(ST)modeling method for distal vessels and theoretically proved its advantages.However,studies that compare the WK and ST models under systemic hemodynamic conditions remain absent.The main purpose of the present study was therefore to first investigate the differences in simulated hemodynamic variables when the WK and ST models were respectively applied to set the distal boundary conditions of a 1D arterial tree model,and then based on which construct models of the cardiovascular system under hypertensive conditions or with tetralogy of Fallot to quantify the relationships between hemodynamic variables and cardiovascular properties so as to provide theoretical references for the treatment of these diseases.The WK and ST models were respectively applied to set the distal boundary conditions of a 1D arterial tree model,with their effective resistance,capacitance and inductance being calibrated to the same values so that quantitative comparisons between the results simulated by the two types of models can be performed.Obtained results showed that the simulated pressure/flow waves were comparable at the aortic level,but their discrepancies went larger from the heart towards the periphery along the arterial network,and,in the meantime,the discrepancies tended to be enlarged by stiffening of central arteries.Our wave analyses revealed that the differential wave reflection patterns originating from the WK and ST models were the major cause of the aforementioned discrepancies.Based on the above findings,the ST modeling method was adopted to represent distal arteries when constructing hemodynamic models for hypertension and tetralogy of Fallot.At the same time,a lumped-parameter model of the capillaries,veins and the heart was coupled to the 1D-ST model of the arterial system to yield a closed-loop cardiovascular model capable of accounting for systemic hemodynamic behaviors.Numerical experiments with the hypertensive model demonstrated that heart rate,the stiffness of central arteries and the radius of distal arteries were the major determinant factors for arterial systolic,pulse and mean pressures and these factors differed significantly in the way and degree in which they affect hemodynamic variables.The model-based results theoretically elucidated the biomechanical mechanisms underlying the differential pressure-lowering effects in central and peripheral arteries resulting from different classes of anti-hypertensive drugs,and,in the meantime,stressed the significance of monitoring central arterial stiffness in the treatment of hypertension.Numerical studies on pulmonary arterial hemodynamics using the cardiovascular model with tetralogy of Fallot found that pulmonary arterial obstruction could considerably restrain pulmonary valve regurgitation,with the degree of restrain being affected by the effective open orifice area of pulmonary valve during flow regurgitation.These findings imply that a reasonable decision-making in the clinical practice should be based firmly on patient-specific cardiovascular status.