Redaelli A, Montevecchi F M
Dipartimento di Bioingegneria, Politecnico di Milano, Italy.
J Biomech Eng. 1996 Nov;118(4):529-37. doi: 10.1115/1.2796040.
The dynamics of intraventricular blood flow, i.e. its rapid evolution, implies the rise of intraventricular pressure gradients (IPGs) characteristic of the inertia-driven events as experimentally observed by Pasipoularides (1987, 1990) and by Falsetti et al. (1986). The IPG time course is determined by the wall contraction which, in turn, depends on the load applied, namely the intraventricular pressure which is the sum of the aortic pressure (i.e., the systemic net response) and the IPG. Hence the IPGs account, at least in part, for the wall movement. These considerations suggest the necessity of a comprehensive analysis of the ventricular mechanics involving both ventricular wall mechanics and intraventricular fluid dynamics as each domain determines the boundary conditions of the other. This paper presents a computational approach to ventricular ejection mechanics based on a fluid-structure interaction calculation for the evaluation of the IPG time course. An axisymmetric model of the left ventricle is utilized. The intraventricular fluid is assumed to be Newtonian. The ventricle wall is thin and is composed of two sets of counter-rotating fibres which behave according to the modified version of Wong's sarcomere model proposed by Montevecchi and Pietrabissa and Pietrabissa et al. (1987, 1991). The full Navier-Stokes equations describing the fluid domain are solved using Galerkin's weighted residual approach in conjunction with finite element approximation (FIDAP). The wall displacement is solved using the multiplane quasi-Newton method proposed by Buzzi Ferraris and Tronconi (1985). The interaction procedure is performed by means of an external macro which compares the flow fields and the wall displacement and appropriately modifies the boundary conditions to reach the simultaneous and congruous convergence of the two problems. The results refer to a simulation of the ventricular ejection with a heart rate of 72 bpm. In this phase the ventricle ejects 61 cm3 (ejection fraction equal to 54 percent) and the ventricular pressure varies from 78 mmHg to 140 mmHg. The IPG show an oscillating behaviour with two major peaks at the beginning (11.09 mmHg) and at the end (4.32 mmHg) of the ejection phase, when the flow rate hardly changes, according to the experimental data. Furthermore the wall displacement, the wall stress and strain, the pressure and velocity fields are calculated and reported.
心室内血流动力学，即其快速演变过程，意味着心室内压力梯度（IPG）的上升，这是由帕西普拉里德斯（1987年、1990年）以及法尔塞蒂等人（1986年）通过实验观察到的惯性驱动事件的特征。IPG的时间进程由心室壁收缩决定，而心室壁收缩又取决于所施加的负荷，即心室内压力，它是主动脉压力（即全身净反应）与IPG之和。因此，IPG至少部分地解释了心室壁的运动。这些考虑表明有必要对心室力学进行全面分析，包括心室壁力学和心室内流体动力学，因为每个领域都决定了另一个领域的边界条件。本文提出了一种基于流固相互作用计算来评估IPG时间进程的心室射血力学计算方法。使用了左心室的轴对称模型。假定心室内流体为牛顿流体。心室壁很薄，由两组反向旋转的纤维组成，其行为符合蒙特韦基、彼得拉比萨以及彼得拉比萨等人（1987年、1991年）提出的对王的肌节模型的修正版本。描述流体域的完整纳维 - 斯托克斯方程采用伽辽金加权残差法结合有限元近似（FIDAP）求解。心室壁位移采用布齐·费拉里斯和特龙科尼（1985年）提出的多平面拟牛顿法求解。相互作用过程通过一个外部宏来执行，该宏比较流场和心室壁位移，并适当修改边界条件，以使两个问题同时且一致地收敛。结果是对心率为72次/分钟时心室射血的模拟。在此阶段，心室射出61立方厘米（射血分数等于54%），心室内压力从78毫米汞柱变化到140毫米汞柱。根据实验数据，IPG呈现出振荡行为，在射血期开始时（11.09毫米汞柱）和结束时（4.32毫米汞柱）有两个主要峰值，此时流速几乎不变。此外，还计算并报告了心室壁位移、壁应力和应变、压力和速度场。
