Modeling of mechanical dysfunction in regional stunned myocardium of the left ventricle

Abstract

Reversible mechanical dysfunction of the myocardium after a single or multiple episode(s) of coronary artery occlusion has been observed in previous studies and is termed myocardial stunning. The hypothesis that stunning could be represented by a decrease in maximum available muscle force in the stunned region was examined by means of a mathematical model that incorporates series viscoelastic elements. A canine experimental model was also employed to demonstrate depressed contractility and a consistent delay of shortening in the stunned region. The mechanical model of the left ventricle was designed to include a normal and stunned region, for which the stunned region was allowed to have variable size. Each region consisted of a volume and time dependent force generator in parallel with a passive elastic force element. The passive elastic element was placed in series with a constant viscosity component and a series elastic component. The model was solved by means of a computer. Passive and active properties of each region could be altered independently. The typical regional measures of muscle performance such as percent shortening, percent bulge, percent thickening, delay of shortening, percent increase in end-diastolic length and other hemodynamic measures were computed. These results were similar to those observed in animal models of stunning. In addition, a nearly linear relationship with end-diastolic length and delay of shortening was predicted by the model. It was concluded that a decrease in the peak isovolumic elastance and augmentation of viscosity effect of creep during stunning can explain mechanical abnormalities of stunned myocardium.

Numerical simulation of cardiovascular dynamics with healthy and diseased heart valves

“…Concentrated parameter studies focus on global analysis of cardiovascular dynamics, in which heart valve dynamics is only part of the model, and the valve is modelled with a very simple description. Among them, most of earlier researchers modelled the heart valve as a diode plus a linear or nonlinear resistance (Drzewiecki et al, 1996;Heldt et al, 2002;Pennati et al, 1997;Vollkron et al, 2002). This description puts more emphasis on the ideal characteristic of the one way flow direction in the heart valve, while the more complex feature of valve dynamics was ignored, so that local hemodynamics in valves such as the regurgitant (reverse) flow were not simulated.…”

Review of Zero-D and 1-D Models of Blood Flow in the Cardiovascular System

“…The simplest models of the heart valve used in 0D studies of cardiovascular dynamics, featured the valve as a diode plus a linear or nonlinear resistance [ 22 , 50 , 69 , 70 ]. The valve has little resistance to the flow when the pressure gradient across it is positive, while the flow is totally stopped when the pressure gradients across it is negative.…”

Left Ventricle–Arterial System Interaction in Heart Failure

“…This in turn gives rise to an incomplete relaxation; before the next cardiac cycle. The diastolic relaxation time constant has been found to be lengthened,21,30 and increased diastolic stiffness, or decreased diastolic compliance, further hinders LV ejection in the following cardiac cycle. Indeed, diastolic compliance has been found to be reduced in HF 31.…”

“…Longer coronary artery occlusion, ie, greater than two hours, more likely produces irreversible damage to cardiac muscle function. 15,18 Even with a brief period of coronary artery occlusion and subsequent release, as observed in myocardial stunning, [19][20][21][22] permanent damage can occur.…”