Mechanical Behavior Of Arteries Research Articles

Numerical Modeling of Nitinol Stent Oversizing in Arteries with Clinically Relevant Levels of Peripheral Arterial Disease: The Influence of Plaque Type on the Outcomes of Endovascular Therapy.

Oversizing of the Nitinol stents in the femoro-popliteal arterial tract is commonly performed by clinicians and further encouraged by stent manufacturers. However, in spite of the procedure's supposed benefits of strong wall apposition and increased luminal gain, its effects on the mechanical behavior of arteries with peripheral arterial disease are not fully clear. In this study, finite element (FE) analyses of endovascular revascularization of an idealized artery with 70% stenosis and three different plaque types have been performed to examine the influence of Nitinol stent oversizing on the arterial stresses and acute lumen gain. The analyses included the simulation of balloon angioplasty to model plaque failure, followed by stent implantation, in which four different oversizing ratios were investigated. Results showed that balloon angioplasty was crucial in determining the stress levels of the artery prior to stent implantation and heavily affected the outcome of endovascular therapy. For all plaque types, Nitinol stent oversizing was found to produce a marginal lumen gain in contrast to a significant increase in arterial stresses. For the arteries with lightly and moderately calcified plaques, oversizing was found to be non-critical; whereas for the arteries with heavily calcified plaques, the procedure should be avoided due to a risk of tissue failure.

How Constitutive Model Complexity can Affect the Capability to Fit Experimental Data: a Focus on Human Carotid Arteries and Extension/Inflation Data

To perform realistic finite element simulations of cardiovascular surgical procedures (such as balloon angioplasty, stenting or bypass), it is necessary to use appropriate constitutive models able to describe the mechanical behavior of the human arterial wall (in healthy and diseased conditions) as well as to properly calibrate the material parameters involved in such constitutive models. Moving from these considerations, the goal of the present study is to compare the reliability of two isotropic phenomenological models and of four structural invariant-based constitutive models, commonly used to describe the passive mechanical behavior of arteries. The arterial wall is modeled as a thick-wall tube with one- and two- layer structure. Residual stresses inclusion is also considered, to evaluate informations on the stress distribution through the wall thickness. The predictive capability of the investigated models is tested using extension/inflation data on human carotid arteries related by two different experimental works available in the literature. The material parameters involved in the investigated models are computed in the least-square sense thought a best fitting procedure, relying on a multi-start optimization algorithm. The good quality of the optimal solution is validated quantitatively computing proper error measures and comparing the model prediction curves. The final outcome of the paper is a critical review of the six considered constitutive models, comparing their formulation and evidencing the more or less capability of such models to fit the considered experimental data.

Mechanical behavior of arteries under inflation and extension

In order to understand the blood vessel of artery responding to medical treatments, there is a need to quantify the biomechanical behavior of the vessel. Using video dimension analyser, mechanical pressure-diameter relationships of passive carotid artery with and without balloon inflated at various axial loads were measured. Inversion test was also analytically modeled to address the heterogeneity of artery due to constituents. The pressure-diameter curves and stress distribution across the arterial wall were calculated. The simulation showed that the inversion tests, in comparison to other mechanical tests, provided additional information to develop the strain energy function describing arterial behavior

The Influence of Pressure and Temperature on the Behavior of the Human Aorta and Carotid Arteries

The thermomechanical behavior of human arteries is still not well characterized despite its importance for understanding arterial physiology, and for evaluating and improving surgical procedures. The aim of this study was to provide, for the first time, experimental data illustrating how the mechanical responses of two types of human artery -the carotid artery and the aorta- are affected by changes in temperature. The mechanical properties of the arteries were derived in vitro from internal pressure-external diameter curves measured at four different temperatures (i.e., 17, 27, 37 and 42 degree C). Coefficients of expansion and stiffness were obtained by thermomechanical analysis. The condition of the arterial wall was determined histologically. The aorta and the carotid artery became slightly more compliant as the temperature increased. In both vessels, the coefficient of expansion depended critically on internal pressure. At low pressures, the coefficient of expansion was negative (i.e., the vessel contracted when heated), whereas close to a specific threshold pressure, which is different for each type of artery, the coefficient became positive. The mechanical behavior of arteries is affected by the combination of internal pressure and temperature. Consequently, the effect of this combination should be taken into account in clinical situations involving a change in temperature. Moreover, the strength of the effect depends on the type of artery under study. As a result, more detailed experimental data focusing on vessels of clinical interest are required.

Computational stress-deformation analysis of arterial walls including high-pressure response

Background Changes in the mechanical behavior of arteries after balloon angioplasty cause cell reactions that may be responsible for restenosis. Hence, the study of the stress-deformation changes in arterial walls following supraphysiological tissue loading is an essential task. Methods A normal LAD coronary artery was modeled and computationally analyzed as a two-layer, thick-walled, anisotropic and inelastic circular tube including residual strains. Each layer was treated as a fibre-matrix composite. The tube was subjected to an axial stretch of 1.1 and a transmural pressure of 750 mm Hg. Since overstretch of remnant non-diseased tissue in lesions is a primary mechanism of lumen enlargement this model approach represents a reasonable first step. Results At physiological loading, the residual stresses led to a significant reduction of the high circumferential stress values at the inner wall, and the stress gradients. At low pressure level the media was the mechanically relevant layer, while at supraphysiological loading, the adventitia was the predominant load-carrying constituent providing a stiff support for ‘redistribution’ of soft plaque components by means of radial compression. After unloading to physiological loading conditions the stress state in the arterial wall differed significantly from that before inflation; the stress gradient in the media even changed its sign. Complete unloading indicated lumen enlargement, material softening and energy dissipation, which is in agreement with experimental studies. Conclusions This method may be useful to improve interventional protocols for reducing the dilatational trauma, and thereby the adverse biological reaction in arterial walls following balloon angioplasty.

MECHANICS OF THE ARTERIAL WALL: REVIEW AND DIRECTIONS

The goals of this article are threefold: to briefly review the theory of finite elasticity and its application to arterial mechanics; to review what is known about the mechanical behavior of arteries in health and disease; and to review several clinically relevant aspects of arterial mechanics, as for example, aging, aneurysms, angioplasty, embolectomy, heat therapies, hypertension, trauma, and the disruption of atherosclerotic plaques. It is shown that, despite a huge literature on arterial mechanics, much remains unknown. In particular, a pressing need exists for detailed nonlinear three-dimensional constitutive relations for the passive and active arterial wall as a function of position along the arterial tree and disease. Arterial mechanics has, therefore, yet to reach its full potential as an important and consistent contributor to vascular medicine and surgery, but the possibilities remain great.

Pressure-volume response of isolated living main pulmonary artery in dogs.

Isolation of the main pulmonary artery by obturation of the right and left branches under conditions which maintained vasal circulation to the wall was achieved by extracorporeal circulation. Pressure-volume response of the segment was measured directly using a reciprocating essentially sinusoidal volume input at rates of 90, 45, and 180 cycles/min. Using volumes which generated physiologic pressures, a steady-state response starting from rest occurred in 300—500 cycles. At steady state the pressure-volume response was linear and unchanged by these cycling rates. The relaxation pattern during the initial phase was consistent with a single mode of response and closely duplicated the stress-relaxation pattern of a single noncycled input of the same volume. In 34 experiments in 11 animals steady-state volume distensibility (DeltaV x 100/V0 DeltaP) was 2.51% cm H2O. Segment geometry was preserved by luminal casting. An ellipsoidal configuration was apparent in the distended state. pulmonary-artery distensibility; mechanical behavior of arteries; stress-relaxation; geometry of arteries; tethering; viscoelastic properties of arteries; dynamic elastic response; coefficient of distensibility Submitted on June 16, 1964