Viscoelasticity reduces the dynamic stresses and strains in the vessel wall: implications for vessel fatigue

Abstract

Zhang W, Liu Y, Kassab GS. Viscoelasticity reduces the dynamic stresses and strains in the vessel wall: implications for vessel fatigue. Am J Physiol Heart Circ Physiol 293: H2355-H2360, 2007. First published June 29, 2007; doi:10.1152/ajpheart.00423.2007.-The mechanical behavior of blood vessels is known to be viscoelastic rather than elastic. The functional role of viscoelasticity, however, has remained largely unclear. The hypothesis of this study is that viscoelasticity reduces the stresses and strains in the vessel wall, which may have a significant impact on the fatigue life of the blood vessel wall. To verify the hypothesis, the pulsatile stress in rabbit thoracic artery at physiological loading condition was investigated with a quasi-linear viscoelastic model, where the normalized stress relaxation function is assumed to be isotropic, while the stress-strain relationship is anisotropic and nonlinear. The artery was subjected to the same boundary condition, and the mechanical equilibrium equation was solved for both the viscoelastic and an elastic (which has a constant relaxation function) model. Numerical results show that, compared with purely elastic response, the viscoelastic property of arteries reduces the magnitudes and temporal variations of circumferential stress and strain. The radial wall movement is also reduced due to viscoelasticity. These findings imply that viscoelasticity may be beneficial for the fatigue life of blood vessels, which undergo millions of cyclic mechanical loadings each year of life.artery; cyclic loading; fatigue life; viscoelastic BIOLOGICAL SOFT TISSUES ARE known to have highly nonlinear stress-strain relations, strongly anisotropic mechanical properties, and significant viscoelastic features (10). Blood vessels are typical soft tissues, and their mechanical behavior is imperative for understanding vascular processes under physiological and pathological conditions. The pseudoelastic formulation (i.e., loading and unloading follow different elastic stressstrain curves) has been widely utilized to investigate salient mechanical characteristics of blood vessels (e.g., Refs. 5,7,8,10,13). In more realistic analyses, the viscoelastic behavior of arterial walls has been studied by many researchers (4,10,12,20,21,23,24,27,29). To reduce the mathematical complexity, the theory of quasi-linear viscoelasticity (10) has been applied to arteries and other living tissues (e.g., Refs. 3,6,11,15,26). One known merit of viscoelasticity in blood vessels is to reduce the wall stress and strain during a sudden increase of mechanical loading, such as in acute hypertension (1). Although this is an interesting protective acute mechanism, the functional role of viscoelasticity in blood vessels and other biological tissues has not been fully understood.From a mechanical point of view, the energy dissipation due to viscoelasticity may produce heat to maintain isothermal conditions in tissues, and the force-deformation hysteresis loop (or phase delay between stress and strain) caused by internal ...

Surrounding tissues affect the passive mechanics of the vessel wall: theory and experiment

“…10 without consideration of the radial constraint; it is significantly overestimated. (14,43) formulate the radial constraint with an equivalent pressure on the outer vessel surface, as the EPP ⌬P here. However, determination of the equivalent pressure was ad hoc.…”

“…For example, Misra and Singh (27) assumed that the perivascular tissue exhibits linear elastic properties. The simpler approach introduces a lumped parameter on the outer vessel surface such as an effective perivascular pressure (EPP) (14,42,43) to simulate the radial constraint. For example, Zhang et al (42) predicted that even a small external compression (10%) causes a large reduction in circumferential stress and tends toward a biaxially (circumferential and axial) uniform strain state for the coronary artery and aorta.…”

Linear and Nonlinear Viscoelastic Modeling of Aorta and Carotid Pressure–Area Dynamics Under In Vivo and Ex Vivo Conditions

“…A number of studies have investigated arterial wall properties using empirical nonlinear elastic models [28,33], hyper-elastic models [26,27,29], viscoelastic models [1,7,19,25,29,35,38,45,46], and autoregressive models [21,22]. However, little work has focused on using coupled dynamic models that account for both nonlinear elastic distention and the “memory” (viscoelastic) contribution to the arterial wall distention and, to our knowledge, no studies have used this information to characterize differences according to vessel type.…”

Corneal Biomechanical Properties and Retinal Vascular Caliber in Children

“…13,14 Like the cornea, vessel walls are known to exhibit viscoelastic properties because of their primarily collagenous composition. [15][16][17][18][19] The mechanical properties of the lamina cribrosa may be linked to those of the cornea through their continuity in the corneoscleral shell, 20 and the lamina cribrosa may be related to retinal vascular caliber because it provides structural support to the proximal retinal vessels. Therefore, in this study, we examined the relationship of corneal biomechanical properties and retinal vascular caliber in young children without glaucoma.…”