Shear modulus of porcine coronary artery: contributions of media and adventitia

Lu, Xiao; Yang, Jimin; Zhao, Jingbo; Gregersen, Hans; Kassab, Ghassan S.

doi:10.1152/ajpheart.00357.2003

Cited by 86 publications

(71 citation statements)

References 18 publications

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“…The protocol for biaxial (inflation and axial extension) testing of coronary arteries was recently described by our group (37,38). Here, we modified the set-up by the addition of ultrasound crystals.…”

Section: Methodsmentioning

confidence: 99%

Right coronary artery becomes stiffer with increase in elastin and collagen in right ventricular hypertrophy

Garcia

Kassab²

2009

Journal of Applied Physiology

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Garcia M, Kassab GS. Right coronary artery becomes stiffer with increase in elastin and collagen in right ventricular hypertrophy. J Appl Physiol 106: 1338 -1346, 2009. First published January 29, 2009 doi:10.1152/japplphysiol.90592.2008.-Changes in blood flow influence the structure, function, mechanical properties, and remodeling of arteries. The objective of the present study was to investigate the role of increased blood flow on the biaxial incremental elastic moduli of the porcine right coronary artery (RCA) and to determine the microstructural basis for the changes in moduli. We hypothesized that an increase in RCA flow will lead to increased stiffness in conjunction with remodeling of elastin and collagen in the vessel wall. The control and experimental groups consisted of five RCA vessels each. The RCA of the experimental group was exposed to 4 wk of flow-overload in right ventricular hypertrophy induced by pulmonary artery banding. Stress-strain relationships were determined and the incremental elastic moduli were derived in the circumferential, axial, and cross directions. The results show a significant increase in the elastic moduli in the circumferential (262.7 Ϯ 15.7 vs. 120.2 Ϯ 12.4 kPa; P Ͻ 0.001), axial (177.8 Ϯ 25.5 vs. 100.3 Ϯ 11.9 kPa; P ϭ 0.025), and cross directions (104.8 Ϯ 8.2 vs. 68.2 Ϯ 8.6 kPa; P ϭ 0.016) of the experimental RCA compared with controls. Multiphoton microscopy was used to assess the changes in elastin and collagen content in the media and adventitia of the vessel wall. We found a significant increase in elastin and collagen area fraction particularly in the adventitial layer. These data suggest stiffening of the vessel wall as a result of increased elastin and more predominantly collagen. stress; strain; wall shear stress; constitutive equation BLOOD VESSELS ARE subjected to the mechanical loading of blood pressure and blood flow throughout the cardiac cycle. The vessels undergo structural and mechanical adaptations in response to changes in the local hemodynamic conditions. For example, changes in blood flow cause changes in fluid wall shear stress (WSS; the tractive frictional force exerted by flowing blood on the inner layer of the vessel wall) by eliciting a wide range of biochemical and physiological responses in experimental (46) and clinical studies (16,22). Studies have demonstrated that a sudden increase in blood flow initiates an enlargement of the arterial lumen that progresses for months as the WSS tends to a homeostatic or normal level (23,25). A gradual increase in blood flow has been reported by several groups to result in outward hypertrophic remodeling of resistance (4,41,44,45,47) and conductive arteries (25,36,39). The flow-induced remodeling may be an attempt to maintain mechanical homeostasis (24,25). When blood flow is elevated in a vessel, the endothelium responds to restore WSS toward homeostatic levels by changing vascular tone, increasing the lumen diameter (44), and potentially altering the function and mechanical properties of the vessel wall. ...

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Section: Methodsmentioning

confidence: 99%

Right coronary artery becomes stiffer with increase in elastin and collagen in right ventricular hypertrophy

Garcia

Kassab²

2009

Journal of Applied Physiology

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“…In the present study, we were careful to preserve one layer while dissecting away the other layer. A cleavage plane exists at the external elastic laminae where the dissection of the two layers is possible without significant damage to one of the layers (21). We previously showed that there is no significant evidence of tearing or damage to the media as determined from histology (21).…”

Section: Experimental and Theoretical Limitations Of Modelmentioning

confidence: 96%

“…A cleavage plane exists at the external elastic laminae where the dissection of the two layers is possible without significant damage to one of the layers (21). We previously showed that there is no significant evidence of tearing or damage to the media as determined from histology (21). Furthermore, the difference in the thickness of the media measured from the intact wall and that of the media where the adventitia was dissected was not statistically significant (21).…”

Section: Experimental and Theoretical Limitations Of Modelmentioning

confidence: 98%

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Biaxial incremental homeostatic elastic moduli of coronary artery: two-layer model

Lu¹,

Pandit²,

Kassab³

2004

American Journal of Physiology-Heart and Circulatory Physiology

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Lu, Xiao, Aditya Pandit, and Ghassan S. Kassab. Biaxial incremental homeostatic elastic moduli of coronary artery: two-layer model. Am J Physiol Heart Circ Physiol 287: H1663-H1669, 2004; 10.1152/ajpheart.00226.2004.-The detailed mechanical properties of various layers of the coronary artery are important for understanding the function of the vessel. The present article is focused on the determination of the incremental modulus in different layers and directions in the neighborhood of the in vivo state. The incremental modulus can be defined for any material subjected to a large deformation if small perturbations in strain lead to small perturbations of stresses in a linear fashion. This analysis was applied to the porcine coronary artery, which was treated as a two-layered structure consisting of an inner intima-media layer and an outer adventitia layer. We adopted a theory based on small-perturbation experiments at homeostatic conditions for determination of incremental moduli in circumferential, axial, and cross directions in the two layers. The experiments were based on inflation and axial stretch. We demonstrate that under homeostatic conditions the incremental moduli are layer-and direction dependent. The incremental modulus is highest in the circumferential direction. Furthermore, in the circumferential direction, the media is stiffer than the whole wall, which is stiffer than the adventitia. In the axial direction, the adventitia is stiffer than the intact wall, which is stiffer than the media. Hence, the coronary artery must be treated as a composite, nonisotropic body. The data acquire physiological relevance in relation to coronary artery health and disease. stress; strain; media; adventitia; constitutive equation THERE IS MOUNTING EVIDENCE that the vessel wall regulates its homeostatic level of stress and strain at in vivo physiological conditions (17). A perturbation of this state such as in hypertension or flow overload leads to growth and remodeling with increased predilection for atherosclerosis. Although deformation or strain can be measured, there is no instrument or method to measure stress. Stress must be calculated from the constitutive equation, i.e., the stress-strain relationship. In general, the stress-strain history relationships of arteries are highly nonlinear (7). A well-accepted approach to nonlinear elasticity uses the incremental formulation. A linearized relationship between the incremental stresses and strains is obtained by subjecting the vessel to a small perturbation about the in vivo condition. Using this approach, one can determine the relation between stress and strain within the physiological regime. In conjunction, measurement of strain under in vivo conditions would yield a value of stress. Hence, the present approach allows the elucidation of the full mechanical (stress, strain, and elastic modulus) status in the vicinity of the in vivo state. Furthermore, knowledge of the material modulus or stiffness is important because it represents an early risk factor for cardio...

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“…Indeed, it is difficult to locate any reliable measurements of any shear moduli. One exceptional set of measurements was obtained by Lu et al [15], who measured the equivalent of μ xy of porcine coronary arteries using a tension-torsion machine. Their data suggest that μ xy ≈ 20 kPa, and therefore it seems that the prediction of the HGO model is an order of magnitude too small.…”

Section: Restrictions On the Strain-energy Functionmentioning

confidence: 99%

Evolution of anisotropy in soft tissue

Murphy

2014

Proc. R. Soc. A.

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The phenomenological approach to the modelling of the mechanical response of arteries usually assumes a reduced form of the strain-energy function in order to reduce the mathematical complexity of the model. A common approach eschews the full basis of seven invariants for the strain-energy function in favour of a reduced set of only three invariants. It is shown that this reduced form is not consistent with the corresponding full linear theory based on infinitesimal strains. It is proposed that compatibility with the linear theory is an essential feature of any nonlinear model of arterial response. Two approaches towards ensuring such compatibility are proposed. The first is that the nonlinear theory reduces to the full six-constant linear theory, without any restrictions being imposed on the constants. An alternative modelling strategy whereby an anisotropic material is compatible with a simpler material in the linear limit is also proposed. In particular, necessary and sufficient conditions are obtained for a nonlinear anisotropic material to be compatible with an isotropic material for infinitesimal deformations. Materials that satisfy these conditions should be useful in the modelling of the crimped collagen fibres in the undeformed configuration.

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Shear modulus of porcine coronary artery: contributions of media and adventitia

Cited by 86 publications

References 18 publications

Right coronary artery becomes stiffer with increase in elastin and collagen in right ventricular hypertrophy

Right coronary artery becomes stiffer with increase in elastin and collagen in right ventricular hypertrophy

Biaxial incremental homeostatic elastic moduli of coronary artery: two-layer model

Evolution of anisotropy in soft tissue

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