A "porohyperelastic" (PHE) material model is described and the theoretical framework presented that allows identification of the necessary material properties functions for soft arterial tissues. A generaliz...
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A "porohyperelastic" (PHE) material model is described and the theoretical framework presented that allows identification of the necessary material properties functions for soft arterial tissues. A generalized Fung form is proposed for the PHE constitutive law in which the two fundamental Lagrangian material properties are the effective strain energy density function, W-e, and the hydraulic permeability, (k) over tilde(ij). The PHE model is based on isotropic forms using W-e = U-e(phi) = 1/2C(0)(e(phi) - 1) and the radial component of permeability, (k) over tilde(RR) = (k) over tilde(RR)(phi), with phi = C-1((I) over bar - 3) + C-2'((I) over bar(2) - 3) + K'(J - 1)(2). The methods for determination of these material properties are illustrated using experimental data from in situ rabbit aortas. Three experiments are described to determine parameters in U-e and (k) over tilde(RR) for the intima and media of the aortas, i.e., (I) undrained tests to determine C-0, C-1', and C-2';(2) drained tests to determine K';and (3) steady-state pressurization tests of intact and de-endothelialized vessels to determine intimal and medial permeability (adventitia removed in these models). Data-reduction procedures are presented that allow determination of (k) over tilde(RR) for the intima and media and U-e for the media using experimental darn. The effectiveness and accuracy of these procedures are studied using input "data" from finite element models generated with the ABAQUS program. The isotropic theory and data-reduction methods give good approximations for the PHE properties of in situ aortas. These methods can be extended to include arterial tissue remodeling and anisotropic behavior when appropriate experimental data are available.
Background. We evaluated human and canine internal thoracic arteries (ITAs) to determine whether the latter is valid for studies relevant to clinical use. Methods. We studied 19 human ITAs obtained from 1 female and 1...
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Background. We evaluated human and canine internal thoracic arteries (ITAs) to determine whether the latter is valid for studies relevant to clinical use. Methods. We studied 19 human ITAs obtained from 1 female and 14 male victims of recent fatal accidents who had no evidence of cardiovascular disease (mean age 39 +/- 19 years;range = 15 to 79 years), and ITAs of 21 randomly-selected mongrel dogs of both sexes, weighing 18-40 kg (average = 24.3 +/- 5.7 kg). Specimens were fixed in formalin at a controlled pressure of 120 mm Hg, before extensive assessment that included intimal thickening, condition of the internal elastic lamina, and number of medial elastic lamellae and vasa vasorum. Results. The canine morphology and histology were similar to the human ITAs, but there was no intimal hyperplasia, and the media and adventitia were thinner (ITAs of humans older than 40 years had significant increases in medial thickness, as well as in overall length). Morphologically and histologically, the left and right canine ITAs were almost completely the same. Conclusions. Canine ITAs are valid for bilateral comparative studies and are a useful tissue source and model for clinically-relevant experimental studies. (C) 1999 by The Society of Thoracic Surgeons.
A porohyperelastic (PHE) theory of large arteries is studied using hyperelastic effective stress and with hydraulic permeability determined as a function of void ratio. The formulation allows the direct application of...
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A porohyperelastic (PHE) theory of large arteries is studied using hyperelastic effective stress and with hydraulic permeability determined as a function of void ratio. The formulation allows the direct application of ABAQUS for the development of finite element models of various soft biological structures. The PHE property, ∂We/∂Eij is equal to the biphasic property, SijSE = ρos∂Ψs/∂Eijs (with Eij = Eijs) and the PHE permeability, k is equal to the biphasic permeability.
Type-2 diabetes mellitus is associated with a 2- to 4-fold increase in the risk of clinical coronary artery disease (CAD), It has been suggested that diabetic subjects without clinical CAD should be treated as aggress...
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Type-2 diabetes mellitus is associated with a 2- to 4-fold increase in the risk of clinical coronary artery disease (CAD), It has been suggested that diabetic subjects without clinical CAD should be treated as aggressively for cardiovascular risk factors as subjects with CAD. This would be warranted if diabetic subjects without clinical CAD would have accelerated CAD similar to that of nondiabetic subjects with symptomatic CAD. To assess this suggestion, we compared the intima-media wall thickness in the common carotid artery (CCA) and internal carotid artery (ICA) in 43 diabetic subjects with clinical CAD, 446 diabetic subjects without clinical CAD, 47 nondiabetic subjects with clinical CAD, and 975 nondiabetic subjects without clinical CAD (all aged 40 to 70 years) in the Insulin Resistance Atherosclerosis Study. All data were adjusted for age, gender, ethnicity, and clinical results. Both diabetes and CAD were associated with increased atherosclerosis in the CCA. Likewise, diabetes wets significantly associated with increased atherosclerosis in the ICA;however, CAD was not associated with ICA intima-media wall thickness. As expected, diabetic subjects with CAD had the greatest intima-media wall thickness, whereas nondiabetic subjects without CAD had the least atherosclerosis. Subjects with diabetes but without CAD had slightly greater intima-media wall thickness than nondiabetic subjects with CAD, although these differences were not statistically significant. Thus, diabetic subjects even without CAD had extensive atherosclerosis in the carotid artery. These results support the suggestion that diabetic subjects should be treated as aggressively for cardiovascular risk factor management as subjects with pre-existing CAD. (C) 2000 by Excerpta Medica, Inc.
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