A Biphasic, Anisotropic Model of the Aortic Wall

2000 ◽  
Vol 123 (1) ◽  
pp. 52-57 ◽  
Author(s):  
Mark Johnson ◽  
John M. Tarbell
Keyword(s):  
Hydraulic Conductivity ◽  
Aortic Wall ◽  
Rabbit Aorta ◽  
Intraluminal Pressure ◽  
Elastic Model ◽  
Experimental Measurements ◽  
Positive Quantity ◽  
Anisotropic Elastic ◽  
Strain Dependent ◽  
Previous Error

A biphasic, anisotropic elastic model of the aortic wall is developed and compared to literature values of experimental measurements of vessel wall radii, thickness, and hydraulic conductivity as a function of intraluminal pressure. The model gives good predictions using a constant wall modulus for pressures less than 60 mmHg, but requires a strain-dependent modulus for pressures greater than this. In both bovine and rabbit aorta, the tangential modulus is found to be approximately 20 times greater than the radial modulus. These moduli lead to predictions that, when perfused in a cylindrical geometry, the aortic volume and its specific hydraulic conductivity are relatively independent of perfusion pressure, in agreement with experimental measurements. M, the parameter that relates specific hydraulic conductivity to tissue dilation, is found to be a positive quantity correcting a previous error in the literature.

A Cytochemical Study of Glucose-6-Phosphatase (G-6-PASE) in Cells Participating in Atherogenesis of Rabbit Aorta

1975 ◽  
Vol 33 ◽  
pp. 460-461
Author(s):  
Sidney D. Kobernick ◽  
Edna A. Elfont ◽  
Neddra L. Brooks
Keyword(s):  
Lipid Metabolism ◽  
New Zealand ◽  
Aortic Wall ◽  
Rabbit Aorta ◽  
Plaque Formation ◽  
Metabolic Changes ◽  
Atherosclerotic Plaques ◽  
Cytochemical Study ◽  
Cellular Alteration ◽  
New Zealand White Rabbits

This cytochemical study was designed to investigate early metabolic changes in the aortic wall that might lead to or accompany development of atherosclerotic plaques in rabbits. The hypothesis that the primary cellular alteration leading to plaque formation might be due to changes in either carbohydrate or lipid metabolism led to histochemical studies that showed elevation of G-6-Pase in atherosclerotic plaques of rabbit aorta. This observation initiated the present investigation to determine how early in plaque formation and in which cells this change could be observed.Male New Zealand white rabbits of approximately 2000 kg consumed normal diets or diets containing 0.25 or 1.0 gm of cholesterol per day for 10, 50 and 90 days. Aortas were injected jin situ with glutaraldehyde fixative and dissected out. The plaques were identified, isolated, minced and fixed for not more than 10 minutes. Incubation and postfixation proceeded as described by Leskes and co-workers.

scholarly journals Modeling Stress-Dependent Anisotropic Elastoplastic Unbound Granular Base in Flexible Pavements

2018 ◽  
Vol 2672 (52) ◽  
pp. 46-56 ◽  
Author(s):  
Yuqing Zhang ◽  
Fan Gu ◽  
Xue Luo ◽  
Bjorn Birgisson ◽  
Robert L. Lytton
Keyword(s):  
Stress Responses ◽  
Compressive Strain ◽  
Flexible Pavements ◽  
Plastic Behavior ◽  
Elastic Model ◽  
Nonlinear Stress ◽  
Anisotropic Elastic ◽  
Base Course ◽  
Granular Base ◽  
Stress Dependent

Unbound granular base (UGB) has a cross-anisotropic and nonlinear (stress-dependent) modulus with a plastic behavior. Existing UGB models address nonlinear cross-anisotropy and plasticity separately. It is unknown how the two characteristics are coupled into a finite element model (FEM) and how this will affect the pavement responses. This study presents a coupled nonlinear cross-anisotropic elastoplastic (NAEP) constitutive model for the UGB and implements it in a weak form equation-based FEM. No material subroutine is needed to address the circular dependence between the stress-dependent anisotropic modulus, structural stress responses, and elastoplastic deformation. The NAEP model was calibrated by triaxial resilient modulus and strength tests and validated using laboratory measurements in a large-scale soil-tank pavement structural test. It is found that the NAEP model is valid and effective in predicting the UGB responses in flexible pavements. The model predicted less horizontal tensile stresses at the base bottom and introduced compressive stresses in the middle and top of the base course. This is caused by an increasing confinement resulting from a horizontal plastic dilation in the base course, which cannot be modeled without considering plasticity. The stress-dependent modulus for the UGB material decreases with depth and the distance from loading centerline. Compared with a nonlinear anisotropic elastic model, the NAEP model predicted the same tensile strain at asphalt layer bottom, a higher base modulus, and a higher subgrade compressive strain. Thus, the nonlinear anisotropic elastic UGB model results in the same fatigue life as the NAEP model but may riskily under-predict rutting damage.

Critical Speeds of Turbomachinery: Computer Predictions vs. Experimental Measurements—Part I: The Rotor Mass—Elastic Model

1987 ◽  
Vol 109 (1) ◽  
pp. 1-7 ◽  
Author(s):  
J. M. Vance ◽  
B. T. Murphy ◽  
H. A. Tripp
Keyword(s):  
Research Program ◽  
Critical Speed ◽  
Natural Frequencies ◽  
Computer Programs ◽  
Elastic Model ◽  
Experimental Measurements ◽  
Critical Speeds ◽  
Improve Accuracy ◽  
Speed Computer ◽  
Rotor Mass

This is the first part (Part I) of two papers describing results of a research program directed at verifying computer programs used to calculate critical speeds of turbomachinery. This research program was undertaken since questions existed about the accuracy of calculations for the second and higher critical speeds. Part I describes improvements in computer programs and data modeling that resulted from comparing measured and calculated “free-free” natural frequencies of several shafts and rotors. Program modifications to improve accuracy include consideration of the effect of disk/shaft attachment stiffness, revised treatment of the end masses, and an improved convergence. Modifications resulting from the study are applicable to many other damped and undamped critical speed computer programs.

EFFECT OF THYROIDECTOMY AND THYROID-STIMULATING HORMONE ON RABBIT AORTA INFLUENCED BY EPINEPHRINE

1962 ◽  
Vol 39 (4) ◽  
pp. 605-614 ◽  
Author(s):  
lb Lorenzen
Keyword(s):  
Arterial Wall ◽  
Aortic Wall ◽  
Rabbit Aorta ◽  
Thyroid Stimulating Hormone ◽  
Simultaneous Injection ◽  
Per Se ◽  
Stimulating Hormone

ABSTRACT The effect of epinephrine on the mucopolysaccharides of the aortic wall in rabbits was studied in thyroidectomized and non-operated animals. In other experiments the effect of thyroid-stimulating hormone (TSH) was investigated after simultaneous injection of epinephrine hydrochloride and after starting the TSH injections one week before the epinephrine injections. Thyroidectomy per se caused no alterations in the aortic content of water, hexosamine, hydroxyproline and in vivo uptake of 35S-sulphate, whereas thyroidectomy inhibited epinephrine-alterations in the aortic wall. This was interpreted as a decreased damage to the arterial wall as a consequence of reduced aortic sensitivity to epinephrine. No effect of TSH on the epinephrine-lesions was demonstrable, probably because of the formation of antihormones.

scholarly journals The interaction of platelets with aortic subendothelium: inhibition of adhesion and secretion by prostaglandin I2

Blood ◽  
1981 ◽  
Vol 58 (2) ◽  
pp. 198-205 ◽  
Author(s):  
B Adelman ◽  
MB Stemerman ◽  
D Mennell ◽  
RI Handin
Keyword(s):  
Platelet Aggregation ◽  
Aortic Wall ◽  
Ex Vivo ◽  
Rabbit Aorta ◽  
Platelet Factor 4 ◽  
Direct Immunofluorescence ◽  
Balloon Injury ◽  
Prostaglandin I2 ◽  
Platelet Factor ◽  
Reduced Surface

Abstract We have studied the effect of prostaglandin I2 on platelet turnover, attachment to the subendothelium, and secretion following balloon deendothelialization of the rabbit aorta. Survival of 51Cr-labeled platelets in the balloon-injured animals remained normal. Thirty minutes after injury, there were 4.52 X 10(6) platelets/sq cm attached to the aortic surface, which was 87% covered by platelets. Although plasma platelet factor 4, as measured by radioimmunoassay, did not rise above the normal level of 6.8 +/- 2.6 ng/ml (mean +/- SEM) during the first hour after balloon injury, platelet factor 4 antigen was detected within the vessel wall by direct immunofluorescence within 30 min of injury. An infusion of 650–850 ng/kg/min prostaglandin I2 completely inhibited platelet aggregation and reduced surface coverage by 84% and platelet attachment by 63%. Animals given 50–100 ng/kg/min prostaglandin I2, which only partially inhibited platelet aggregation, had 70% of the aortic surface covered by platelets. Platelet factor 4 antigen was also detected within the aortic wall. Platelet attachment was normal in animals that had been given 850 ng/kg/min prostaglandin I2 prior to balloon injury but sacrificed after the infusion was stopped and ex vivo platelet aggregation had returned to normal.

Mechanism analysis on ground settlement induced by vacuum removal

2019 ◽  
pp. 002072091989755
Author(s):  
Jian Liu ◽  
Chuanyang Liang ◽  
Rui Chen ◽  
Guoxiong Mei ◽  
Yuedong Wu
Keyword(s):  
Clayey Soil ◽  
Ground Deformation ◽  
Axial Strain ◽  
Vertical Direction ◽  
Elastic Model ◽  
Mechanism Analysis ◽  
Clayey Soils ◽  
Ground Settlement ◽  
Surcharge Preloading ◽  
Anisotropic Elastic

Due to the settlement hazards induced by the soft clayey soils, vacuum preloading has been widely used all over the world. Many studies focus on the process of vacuum application but the process of vacuum removal is generally ignored. Different from observations on surcharge preloading, ground settlement rather than heave occurred during vacuum removal. In this study, a stress-controlled triaxial test was carried out to simulate both processes of vacuum application and removal applied on a clayey soil and hence the mechanism of ground settlement induced by vacuum removal is discussed. Compressive axial strain was observed during the decrease of isotropic stress that simulated vacuum removal. To better understand the observed deformation characteristics of the clayey soils during vacuum removal, in this study, a simple anisotropic elastic model was used. The happening of ground settlement of the clayey soil during vacuum removal is mainly because that the Young’s modulus in the vertical direction is higher than that in the horizontal direction. Lateral extension is dominant for the ground deformation during vacuum removal.

scholarly journals Aquaporin-1 facilitates pressure-driven water flow across the aortic endothelium

2015 ◽  
Vol 308 (9) ◽  
pp. H1051-H1064 ◽  
Author(s):  
Tieuvi Nguyen ◽  
Jimmy Toussaint ◽  
Yan Xue ◽  
Chirag Raval ◽  
Limary Cancel ◽  
...  
Keyword(s):  
Hydrostatic Pressure ◽  
Hydraulic Conductivity ◽  
Osmotic Pressure ◽  
Aortic Wall ◽  
Water Channel ◽  
Sprague Dawley ◽  
Aquaporin 1 ◽  
Pressure Driven ◽  
Aortic Endothelial

Aquaporin-1, a ubiquitous water channel membrane protein, is a major contributor to cell membrane osmotic water permeability. Arteries are the physiological system where hydrostatic dominates osmotic pressure differences. In the present study, we show that the walls of large conduit arteries constitute the first example where hydrostatic pressure drives aquaporin-1-mediated transcellular/transendothelial flow. We studied cultured aortic endothelial cell monolayers and excised whole aortas of male Sprague-Dawley rats with intact and inhibited aquaporin-1 activity and with normal and knocked down aquaporin-1 expression. We subjected these systems to transmural hydrostatic pressure differences at zero osmotic pressure differences. Impaired aquaporin-1 endothelia consistently showed reduced engineering flow metrics (transendothelial water flux and hydraulic conductivity). In vitro experiments with tracers that only cross the endothelium paracellularly showed that changes in junctional transport cannot explain these reductions. Percent reductions in whole aortic wall hydraulic conductivity with either chemical blocking or knockdown of aquaporin-1 differed at low and high transmural pressures. This observation highlights how aquaporin-1 expression likely directly influences aortic wall mechanics by changing the critical transmural pressure at which its sparse subendothelial intima compresses. Such compression increases transwall flow resistance. Our endothelial and historic erythrocyte membrane aquaporin density estimates were consistent. In conclusion, aquaporin-1 significantly contributes to hydrostatic pressure-driven water transport across aortic endothelial monolayers, both in culture and in whole rat aortas. This transport, and parallel junctional flow, can dilute solutes that entered the wall paracellularly or through endothelial monolayer disruptions. Lower atherogenic precursor solute concentrations may slow their intimal entrainment kinetics.

Aortic Wall Mechanics: A Geometry-Driven Problem

2011 ◽  
Author(s):  
Samarth S. Raut ◽  
Peng Liu ◽  
Anirban Jana ◽  
Ender A. Finol
Keyword(s):  
Risk Assessment ◽  
Aortic Wall ◽  
Wall Stress ◽  
Aneurysm Rupture ◽  
Intraluminal Pressure ◽  
Wall Material ◽  
Patient Specific ◽  
Rupture Risk ◽  
Constitutive Material Model ◽  
Constitutive Material

Abdominal Aortic Aneurysm (AAA) is a vascular disease that occurs predominantly in people over 60 years of age. The rupture of an AAA is a catastrophic event associated with up to a 90% mortality rate. Hence, it is important for vascular surgeons to justify the risk of repair vis-à-vis the risk of aneurysm rupture. In clinical practice, rupture risk assessment is based on measuring the maximum aneurysm diameter where 5.5 cm is accepted as the critical size for recommending (surgical or endovascular) intervention. However, this criterion is based on an extensive history of evidence-based medicine rather than an individualized assessment of the aneurysm’s potential to rupture. Primary among the biomechanical factors associated with the rupture assessment of an AAA is mechanical wall stress, which is dependent on the accuracy of the geometry reconstruction, intraluminal pressure loading and the constitutive material model used for the aortic wall. We hypothesize that in unruptured, asymptomatic AAA, the wall mechanics is the outcome of primarily the patient specific aneurysm shape and to a lesser extent, the constitutive material property model used to characterize the vascular wall. Evaluating the relative contributions of wall material properties and AAA geometry to wall mechanics estimation will increase our understanding of the factors that influence peak wall stress as an indicator for rupture risk assessment. In the present work, we evaluate the aforementioned hypothesis using a size-matched approach.

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