scholarly journals Effects of elastin degradation and surrounding matrix support on artery stability

2012 ◽  
Vol 302 (4) ◽  
pp. H873-H884 ◽  
Author(s):  
Avione Y. Lee ◽  
Boyang Han ◽  
Shawn D. Lamm ◽  
Cesar A. Fierro ◽  
Hai-Chao Han
Keyword(s):  
Critical Pressure ◽  
Mechanical Stability ◽  
Vascular Diseases ◽  
Surrounding Tissue ◽  
Mechanical Instability ◽  
Mechanical Stiffness ◽  
Surrounding Matrix ◽  
Elastin Degradation ◽  
Before And After ◽  
Critical Buckling Pressure

Tortuous arteries are often associated with aging, hypertension, atherosclerosis, and degenerative vascular diseases, but the mechanisms are poorly understood. Our recent theoretical analysis suggested that mechanical instability (buckling) may lead to tortuous blood vessels. The objectives of this study were to determine the critical pressure of artery buckling and the effects of elastin degradation and surrounding matrix support on the mechanical stability of arteries. The mechanical properties and critical buckling pressures, at which arteries become unstable and deform into tortuous shapes, were determined for a group of five normal arteries using pressurized inflation and buckling tests. Another group of nine porcine arteries were treated with elastase (8 U/ml), and the mechanical stiffness and critical pressure were obtained before and after treatment. The effect of surrounding tissue support was simulated using a gelatin gel. The critical pressures of the five normal arteries were 9.52 kPa (SD 1.53) and 17.10 kPa (SD 5.11) at axial stretch ratios of 1.3 and 1.5, respectively, while model predicted critical pressures were 10.11 kPa (SD 3.12) and 17.86 kPa (SD 5.21), respectively. Elastase treatment significantly reduced the critical buckling pressure ( P < 0.01). Arteries with surrounding matrix support buckled into multiple waves at a higher critical pressure. We concluded that artery buckling under luminal pressure can be predicted by a buckling equation. Elastin degradation weakens the arterial wall and reduces the critical pressure, which thus leads to tortuous vessels. These results shed light on the mechanisms of the development of tortuous vessels due to elastin deficiency.

scholarly journals EFFECTS OF GEOMETRIC VARIATIONS ON THE BUCKLING OF ARTERIES

2011 ◽  
Vol 03 (02) ◽  
pp. 385-406 ◽  
Author(s):  
PARAG DATIR ◽  
AVIONE Y. LEE ◽  
SHAWN D. LAMM ◽  
HAI-CHAO HAN
Keyword(s):  
Cross Sections ◽  
Critical Pressure ◽  
Arterial Wall ◽  
Mechanical Stability ◽  
Longitudinal Axis ◽  
Nonlinear Material ◽  
Mechanical Instability ◽  
Element Analysis ◽  
Buckling Behavior ◽  
Oval Cross Section

Arteries often demonstrate geometric variations such as elliptic and eccentric cross sections, stenosis, and tapering along the longitudinal axis. Effects of these variations on the mechanical stability of the arterial wall have not been investigated. The objective of this study was to determine the buckling behavior of arteries with elliptic, eccentric, stenotic, and tapered cross sections. The arterial wall was modeled as a homogeneous anisotropic nonlinear material. Finite element analysis was used to simulate the buckling process of these arteries under lumen pressure and axial stretch. Our results demonstrated that arteries with an oval cross section buckled in the short axis direction at lower critical pressures as compared to circular arteries. Eccentric cross sections, stenosis, and tapering also decreased the critical pressure. Stenosis led to dramatic pressure variations along the vessel and reduced the buckling pressure. In addition, tapering shifted the buckling deformation profile of the artery towards the distal end. We conclude that geometric variations reduce the critical pressure of arteries and thus make the arteries more prone to mechanical instability than circular cylindrical arteries. These results improve our understanding of the mechanical behavior of arteries.

scholarly journals Mechanical Stability of Hybrid Corrugated Sandwich Plates under Fluid-Structure-Thermal Coupling for Novel Thermal Protection Systems

2020 ◽  
Vol 10 (8) ◽  
pp. 2790
Author(s):  
Wenzheng Zhuang ◽  
Chao Yang ◽  
Zhigang Wu
Keyword(s):  
Mechanical Stability ◽  
Thermal Protection ◽  
Element Model ◽  
Parameter Study ◽  
The Novel ◽  
Thermal Coupling ◽  
Mechanical Instability ◽  
Fluid Structure ◽  
Thermal Protection Systems ◽  
Protection Systems

Hybrid corrugated sandwich (HCS) plates have become a promising candidate for novel thermal protection systems (TPS) due to their multi-functionality of load bearing and thermal protection. For hypersonic vehicles, the novel TPS that performs some structural functions is a potential method of saving weight, which is significant in reducing expensive design/manufacture cost. Considering the novel TPS exposed to severe thermal and aerodynamic environments, the mechanical stability of the HCS plates under fluid-structure-thermal coupling is crucial for preliminary design of the TPS. In this paper, an innovative layerwise finite element model of the HCS plates is presented, and coupled fluid-structure-thermal analysis is performed with a parameter study. The proposed method is validated to be accurate and efficient against commercial software simulation. Results have shown that the mechanical instability of the HCS plates can be induced by fluid-structure coupling and further accelerated by thermal effect. The influences of geometric parameters on thermal buckling and dynamic stability present opposite tendencies, indicating a tradeoff is required for the TPS design. The present analytical model and numerical results provide design guidance in the practical application of the novel TPS.

Criterion of Mechanical Instability in Inhomogeneous Atomic System

2005 ◽  
Vol 482 ◽  
pp. 127-130 ◽  
Author(s):  
Yoshitaka Umeno ◽  
Takayuki Kitamura
Keyword(s):  
Mechanical Stability ◽  
Atomic System ◽  
Instability Criterion ◽  
Fundamental Issue ◽  
Mechanical Instability ◽  
Atomic Systems ◽  
Uniform Deformation ◽  
Atomic Structures ◽  
Homogeneous Structures ◽  
Deformation Modes

The mechanical stability of a material is a fundamental issue in strength of atomic systems. Although the criterion of the mechanical stability of homogeneous structures such as perfect crystals have been successfully investigated so far, the criterion has not been able to be precisely evaluated in the cases of non-uniform deformations or bodies of inhomogeneous atomic structures. Now we present an instability criterion of an arbitrary atomic structure based on the energy balance of the whole system. This method gives the mathematically rigorous condition for the onset of an unstable deformation in any inhomogeneous atomic system. Furthermore, the method can be applied to any type of potential field, which means that ab initio evaluations of the mechanical instability of inhomogeneous structure under non-uniform deformation will be possible. The validity of the method is clarified by the application to tension of a cracked body. The onsets of unstable deformations and their deformation modes are precisely evaluated by the method.

The Critical Buckling Pressure of Arteries

2007 ◽  
Author(s):  
Cesar A. Fierro ◽  
Kurtis Johnson ◽  
Hai-Chao Han
Keyword(s):  
Internal Pressure ◽  
Critical Pressure ◽  
Axial Strain ◽  
Critical Buckling Pressure

Artery stability is essential to normal arterial functions. This study examined the critical internal pressure at which arteries buckle. The critical pressure was found to be strongly related to the axial strain in the arteries.

Critical Buckling Pressure of Veins

2008 ◽  
Author(s):  
Ricky Martinez ◽  
Cesar A. Fierro ◽  
Hai-Chao Han
Keyword(s):  
Critical Pressure ◽  
Varicose Veins ◽  
Axial Strain ◽  
Venous Pressure ◽  
Underlying Mechanism ◽  
Venous Hypertension ◽  
Chronic Venous Disease ◽  
Venous Disease ◽  
Jugular Veins ◽  
Critical Buckling Pressure

Vein tortuosity is often seen as a consequence of venous hypertension and chronic venous disease. However, the underlying mechanism of vein tortuosity is unclear. The aim of this study was to test the hypothesis that hypertensive pressure causes vein buckling that leads to tortuous veins. We determined the buckling pressure of porcine jugular veins and tested the mechanical properties of these veins. Our results demonstrated that veins buckle when the transmural pressure exceeds a critical pressure that is not much higher than normal venous pressure. The critical pressure was found to be strongly related to the axial strain in the veins. Our results are useful in understanding the development of varicose veins.

scholarly journals Characterization and validation of a chronic retinal neovascularization rabbit model by evaluating the efficacy of anti-angiogenic and anti-inflammatory drugs

2022 ◽  
Vol 15 (1) ◽  
pp. 15-22
Author(s):  
Sandeep Kumar ◽  
◽  
Nicholas Cook ◽  
Glenwood Gum ◽  
Vatsala Naageshwaran ◽  
...  
Keyword(s):  
Rabbit Model ◽  
Vascular Diseases ◽  
Inflammatory Cells ◽  
Retinal Hemorrhage ◽  
Vascular Leakage ◽  
Retinal Neovascularization ◽  
Fundus Photography ◽  
Duration Of Action ◽  
Before And After ◽  
Anti Inflammatory

AIM: To establish a rabbit model with chronic condition of retinal neovascularization (RNV) induced by intravitreal (IVT) injection of DL-2-aminoadipic acid (DL-AAA), a retinal glial (Müller) cell toxin, extensive characterization of DL-AAA induced angiographic features and the suitability of the model to evaluate anti-angiogenic and anti-inflammatory therapies for ocular vascular diseases. METHODS: DL-AAA (80 mmol/L) was administered IVT into both eyes of Dutch Belted rabbit. Post DL-AAA delivery, clinical ophthalmic examinations were performed weekly following modified McDonald-Shadduck Scoring System. Color fundus photography, fluorescein angiography (FA), and optical coherence tomography (OCT) procedures were performed every 2 or 4wk until stable retinal vascular leakage was observed. Once stable retinal leakage (12wk post DL-AAA administration) was established, anti-vascular endothelial growth factor (VEGF) (bevacizumab, ranibizumab and aflibercept) and anti-inflammatory (triamcinolone, TAA) drugs were tested for their efficacy after IVT administration. Fluorescein angiograms were scored before and after treatment following a novel grading system, developed for the DL-AAA rabbit model. RESULTS: Post DL-AAA administration, eyes were presented with moderate to severe retinal/choroidal inflammation which was accompanied by intense vitreous flare and presence of inflammatory cells in the vitreous humor. Retinal hemorrhage was restricted to the tips of neo-retinal vessels. FA revealed maximum retinal vascular leakage at 2wk after DL-AAA injection and then persisted as evidenced by stable mean FA scores in weeks 8 and 12. Retinal vascular angiographic and tomographic features were stable and consistent up to 36mo among two different staggers induced for RNV at two different occasions. Day 7, mean FA scores showed that 1 µg/eye of bevacizumab, ranibizumab, aflibercept and 2 µg/eye of TAA suppress 65%, 90%, 100% and 50% retinal vascular leakage, respectively. Day 30, bevacizumab and TAA continued to show 66% and 44% suppression while ranibizumab effect was becoming less effective (68%). In contrast, aflibercept was still able to fully (100%) suppress vascular leakage on day 30. On day 60, bevacizumab, ranibizumab and TAA showed suppression of 7%, 12%, and 9% retinal vascular leakage, respectively, however, aflibercept continued to be more effective showing 50% suppression of vascular leakage. CONCLUSION: The DL-AAA rabbit model mimics RNV angiographic features like RNV and chronic retinal leakage. Based on these features the DL-AAA rabbit model provides an invaluable tool that could be used to test the therapeutic efficacy and duration of action of novel anti-angiogenic formulations, alone or in combination with anti-inflammatory compounds.

scholarly journals The effect of chemotherapy on endothelial function and microcirculation in patients with gastric cancer

Kardiologiia ◽  
2020 ◽  
Vol 60 (2) ◽  
pp. 89-95
Author(s):  
Yu. Yu. Kirichenko ◽  
I. S. Ilgisonis ◽  
Yu. N. Belenkov ◽  
E. V. Privalova ◽  
Yu. I. Naymann ◽  
...  
Keyword(s):  
Gastric Cancer ◽  
Endothelial Dysfunction ◽  
Healthy Volunteers ◽  
Cancer Patients ◽  
Vascular Diseases ◽  
Vascular Wall ◽  
Capillary Network ◽  
Wall Stiffness ◽  
Before And After ◽  
Cardio Vascular

Objective. To evaluate and study the dynamics of endothelial dysfunction instrumental indicators, vascular wall stiffness and microcirculation state in patients with gastric cancer (adenocarcinoma) before and after chemotherapy; compare it with the results obtained from healthy volunteers and patients with cardio-vascular diseases.Materials and Methods. The study included 65 people: 25 healthy volunteers, 15 patients with known cardio-vascular diseases (CVD) and 25 patients with histologically confirmed gastric cancer (adenocarcinoma) stage 2—4 who underwent surgical treatment followed by chemotherapy according to the FOLFOX, XELOX, and XP regimes. For non-invasive assessment of the vascular wall’s state of large vessels and microcirculation, all patients in the main group underwent computer nailfold capillaroscopy and finger photoplethysmography before chemotherapy and within a month after the completion of the last course. For healthy volunteers and patients with CVD, the above studies were performed once during the examination.Results. The data obtained indicate a significant increase in the reflection index of small muscle arteries (RI) and the stiffness index of large conducting arteries (aSI) during chemotherapy. In cancer patients, even before the treatment, endothelial dysfunction was detected, which significantly worsened after treatment (occlusion index (IO) before and after chemotherapy 1.7 (1.38; 1.9) vs. 1.3 (1.2; 1.5), p<0.0002, respectively). Significant differences in the compared indices in cancer patients and CVD group were revealed only after chemotherapy. Significant structural and functional disorders of capillaries were noted in the studied groups, which also worsened during chemotherapy in the main group (density of the capillary network at rest 43.23cap/mm2 vs. 42.19cap/mm2, p <0.01, respectively; density of the capillary network after the reactive hyperemia test 46.77cap/mm2 vs. 44.11cap/mm2, p<0,02, respectively).Conclusion. In this study, for the first time, the dynamics of endothelial dysfunction indicators, vascular wall stiffness and microcirculation state in patients with gastric cancer were studied, and a reliable increasing of these changes was proved during chemotherapy. The results indicate the need for a further search for accurate and effective methods of identifying early signs of close and distant vasculotoxicity, the development of individual prevention programs in order to significantly reduce the risk of cardiovascular events during and after chemotherapy.

scholarly journals Effect of Morphology and Mechanical Stability of Nanometric Platinum Layer on Nickel Foam for Hydrogen Evolution Reaction

Energies ◽  
2019 ◽  
Vol 12 (16) ◽  
pp. 3116
Author(s):  
Rachela G. Milazzo ◽  
Stefania M. S. Privitera ◽  
Silvia Scalese ◽  
Salvatore A. Lombardo
Keyword(s):  
Hydrogen Evolution ◽  
Hydrogen Evolution Reaction ◽  
Deposition Time ◽  
Mechanical Stability ◽  
Nickel Foam ◽  
Linear Sweep Voltammetry ◽  
Electrochemical Activity ◽  
Alkaline Electrolyte ◽  
Mechanical Instability ◽  
Platinum Layer

Platinum thin films are deposited on open-cell nickel foam with porosity of 95% via spontaneous galvanic displacement. Ni foams with different morphologies and pore size are compared and characterized by electrochemical and structural analysis techniques. The effect of Pt coating on the electrochemical activity is studied by using the Pt coated foam as electrode material for hydrogen evolution reaction in an aqueous alkaline electrolyte. The electrocatalytic activity of the electrodes is evaluated using linear sweep voltammetry curves and Tafel plots as a function of deposition time. The comparison with scanning electron microscopy analyses demonstrates that the catalytic activity has a maximum when the platinum film completely covers the Ni surface. The further increase of the Pt thickness leads to mechanical instability with crack formation and delamination. The effect of the foam morphology on the Pt deposition rate has been evaluated and discussed, determining the minimum Pt amount required to achieve the maximum electrochemical activity, as well as the maximum thickness in order to assure stable characteristics before delamination occurs.

Mechanical properties and structure–function trade-offs in secondary xylem of young roots and stems

2019 ◽  
Vol 70 (14) ◽  
pp. 3679-3691 ◽  
Author(s):  
Lenka Plavcová ◽  
Friederike Gallenmüller ◽  
Hugh Morris ◽  
Mohammad Khatamirad ◽  
Steven Jansen ◽  
...  
Keyword(s):  
Wood Density ◽  
Cell Walls ◽  
Mechanical Stability ◽  
Secondary Xylem ◽  
Mechanical Stiffness ◽  
Xylem Structure ◽  
Major Constraint ◽  
Trade Offs ◽  
Clematis Vitalba ◽  
Torsional Properties

AbstractBending and torsional properties of young roots and stems were measured in nine woody angiosperms. The variation in mechanical parameters was correlated to wood anatomical traits and analysed with respect to the other two competing functions of xylem (namely storage and hydraulics). Compared with stems, roots exhibited five times greater flexibility in bending and two times greater flexibility in torsion. Lower values of structural bending and structural torsional moduli (Estr and Gstr, respectively) of roots compared with stems were associated with the presence of thicker bark and a greater size of xylem cells. Across species, Estr and Gstr were correlated with wood density, which was mainly driven by the wall thickness to lumen area ratio of fibres. Higher fractions of parenchyma did not translate directly into a lower wood density and reduced mechanical stiffness in spite of parenchyma cells having thinner, and in some cases less lignified, cell walls than fibres. The presence of wide, partially non-lignified rays contributed to low values of Estr and Gstr in Clematis vitalba. Overall, our results demonstrate that higher demands for mechanical stability in self-supporting stems put a major constraint on xylem structure, whereas root xylem can be designed with a greater emphasis on both storage and hydraulic functions.

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