Academic literature on the topic 'Aortic tissue'
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Journal articles on the topic "Aortic tissue"
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Torfgård, Krishna, Johan Ahlner, Krister L. Axelsson, Björn Norlander, and Åke Bertler. "Tissue levels of glyceryl trinitrate and cGMP after in vivo administration in rat, and the effect of tolerance development." Canadian Journal of Physiology and Pharmacology 69, no. 9 (September 1, 1991): 1257–61. http://dx.doi.org/10.1139/y91-184.
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The present study compares the tissue distribution of glyceryl trinitrate (GTN) in plasma, heart, brain, aortic tissue, and adipose tissue from GTN tolerant and GTN nontolerant rats at various time points. Furthermore, the cGMP levels in brain, heart, and aortic tissue were studied at various time points as well as the concentration–effect relationship for GTN in aorta isolated at different time points after the last exposure to GTN. Concentrations of GTN were found to be higher in all tissues studied as compared with plasma, and the concentrations of GTN were higher in tissues from tolerant rats as compared with nontolerant rats, except for aortic tissue. Concentration–effect curves obtained in vitro showed that aortic smooth muscle was still tolerant 24 h after the last dose of GTN. The cGMP level in brain was significantly increased by 40% 2 h after a single dose of GTN (50 mg/kg) and in aortic tissue by 50% at 15 min and at 2 h after a single dose of GTN (50 mg/kg). There was no effect on cGMP in brain, while an increase was seen in aortic tissue 15 min after the last dose in tolerant animals. No change in cGMP level was seen in heart neither in nontolerant nor in tolerant animals at 15 min and at 2 h. No effect on cGMP levels in brain, heart, and aortic tissue was seen 8, 16, and 24 h after exposure to GTN in either tolerant or nontolerant rats. In conclusion, GTN does not involve the cGMP system in heart, and tolerance development caused a less pronounced GTN-induced cGMP increase in aortic tissue. Furthermore, the cGMP elevation in tissues does not correlate with GTN levels in tissues.Key words: glyceryl trinitrate, cGMP, tolerance, tissue distribution, rat.
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Wright, Gary. "Use-dependent decline in rat aorta sensitivity to contraction by potassium." Canadian Journal of Physiology and Pharmacology 69, no. 7 (July 1, 1991): 921–28. http://dx.doi.org/10.1139/y91-140.
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Aortic rings excised from rats at 12 weeks of age showed a decrease in responsiveness during repeated contraction by increasing potassium concentration. By comparison, aortic rings obtained from rats at 22 and 26 weeks exhibited less loss or an increase in responsiveness to high potassium concentration during repeated contraction. The decrease in responsiveness to potassium in aortae of young rats was not due to the extended interval of incubation of the tissue in vitro. Aortic rings incubated without stimulation for 4 h following a reference contraction showed no change in contractile response to potassium. However, the magnitude of loss in responsiveness to potassium did appear to be related to the potassium concentration and the length of time the tissues were exposed to the high potassium solutions. Contraction of the tissue at 60 versus 30 mM KCl or extending the interval in depolarizing solution from 15 to 60 min significantly enhanced the decline in tissue responsiveness to potassium. The interruption of a series of potassium-induced contractions by exposure of the tissue to contractile (serotonin, norepinephrine) or relaxant (acetylcholine, isoproterenol) stimuli had no effect on the loss in responsiveness to potassium. However, injection of the calcium channel agonist, Bay K 8644, into the incubation media restored responsiveness to potassium. Concentration–response curves indicated that both sensitivity and the maximal response to potassium were reduced in aortic rings repeatedly contracted with potassium. Bay K 8644 addition immediately following the control contraction significantly increased sensitivity and the maximal response to potassium compared with the control contraction. After tissues had been repeatedly contracted by potassium, Bay K 8644 restored tissue sensitivity and the maximum response to the control level. The results indicate that aortic tissues of young rats are subject to desensitization to potassium stimulation during repeated exposure in vitro. The restoration of tissue sensitivity by Bay K 8644 suggests that this desensitization centers on decreased effectiveness of the voltage-dependent mechanism for increasing intracellular concentration of free calcium and the activation of the contractile protein.Key words: concentration–response, depolarization, vascular smooth muscle, tension.
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Behr-Roussel, Delphine, Diane Gorny, Katell Mevel, Sandrine Compagnie, Patrick Kern, Virgine Sivan, Jacques Bernabé, Martin P. Bedigian, Laurent Alexandre, and François Giuliano. "Erectile dysfunction: an early marker for hypertension? A longitudinal study in spontaneously hypertensive rats." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 288, no. 1 (January 2005): R276—R283. http://dx.doi.org/10.1152/ajpregu.00040.2004.
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Erectile dysfunction (ED) is another manifestation of vascular disease. We evaluated the natural history of ED in the spontaneously hypertensive rat (SHR) and the respective participation of associated pathophysiological modifications, i.e., endothelial dysfunction and tissue remodeling. SHR and their normotensive counterparts [Wistar-Kyoto rats (WKY)] of 6, 12, and 24 wk of age ( n = 12) were used to evaluate erectile function, erectile and aortic tissue reactivity, and remodeling. Erectile responses in SHR are reduced at all ages ( P < 0.001). In both aortic and erectile tissues of SHR and WKY, relaxations to ACh are altered progressively with age, although more markedly in SHR. They are decreased at 12 wk of age in erectile tissue of SHR compared with WKY (maximal relaxation: −19.2 ± 2.8% vs. −28.3 ± 3.9%, P < 0.001) but only at 24 wk of age in aortas (−47.9 ± 6.4% vs. −90.5 ± 2.9%, P < 0.001). Relaxations to sodium nitroprusside are unaltered in aortic rings of both strains but enhanced in erectile tissue of SHR at 12 wk of age. Major modifications in the distribution of collagen I, III, and V in SHR occur in both types of tissue and are detectable sooner in erectile tissue compared with aortic tissue. The onset of ED is detectable before the onset of hypertension in the SHR. Structural and functional alterations, while similar, occur earlier in erectile compared with vascular tissue. If confirmed in humans, ED could be an early warning sign for hypertension, and common therapeutic strategies targeting both ED and hypertension could be investigated.
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Zhao, Dong-E., Ruo-Bing Li, Wei-Yong Liu, Gang Wang, Shi-Qiang Yu, Cheng-Wei Zhang, Wen-Sheng Chen, and Geng-Xu Zhou. "Tissue-Engineered Heart Valve on Acellular Aortic Valve Scaffold: In-Vivo Study." Asian Cardiovascular and Thoracic Annals 11, no. 2 (June 2003): 153–56. http://dx.doi.org/10.1177/021849230301100214.
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The feasibility of constructing a tissue-engineered heart valve on an acellular porcine aortic valve leaflet was evaluated. A detergent and enzymatic extraction process was developed to remove the cellular components from porcine aortic valves. The acellular valve leaflets were seeded for 7 days in vitro with cells from canine arterial wall and endothelial cells. The constructs were implanted into the lumens of 6 canine abdominal aortas to assess the reconstruction of the valve leaflets. It was found that all cellular components had been removed from the porcine aortic valves. The valve leaflets were completely reconstructed at the end of the 10th week in vivo. Scanning electron microscopy showed that the valve leaflets were partially covered with endothelial cells. It was concluded that porcine aortic valves can be decellularized by the detergent and enzymatic extraction process and it is feasible to construct a tissue-engineered heart valve in vivo on an acellular valve scaffold.
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Li, Yanming, Pingping Ren, Ashley Dawson, Hernan G. Vasquez, Waleed Ageedi, Chen Zhang, Wei Luo, et al. "Single-Cell Transcriptome Analysis Reveals Dynamic Cell Populations and Differential Gene Expression Patterns in Control and Aneurysmal Human Aortic Tissue." Circulation 142, no. 14 (October 6, 2020): 1374–88. http://dx.doi.org/10.1161/circulationaha.120.046528.
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Background: Ascending thoracic aortic aneurysm (ATAA) is caused by the progressive weakening and dilatation of the aortic wall and can lead to aortic dissection, rupture, and other life-threatening complications. To improve our understanding of ATAA pathogenesis, we aimed to comprehensively characterize the cellular composition of the ascending aortic wall and to identify molecular alterations in each cell population of human ATAA tissues. Methods: We performed single-cell RNA sequencing analysis of ascending aortic tissues from 11 study participants, including 8 patients with ATAA (4 women and 4 men) and 3 control subjects (2 women and 1 man). Cells extracted from aortic tissue were analyzed and categorized with single-cell RNA sequencing data to perform cluster identification. ATAA-related changes were then examined by comparing the proportions of each cell type and the gene expression profiles between ATAA and control tissues. We also examined which genes may be critical for ATAA by performing the integrative analysis of our single-cell RNA sequencing data with publicly available data from genome-wide association studies. Results: We identified 11 major cell types in human ascending aortic tissue; the high-resolution reclustering of these cells further divided them into 40 subtypes. Multiple subtypes were observed for smooth muscle cells, macrophages, and T lymphocytes, suggesting that these cells have multiple functional populations in the aortic wall. In general, ATAA tissues had fewer nonimmune cells and more immune cells, especially T lymphocytes, than control tissues did. Differential gene expression data suggested the presence of extensive mitochondrial dysfunction in ATAA tissues. In addition, integrative analysis of our single-cell RNA sequencing data with public genome-wide association study data and promoter capture Hi-C data suggested that the erythroblast transformation-specific related gene( ERG ) exerts an important role in maintaining normal aortic wall function. Conclusions: Our study provides a comprehensive evaluation of the cellular composition of the ascending aortic wall and reveals how the gene expression landscape is altered in human ATAA tissue. The information from this study makes important contributions to our understanding of ATAA formation and progression.
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Chowdhury, Ujjwal Kumar, Lakshmi Kumari Sankhyan, Sheil Avneesh, Ruma Ray, Mani Kalaivani, Suruchi Hasija, and Abhinavsingh Chauhan. "Histologic Abnormalities of the Ascending Aorta: Effects on Aortic Remodeling after Intracardiac Repair of Tetralogy of Fallot." Texas Heart Institute Journal 47, no. 2 (April 1, 2020): 86–95. http://dx.doi.org/10.14503/thij-17-6279.
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We evaluated aortic tissue specimens from patients undergoing tetralogy of Fallot repair, to determine whether histologic abnormalities affect postsurgical aortic remodeling and other patient-related variables. Using light microscopy, we studied full-thickness aortic wall tissue operatively excised from 118 consecutive patients undergoing intracardiac repair of tetralogy of Fallot. We performed multiple linear regression analysis to identify independent predictors of change in aortic root dimensions, which we measured with echocardiography after repair and every 3 months thereafter. Thirty histologically normal specimens were used as controls. Elastic fiber fragmentation was found in 74.6% of the abnormal specimens, mucoid extracellular matrix accumulation in 49.2%, smooth muscle cell nuclei loss in 39%, smooth muscle cell disorganization in 28.8%, and medial fibrosis in 52.5%. At a mean follow-up time of 83.55 ± 42.08 months, mean aortic sinotubular diameter decreased from 28.79 ± 9.15 to 27.16 ± 8.52 mm/m2 (r =–0.43; P <0.001). Aortic sinotubular diameter decreased by 0.6 mm/m2 among females (β =0.6, SE=0.31; P =0.05) and by 0.88 mm/m2 in patients who had elastic fiber fragmentation or loss (β =0.88, SE=0.38; P =0.02). In bivariate and multiple linear regression analysis, duration of follow-up emerged as an independent predictor of aortic remodeling. The aortic histopathologic changes in our patients had an independent negative impact on the degree of aortic remodeling after surgery. We observed the most improved aortic sinotubular diameter in patients who had either histologically normal aortas or aortas with elastic fragmentation.
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Harky, Amer, Rizwan Iqbal, Vincenzo Giordano, and Ahmed Al-Adhami. "Aortic endovascular stenting in patients with systemic connective tissue disorders: does the prohibitive dogma still stand tall?" Journal of International Medical Research 48, no. 2 (July 29, 2019): 030006051986396. http://dx.doi.org/10.1177/0300060519863963.
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Endovascular repair of thoracic aortic diseases can provide satisfactory outcomes in elective and certain emergency cases involving the descending thoracic and aortic arch. However, open repair remains the gold standard method of aortic root pathologies and certain aortic arch pathologies, such as extended dissection. Nevertheless, the use of endovascular stenting in patients with connective tissue disorders has not been fully explored because the aortic tissues are fragile and the likelihood of keeping the stent in place is low because of its progressive dilatation and subsequent requirement for open repair at a later stage when the stent graft fails. Our brief review focuses on current evidence of the use of stents in patients with connective tissue disorders and whether such practice can be expanded further.
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Alakhtar, Ali, Alexander Emmott, Cornelius Hart, Rosaire Mongrain, Richard L. Leask, and Kevin Lachapelle. "3D printed ascending aortic simulators with physiological fidelity for surgical simulation." BMJ Simulation and Technology Enhanced Learning 7, no. 6 (June 21, 2021): 536–42. http://dx.doi.org/10.1136/bmjstel-2021-000868.
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IntroductionThree-dimensional (3D) printed multimaterial ascending aortic simulators were created to evaluate the ability of polyjet technology to replicate the distensibility of human aortic tissue when perfused at physiological pressures.MethodsSimulators were developed by computer-aided design and 3D printed with a Connex3 Objet500 printer. Two geometries were compared (straight tube and idealised aortic aneurysm) with two different material variants (TangoPlus pure elastic and TangoPlus with VeroWhite embedded fibres). Under physiological pressure, β Stiffness Index was calculated comparing stiffness between our simulators and human ascending aortas. The simulators’ material properties were verified by tensile testing to measure the stiffness and energy loss of the printed geometries and composition.ResultsThe simulators’ geometry had no effect on measured β Stiffness Index (p>0.05); however, β Stiffness Index increased significantly in both geometries with the addition of embedded fibres (p<0.001). The simulators with rigid embedded fibres were significantly stiffer than average patient values (41.8±17.0, p<0.001); however, exhibited values that overlapped with the top quartile range of human tissue data suggesting embedding fibres can help replicate pathological human aortic tissue. Biaxial tensile testing showed that fiber-embedded models had significantly higher stiffness and energy loss as compared with models with only elastic material for both tubular and aneurysmal geometries (stiffness: p<0.001; energy loss: p<0.001). The geometry of the aortic simulator did not statistically affect the tensile tested stiffness or energy loss (stiffness: p=0.221; energy loss: p=0.713).ConclusionWe developed dynamic ultrasound-compatible aortic simulators capable of reproducing distensibility of real aortas under physiological pressures. Using 3D printed composites, we are able to tune the stiffness of our simulators which allows us to better represent the stiffness variation seen in human tissue. These models are a step towards achieving better simulator fidelity and have the potential to be effective tools for surgical training.
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Pedroza, Albert J., Yasushi Tashima, Rohan Shad, Paul Cheng, Robert Wirka, Samantha Churovich, Ken Nakamura, et al. "Single-Cell Transcriptomic Profiling of Vascular Smooth Muscle Cell Phenotype Modulation in Marfan Syndrome Aortic Aneurysm." Arteriosclerosis, Thrombosis, and Vascular Biology 40, no. 9 (September 2020): 2195–211. http://dx.doi.org/10.1161/atvbaha.120.314670.
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Objective: To delineate temporal and spatial dynamics of vascular smooth muscle cell (SMC) transcriptomic changes during aortic aneurysm development in Marfan syndrome (MFS). Approach and Results: We performed single-cell RNA sequencing to study aortic root/ascending aneurysm tissue from Fbn1 C1041G/ + (MFS) mice and healthy controls, identifying all aortic cell types. A distinct cluster of transcriptomically modulated SMCs (modSMCs) was identified in adult Fbn1 C1041G/ + mouse aortic aneurysm tissue only. Comparison with atherosclerotic aortic data (ApoE −/− mice) revealed similar patterns of SMC modulation but identified an MFS-specific gene signature, including plasminogen activator inhibitor-1 ( Serpine1 ) and Kruppel-like factor 4 ( Klf4 ). We identified 481 differentially expressed genes between modSMC and SMC subsets; functional annotation highlighted extracellular matrix modulation, collagen synthesis, adhesion, and proliferation. Pseudotime trajectory analysis of Fbn1 C1041G/ + SMC/modSMC transcriptomes identified genes activated differentially throughout the course of phenotype modulation. While modSMCs were not present in young Fbn1 C1041G/ + mouse aortas despite small aortic aneurysm, multiple early modSMCs marker genes were enriched, suggesting activation of phenotype modulation. modSMCs were not found in nondilated adult Fbn1 C1041G/ + descending thoracic aortas. Single-cell RNA sequencing from human MFS aortic root aneurysm tissue confirmed analogous SMC modulation in clinical disease. Enhanced expression of TGF-β (transforming growth factor beta)-responsive genes correlated with SMC modulation in mouse and human data sets. Conclusions: Dynamic SMC phenotype modulation promotes extracellular matrix substrate modulation and aortic aneurysm progression in MFS. We characterize the disease-specific signature of modSMCs and provide temporal, transcriptomic context to the current understanding of the role TGF-β plays in MFS aortopathy. Collectively, single-cell RNA sequencing implicates TGF-β signaling and Klf4 overexpression as potential upstream drivers of SMC modulation.
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Tascini, Carlo, Antonello Di Paolo, Roberta Poletti, Sarah Flammini, Michele Emdin, Ilaria Ciullo, Enrico Tagliaferri, Annette Moter, and Francesco Menichetti. "Daptomycin Concentrations in Valve Tissue and Vegetation in Patients with Bacterial Endocarditis." Antimicrobial Agents and Chemotherapy 57, no. 1 (October 22, 2012): 601–2. http://dx.doi.org/10.1128/aac.01608-12.
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ABSTRACTIn a patient with mitral-aortic native-valveStreptococcus oralisendocarditis, daptomycin concentrations in aortic and mitral valves were 8.6 and 30.8 μg/g, respectively, and 26 μg/g in the mitral vegetation. In the case of porcine-aortic-valveStaphylococcus epidermidisendocarditis, the daptomycin concentrations were 53.1 μg/g in the valve and 18.1 μg/g in perivalvular tissues. Daptomycin achieved apparently adequate tissue concentrations.S. epidermidiswas eradicated, whereasStreptococcus oralispersisted, and its daptomycin MIC displayed a 4-fold increase.
Dissertations / Theses on the topic "Aortic tissue"
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Nowell, Justin L. "Anticoagulation Following Tissue Aortic Valve Replacement." Thesis, St George's, University of London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.517184.
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Liu, Janet. "Design of a Novel Tissue Culture System to Subject Aortic Tissue to Multidirectional Bicuspid Aortic Valve Wall Shear Stress." Wright State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=wright1527077368757049.
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Smuts, Adriaan Nicolaas. "Design of tissue leaflets for a percutaneous aortic valve." Thesis, Stellenbosch : University of Stellenbosch, 2009. http://hdl.handle.net/10019.1/1625.
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MScEngThesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009.
In this project the shape and attachment method of tissue leaflets for a percutaneous aortic valve is designed and tested as a first prototype. Bovine and kangaroo pericardium was tested and compared with natural human valve tissue by using the Fung elastic constitutive model for skin. Biaxial tests were conducted to determine the material parameters for each material. The constitutive model was implemented using finite element analysis (FEA) by applying a user-specified subroutine. The FEA implementation was validated by simulating the biaxial tests and comparing it with the experimental data. Concepts for different valve geometries were developed by incorporating valve design and performance parameters, along with stent constraints. Attachment techniques and tools were developed for valve manufacturing. FEA was used to evaluate two concepts. The influence of effects such as different leaflet material, material orientation and abnormal valve dilation on the valve function was investigated. The stress distribution across the valve leaflet was examined to determine the appropriate fibre direction for the leaflet. The simulated attachment forces were compared with suture tearing tests performed on the pericardium to evaluate suture density. In vitro tests were conducted to evaluate the valve function. Satisfactory testing results for the prototype valves were found which indicates the possibility for further development and refinement.
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Kermani, Golriz. "Characterization of Rate Dependency and Inhomogeneity of Aortic Tissue." Diss., Temple University Libraries, 2016. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/412554.
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Mechanical EngineeringPh.D.
Traumatic aortic rupture (TAR) is one of the leading causes of morbidity and mortality in motor-vehicle accidents with the majority of injuries occurring in the peri-isthmus region. To date, the mechanisms of aorta injury are poorly understood as this injury cannot be replicated reliably in cadaver crash tests. Due to inconclusiveness of the experimental tests, finite element (FE) modeling is often used to gain a better insight into the mechanisms of TAR. However, the FE models are also hindered by many unknowns particularly the soft tissues biomechanical responses. A crucial step to improve the FE models of blunt chest trauma is to advance our understanding of the local mechanical properties of aortic tissue subject to high loading rates associated with TAR. The objective of this dissertation was to investigate the effects of tissue rate dependency and inhomogeneity in the modeling of loading conditions that lead to TAR. The material properties of human aorta in large deformations and high loading rates were characterized based on oscillatory biaxial tests. It was shown that a quasilinear viscoelastic (QLV) model with the instantaneous elastic response of the second order and the reduced relaxation function with one exponentially decaying term could describe the experimental results between 20 Hz and 130 Hz. The obtained decay rates (in the range of 70 to 550 s-1) were 10 to 100 folds higher than previously reported values and showed significant rate dependence within 10 ms after the loading. It was shown that the rate dependent properties, similar to the elastic properties, were anisotropic with generally higher decay rate and stiffness observed in the circumferential direction compared to the longitudinal direction. The inhomogeneity of porcine descending thoracic aorta was characterized in three dimensions using a nano-indentation technique and QLV modeling approach. The tests were conducted in the axial, circumferential, and radial orientations with about 100 micrometer spatial resolution. Aortic tissue was divided into 10 regions across the thickness, 4 quadrants in the circumferential direction, and 3 sections in the longitudinal direction. While across the thickness, the results in different orientations were significantly different, four distinct layers were identified that were matched with the anatomical features. In the axial direction, the medial quadrant, and in all directions, the proximal DTA had the lowest stiffness. The results predict that under equal stresses, the inner layers of the medial quadrant in upper DTA would undergo more strains and will be therefore more prone to failure. This prediction is in agreement with clinical observations. The inhomogeneity and rate dependency of aorta were implemented in the Global Human Body Models Consortium full-body FE model. It was demonstrated that in a simulation of blunt chest impact, both features significantly affected the tissue strain levels particularly in the isthmus, arch, and ascending aorta. Accurate quantifications of these features are essential to assess the risk of aortic injury based on FE models.
Temple University--Theses
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Korossis, Sotirios Anastasios. "Biomechanics and hydrodynamics of decellularised aortic valves for tissue engineering." Thesis, University of Leeds, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270873.
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Rastgar, Agah Mobin. "Material Characterization of Aortic Tissue for Traumatic Injury and Buckling." Diss., Temple University Libraries, 2015. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/324268.
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Mechanical EngineeringPh.D.
While traumatic aortic injury (TAI) and rupture (TAR) continue to be a major cause of morbidity and mortality in motor vehicle accidents, its underlying mechanisms are still not well understood. Different mechanisms such as increase in intraluminal pressure, relative movement of aorta with respect to mediastinal structures, direct impact to bony structures have been proposed as contributing factors to TAI/TAR. At the tissue level, TAI is assumed to be the result of a complex state of supra-physiological, high rate, and multi-axial loading. A major step to gain insight into the mechanisms of TAI is a characterization of the aortic tissue mechanical and failure properties under loading conditions that resemble traumatic events. While the mechanical behavior of arteries in physiological conditions have been investigated by many researchers, this dissertation was motivated by the scarcity of reported data on supra-physiological and high rate loading conditions of aorta. Material properties of the porcine aortic tissue were characterized and a Fung-type constitutive model was developed based on ex-vivo inflation-extension of aortic segments with intraluminal pressures covering a range from physiological to supra-physiological (70 kPa). The convexity of the material constitutive model was preserved to ensure numerical stability. The increase in ë_è from physiological pressure (13 kPa) to 70 kPa was 13% at the outer wall and 22% at the inner wall while in this pressure range, the longitudinal stretch ratio ë_z increased 20%. A significant nonlinearity in the material behavior was observed as in the same pressure range, the circumferential and longitudinal Cauchy stresses at the inner wall were increased 16 and 18 times respectively. The effect of strain-rate on the mechanical behavior and failure properties of the tissue was characterized using uniaxial extension experiments in circumferential and longitudinal directions at nominal strain rates of 0.3, 3, 30 and 400 s-1. Two distinct states of failure initiation (FI) and ultimate tensile strength (UTS) were identified at both directions. Explicit direct relationships were derived between FI and UTS stresses and strain rate. On the other hand, FI and UTS strains were rate independent and therefore strain was proposed as the main mechanism of failure. On average, engineering strain at FI was 0.85±0.03 for circumferential direction and 0.58±0.02 for longitudinal direction. The engineering strain at UTS was not different between the two directions and reached 0.89±0.03 on average. Tissue pre-failure linear moduli showed an average of 60% increase over the range of strain rates. Using the developed material model, mechanical stability of aorta was studied by varying the loading parameters for two boundary conditions, namely pinned-pinned boundary condition (PPBC) and clamped-clamped boundary condition (CCBC). The critical pressure for CCBC was three times higher than PPBC. It was shown that the relatively free segment of aorta at the isthmus region may become unstable before reaching the peak intraluminal pressures that occur during a trauma. The mechanical instability mechanism was proposed as a contributing factor to TAI, where elevations in tissue stresses and strains due to buckling may increase the risk of injury.
Temple University--Theses
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Treibel, Thomas Alexander. "Aortic stenosis : a myocardial disease : insights from myocardial tissue characterisation." Thesis, University College London (University of London), 2017. http://discovery.ucl.ac.uk/1574742/.
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Aortic stenosis (AS) is a disease of not just the valve, but also of the myocardium. Patient symptoms and outcome are determined by the myocardial response; a crucial but poorly understood process. Diffuse and focal myocardial fibrosis play a key role. Until recently, both could only be assessed using invasive histology, but now cardiovascular magnetic resonance (CMR) offers late gadolinium enhancement (LGE) and extracellular volume fraction (ECV) techniques. In this thesis, I developed new methods to quantify ECV by synthetic ECV and cardiac CT. I then explored myocardial remodelling and fibrosis in patients with severe AS undergoing aortic valve replacement (AVR) using myocardial biopsy, CMR, biomarkers and a wide range of clinical parameters. Prior to AVR, CMR in patients with severe AS revealed important differences in myocardial remodelling between sexes, otherwise missed on echocardiography alone. Given apparently equal valve severity, the myocardial response to AS appeared unexpectedly maladaptive in men compared to women. Intra-operative myocardial biopsy revealed three pattern of fibrosis: endocardial fibrosis, microscars (mainly in the subendomyocardium), and diffuse interstitial fibrosis. Biopsy best captured the transmural gradient of fibrosis and microscars, while on CMR, LGE captured mainly microscars and ECV captured mid-myocardial related functional changes beyond LGE. Combining LGE and ECV allowed better stratification of AS patients. Incidentally, I found that 6% of AS patients older then 65 years had wild-type transthyretin amyloid deposits on cardiac biopsy, which was associated with poor outcome. This is now the basis of a BHF research fellowship. Following AVR, I demonstrated for the first time non-invasively that diffuse fibrosis regresses (focal fibrosis did not), which is accompanied by structural and functional improvements suggesting that human diffuse fibrosis is plastic, measurable by CMR and a potential therapeutic target.
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Luo, Yuanming. "Local properties and rupture characteristics of thoracic aortic aneurysm tissue." Diss., University of Iowa, 2018. https://ir.uiowa.edu/etd/6186.
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Ascending thoracic aortic aneurysms (ATAAs) are focal dilatations in the aorta that are prone to rupture or dissect. Currently, the clinically used indicator of the rupture risk is the diameter. However, it has been demonstrated that the diameter alone may not properly predict the risk. To evaluate the rupture risk, one must look into the local mechanical conditions at the rupture site and understand how rupture is triggered in the tissue which is a layered fibrous media. A challenge facing experimental studies of ATAA rupture is that the ATAA tissue is highly heterogeneous; experimental protocols that operate under the premise of tissue homogeneity will have difficulty delineating the heterogeneous properties. In general, rupture initiates at the location where the micro-structure starts to break down and consequently, it is more meaningful to investigate the local conditions at the rupture site.
In this work, a combined experimental and computational method was developed and employed to characterize wall stress, strain, and property distributions in harvested ATAA samples to a sub-millimeter resolution. The results show that all tested samples exhibit a significant degree of heterogeneous in their mechanical properties. Large inter-subject variability is also observed. A heterogeneous anisotropic finite strain hyperelastic model was introduced to describe the tissue; the distributions of the material parameters were identified. The elastic energy stored in the tissue was computed. It was found that the tissue fractures preferentially in the direction of the highest stiffness, generating orifices that are locally transverse to the peak stiffness direction. The rupture appears to initiate at the position absorbed of the highest energy.
Machine learning was used to classify the curves at rupture and non-rupture locations. Features including material properties and curve geometric characteristics were used. The work showed that the rupture and non-rupture states can indeed be classified using pre-rupture response features. Support vector machine(SVM) and random forest algorithm was employed to provide insight on the importance of the features. Inspired by the importance scores provided by random forest, the rupture groups were interrogated and some strong correlations between the strength and the response features were revealed. In particular, it was found that the strength correlates strongly with the tension at the point where the curvature of the total tension strain curve attains maximum, which occurs early in the response.
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Joda, Akram Abdelazim Osman. "Fluid-structure interaction of the aortic valve for tissue engineering applications." Thesis, University of Leeds, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.550815.
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Currently, tissue-engineered heart valves (TEHV) have shown a great prospective to replace the conventional prosthetics heart valves for their ability to grow and remodel. It is well established that in order for the seeded cells to behave in an appropriate manner and infiltrate, populate and remodel during in vitro culture, they need to be exposed to appropriate levels of mechanical stimulation that favour the regeneration of the valve-equivalent tissue with appropriate valvular-tissue- specific functionality. Mathematical modelling is an important tool that can be used alongside TEHV bioreactors with a view to optimising their function by relating the stress-strain distributions in the valve leaflets to the flow and pressure conditions generated by the bioreactor. For that, physiologically accurate 3D fluid structure interaction (FSI) models of fresh and decellularised aortic valves were developed. At first two FSI methods were used to study FSI of a 20 aortic valve, the Arbitrary Lagrangian Eulerian (ALE) method and the Multi-Material Arbitrary Lagrangian Eulerian (MM- ALE) method. The ALE method uses a dynamic mesh in the fluid domain to account for the valve deformations, while in the MM-ALE method, the fluid mesh remains fixed during the computation. Good agreement was found between the results of the two FSI methods. Furthermore, the MM-ALE method was employed to perform FSI of a bileaflet mechanical valve and the results were validated by comparison with pulsatile flow experim~nts. 3D FSI models of the natural aortic valve were developed using three material models for the leaflet (nonlinear isotropic, fiber-reinforced and Fung-type nonlinear orthotropic) and comparisons were conducted to in vivo and in vitro data. Finally, FSI models of decellularised aortic valve scaffolds cultured in vitro under different operation conditions were performed using the nonlinear orthotropic model for optimising a TEHV bioreactor.
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Fraser, Katharine H. "Computational estimation of haemodynamics and tissue stresses in abdominal aortic aneurysms." Thesis, University of Edinburgh, 2007. http://hdl.handle.net/1842/24588.
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Abdominal aortic aneurysm is a vascular disease involving a focal dilation of the aorta. The exact cause is unknown but possibilities include infection and weakening of the connective tissue. Risk factors include a history of atherosclerosis, current smoking and a close relative with the disease. Although abdominal aortic aneurysm can affect anyone, it is most often seen in older men, and may be present in up to 5.9% of the population aged 80 years. Biomechanical factors such as tissue stresses and shear stresses have been shown to play a part in aneurysm progression, although the specific mechanisms are still to be determined. The growth rate of the abdominal aortic aneurysm has been found to correlate with the peak stress in the aneurysm wall and the blood flow is thought to influence disease development. In order to resolve the connections between biology and biomechanics, accurate estimations of the forces involved are required. The first part of this thesis assesses the use of computational fluid dynamics for modelling haemodynamics in abdominal aortic aneurysms. Boundary conditions from the literature on healthy patients are used, along with patient specific aneurysm geometries, to obtain a first estimate of blood flow patterns and haemodynamic wall parameters within the aneurysms. The use of healthy patient boundary conditions is difficult to justify as the presence of the aneurysm is likely to alter the flow rate in the aorta. This is investigated with a Doppler ultrasound study of blood velocities in the normal and aneurysmal aorta. Archetypal waveforms reveal a significant difference in the diastolic maximum of young healthy volunteers and AAA patients. The archetypal aortic velocity wave for patients with abdominal aortic aneurysm is used to calculate the haemodynamics in a group of patients and these calculations are compared with those obtained using patient specific boundary conditions, and with phase-contrast magnetic resonance imaging measurements of blood velocity. With the correct z-velocity profile at the entrance to a short inlet section proximal to the aneurysm, the calculated velocities agreed qualitatively with the measured velocities. However, the velocities calculated using the correct inlet flow rate, but a simple velocity profile, are quite different from the measurements. These results show that the correct velocity profile at the aneurysm entrance is required to predict velocities within the aneurysm cavity. In reality the blood and the artery wall interact: the blood flow domain continually dilates and contracts, altering the flow patterns; the flow controls the pressure on the wall and therefore the stresses within it. The influence of this fluid-structure interaction on the blood flow and tissue stresses is investigated in axially symmetric models of abdominal aortic aneurysm. Modelling of the complete fluid-structure interaction reveals how the pressure and flow waves are distorted by the aneurysm geometry. This distortion, which is absent from both static pressure and one way coupled models, accounts for the small errors in tissue and wall shear stresses obtained when using these models with lower computational complexity. These errors vary with the type of modelling as well as the aneurysm diameter and elasticity. A one dimensional, lumped parameter model of the aneurysm is developed to elucidate the effect of aneurysm geometry on the propagation of pressure and flow waves. It reveals interesting consequences of the diameter of the aneurysm on its inductance and resistance, and its use in improving the outlet pressure boundary condition is investigated.
Books on the topic "Aortic tissue"
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Webster, Ellis Lorenzo. Analysis of tissue inhibitor of metalloproteases (TIMP) as the unifying entity in the etiology of abdominal aortic aneurysms. [S.l: s.n.], 1991.
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Enrique, Criado, and SpringerLink (Online service), eds. Aortic Aneurysms: Pathogenesis and Treatment. Totowa, NJ: Humana Press, 2009.
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Morsi, Yos S. Tissue Engineering of the Aortic Heart Valve: Fundamentals and Developments. Nova Science Publishers, Incorporated, 2012.
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Basso, Cristina, Gaetano Thiene, and Siew Yen Ho. Heart valve disease (aortic valve disease): anatomy and pathology of the aortic valve. Oxford University Press, 2016. http://dx.doi.org/10.1093/med/9780198726012.003.0031.
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The gross features of the aortic valve apparatus, consisting of three semilunar leaflets, three interleaflet triangles, three commissures, and the aortic wall, are discussed both in terms of normal and pathological anatomy. The concept of aortic annulus and the relationship of the aortic valve with the coronary arteries, the membranous septum, and conduction system and the mitral valve are addressed. When dealing with pathology, the chapter focuses on the main distinctive features of aortic valve stenosis and aortic valve incompetence. Regarding the former, the abnormalities reside in the cusps, either two or three in number, with cusp thickening, and calcification with or without commissural fusion (thus distinguishing senile and chronic rheumatic valve disease); in the latter, the gross changes can affect either the cusps (infective endocarditis with tissue perforation/laceration and rheumatic valve disease with tissue retraction) or the aortic wall (ascending aorta aneurysm either inflammatory or degenerative). The distinctive gross abnormalities in the various conditions are illustrated.
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Tribouilloy, Christophe, Patrizio Lancellotti, Ferande Peters, José Juan Gómez de Diego, and Luc A. Pierard. Heart valve disease (aortic valve disease): aortic regurgitation. Oxford University Press, 2016. http://dx.doi.org/10.1093/med/9780198726012.003.0033.
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Echocardiography is the cornerstone examination for the assessment of aortic regurgitation (AR): it provides reliable evaluation of the aortic valve and allows diagnosis and identification of the mechanism of regurgitation. The specific aetiology of the disease can be identified in the majority of cases. A combination of quantitative and quantitative Doppler and two-dimensional (2D) echocardiographic parameters allows the evaluation of the severity of AR and determination of the haemodynamic and left ventricular function repercussions. Echocardiography allows the detection of associated lesions of the aortic root or other valves. In symptomatic patients, echocardiography is essential to confirm the severity of AR. In asymptomatic patients with moderate or severe AR, echocardiography is essential for regular follow-up, by providing precise and reproducible measurements of LV dimensions and function, and for identifying patients who should be considered for elective surgical intervention. In most cases, transthoracic echocardiography (TTE) provides all of the necessary information and transoesophageal echocardiography in usually not required. Real-time three-dimensional (3D) TTE can be complementary to 2D echocardiography for the assessment of the mechanism and quantification of AR by increasing the level of confidence, especially when 2D echocardiographic data are inconclusive or discordant with clinical findings. Tissue Doppler imaging and especially the speckle tracking method are promising approaches to detect early LV dysfunction in patients with asymptomatic severe AR. Echocardiography is therefore the key examination for the assessment of AR and at the centre of the strategic discussion concerning the indications and timing of surgery.
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Prapa, Matina, and S. Yen Ho. Arterial wall remodelling in congenital heart disease. Edited by José Maria Pérez-Pomares, Robert G. Kelly, Maurice van den Hoff, José Luis de la Pompa, David Sedmera, Cristina Basso, and Deborah Henderson. Oxford University Press, 2018. http://dx.doi.org/10.1093/med/9780198757269.003.0024.
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The thoracic aorta is the second most common site of aneurysm formation after the abdominal aorta. Thoracic aortic aneurysms (TAAs) often result from medial wall degeneration secondary to genetic aberrations. Over recent decades, unprecedented research in the field of connective tissue disease has led to identification of key molecular pathways involved in TAA formation. Prolonged survival of congenital heart disease patients following successful reparative surgery has also led to increased incidence of TAA in this context with extensive investigations of underlying mechanisms. This chapter summarizes breakthrough discoveries in congenital arterial wall remodelling and discusses their potential clinical applications.
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Lancellotti, Patrizio, and Bernard Cosyns. Assessment of Diastolic Function. Oxford University Press, 2016. http://dx.doi.org/10.1093/med/9780198713623.003.0005.
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Diastole is the part of the cardiac cycle starting at aortic valve closure and ending at mitral valve closure. Evaluation of diastolic function by echocardiography is useful to diagnose heart failure with preserved ejection fraction, and regardless of ejection fraction, echocardiography can be used to estimate left ventricular filling pressure. Assessment of diastolic function includes analysis of left ventricular relaxation and compliance, left atrial and left ventricular filling pressures. This chapter describes the phases of diastole and covers the integrated approach of LV diastolic function through M-Mode and 2D/3D echocardiography, pulsed-wave Doppler echocardiography, and pulsed-wave tissue Doppler echocardiography.
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Reich, David L., Stephan A. Mayer, and Suzan Uysal, eds. Neuroprotection in Critical Care and Perioperative Medicine. Oxford University Press, 2017. http://dx.doi.org/10.1093/med/9780190280253.001.0001.
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Clinicians caring for patients are challenged by the task of protecting the brain and spinal cord in high-risk situations. These include following cardiac arrest, in critical care settings, and during complex procedural and surgical care. This book provides a comprehensive overview of various types of neural injury commonly encountered in critical care and perioperative contexts and the neuroprotective strategies used to optimize clinical outcomes. In addition to introductory chapters on the physiologic modulators of neural injury and pharmacologic neuroprotectants, the topics covered include: imaging assessment; tissue biomarker identification; monitoring; assessment of functional outcomes and postoperative cognitive decline; traumatic brain injury; cardiac arrest and heart-related issues such as valvular and coronary artery bypass surgery, aortic surgery and stenting, and vascular and endovascular surgery; stroke; intracerebral hemorrhage; mechanical circulatory support; sepsis and acute respiratory distress syndrome; neonatal issues; spinal cord injury and spinal surgery; and issues related to general, orthopedic, peripheral vascular, and ear, nose and throat surgeries.
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Schwitter, Juerg, and Jens Bremerich. Cardiac magnetic resonance in the intensive and cardiac care unit. Oxford University Press, 2015. http://dx.doi.org/10.1093/med/9780199687039.003.0023.
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Current applications of cardiac magnetic resonance offer a wide spectrum of indications in the setting of acute cardiac care. In particular, cardiac magnetic resonance is helpful for the differential diagnosis of chest pain by the detection of ischaemia, myocardial stunning, myocarditis, and pericarditis. Also, Takotsubo cardiomyopathy and acute aortic diseases can be evaluated by cardiac magnetic resonance and are important differential diagnoses in patients with acute chest pain. In patients with restricted windows for echocardiography, according to guidelines, cardiac magnetic resonance is the method of choice to evaluate complications of an acute myocardial infarction. In an acute myocardial infarction, cardiac magnetic resonance allows for a unique characterization of myocardial damage by quantifying necrosis, microvascular obstruction, oedema (i.e. area at risk), and haemorrhage. These features will help us to understand better the pathophysiological events during infarction and will also allow us to assess new treatment strategies in acute myocardial infarction. To which extent the information on tissue damage will guide patient management is not yet clear, and further research, e.g. in the setting of the European Cardiovascular MR registry, is ongoing to address this issue. Recent studies also demonstrated the possiblity to reduce costs in the management of acute coronary syndromes when cardiac magnetic resonance is integrated into the routine work-up. In the near future, applications of cardiac magnetic resonance will continue to expand in the acute cardiac care units, as manufacturers are now strongly focusing on this aspect of user-friendliness. Finally, in the next decade or so, magnetic resonance imaging of other nuclei, such as fluorine and carbon, might become a reality in clinics, which would allow for metabolic and targeted molecular imaging with excellent sensitivity and specificity.
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Schwitter, Juerg, and Jens Bremerich. Cardiac magnetic resonance in the intensive and cardiac care unit. Oxford University Press, 2016. http://dx.doi.org/10.1093/med/9780199687039.003.0023_update_001.
Full textAbstract:
Current applications of cardiac magnetic resonance offer a wide spectrum of indications in the setting of acute cardiac care. In particular, cardiac magnetic resonance is helpful for the differential diagnosis of chest pain by the detection of ischaemia, myocardial stunning, myocarditis, and pericarditis. Also, Takotsubo cardiomyopathy and acute aortic diseases can be evaluated by cardiac magnetic resonance and are important differential diagnoses in patients with acute chest pain. In patients with restricted windows for echocardiography, according to guidelines, cardiac magnetic resonance is the method of choice to evaluate complications of an acute myocardial infarction. In an acute myocardial infarction, cardiac magnetic resonance allows for a unique characterization of myocardial damage by quantifying necrosis, microvascular obstruction, oedema (i.e. area at risk), and haemorrhage. These features will help us to understand better the pathophysiological events during infarction and will also allow us to assess new treatment strategies in acute myocardial infarction. To which extent the information on tissue damage will guide patient management is not yet clear, and further research, e.g. in the setting of the European Cardiovascular MR registry, is ongoing to address this issue. Recent studies also demonstrated the possiblity to reduce costs in the management of acute coronary syndromes when cardiac magnetic resonance is integrated into the routine work-up. In the near future, applications of cardiac magnetic resonance will continue to expand in the acute cardiac care units, as manufacturers are now strongly focusing on this aspect of user-friendliness. Finally, in the next decade or so, magnetic resonance imaging of other nuclei, such as fluorine and carbon, might become a reality in clinics, which would allow for metabolic and targeted molecular imaging with excellent sensitivity and specificity.
Book chapters on the topic "Aortic tissue"
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Morgant, Marie-Catherine, and Ismail El-Hamamsy. "Connective Tissue Disorders." In Aortic Regurgitation, 77–88. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-74213-7_9.
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Sheppard, Mary N. "Aortic Connective Tissue Histopathology." In Surgical Management of Aortic Pathology, 513–22. Vienna: Springer Vienna, 2019. http://dx.doi.org/10.1007/978-3-7091-4874-7_33.
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Drozdz, J., R. Erbel, and J. Zamorano. "Aortic Wall Velocity." In Atlas of Tissue Doppler Echocardiography — TDE, 115–31. Heidelberg: Steinkopff, 1995. http://dx.doi.org/10.1007/978-3-642-47067-7_12.
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Konertz, Wolfgang F., S. Holinski, S. Dushe, A. Weymann, W. Erdbrügger, S. Posner, M. Stein-Konertz, and P. Dohmen. "Tissue engineering with a decellularized valve matrix." In Aortic Root Surgery, 574–78. Heidelberg: Steinkopff, 2010. http://dx.doi.org/10.1007/978-3-7985-1869-8_43.
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Stamm, Christof, N. Grabow, and G. Steinhoff. "Biomatrix-polymer hybrid material for heart valve tissue engineering." In Aortic Root Surgery, 551–63. Heidelberg: Steinkopff, 2010. http://dx.doi.org/10.1007/978-3-7985-1869-8_41.
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Verstraeten, Aline, and Bart Loeys. "Clinical Aspects of Heritable Connective Tissue Disorders." In Surgical Management of Aortic Pathology, 523–30. Vienna: Springer Vienna, 2019. http://dx.doi.org/10.1007/978-3-7091-4874-7_34.
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Pepper, John. "External Aortic Support and Other Alternative Strategies in the Management of Aortic Pathology of Patients with Connective Tissue Disorders." In Aortic Dissection and Acute Aortic Syndromes, 469–82. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-66668-2_33.
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Morota, Tetsuro, and Minoru Ono. "Valve Surgery to Treat Connective Tissue Disease: Comparison Between Valve Replacement and Aortic Root Replacement." In Aortic Valve Preservation, 147–51. Singapore: Springer Singapore, 2019. http://dx.doi.org/10.1007/978-981-13-2068-2_21.
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Schoenhoff, Florian S., and Thierry P. Carrel. "Aortic Dissection in Patients with Disorders of Connective Tissue." In Surgical Management of Aortic Pathology, 575–87. Vienna: Springer Vienna, 2019. http://dx.doi.org/10.1007/978-3-7091-4874-7_40.
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Phillippi, Julie A., Salvatore Pasta, and David A. Vorp. "Biomechanics and Pathobiology of Aortic Aneurysms." In Studies in Mechanobiology, Tissue Engineering and Biomaterials, 67–118. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011. http://dx.doi.org/10.1007/8415_2011_84.
Full textConference papers on the topic "Aortic tissue"
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Lin, Kathleen, Benjamin Berkowitz, and Madhavan L. Raghavan. "Penetration Mechanics of Endovascular Stent Graft Barbs in Aortic Tissue." In ASME 2011 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2011. http://dx.doi.org/10.1115/sbc2011-53357.
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Endovascular stent grafts with barbs — tiny needle-like pins that provide active fixation — are increasingly used for treating aortic aneurysms and dissections. Characterization of barb penetration mechanics may help improve stent-graft designs. Barb angle varies among manufacturers (10–50°). But little is known regarding aortic wall penetration characteristics in relationship to barb angle. There is a body of work on needle insertion properties such as insertion forces into soft tissues. However, there have not been specific studies involving the aorta and the relationship between entry angle and entry force. Kratzberg et al. [1,2] demonstrated that barb angle was closely related to penetration angle and that lower angles between the barb and the body of the aortic stent-graft resulted in better penetration probability and fixation strength in the aortic wall. In order to assess why lower barb angles (i.e., barb axis closer to the graft axis) resulted in better penetration, this study investigates the relationship between barb penetration angle and aortic tissue entry force and compared it to a homogeneous control membrane made of silicone.
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Balguid, Angelique, Anita Mol, Niels Driessen, Carlijn Bouten, and Frank Baaijens. "Stress Dependent Collagen Fibril Diameter Distribution in Human Aortic Valves." In ASME 2007 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2007. http://dx.doi.org/10.1115/sbc2007-175644.
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The mechanical properties of collagenous tissues are known to depend on a wide variety of factors, such as the type of tissue and the composition of its extracellular matrix. Relating mechanical roles to individual matrix components in such a complex system is difficult, if not impossible. However, as collagen is the main load bearing component in connective tissues, the relation between collagen and tissue biomechanics has been studied extensively in various types of tissues. The type of collagen, the amount and type of inter- and intramolecular covalent cross-links and collagen fibril morphology are involved in the tissues mechanical behavior (Beekman et al., 1997; Parry et al., 1978; Avery and Bailey, 2005). From literature it is known that the the collagen fibril diameter distribution can be directly related to the mechanical properties of the tissue. In particular, the diameter distribution of collagen fibrils is largely determined by the tissues requirement for tensile strength and elasticity (Parry et al., 1978).
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Tremblay, Dominique, Raymond Cartier, Louis Leduc, Rosaire Mongrain, and Richard Leask. "Circumferential Variation of Mechanical Properties of Ascending Aorta (AA): A Comparative Study of Healthy and Dilated AA." In ASME 2007 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2007. http://dx.doi.org/10.1115/sbc2007-176709.
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The biomechanics within the ascending aorta (AA) characterizes the pressure and flow for the entire vascular system. In the aortic wall, it is the structured medial layer that is responsible for the mechanical properties of the AA. The mechanical properties are determined to a large extent by the composition of elastin, collagen and smooth muscle cells (SMCs). Changes in AA biomechanics that arise with age and/or disease can lead to cardiovascular complications and death. Most studies that have investigated the biomechanics of these diseases have assumed homogeneous and isotropic aortic wall properties. Very little work has been done in vitro to determine the local mechanical properties of human vascular tissue. In order to better understand the biomechanics of the human AA, the local properties of pathologic AA tissue from both tricuspid and bicuspid aortic valve patients have been studied and compared with the properties of healthy aortas.
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Maddali, Muralikrishna, Chirag S. Shah, and King H. Yang. "Finite Element Modeling of Aortic Tissue Using High Speed Experimental Data." In ASME 2005 International Mechanical Engineering Congress and Exposition. ASMEDC, 2005. http://dx.doi.org/10.1115/imece2005-82083.
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Traumatic rupture of the aorta (TRA) is responsible for 10% to 20% of motor vehicle fatalities [1]. Both finite element (FE) modeling and experimental investigations have enhanced our understanding of the injury mechanisms associated with TRA. Because accurate material properties are essential for the development of correct and authoritative FE model predictions, the objective of the current study was to identify a suitable material model and model parameters for aorta tissue that can be incorporated into FE aorta models for studying TRA. An Ogden rubber material (Type 77B in LS-DYNA 970) was used to simulate a series of high speed uniaxial experiments reported by Mohan [2] using a dumbbell shaped FE model representing human aortic tissue. Material constants were obtained by fitting model simulation results against experimentally obtained corridors. The sensitivity of the Ogden rubber material model was examined by altering constants G and alpha (α) and monitoring model behavior. One single set of material constants (α = 25.3, G = 0.02 GPa, and μ = 0.6000E-06 GPa) was found to fit uniaxial data at strain rates of approximately 100 s−1 for both younger and older aortic tissue specimens. Until a better material model is derived and other experimental data are obtained, it is recommended that the Ogden material model and associated constants derived from the current study be used to represent aorta tissue properties when using FE methods to investigate mechanisms of TRA.
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Darvish, Kurosh, Libor Lobovsky, and Sang-Hyun Lee. "Analysis and Modeling of Aortic Tissue Material Properties." In ASME 2004 International Mechanical Engineering Congress and Exposition. ASMEDC, 2004. http://dx.doi.org/10.1115/imece2004-61784.
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A hyperelastic material with linear viscoelasticity was used to characterize the mechanical behavior of aortic tissue based on literature and new experimental data. It was shown that the previous data led to contradictory uniaxial and biaxial responses. A set of new material properties were identified which closely described the experimental data for strains below 40%.
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Talman, Eric, and Jeffery Poehlmann. "Mechanical Strength of PhotoFix® and Glutaraldehyde Treated Porcine Aortic Valve Wall Tissue." In ASME 1999 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/imece1999-0394.
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Abstract The use of prosthetic heart valves manufactured from porcine aortic valves is commonplace. The standard design incorporates a valve mounted on a plastic or metal stent to facilitate implantation. More recently stentless valves have gained favor. These valves include the intact aortic root or a composite design. Composite valves are assembled using tissue from different valves cut axially along the aorta between valve leaflets. Composite designs are used to eliminate the right coronary leaflet substantially reducing the associated muscle shelf which has been the cause of high re-operation rates in the past (1). We are developing a tri-composite, PhotoFix® stentless valve, combining three non-coronary leaflets and it is the goal of this study to examine the mechanical strength of the associated aortic tissue. This is being done to ensure adequate strength of the material to withstand physiological loading. The strength will be compared to estimated in vivo loading conditions as well as to the strength of tissue from a commercially available glutaraldehyde fixed product.
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Merryman, W. David, Paul D. Bieniek, Farshid Guilak, and Michael S. Sacks. "Aortic Valve Interstitial Cell Viscoelasticity." In ASME 2007 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2007. http://dx.doi.org/10.1115/sbc2007-176694.
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Long term tissue-level durability of the aortic valve (AV) is maintained by the cell populations residing both in the interstitium and on the epithelium. Due to the dynamic environment in which the AV interstitial cells (AVICs) function, recent work has examined the mechano-dependent, biosynthetic and contractile response of these cells [1–4]. Many idealized assumptions have been made about mechanical properties [1, 4], ECM connectivity [2], and deformations that the AVICs undergo during diastole [3]. These assumptions include that the AVICs are elastic, homogenous materials that deformation in an affine sense with the tissue.
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Vorp, David A., Michael S. Sacks, Brian J. Schiro, and Michel S. Makaroun. "Biaxial Mechanical Behavior of Aneurysmal and Nonaneurysmal Human Abdominal Aorta: Preliminary Results." In ASME 2000 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/imece2000-2532.
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Abstract Rupture of abdominal aortic aneurysm (AAA) is currently the 13th leading cause of death in the US and represents a mechanical failure of the diseased aortic wall. Therefore, accurate estimation of the wall stress distribution in AAA may be a clinically useful tool to predict their risk of rupture [1]. A necessary precursor to an accurate stress analysis is an appropriate representation of the constitutive behavior of the AAA wall. Many previous biomechanical analyses of AAA have employed a linearly elastic constitutive behavior [2,3]. However, we have shown that the AAA wall is nonlinearly elastic [4] and undergoes large strain in-vivo [5]. With this as motivation, we recently developed an isotropic, nonlinearly elastic, large strain constitutive model for AAA wall based on uniaxial tensile testing data [6]. The assumption of isotropy was not validated, however. Utilization of an isotropic material symmetry in models of anisotropic structures may lead to significant errors in stress distribution [7]. Indeed, experiments suggest that the nonaneurysmal aorta is anisotropic (orthotropic) [8,9], but the material symmetry of AAA is not presently known. Moreover, most of the previous work investigating the material symmetry of aorta has been performed on animal tissue. To evaluate the anisotropy of aortic tissue, biaxial experimentation is necessary. There has been very little published work involving the biaxial experimentation of human aortic tissue, and none for AAA tissue. We present here a preliminary evaluation of the biaxial mechanical behavior of human aneurysmal and nonaneurysmal abdominal aorta.
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Kinkaid, Jeffrey N., Steven P. Marra, Francis E. Kennedy, and Mark F. Fillinger. "Inflation Testing as a Means of Measuring Failure Strength of Aortic Tissue." In ASME 2003 International Mechanical Engineering Congress and Exposition. ASMEDC, 2003. http://dx.doi.org/10.1115/imece2003-43102.
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Abdominal Aortic Aneurysms (AAAs) are localized enlargements of the aorta. If untreated, AAAs will grow irreversibly until rupture occurs. Ruptured AAAs are usually fatal and are a leading cause of death in the United States, killing 15,000 per year (National Center for Health Statistics, 2001). Surgery to repair AAAs also carries mortality risks, so surgeons desire a reliable tool to evaluate the risk of rupture versus the risk of surgery.
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Pichamuthu, Joseph E., Julie A. Phillippi, Deborah A. Cleary, Douglas W. Chew, John Hempel, Thomas G. Gleason, and David A. Vorp. "Association of Mechanical Properties and Collagen Content With Valve Morphology in Ascending Thoracic Aortic Aneurysmal Tissue." In ASME 2011 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2011. http://dx.doi.org/10.1115/sbc2011-53873.
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Bicuspid aortic valve (BAV) is the most common congenital heart malformation occurring in 1–2% of the population with a high rate of morbidity [1]. There is a significantly higher rate of dilation of the aortic root in adults with a BAV when compared to the normal population and this condition is often associated with ascending thoracic aortic aneurysm (ATAA). ATAA is characterized as an enlargement of the aorta to twice its normal diameter. If left untreated, ATAA can lead to aortic dissection or rupture. Therefore, ATAA is recommended for prophylactic surgery when its diameter reaches about 5.5 cm. However, in certain high-risk cases, such as patients with BAV, ATAA may rupture when its diameter is less than 5.5 cm. Since ATAA dissection and rupture are biomechanical phenomena, better mechanical models are needed to more accurately predict these events over the predictive capability of diameter alone.
Reports on the topic "Aortic tissue"
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Kanner, Joseph, Edwin Frankel, Stella Harel, and Bruce German. Grapes, Wines and By-products as Potential Sources of Antioxidants. United States Department of Agriculture, January 1995. http://dx.doi.org/10.32747/1995.7568767.bard.
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Several grape varieties and red wines were found to contain large concentration of phenolic compounds which work as antioxidant in-vitro and in-vivo. Wastes from wine production contain antioxidants in large amounts, between 2-6% on dry material basis. Red wines but also white wines were found to prevent lipid peroxidation of turkey muscle tissues stored at 5oC. The antioxidant reaction of flavonoids found in red wines against lipid peroxidation were found to depend on the structure of the molecule. Red wine flavonoids containing an orthodihydroxy structure around the B ring were found highly active against LDL and membrane lipid peroxidation. The antioxidant activity of red wine polyphenols were also found to be dependent on the catalyzer used. In the presence of H2O2-activated myoglobin, the inhibition efficiency was malvidin 3-glucoside>catechin>malvidin>resveratol. However, in the presence of an iron redox cycle catalyzer, the order of effectiveness was resveratol>malvidin 3-glucoside = malvidin>catechin. Differences in protein binding were found to affect antioxidant activity in inhibiting LDL oxidation. A model protein such as BSA, was investigated on the antioxidant activity of phenolic compounds, grape extracts, and red wines in a lecithin-liposome model system. Ferulic acid followed by malvidin and rutin were the most efficient in inhibiting both lipid and protein oxidation. Catechin, a flavonal found in red-wines in relatively high concentration was found to inhibit myoglobin catalyzed linoleate membrane lipid peroxidation at a relatively very low concentration. This effect was studied by the determination of the by-products generated from linoleate during oxidation. The study showed that hydroperoxides are catalytically broken down, not to an alcohol but most probably to a non-radical adduct. The ability of wine-phenolics to reduce iron and from complexes with metals were also demonstrated. Low concentration of wine phenolics were found to inhibit lipoxygenase type II activity. An attempt to understand the bioavailability in humans of antocyanins from red wine showed that two antocyanins from red wine were found unchanged in human urine. Other antocyanins seems to undergo molecular modification. In hypercholesterolemic hamsters, aortic lipid deposition was significantly less in animals fed diets supplemented with either catechin or vitamin E. The rate of LDL accumulation in the carotid arteries was also significantly lower in the catechin and vitamin E animal groups. These results suggested a novel mechanism by which wine phenolics are associated with decreased risk of coronary heart diseases. This study proves in part our hypothesis that the "French Paradox" could be explained by the action of the antioxidant effects of phenolic compounds found at high concentration in red wines. The results of this study argue that it is in the interest of public health to increase the consumption of dietary plant falvonoids. Our results and these from others, show that the consumption of red wine or plant derived polyphenolics can change the antioxidant tone of animal and human plasma and its isolated components towards oxidative reactions. However, we need more research to better understand bioavailability and the mechanism of how polyphenolics affect health and disease.