Download or read book On the Quantification of Arterial Wall Mechanical Properties Using Invasive and Non invasive Experimental Investigations and Analytical Techniques written by Alessandro Giudici and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Experimental Investigation of Arteries Mechanical Properties written by Ofry Efraim Yossef and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Cardiovascular diseases such as aneurisms, atherosclerosis, arterial dissection and hypertension are a leading cause for mortality in the western world. Therefore, understanding and characterization of the mechanical behavior of the arterial wall is of high importance.The mechanical response is a combined passive and active response due to the contraction of smooth muscle cells (SMCs) in the arterial wall. The passive response is attributed to the collagen fibers and elastin fibrils. For a mechanical model that describes arteries properly,both passive and active responses must be investigated. Experiments to investigate biological tissues are complex and therefore a reliable, accurate system and well defined experimental protocol are needed. Furthermore, due to the large variations between test samples, a series of experiments is required for statistically relevant data. A common assumption in the biomechanical community is that arteries are incompressible under physiological conditions. This assumption is due to the high content of water in the artery wall, which is considered incompressible. An experimental-based determination of the level of compressibility is therefore of biomechanical interest, but not easily determined because of difficulties to accurately measure very small differences in volume under a physiological pressure.Therefore, the goals of this M.Sc thesis were a) to provide an experimental-based answer to the level of compressibility of arteries, b) to expand the capabilities of an experimental system, improve its reliability and operational options, c) to perform a large number of experiments on arteries in order to create a database for the determination of material parameters. Experimental evidence on the compressibility of arteries under normal physiological pressure range is provided using a precise experimental apparatus. Nineteen experiments on porcine common carotid were performed by two students and the results were analyzed by the author with the conclusion that: in the physiological pressure range (50to 200 mmHg), a relative volume change of 0.2-5% was obtained, lower compared to the sapheneous and femoral arteries (2-6% ). Most of the arteries had a relative volume change of 0.2-1.5%. Details are given in Chapter 2 which is based on a paper published in JMBBM. An apparatus used to investigate the passive and active response of arteries was enhanced.The pressure was oscillating, unstable and not controlled, the control program was not reliable, the system had only manual operation abilities and diameter was unknown during tests. These limitations were removed. The enhanced apparatus is described in detail in Chapter 3 along with numerous experiments which prove its proper functionality. Experiments for the investigation of the passive response of human left internal mammaryartery (LIMA) (one Radial) using the improved apparatus were made which demonstrate that a typical axial in-vivo stretch ratio for human LIMA is 1.1-1.15. A series of experiments attempting to activate the smooth muscle cells (SMC's) were performed. Since the obtained human arteries provided were soaked in a vasodilator (papaverine) during surgeries, the SMC response was disabled despite "washing" them in physiological solution.Due to the inability to receive un-soaked human arteries, porcine arteries were investigated. A series of seven experiments for the investigation of the active response in porcine arteries were performed showing a maximum change of 17-27% in the diameter at 80 mmHg. The results and conclusions from those experiments and experiments on human arteries for passive response are presented in Chapter 3" -- abstract.

Download or read book Experimental Investigation of Arteries Mechanical Properties written by Ofry Efraim Yossef and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "Cardiovascular diseases such as aneurisms, atherosclerosis, arterial dissection and hypertension are a leading cause for mortality in the western world. Therefore, understanding and characterization of the mechanical behavior of the arterial wall is of high importance.The mechanical response is a combined passive and active response due to the contraction of smooth muscle cells (SMCs) in the arterial wall. The passive response is attributed to the collagen fibers and elastin fibrils. For a mechanical model that describes arteries properly,both passive and active responses must be investigated. Experiments to investigate biological tissues are complex and therefore a reliable, accurate system and well defined experimental protocol are needed. Furthermore, due to the large variations between test samples, a series of experiments is required for statistically relevant data. A common assumption in the biomechanical community is that arteries are incompressible under physiological conditions. This assumption is due to the high content of water in the artery wall, which is considered incompressible. An experimental-based determination of the level of compressibility is therefore of biomechanical interest, but not easily determined because of difficulties to accurately measure very small differences in volume under a physiological pressure.Therefore, the goals of this M.Sc thesis were a) to provide an experimental-based answer to the level of compressibility of arteries, b) to expand the capabilities of an experimental system, improve its reliability and operational options, c) to perform a large number of experiments on arteries in order to create a database for the determination of material parameters. Experimental evidence on the compressibility of arteries under normal physiological pressure range is provided using a precise experimental apparatus. Nineteen experiments on porcine common carotid were performed by two students and the results were analyzed by the author with the conclusion that: in the physiological pressure range (50to 200 mmHg), a relative volume change of 0.2-5% was obtained, lower compared to the sapheneous and femoral arteries (2-6% ). Most of the arteries had a relative volume change of 0.2-1.5%. Details are given in Chapter 2 which is based on a paper published in JMBBM. An apparatus used to investigate the passive and active response of arteries was enhanced.The pressure was oscillating, unstable and not controlled, the control program was not reliable, the system had only manual operation abilities and diameter was unknown during tests. These limitations were removed. The enhanced apparatus is described in detail in Chapter 3 along with numerous experiments which prove its proper functionality. Experiments for the investigation of the passive response of human left internal mammaryartery (LIMA) (one Radial) using the improved apparatus were made which demonstrate that a typical axial in-vivo stretch ratio for human LIMA is 1.1-1.15. A series of experiments attempting to activate the smooth muscle cells (SMC's) were performed. Since the obtained human arteries provided were soaked in a vasodilator (papaverine) during surgeries, the SMC response was disabled despite "washing" them in physiological solution.Due to the inability to receive un-soaked human arteries, porcine arteries were investigated. A series of seven experiments for the investigation of the active response in porcine arteries were performed showing a maximum change of 17-27% in the diameter at 80 mmHg. The results and conclusions from those experiments and experiments on human arteries for passive response are presented in Chapter 3" -- abstract.

Download or read book Mechanical Properties of Arteries written by Jan-Lucas Gade and published by Linköping University Electronic Press. This book was released on 2021-01-27 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this dissertation, a method is proposed that identifies the mechanical properties of arteries in vivo. The mechanical properties of an artery are linked to the development of cardiovascular diseases. The possibility to identify the mechanical properties of an artery inside the human body could, thus, facilitate disease diagnostization, treatment and monitoring. Supplied with information obtainable in the clinic, typically limited to time-resolved pressure-radius measurement pairs, the proposed in vivo parameter identification method solves a non-convex minimization problem to determine parameters related to the mechanical properties of the blood vessel. The artery is treated as a homogeneous, incompressible, residual stress-free, thin-walled tube consisting of an elastin dominated matrix with embedded collagen fibers. To validate the in vivo parameter identification method, in silico arteries in the form of finite element models are created using published data for the human abdominal aorta. With these in silico arteries which serve as mock experiments with pre-defined material parameters and boundary conditions, in vivo-like pressure-radius data sets are generated. The mechanical properties of the in silico arteries are then determined using the proposed parameter identification method. By comparing the identified and the pre-defined parameters, the identification method is quantitatively validated and it is shown that the parameters agree well for healthy arteries. Furthermore, the identified parameters are used to compare the stress state in the arterial model and in the in silico arteries. The stress state is thereby decomposed into an isotropic and an anisotropic component which are primarily associated with the elastin dominated matrix and the collagen fibers, respectively. The comparison of the decomposed stress states shows a close agreement for arteries exhibiting a physiological stress gradient. Another important aspect is the identification of parameters by solving a non-convex minimization problem. The non-convexity of the problem implies that incorrect parameter values, corresponding to local minima, may be found when common gradient-based solution techniques are employed. A problem-specific global algorithm based on the branch-and-bound method is, therefore, created which ensures that the global minimum and accordingly the correct parameters are obtained. It turns out that the gradient-based solution technique identifies the correct parameters if certain requirements are met, among others the use of the heuristic multi-start method. In a last step, the in vivo parameter identification method is extended to also identify parameters related to smooth muscle contraction. To prevent an overparameterization caused by the increased number of model parameters, the model is simultaneously fit to clinical data measured during three different arterial conditions: basal; constricted; and dilated. Despite the simple contraction model the extended method fits the clinical data well. Finally, in this dissertation it is shown that the proposed in vivo parameter identification method identifies the mechanical properties of arteries well. An open question for future research is how this method can be applied in a clinical setting to facilitate cardiovascular disease diagnostization, treatment and monitoring.

Download or read book Novel Theoretical and Experimental Frameworks for Multiscale Quantification of Arterial Mechanics written by Ruoya Wang and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The mechanical behavior of the arterial wall is determined by the composition and structure of its internal constituents as well as the applied traction-forces, such as pressure and axial stretch. The purpose of this work is to develop new theoretical frameworks and experimental methodologies to further the understanding of arterial mechanics and role of the various intrinsic and extrinsic mechanically motivating factors. Specifically, residual deformation, matrix organization, and perivascular support are investigated in the context of their effects on the overall and local mechanical behavior of the artery. We propose new kinematic frameworks to determine the displacement field due to residual deformations previously unknown, which include longitudinal and shearing residual deformations. This allows for improved predictions of the local, intramural stresses of the artery. We found distinct microstructural differences between the femoral and carotid arteries from non-human primates. These arteries are functionally and mechanically different, but are geometrically and compositionally similar, thereby suggesting differences in their microstructural alignments, particularly of their collagen fibers. Finally, we quantified the mechanical constraint of perivascular support on the coronary artery by mechanically testing the artery in-situ before and after surgical exposure.

Download or read book Non invasive Assessment of Arterial Wavespeed and Endothelial Function written by Mehdiye Sardarlou and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Previous work has shown that nitric oxide production alters the relative height of the dicrotic notch (RHDN) in the peripheral arterial pulse of rabbits (Weinberg et al., 2001) and people (Chowienczyk et al., 1999), most likely through an influence on wave reflection. Preliminary evidence in both species shows that administration of glucose also alters notch height or augmentation index (AI), putatively because glucose stimulates the release of insulin which in turn stimulates the release of nitric oxide. This phenomenon could form the basis of a simple, non-invasive test of endothelial function. The work described in this thesis was designed to assess further the effect of glucose on arterial wavespeed (as a measure of stiffness), wave reflection and waveform. In the first study, an MR scanner was used to obtain brachial artery diameters and blood flow rates through the cardiac cycle in healthy volunteers before and after oral administration of glucose. In preliminary trials, MR images were processed in MATLAB® using different image analysis techniques; normalised cross correlation (NCC), a well-established method, was chosen for the automated acquisition of diameter and velocity waveforms. Pulse wave behaviour was then analysed using the diameter-velocity form of Wave Intensity Analysis (WIA) method, recently developed by Feng and Khir (2010). The study failed to show the expected effects of glucose. Furthermore, the diameter distentions detected for the brachial artery during the cardiac cycle appeared unphysiologically high and the calculated wave speeds appeared unphysiologically low. There were three possible sources of error: (1) the image analysis technique used to determine diameter waveforms, (2) the derivation of the new diameter-velocity form of WIA, and (3) the sugar hypothesis itself. The rest of the thesis describes investigations of these potential problems. To check the NCC-based image analysis methods, they were used in a study of aortic MR data that had previously been analysed by other methods (Li et al., 2010). Similar to the brachial artery/sugar experiment, non-physiological wavespeed values and high diameter distenstions were obtained, presumably due to an inaccuracy of the NCC image analysis technnique. Additionally, the wave behaviour in different aortic locations did not agree with well-established properties, presumably due to errors in the new WIA method. An attempt was made to find a consistent relation between NCC-derived diameters and manually-derived diameters, in order to develop a method for correcting the NCC data. However, no consistent relationship was found. This study provided additional evidence that the NCC method used in conjunction with noisy MRI data is unreliable. To assess the sugar-vasodilatation hypothesis, volume waveforms in the finger and pressure waveforms in the radial artery were measured by, respectively, photoplethysmography (PPG) and applanation tonometry, before and after the administration of a glucose or control drink to healthy volunteers. The radial pressure waveforms were used to calculate central aortic pressure waveforms, using the generalised transfer function described by Karamanoglu et al. (1993). Al, RHDN and the relative height of the diastolic peak (RHDP) of these waveforms were analysed. Despite the small sample size, a significant result was obtained for PPG RHDN, and borderline trends were obtained for other indices. Overall, the results were interpreted as supporting the hypothesis. Finally, the reliability of using the new diameter-velocity method of WIA was compared with the original pressure-velocity method in a polyurethane model of the aorta and its major branches. Pressure, velocity and diameter along the aorta to the femoral artery, and along arm vessels, were measured in the model and wave behaviour in the brachial artery and aorta was examined using both forms of WIA. Additionally, the aorta of the model was wrapped with tape or cling film in order to alter its compliance, an effect that was expected in the real circulation after the administration of glucose. Effects of aortic stiffening on wavespeed and wave intensity were observed in the aorta and arm arteries. However, the diameter-velocity form of WIA gave results that disagreed strongly with theoretical predictions. There may therefore be practically insupportable assumption in its derivation. In conclusion, it appears that both the NCC-MRI method and the diameter-velocity theory used in the initial brachial artery study may be unreliable. Some evidence was obtained for the hypothesised effect of sugar using other techniques.

Download or read book A Computational Stress Deformation Analysis of Arterial Wall Tissue written by Ryan Taylor Krone and published by . This book was released on 2010 with total page 240 pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding the mechanical behavior of arterial walls under various physiological loading and boundary conditions is essential for achieving the following: (1) improved therapeutics that are based on mechanical procedures (e.g. arterial segmenting and suturing), (2) study of mechanical factors that may trigger the onset of arterial aneurysms (i.e. focal blood-filled dilatation of the vessel wall caused by disease) and (3) investigations on tissue variations due to health, age, hypertension and atherosclerosis, all of which hold immense clinical relevance. In general, the physiological conditions on an any arterial segment can include axial stretch, torsional twist and transmural (internal, radial) pressure which often provoke large wall-tissue deformations that require theories of continuum hyperelasticity. Further, the presence of collagen fibers throughout the two structural layers (media, adventitia) of the arterial wall require anisotropic strain energy functions for more histological accurate models. Nonlinear computational methods are therefore essential for this class of boundary-value-problems (BVPs) which often do not contain closed-form solutions. We begin by modeling the arterial vessel wall as a thin sheet in the form of a circular cylinder in the reference configuration. We seek to employ a bio-type strain energy function on this constitutive framework to investigate the onset of non-linear instabilities in a thin-walled, hyperelastic tube under (remote) axial stretch and internal pressure. Viscoelastic effects are also considered in this model. We then build to investigating the effects of various combinations of axial stretch and transmural pressure on the global deformation and through-thickness stress and strain fields of an arterial segment modeled as a two-layer, fiber-reinforced composite and idealized as a thick-walled cylinder in the reference configuration. We further consider (in both models) the presence of local tissue lesions, or portions of the arterial wall having either stiffer (i.e. thrombosis or scar tissue) or softer (i.e. diseased tissue) material characteristics, relative to the surrounding tissue. We account for this by appropriately scaling the elastic constants of the strain energy functions for regions with a lesion and without. For the three-dimensional model, we employ the strain energy function of Holzapfel et al. which has been modified by constraints on the principal invariants by Balzani et al. in order to ensure material polyconvexity. We choose a particular vessel, the human common carotid (HCC) artery, with appropriate geometric and material properties found from various experimentally-based studies (e.g. Fung et al.). We focus on distinct elastic constants for each layer (media, adventitia) that have been obtained through biaxial (i.e. not simply uniaxial data - reasons for this are discussed later) testing of in vitro HCC arteries. The loading conditions are combinations of axial extension and transmural pressure, in the presence and absence of material lesions. The loading is consistent with in vivo conditions on a general segment of the vessel wall. We find that as a two-dimensional surface, the overall deformation from internal pressure (i.e. the bulge) depends on the magnitude and, more importantly, the rate of axial stretch and transmural pressure, the elastic material parameters of the bio-strain energy function, and of course local inhomogeneities in the material description of the tissue. When modeled as a three-dimensional solid undergoing pure axial stretch, the majority of the stress is in the medial tissue, which displays a significant gradient in the axial direction, whereas the stress in the adventitia is constant throughout the length of the vessel. For supra-physiological pressures (i.e. 20-30 kPa, or about 50% higher than in vivo conditions) the adventitia contributes to the load sharing and the gradient in the medial layer evens out. For narrow (2% of the length), stiff (100x stiffer than surrounding tissue), ring-like lesions under the same pressures and axial stretch, the overall vessel deformation is considerably smaller in the radial direction. The overall segment shape is stabilized by this type of material abnormality. For local spot-like stiff (100x stiffer than surrounding tissue) lesions, the deformation leads to an inward bulge (i.e. a clot) that will likely affect fluid flow characteristics, hence growth and remodeling of the tissue at the wall. For these loading conditions, when the spot-like and ring-like lesions are approximately two-times softer than the surrounding tissue, no significant differences appear in the stress and strain fields.

Download or read book Pan Vascular Medicine written by Peter Lanzer and published by Springer. This book was released on 2013-12-20 with total page 1923 pages. Available in PDF, EPUB and Kindle. Book excerpt: The textbook provides an interdisciplinary and integrated perspective of modern vascular cure. Written by experts the text proceeds from fundamental principles to advanced concepts. The book is divided into four parts, each focusing on different basic concepts of vascular cure. All fundamental principles of the area are clearly explained to facilitate vascular diagnostics and treatment in clinical practice. It is aimed at junior practitioners and experts.

Download or read book Magnetic Resonance Elastography written by Sudhakar K. Venkatesh and published by Springer. This book was released on 2014-10-01 with total page 143 pages. Available in PDF, EPUB and Kindle. Book excerpt: The first book to cover the groundbreaking development and clinical applications of Magnetic Resonance Elastography, this book is essential for all practitioners interested in this revolutionary diagnostic modality. The book is divided into three sections. The first covers the history of MRE. The second covers technique and clinical applications of MRE in the liver with respect to fibrosis, liver masses, and other diseases. Case descriptions are presented to give the reader a hands-on approach. The final section presents the techniques, sequence and preliminary results of applications in other areas of the body including muscle, brain, lung, heart, and breast.

Download or read book Application of Synthetic Aperture Imaging to Non invasive Vascular Elastography written by Sanghamithra Korukonda and published by . This book was released on 2012 with total page 270 pages. Available in PDF, EPUB and Kindle. Book excerpt: "The health of the carotid artery is an important indicator of cardiovascular disease (CVD). The advent of CVD results in reduced elasticity and flexibility of the arterial wall. These changes in elasticity can be measured using non-invasive vascular elastography (NIVE). Elastography is performed by subjecting the tissue under investigation to a form of mechanical excitation. The resultant tissue displacement is measured and used to compute the spatial variation of strain within the tissue. These strain maps, known as elastograms, serve as surrogates for tissue elasticity. While elastography can be performed with any imaging modality, ultrasound is portable, inexpensive and has high frame rates, making it ideal for diagnostic screening purposes. However, linear array based elastography can accurately estimate displacement only in the axial direction. Consequently, NIVE cannot characterize strain across artery cross-sections, restricting the diagnostic value of this technique. The objective of this thesis was to investigate the feasibility of using synthetic aperture (SA) imaging to accurately estimate the 2D displacement vector, thereby enhancing the performance of NIVE. We demonstrated, through simulation and experiment, that SA imaging can accurately measure both axial and lateral displacements. These displacements generate high quality radial and circumferential strain elastograms of the arterial cross-section. Compared to conventional ultrasound elastography, SA elastography improved the error in lateral displacements and the resultant strain elastograms by an order of magnitude. However, the low frame rates and large data volumes required by SA imaging render this approach clinically inviable. To overcome this limitation, we developed a sparse array based elastography system. We demonstrated that as few as eight transmit elements can generate strain elastograms with a 16x improvement in frame rate and data volume, at a minimal loss of image quality. The efficacy of sparse array elastography was compared to that of a compounded plane wave imaging system. It was demonstrated that sparse array imaging displayed higher lateral sensitivity thereby producing strain elastograms with 20% improved image quality. From the success of this novel approach to elastography, it was concluded that further development and integration on a commercial ultrasound system would greatly enhance clinical use"--Leaf vi.

Download or read book Applied Mechanics Reviews written by and published by . This book was released on 1987 with total page 338 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Research Awards Index written by and published by . This book was released on 1989 with total page 776 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book PanVascular Medicine written by Peter Lanzer and published by Springer. This book was released on 2015-03-30 with total page 5004 pages. Available in PDF, EPUB and Kindle. Book excerpt: ​Vascular management and care has become a truly multidisciplinary enterprise as the number of specialists involved in the treatment of patients with vascular diseases has steadily increased. While in the past, treatments were delivered by individual specialists, in the twenty-first century a team approach is without doubt the most effective strategy. In order to promote professional excellence in this dynamic and rapidly evolving field, a shared knowledge base and interdisciplinary standards need to be established. Pan Vascular Medicine, 2nd edition has been designed to offer such an interdisciplinary platform, providing vascular specialists with state-of-the art descriptive and procedural knowledge. Basic science, diagnostics, and therapy are all comprehensively covered. In a series of succinct, clearly written chapters, renowned specialists introduce and comment on the current international guidelines and present up-to-date reviews of all aspects of vascular care.

Download or read book Cumulated Index Medicus written by and published by . This book was released on 2000 with total page 1808 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Arterial Stiffness in Hypertension written by Michel Safar and published by Elsevier Health Sciences. This book was released on 2006-04-21 with total page 618 pages. Available in PDF, EPUB and Kindle. Book excerpt: Main headings: I. Basic concepts of pulsatile arterial hemodynamics. - II. Pathophysiological mechanisms. - III. Arterial stiffness, wave reflections, cardiovascular risk and end-organ damage. - IV. Clinical aspects of arterial stiffness and wave reflections. - V. Therapeutic aspects of arterial stiffness and wave reflections.

Download or read book A Portrait of State of the Art Research at the Technical University of Lisbon written by Manuel Seabra Pereira and published by Springer Science & Business Media. This book was released on 2007-11-24 with total page 605 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book celebrates the 75th anniversary of The Technical University of Lisbon (UTL). It provides a compelling picture of current state-of-art research at UTL. It contains the edited version of the invited lectures from a two day Symposium and brings together a comprehensive summary of high quality research contributions across basic and applied sciences. A broad spectrum of topics is covered reflecting UTL’s worldwide recognition.

Download or read book Basic Sciences for MCEM written by Chetan Trivedy and published by CRC Press. This book was released on 2016-05-15 with total page 771 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is a dedicated resource for those sitting the Part A of the MCEM (Membership of the College of Emergency Medicine) examination. It forms an essential revision guide for emergency trainees who need to acquire a broad understanding of the basic sciences, which underpin their approach to clinical problems in the emergency department. Common clinical scenarios are used to highlight the essential underlying basic science principles, providing a link between clinical management and a knowledge of the underlying anatomical, physiological, pathological and biochemical processes. Multiple choice questions with reasoned answers are used to confirm the candidates understanding and for self testing. Unlike other recent revision books which provide MCQ questions with extended answers, this book uses clinical cases linked to the most recent basic science aspects of the CEM syllabus to provide a book that not only serves as a useful revision resource for the Part A component of the MCEM examination, but also a unique way of understanding the processes underlying common clinical cases seen every day in the emergency department. This book is essential for trainees sitting the Part A of the MCEM exam and for clinicians and medical students who need to refresh their knowledge of basic sciences relevant to the management of clinical emergencies.