130 research outputs found
CFD Analysis of Strategies to Improve Oxygen Availability in the AMC Bioartificial Liver
No full textEffective Orifice Area during Exercise in Bileaflet Mechanical Valve Prostheses
No full textBackground: The aims of this study were to investigate the evolution of the transprosthetic pressure gradient and effective orifice area (EOA) during dynamic bicycle exercise in bileaflet mechanical heart valves and to explore the relationship with exercise capacity. Methods: Patients with bileaflet aortic valve replacement (n = 23) and mitral valve replacement (MVR; n = 16) prospectively underwent symptom-limited supine bicycle exercise testing with Doppler echocardiography and respiratory gas analysis. Transprosthetic flow rate, peak and mean transprosthetic gradient, EOA, and systolic pulmonary artery pressure were assessed at different stages of exercise. Results: EOA at rest, midexercise, and peak exercise was 1.66 +/- 0.23, 1.56 +/- 0.30, and 1.61 +/- 0.28 cm(2), respectively (P = .004), in aortic valve replacement patients and 1.40 +/- 0.21, 1.46 +/- 0.27, and 1.48 +/- 0.25 cm(2), respectively (P = .160), in MVR patients. During exercise, the mean transprosthetic gradient and the square of transprosthetic flow rate were strongly correlated (r = 0.65 [P < .001] and r = 0.84 [P < .001] for aortic valve replacement and MVR, respectively), conforming to fundamental hydraulic principles for fixed orifices. Indexed EOA at rest was correlated with exercise capacity in MVR patients only (Spearman r = 0.68, P = .004). In the latter group, systolic pulmonary artery pressures during exercise were strongly correlated with the peak transmitral gradient (r = 0.72, P < .001). Conclusions: In bileaflet mechanical valve prostheses, there is no clinically relevant increase in EOA during dynamic exercise. Transprosthetic gradients during exercise closely adhere to the fundamental pressure-flow relationship. Indexed EOA at rest is a strong predictor of exercise capacity in MVR patients. This should be taken into account in therapeutic decision making and prosthesis selection in young and dynamic patients.Dr. Bertrand is supported by a grant from the Research Foundation-Flanders (11N7214N). Drs. Bertrand and Vandervoort are researchers for the Limburg Clinical Research Program UHasselt-ZOL-Jessa, supported by the foundation Limburg Sterk Merk, Hasselt University, Ziekenhuis Oost-Limburg, and Jessa Hospital. Dr. Dion has received consulting fees from Edwards Lifesciences, Johnson & Johnson, Sorin, Medtronic, and St. Jude Medical
Advances in biomedical engineering
No full textThe aim of this essential reference is to bring together the interdisciplinary areas of biomedical engineering education. Contributors review the latest advances in biomedical engineering research through an educational perspective, making the book useful for students and professionals alike. Topics range from biosignal analysis and nanotechnology to biophotonics and cardiovascular medical devices. - Provides an educational review of recent advances - Focuses on biomedical high technology - Features contributions from leaders in the field.The aim of this essential reference is to bring together the interdisciplinary areas of biomedical engineering education. Contributors review the latest advances in biomedical engineering research through an educational perspective, making the book useful for students and professionals alike. Topics range from biosignal analysis and nanotechnology to biophotonics and cardiovascular medical devices. - Provides an educational review of recent advances - Focuses on biomedical high technology - Features contributions from leaders in the field.Chapter 1. Review of Research in Cardiovascular Devices -- D. Zbigniew Nawrat -- Chapter 2. Biomechanical modelling of Stents: Survey 1997-2007 -- Matthieu De Beule -- Chapter 3. Signal Extraction in Multisensor Biomedical Recordings -- V. Zarzoso, R. Phlypo, O. Meste and P. Comon -- Chapter 4. Fluorescence Lifetime Spectroscopy and Imaging of Visible Fluorescent Proteins -- Ankur Jain, Christian Blum and Vinod Subramaniam -- Chapter 5. Monte Carlo Simulations in Nuclear Medicine Imaging -- Steven Staelens and Irene Buvat -- Chapter 6. Biomedical Visualization -- Chris R. Johnson and Xavier Tricoche.Includes bibliographical references and index.Print version record.Elsevie
Studie van de interactie van triorganotindonors R₃SnX (X=Cl,I,Br,NCO,NCS) met anorganische acceptoren (I₂, ICl,Br₂) en tetracyanoethyleen
No full textTime-resolved PIV technique for high temporal resolution measurement of mechanical prosthetic aortic valve fluid dynamics
No full text Prosthetic heart valves (PHVs) have been used to replace diseased native valves for more than five decades. Among these, mechanical PHVs are the most frequently implanted. Unfortunately, these devices still do not achieve ideal behavior and lead to many complications, many of which are related to fluid mechanics. The fluid dynamics of mechanical PHVs are particularly complex and the fine-scale characteristics of such flows call for very accurate experimental techniques. Adequate temporal resolution can be reached by applying time-resolved PIV, a high-resolution dynamic technique which is able to capture detailed chronological changes in the velocity field. The aim of this experimental study is to investigate the evolution of the flow field in a detailed time domain of a commercial bileaflet PHV in a mock-loop mimicking unsteady conditions, by means of time-resolved 2D Particle Image Velocimetry (PIV). The investigated flow field corresponded to the region immediately downstream of the valve plane. Spatial resolution as in “standard” PIV analysis of prosthetic valve fluid dynamics was used. The combination of a Nd:YLF high-repetition-rate double-cavity laser with a high frame rate CMOS camera allowed a detailed, highly temporally resolved acquisition (up to 10000 fps depending on the resolution) of the flow downstream of the PHV. Features that were observed include the non-homogeneity and unsteadiness of the phenomenon and the presence of large-scale vortices within the field, especially in the wake of the valve leaflets. Furthermore, we observed that highly temporally cycle-resolved analysis allowed the different behaviors exhibited by the bileaflet valve at closure to be captured in different acquired cardiac cycles. By accurately capturing hemodynamically relevant time scales of motion, time-resolved PIV characterization can realistically be expected to help designers in improving PHV performance and in furnishing comprehensive validation with experimental data on fluid dynamics numeric modelling. </jats:p
Fluid-structure interaction modelling of left ventricular filling
No full textNon-invasive diagnosis of diastolic dysfunction remains difficult in clinical practice. Non-invasive assessment of the flow field within the left ventricle (LV) using color M-mode Doppler (CMD) echocardiography provides a potential technique that can differentiate between the normal and diseased heart.
A computer model is developed describing three-dimensional axi-symmetrical LV filling flow. The simulation results show that the hydrodynamical mechanism of LV flow wave propagation, as observed on 2D color and color M-mode Doppler echocardiograms, is the propagation of a vortex in the LV cavity
Measurement of the short-term viscoelastic properties of the periodontal ligament using stress relaxation
No full textThe periodontal ligament (PDL) plays an important role in initiating tooth movement when loads are applied to teeth with orthodontic appliances. It is also the most accessible ligament in the human body as it can be directly manipulated (via the teeth) without surgical intervention.Findings are presented here from a prototype palpation device for making load-displacement measurements, intended ultimately for in vivo use on humans. Here, the device is applied in vitro to a number of pig-jaws to assess its ability to distinguish visco-elastic properties of the PDL.Four jaws were tested, each test consisting of the application of a series of step displacements to the second mandibular premolar, and allowing the stress to relax over a period of up to 35 seconds. The resulting stress relaxation curves are described by a three-parameter visco-elastic model with two elastic parameters and one viscous parameter. The values of these parameters are consistent between animals and between tests on a given animal, and are reasonably consistent with other authors.</p
Physical and dynamic models of the eye for tonometry applications
No full textA new approach to measuring intraocular pressure (IOP) and central corneal thickness (CCT) has been developed. This dynamic contact system measures the static stiffness and dynamic modulus (expressed as an amplitude ratio and phase lag) of the eyeball and a dynamic model has been developed which allows separation of the contributions of CCT and IOP. Three different mechanical eyeball configurations have been investigated, simulating different behaviours of a real eyeball. Preliminary results show significant differences in phase lag, dynamic modulus and mean ratio for using different CCT and IOP. © 2009 Springer Berlin Heidelberg.</p
Stent design for gastrointestinal leakage
No full textStents are largely used to counteract and relieve duct or vessel obstructions. The purpose of this current study is to select a biodegradable, antibacterial and environmentally friendly material to design and prepare a stent to counteract anastomotic leakage following gastrointestinal surgery. A precast moulding process was used to prepare medium molecular weight chitosan scaffolds, for stent design. Chitosan samples were prepared by opening the bonds of the material in acetic acid, moulding the material and curing the mouldings in sodium hydroxide. The film like mouldings were wound around a metallic rod, fixing the layers together with un-cured chitosan and subsequently curing the chitosan layers together with sodium hydroxide producing the stent like shape. Tensile and tensile creep strength of the chitosan material was investigated. This research concluded that chitosan can be moulded into a stent like geometry. Mechanical testing showed the tensile and tensile creep strength were repeatable and could be predetermined. This indicates that chitosan is a suitable material for the further development of a biodegradable stent designed to counteract gastrointestinal leakage
Left ventricular flow propagation velocity: insights from a combined hydraulic and numerical model study.
No full text- …
