1,720,967 research outputs found
Numerical simulation of mechanical transport behaviour of a porous, hydroxyapatite-based bone graft
No full textMultiscale models of the cardiovascular system applied to the study of the flow in a carotid bifurcation
No full textApplication of the multiscale approach to investigate fluidynamics in surgical procedures for the treatment of congenotal heart diseases
No full textToward optimal hemodynamics: computer modeling of the fontan circuit
No full textThe construction of efficient designs with minimal
energy losses is especially important for cavopulmonary
connections. The science of computational fluid dynamics
has been increasingly used to study the hemodynamic performance of surgical operations. Three-dimensional
computer models can be accurately constructed of typical
cavopulmonary connections used in clinical practice based
on anatomic data derived from magnetic resonance scans,
angiocardiograms, and echocardiograms. Using these
methods, the hydraulic performance of the hemi-Fontan,
bidirectional Glenn, and a variety of types of completion
Fontan operations can be evaluated and compared. This
methodology has resulted in improved understanding and
design of these surgical operations
Modelling drug elution from stents: effects of reversible binding in the vascular wall and degradable polymeric matrix.
No full textToday the most popular approach for the prevention of the restenosis consists in the use of the drug eluting stents. The stent acts as a source of drug, from a coating or from a reservoir, which is transported into and through the artery wall. In this study, the behaviour of a model of a hydrophilic drug (heparin) released from a coronary stent into the arterial wall is investigated. The presence of the specific binding site action is modelled using a reversible chemical reaction that explains the prolonged presence of drug in the vascular tissue. An axi-symmetric model of a single stent strut is considered. First an advection-diffusion problem is solved using the finite element method. Then a simplified model with diffusion only in the arterial wall is compared with: (i) a model including the presence of reversible binding sites in the vascular wall and (ii) a model featuring a drug reservoir made of a degradable polymeric matrix. The results show that the inclusion of a reversible binding for the drug leads to delayed release curves and that the polymer erosion affects the drug release showing a quicker elution of the drug from the stent
Toward the development of a fully elastic mitral ring: preliminary, acute, in vivo evaluation of physiomechanical behavior.
No full textOBJECTIVES: The optimal repair of functional mitral regurgitation is still debated. No device is able to simultaneously abolish mitral regurgitation and replicate natural mitral annular dynamics. We have tested a fully elastic mitral ring in an acute animal study with the purpose of evaluating (1) ring design and implantation technique, (2) elastic performance, and (3) acute effects on the native mitral annulus. METHODS: Ten healthy sheep underwent surgical implantation of mitral devices, the elastic component of which is represented by a helicoid metallic spring. Preimplantation and postimplantation echocardiographic parameter measurements to evaluate annular dynamics and ventricular function comprise mitral annular motion, systolic tissue Doppler imaging peak wave, transmitral pressure gradient, peak transmitral flow velocity, and ejection fraction. Postimplantation angiographic analysis allowed measurement of the mitral annular area and perimeter variations by means of segmentation of the radiopaque mitral device contour. RESULTS: No significant difference in terms of ejection fraction (P = .13) and systolic tissue Doppler imaging peak wave (P = .87) was found before and after implantation. Mitral annular motion (1.16 cm) was preserved. The percentage of systolic annular reduction derived from angiographic analysis was 14.1% (range, 7.7%-19.7%) in terms of area and 7.2% (range, 4.9%-10.0%) in terms of perimeter. CONCLUSIONS: A mitral elastic ring, implantable by using a standard technique, acutely preserves mitral annular dynamics, allowing area and perimeter changes. Further chronic study is needed to verify the biocompatibility and durability of the device
Effects of different stent designs on local hemodynamics in stented arteries
Full text linkFollowing the deployment of a coronary stent and disruption of an atheromatous plaque, the deformation of the arterial wall and the presence of the stent struts create a new fluid dynamic field, which can cause an abnormal biological response. In this study 3D computational models were used to analyze the fluid dynamic disturbances induced by the placement of a stent inside a coronary artery. Stents models were first expanded against a simplified arterial plaque, with a solid mechanics analysis, and then subjected to a fluid flow simulation under pulsatile physiological conditions. Spatial and temporal distribution of arterial wall shear stress (WSS) was investigated after the expansion of stents of different designs and different strut thicknesses. Common oscillatory WSS behavior was detected in all stent models. Comparing stent and vessel wall surfaces, maximum WSS values (in the order of 1 Pa) were located on the stent surface area. WSS spatial distribution on the vascular wall surface showed decreasing values from the center of the vessel wall portion delimited by the stent struts to the wall regions close to the struts. The hemodynamic effects induced by two different thickness values for the same stent design were investigated, too, and a reduced extension of low WSS region (<0.5 Pa) was observed for the model with a thicker strut
Multiscale Modelling of the cardiovascular system: application to the study of pulmonary and coronary perfusions in univentricular circulation
No full textThe objective of this studyis to compare the coronaryand pulmonaryblood flow dynamics resulting from two configurations of
systemic-to-pulmonary artery shunts currently utilized during the Norwood procedure: the central (CS) and modified Blalock
Taussig (MBTS) shunts. A lumped parameter model of the neonatal cardiovascular circulation and detailed 3-D models of the shunt
based on the finite volume method were constructed. Shunt sizes of 3, 3.5 and 4mm were considered. A multiscale approach was
adopted to prescribe appropriate and realistic boundaryconditions for the 3-D models of the Norwood circulation. Results showed
that the average shunt flow rate is higher for the CS option than for the MBTS and that pulmonaryflow increases with shunt size for
both options. Cardiac output is higher for the CS option for all shunt sizes. Flow distribution between the left and the right
pulmonaryarteries is not completely balanced, although for the CS option the discrepancyis low (50–51% of the pulmonaryflow to
the right lung) while for the MBTS it is more pronounced with larger shunt sizes (51–54% to the left lung). The CS option favors
perfusion to the right lung while the MBTS favors the left. In the CS option, a smaller percentage of aortic flow is distributed to the
coronarycirculation, while that percentage rises for the MBTS. These findings mayhave important implications for coronaryblood
flow and ventricular function
Multiscale modelling in biofluidynamics: application to reconstructive paediatric cardiac surgery.
No full textMultiscale computing is a challenging area even in biomechanics. Application of such a methodology to quantitatively compare
postoperative hemodynamics in congenital heart diseases is very promising. In the treatment of hypoplastic left heart syndrome,
which is a congenital heart disease where the left ventricle is missing or very small, the necessity to feed the pulmonary and systemic circulations is obtained with an interposition shunt. Two main options are available and differ from the sites of anastomoses: (i) the systemic-to-pulmonary conduit (Blalock–Taussig shunt known as the Norwood Operation (NO)) connecting the innominate artery (NO-BT) or the aorta (NO-CS) to the right pulmonary artery and (ii) the right ventricle to pulmonary artery shunt (known as Sano operation (SO)). The proposition that the SO is superior to the NO remains controversial.
3-D computer models of the NO (NO-BT and NO-CS) and SO were developed and investigated using the finite volume method.
Conduits of 3, 3.5 and 4mm were used in the NO models, whereas conduits of 4, 5 and 6mm were used in the SO model. The hydraulic nets (lumped resistances, compliances, inertances and elastances) which represent the systemic, coronary and pulmonary circulations and the heart were identical in the two models. A multiscale approach was adopted to couple the 3-D models with the circulation net. Computer simulation results were compared with post-operative catheterization data.
Results showed that (i) there is a good correlation between predicted and observed data: higher aortic diastolic pressure, decreased pulmonary arterial pressure, lower pulmonary-to-systemic flow ratio and higher coronary perfusion pressure in SO; (ii) there is a minimal regurgitant flow in the SO conduit.
The close correlation between predicted and observed clinical data supports the use of mathematical modelling, with a mandatory multiscale approach, in the design and assessment of surgical procedures
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