Abstract: It is known that the heart interacts with and adapts to
its venous and arterial loading conditions. Various experimental
studies and modeling approaches have been developed to investigate
the underlying mechanisms. This paper presents a model of the left
ventricle derived based on nonlinear stress-length myocardial
characteristics integrated over truncated ellipsoidal geometry, and
second-order dynamic mechanism for the excitation-contraction
coupling system. The results of the model presented here describe the
effects of the viscoelastic damping element of the electromechanical
coupling system on the hemodynamic response. Different heart rates
are considered to study the pacing effects on the performance of the
left-ventricle against constant preload and afterload conditions under
various damping conditions. The results indicate that the pacing
process of the left ventricle has to take into account, among other
things, the viscoelastic damping conditions of the myofilament
excitation-contraction process.
Abstract: Coronary artery bypass grafts (CABG) are widely
studied with respect to hemodynamic conditions which play
important role in presence of a restenosis. However, papers which
concern with constitutive modeling of CABG are lacking in the
literature. The purpose of this study is to find a constitutive model for
CABG tissue. A sample of the CABG obtained within an autopsy
underwent an inflation–extension test. Displacements were
recoredered by CCD cameras and subsequently evaluated by digital
image correlation. Pressure – radius and axial force – elongation
data were used to fit material model. The tissue was modeled as onelayered
composite reinforced by two families of helical fibers. The
material is assumed to be locally orthotropic, nonlinear,
incompressible and hyperelastic. Material parameters are estimated
for two strain energy functions (SEF). The first is classical
exponential. The second SEF is logarithmic which allows
interpretation by means of limiting (finite) strain extensibility.
Presented material parameters are estimated by optimization based
on radial and axial equilibrium equation in a thick-walled tube. Both
material models fit experimental data successfully. The exponential
model fits significantly better relationship between axial force and
axial strain than logarithmic one.
Abstract: Functional Magnetic Resonance Imaging(fMRI) is a
noninvasive imaging technique that measures the hemodynamic
response related to neural activity in the human brain. Event-related
functional magnetic resonance imaging (efMRI) is a form of
functional Magnetic Resonance Imaging (fMRI) in which a series of
fMRI images are time-locked to a stimulus presentation and averaged
together over many trials. Again an event related potential (ERP) is a
measured brain response that is directly the result of a thought or
perception. Here the neuronal response of human visual cortex in
normal healthy patients have been studied. The patients were asked
to perform a visual three choice reaction task; from the relative
response of each patient corresponding neuronal activity in visual
cortex was imaged. The average number of neurons in the adult
human primary visual cortex, in each hemisphere has been estimated
at around 140 million. Statistical analysis of this experiment was
done with SPM5(Statistical Parametric Mapping version 5) software.
The result shows a robust design of imaging the neuronal activity of
human visual cortex.
Abstract: The recent advances in computational fluid dynamics
(CFD) can be useful in observing the detailed hemodynamics in
cerebral aneurysms for understanding not only their formation and
rupture but also for clinical evaluation and treatment. However,
important hemodynamic quantities are difficult to measure in vivo. In
the present study, an approximate model of normal middle cerebral
artery (MCA) along with two cases consisting broad and narrow
saccular aneurysms are analyzed. The models are generated in
ANSYS WORKBENCH and transient analysis is performed in
ANSYS-CFX. The results obtained are compared for three cases and
agree well with the available literature.
Abstract: It is known that the heart interacts with and adapts to its venous and arterial loading conditions. Various experimental studies and modeling approaches have been developed to investigate the underlying mechanisms. This paper presents a model of the left ventricle derived based on nonlinear stress-length myocardial characteristics integrated over truncated ellipsoidal geometry, and second-order dynamic mechanism for the excitation-contraction coupling system. The results of the model presented here describe the effects of the viscoelastic damping element of the electromechanical coupling system on the hemodynamic response. Different heart rates are considered to study the pacing effects on the performance of the left-ventricle against constant preload and afterload conditions under various damping conditions. The results indicate that the pacing process of the left ventricle has to take into account, among other things, the viscoelastic damping conditions of the myofilament excitation-contraction process. The effects of left ventricular dimensions on the hemdynamic response have been examined. These effects are found to be different at different viscoelastic and pacing conditions.
Abstract: Recurrence of aneurysm rupture can be attributed to
coil migration and compaction. In order to verify the effects of
hemodynamics on coil compaction and migration, we analyze the
forces and displacements on the coil bundle using a computational
method. Lateral aneurysms partially filled coils are modeled, and
blood flow fields and coil deformations are simulated considering
fluid and solid interaction. Effects of aneurysm neck size and parent
vessel geometry are also investigated. The results showed that coil
deformation was larger in the aneurysms with a wider neck. Parent
vessel geometry and aneurysm neck size also affected mean pressure
force profiles on the coil surface. Pressure forces were higher in wide
neck models with curved parent vessel geometry. Simulation results
showed that coils in the wide neck aneurysm with a curved parent
vessel may be displaced and compacted more easily.