43 research outputs found
A 3D porous media liver lobule model: the importance of vascular septa and anisotropic permeability for homogeneous perfusion
Fingerprinting Soft Materials: A Framework for Characterizing Nonlinear Viscoelasticity
We introduce a comprehensive scheme to physically quantify both viscous and
elastic rheological nonlinearities simultaneously, using an imposed large
amplitude oscillatory shear (LAOS) strain. The new framework naturally lends a
physical interpretation to commonly reported Fourier coefficients of the
nonlinear stress response. Additionally, we address the ambiguities inherent in
the standard definitions of viscoelastic moduli when extended into the
nonlinear regime, and define new measures which reveal behavior that is
obscured by conventional techniques.Comment: 10 pages, 3 figures, full-page double-space preprint forma
Mathematical model of blood and interstitial flow and lymph production in the liver.
We present a mathematical model of blood and interstitial flow in the liver. The liver is treated as a lattice of hexagonal \u2018classic\u2019 lobules, which are assumed to be long enough that end effects may be neglected and a
two-dimensional problem considered. Since sinusoids and lymphatic vessels are numerous and small compared to the lobule, we use a homogenized approach, describing the sinusoidal and interstitial spaces as porous media. We model plasma filtration from sinusoids to the interstitium, lymph uptake by lymphatic ducts, and lymph outflow from the liver
surface. Our results show that the effect of the liver surface only penetrates a depth of a few lobules\u2019 thickness into the tissue. Thus, we separately consider a single lobule lying sufficiently far from all external boundaries that we may regard it as being in an infinite lattice, and also a model of the region near the liver surface. The model predicts that slightly more lymph is produced by interstitial fluid flowing through the liver surface than that taken up by the lymphatic vessels in the liver and that the on-peritonealized region of the surface of the liver results in the total lymph production (uptake by lymphatics plus fluid crossing surface) being about 5 % more than if the entire surface were covered by the Glisson\u2013peritoneal membrane. Estimates of lymph outflow through the surface of the liver are in good agreement with experimental data. We also study the effect of non-physiological values of the controlling parameters, particularly focusing
on the conditions of portal hypertension and ascites. To our knowledge, this is the first attempt to model lymph production in the liver. The model provides clinically relevant information about lymph outflow pathways and predicts the systemic response to pathological variations
A structured approach for governing sustainable heat transitions in building renovation of towns and cities
This is the final version. Available on open access from IOP Publishing via the DOI in this record. Pioneer cities have demonstrated a willingness and capability to decarbonise local heat systems, but support is needed to scale up action. Heat decarbonisation is not simply a technical challenge, but also a political and social one; stakeholders must inform decisions about appropriate technological and policy solutions and will, in turn, be affected by them. Taking three dimensions of stakeholders, technology, and policy, a structured approach which centres stakeholders is presented to help local government to collaboratively find appropriate technology and policy solutions, both at the strategic scale across the municipality and in localised pilot projects, and explores how to initialise and support heat decarbonisation in more cities.European Regional Development Fund (ERDF)Province of South-Holland (Netherlands)Ministry of Economic Affairs and Climate Policy (Netherlands
Neighborhood Racial Characteristics, Credit History, and Bankcard Credit in Indian Country
Numerical simulation of extrusion process and die design for industrial profile, using multimode pom–pom model
Rigorous mathematical optimization of synthetic hepatic vascular trees
In this paper, we introduce a new framework for generating synthetic vascular
trees, based on rigorous model-based mathematical optimization. Our main
contribution is the reformulation of finding the optimal global tree geometry
into a nonlinear optimization problem (NLP). This rigorous mathematical
formulation accommodates efficient solution algorithms such as the interior
point method and allows us to easily change boundary conditions and constraints
applied to the tree. Moreover, it creates trifurcations in addition to
bifurcations. A second contribution is the addition of an optimization stage
for the tree topology. Here, we combine constrained constructive optimization
(CCO) with a heuristic approach to search among possible tree topologies. We
combine the NLP formulation and the topology optimization into a single
algorithmic approach. Finally, we attempt the validation of our new model-based
optimization framework using a detailed corrosion cast of a human liver, which
allows a quantitative comparison of the synthetic tree structure to the tree
structure determined experimentally down to the fifth generation. The results
show that our new framework is capable of generating asymmetric synthetic trees
that match the available physiological corrosion cast data better than trees
generated by the standard CCO approach.Comment: 25 pages, 16 figures, 3 table
A 3D Porous Media Liver Lobule Model: the Importance of Vascular Septa and Anisotropic Permeability for Homogeneous Perfusion
The hepatic blood circulation is complex, particularly at the microcirculatory level. Previously, 2D liver lobule models using porous
media and a 3D model using real sinusoidal geometries have been
developed. We extended these models to investigate the role of vascular
septa (VS) and anisotropic permeability.
The lobule was modelled as a hexagonal prism (with or without
VS) and the tissue treated as a porous medium (isotropic or anisotropic
permeability). Models were solved using computational fluid dynamics.
VS inclusion resulted in more spatially homogeneous perfusion.
Anisotropic permeability resulted in a larger axial velocity component
than isotropic. A parameter study revealed that results are most sensitive to the lobule size and radial pressure drop.
Our model provides insight into hepatic microhemodynamics, and
suggests that inclusion of VS in the model leads to perfusion patterns that
are likely to reflect physiological reality. The model has potential for
applications to unphysiological and pathological conditions
162 MODELLING OF THE HEPATIC CIRCULATION BY COMBINING VASCULAR CORROSION CASTING AND MICRO-CT IMAGING
Flow competition between hepatic arterial and portal venous flow during hypothermic machine perfusion preservation of porcine livers
Hypothermic machine perfusion (HMP) is regarded as a better preservation method for donor livers than cold storage. During HMP, livers are perfused through the inlet blood vessels, namely the hepatic artery (HA) and the portal vein (PV). In previous HMP feasibility studies of porcine and human livers, we observed that the PV flow decreased while the HA flow increased. This flow competition restored either spontaneously or by lowering the HA pressure (PHA). Since this phenomenon had never been observed before and because it affects the HMP stability, it is essential to gain more insight into the determinants of flow competition. To this end, we investigated the influence of the HMP boundary conditions on liver flows during controlled experiments. This paper presents the flow effects induced by increasing PHA and by obstructing the outlet blood vessel, which is the vena cava inferior (VCI). Flow competition was evoked by increasing PHA to 55-70 mmHg, as well as by obstructing the VCI. Remarkably, a severe obstruction resulted in a repetitive and alternating tradeoff between the HA and PV flows. These phenomena could be related to intra-sinusoidal pressure alterations. Consequently, a higher PHA is most likely transmitted to the sinusoidal level. This increased sinusoidal pressure reduces the pressure drop between the PV and the sinusoids, leading to a decreased PV perfusion. Flow competition has not been encountered or evoked under physiological conditions and should be taken into account for the design of liver HMP protocols. Nevertheless, more research is necessary to determine the optimal parameters for stable HMP.status: publishe