Wall shear stress and arterial performance: two approaches based on engineering

This is the Abstract of the Article. Copyright @ 2009 Oxford University.This crucially important subject generates a very wide literature and the recent authoritative ‘in vivo’ review of Reneman et al [1] (& [2]), with Vennemann et al [3], are taken as seminal. In this paper we use approaches based on conventional engineering to address two key issues raised in [1]. The first is that of basic theory. To what extent can underlying fluid flow theory complement the in vivo understanding of wall shear stress (WSS)? In [1], which is sub-titled Discrepancies with Theory’, Poiseuille’s Law is used, extended to Murray’s Law in [2]. But they do ’not hold in vivo’ [2] because ‘we are dealing with non-Newtonian fluid, distensible vessels, unsteady flows, and too short entrance lengths’ [1].This comment coincides with the four factors Xu and Collins identified in their early Review of numerical analysis for bifurcations [4]. Subsequently they addressed these factors, with an engineering-based rationale of comparing predictions of Computational Fluid Dynamics (CFD) with Womersley theory, in vitro and in vivo data. This rationale has yet to be widely adopted, possibly due to computing complexities and the wide boundary condition data needed. This is despite uncertainties in current in vivo WSS [2]. Secondly, [1] and [2] focus on endothelial function. WSS is an ‘important determinant of arterial diameter’ and ‘mean (M)WSS is regulated locally’. One pointer is the possible importance of the glycocalyx, so that ‘endothelial cells are not seeing WSS’ and which ‘may be involved in the regulation of the total blood flow’ [3]. A typical glycocalyx is shown in [3]. Such a model should focus on adaptation of arterial diameter by ‘nitric oxide and prostaglandins’ [1]. So, using an engineering approach, can we construct a model for local regulation of MWSS? Again, remarks from [1]-[3] resonate with the conclusions of a review of nanoscale physiological flows [5] undertaken as part of an early Nanotechnology Initiative of the UK’s EPSRC. In [5] is illustrated the fractal nature of the intestinal villi-glycocalyx geometry, together with an engineering-style control loop for nitric oxide release and arterial diameter-flow rate control. Within our discussion we report two studies to obtain CFD predictive data very close to the endothelial surface. In both cases we compared two independent codes, respectively two CFD codes, and CFD and Lattice Boltzmann solvers. We also give an updated version of the endothelium control loop

The thermodynamics of metabolism, cardiovascular performance and exercise, in health and diabetes: The objective of clinical markers

Extensive experience in UK National Health Service metabolic syndrome/type 2 diabetes clinics highlights the need for convenient clinical marker(s) which can be readily used to indicate the success or otherwise of alternative therapies. In this paper we study the metabolic context of the healthy and diseased states, which points to the haemodynamics being a possible key in identifying candidate markers. Human metabolism relates to two elemental thermodynamic systems, the individual cell and the human body in its entirety. The fundamental laws of thermodynamics apply to humans, animals, and their individual cells for both healthy and diseased conditions. as they are to classic heat engines. In compliance with the second law enhanced levels of heat are generated under exercise, heat itself being another factor modulating the cardiovascular response to physical exercise. Nutrients and oxygen uptake occurs via the digestive system and lungs, respectively, leading to ATP production by the established metabolic pathways: this is controlled by insulin. These are then delivered to the cells via the haemodynamic system to satisfy local metabolic need. The supply and demand of oxygen are finely regulated, in part, via oxygen-dependent release of ATP from the circulating erythrocytes. Energy supply and demand are regulated to sustain muscle activity resulting in the body’s output of measurable thermodynamic work—i.e. exercise. Recently a dynamic pathway model allowing quantification of ATP release from the erythrocytes and its contribution to oxygen supply regulation has been published. However, metabolic uptake is well known to be greatly affected by disease such as the highly prevalent diabetes type 2 with insulin resistance and beta cell dysfunction having mechanistic roles. In 2010, over 25% of residents above 65 in the USA had diabetes 2. The complexity of the metabolic pathways means that monitoring of patient-specific treatment would be beneficial from a diabetic marker which may be haemodynamic-related and traceable via the local fluid dynamics

Research reports on the diagnosis and detection; environment and infection; and evaluation of interventions on infectious diseases.

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Superposition as memory: unlocking quantum automatic complexity

Imagine a lock with two states, "locked" and "unlocked", which may be manipulated using two operations, called 0 and 1. Moreover, the only way to (with certainty) unlock using four operations is to do them in the sequence 0011, i.e., $0^n1^n$ where $n=2$. In this scenario one might think that the lock needs to be in certain further states after each operation, so that there is some memory of what has been done so far. Here we show that this memory can be entirely encoded in superpositions of the two basic states "locked" and "unlocked", where, as dictated by quantum mechanics, the operations are given by unitary matrices. Moreover, we show using the Jordan--Schur lemma that a similar lock is not possible for $n=60$. We define the semi-classical quantum automatic complexity $Q_{s}(x)$ of a word $x$ as the infimum in lexicographic order of those pairs of nonnegative integers $(n,q)$ such that there is a subgroup $G$ of the projective unitary group PU$(n)$ with $|G|\le q$ and with $U_0,U_1\in G$ such that, in terms of a standard basis $\{e_k\}$ and with $U_z=\prod_k U_{z(k)}$, we have $U_x e_1=e_2$ and $U_y e_1 \ne e_2$ for all $y\ne x$ with $|y|=|x|$. We show that $Q_s$ is unbounded and not constant for strings of a given length. In particular, $$Q_{s}(0^21^2)\le (2,12) < (3,1) \le Q_{s}(0^{60}1^{60})$$ and $Q_s(0^{120})\le (2,121)$.Comment: Lecture Notes in Computer Science, UCNC (Unconventional Computation and Natural Computation) 201

Modelling wall shear stress in small arteries using LBM and FVM

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.In this study a finite-volume discretisation of a Lattice Boltzmann equation over unstructured grids is presented. The new scheme is based on the idea of placing the unknown fields at the nodes of the mesh and evolve them based on the fluxes crossing the surfaces of the corresponding control volumes. The method, named unstructured Lattice Boltzmann equation (ULBE) is compared with the classical finite volume method (FVM) and is applied here to the problem of blood flow over the endothelium in small arteries. The study shows a significant variation and a high sensitivity of wall shear stress to the endothelium corrugation degree

Optical Coherence Tomography – Variations on a Theme

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Optical Coherence Tomography (OCT) has developed extensively over the last 23 years. This paper reviews some of the imaging techniques based on OCT with particular reference to the trade-offs between lateral and axial resolution, working distance, imaging depth, acquisition speed (enabling real time observation and 3D imaging), imaged area/volume, contrast enhancement – including velocity measurement, and system complexity – including detectors, light sources and the optical path. The majority of applications of OCT are biomedical, especially ophthalmology, endoscopy and intravascular imaging. However, some industrial applications are emerging particularly for non-destructive testing and quality control, such as in the production of MEMS devices, or the non-destructive detection of sub-surface strain fields in injected moulded polymer parts

Near wall hemodynamics: Modelling the glycocalyx and the endothelial surface

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.In this paper a coarse-grained model for blood flow in small arteries is presented. Blood is modelled as a two-component incompressible fluid: the plasma and corpuscular elements dispersed in it. The latter are modelled as deformable liquid droplets having greater density and viscosity. Interfacial surface tension and membrane effects are present to mimic key properties and to avoid droplets’ coalescence. The mesoscopic model also includes the presence of the wavy wall, due to the endothelial cells and incorporates a representation of the glycocalyx, covering the vessel wall. The glycocalyx is modelled as a porous medium, the droplets being subjected to a repulsive elastic force when approaching it, during their transit. Preliminary simulations are intended to show the influence of the undulation on the wall together with that of the glycocalyx

Manuscript Architect: a Web application for scientific writing in virtual interdisciplinary groups

BACKGROUND: Although scientific writing plays a central role in the communication of clinical research findings and consumes a significant amount of time from clinical researchers, few Web applications have been designed to systematically improve the writing process. This application had as its main objective the separation of the multiple tasks associated with scientific writing into smaller components. It was also aimed at providing a mechanism where sections of the manuscript (text blocks) could be assigned to different specialists. Manuscript Architect was built using Java language in conjunction with the classic lifecycle development method. The interface was designed for simplicity and economy of movements. Manuscripts are divided into multiple text blocks that can be assigned to different co-authors by the first author. Each text block contains notes to guide co-authors regarding the central focus of each text block, previous examples, and an additional field for translation when the initial text is written in a language different from the one used by the target journal. Usability was evaluated using formal usability tests and field observations. RESULTS: The application presented excellent usability and integration with the regular writing habits of experienced researchers. Workshops were developed to train novice researchers, presenting an accelerated learning curve. The application has been used in over 20 different scientific articles and grant proposals. CONCLUSION: The current version of Manuscript Architect has proven to be very useful in the writing of multiple scientific texts, suggesting that virtual writing by interdisciplinary groups is an effective manner of scientific writing when interdisciplinary work is required

Long-term exposure of mouse pancreatic islets to oleate or palmitate results in reduced glucose-induced somatostatin and oversecretion of glucagon

AIMS/HYPOTHESIS: Long-term exposure to NEFAs leads to inhibition of glucose-induced insulin secretion. We tested whether the release of somatostatin and glucagon, the two other major islet hormones, is also affected. METHODS: Mouse pancreatic islets were cultured for 72 h at 4.5 or 15 mmol/l glucose with or without 0.5 mmol/l oleate or palmitate. The release of glucagon and somatostatin during subsequent 1 h incubations at 1 or 20 mmol/l glucose as well as the islet content of the two hormones were determined. Lipid-induced changes in islet cell ultrastructure were assessed by electron microscopy. RESULTS: Culture at 15 mmol/l glucose increased islet glucagon content by approximately 50% relative to that observed following culture at 4.5 mmol/l glucose. Inclusion of oleate or palmitate reduced islet glucagon content by 25% (at 4.5 mmol/l glucose) to 50% (at 15 mmol/l glucose). Long-term exposure to the NEFA increased glucagon secretion at 1 mmol/l glucose by 50% (when islets had been cultured at 15 mmol/l glucose) to 100% (with 4.5 mmol/l glucose in the culture medium) and abolished the inhibitory effect of 20 mmol/l glucose on glucagon secretion. Somatostatin content was unaffected by glucose and lipids, but glucose-induced somatostatin secretion was reduced by approximately 50% following long-term exposure to either of the NEFA, regardless of whether the culture medium contained 4.5 or 15 mmol/l glucose. Ultrastructural evidence of lipid deposition was seen in &lt;10% of non-beta cells but in &gt;80% of the beta cells. CONCLUSIONS/INTERPRETATION: Long-term exposure to high glucose and/or NEFA affects the release of somatostatin and glucagon. The effects on glucagon secretion are very pronounced and in type 2 diabetes in vivo may aggravate the hyperglycaemic effects due to lack of insulin

Cervical dysplasia in patients with systemic lupus erythematosus

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