Simulation of a detoxifying organ function: Focus on hemodynamics modeling and convection‐reaction numerical simulation in microcirculatory networks

International audienceWhen modeling a detoxifying organ function, an important component is the impact of flow on the metabolism of a compound of interest carried by the blood. We here study the effects of red blood cells (such as the Fahraeus-Lindqvist effect and plasma skimming) on blood flow in typical microcirculatory components such as tubes, bifurcations and entire networks, with particular emphasis on the liver as important representative of detoxifying organs. In one of the plasma skimming models, under certain conditions, oscillations between states are found and analyzed in a methodical study to identify their causes and influencing parameters. The flow solution obtained is then used to define the velocity at which a compound would be transported. A convection-reaction equation is studied to simulate the transport of a compound in blood and its uptake by the surrounding cells. Different types of signal sharpness have to be handled depending on the application to address different temporal compound concentration profiles. To permit executing the studied models numerically stable and accurate, we here extend existing transport schemes to handle converging bifurcations, and more generally multi-furcations. We study the accuracy of different numerical schemes as well as the effect of reactions and of the network itself on the bolus shape. Even though this study is guided by applications in liver micro-architecture, the proposed methodology is general and can readily be applied to other capillary network geometries, hence to other organs or to bioengineered network designs

The impact of various backboard configurations on compression stiffness in a manikin study of CPR

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Modeling and simulation of the effects of axial diffusion on fuel-air mixing lengths in micro-power systems

An analytical model for fuel-oxidizer mixing that incorporates both axial and radial diffusion is developed to predict the mixing length - the distance required for fuel and oxidizer to mix via diffusive transport - in axisymmetric micro-power system configurations. The results are compared with mixing length estimates obtained for the case of mixing by radial diffusion only i.e. the traditional Burke-Schumann theory. The mixing length predictions are also compared with the results of inviscid CFD simulations of low Reynolds number fueloxidizer mixing in axisymmetric micro-power system configurations. The results indicate that axial diffusion becomes important for Re < 20 and imposes a limit on the extent to which it is possible (from a fuel-air mixing point of view) to miniaturize a power system

A scoping review of important urinary catheter induced complications.

This study presents a scoping review of the literature on the morbidity and mortality associated with several common complications of urinary catheterization. Data gathered from the open literature were analyzed graphically to gain insights into the most important urinary catheter induced complications. The results reveal that the most significant catheter complications are severe mechanical trauma (perforation, partial urethral damage and urinary leakage), symptomatic bacterial infection, and anaphylaxis, catheter toxicity and hypersensitivity. The data analysis also revealed that the complications with the highest morbidity are all closely related to the mechanical interaction of the catheter with the urethra. This suggests that there is a strong need for urinary catheter design to be improved to minimize mechanical interaction, especially mechanical damage to the urinary tract, and to enhance patient comfort. Several urinary catheter design directions have been proposed based on tribological principles. Among the key recommendations is that catheter manufacturers develop catheter coatings which are both hydrophilic and antibacterial, and which maintain their antibacterial patency for at least 90 days

The Electrical Impedance of Pulsatile Blood Flowing Through Rigid Tubes: An Experimental Investigation

Small fluctuations present in an Impedance Cardiogram are often dismissed as noise, but may be due to unknown physiological origins. One such origin suggested in literature is the impedance variation induced by changes in red blood cell orientation during pulsatile blood flow. This study investigated the relationship between the impedance, velocity and acceleration of blood as it pulses during the cardiac cycle. This was achieved experimentally by pumping blood through rigid tubes in a mock circulatory system while measuring the impedance and velocity of the blood. Analysis of collected data confirms that impedance responds to changes in both velocity and acceleration. During acceleration, impedance and velocity are linearly related. However, during deceleration, it was found that the relationship between impedance and velocity is non linear. As velocity increases, the relationship becomes linear with a reducing slope. This indicates that for the same change in acceleration at low velocities, the impedance response is significantly larger than at higher velocities. Experimental data demonstrating these trends is presented for varied pulse rates (20 – 100 beats per minute), stroke volumes (20 – 60 ml) and systolic/diastolic ratios (50/50 – 30/70)

The influence of leaflet skin friction and stiffness on the performance of bioprosthetic aortic valves

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Application of the finite element method in the fatigue life prediction of a stent for a percutaneous heart valve

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Numerical Study of Heat Transfer in Film Cooled Thrust Chambers

Film cooling as a thermal protection for the walls of liquid rocket engines is studied numerically for hydrogen and methane thrust chamber tests. The aim is to verify the capability of the Reynolds Average Navier-Stokes model to capture the basic characteristics of film-cooled thrust chambers, considering a simplified approach, named pseudo-injector approach, which does not model propellant injection and combustion. This assumption allows a great saving in computational time, in particular when considering 3D simulations. The present study takes its origin from the European Community In-Space Propulsion 1 (ISP-1) program where, among various projects, an experimental campaign has been designed to study the film cooling technique in an oxygen/methane thrust chamber and to provide a database for computational fluid dynamics validation. The results show that the present approach gives good results in terms of heat flux characterization, in particular when dealing with test cases of high chamber pressure. © 2012 by B. Betti, E. Martelli, F. Nasuti, M. Onofri