Plasma levels of endothelin-1 after a pulmonary embolism of bone marrow fat

BACKGROUND: During orthopedic surgery, embolization of bone marrow fat can lead to potentially fatal, intra-operative cardiovascular deterioration. Vasoactive mediators may also be released from the bone marrow and contribute to these changes. Increased plasma levels of endothelin-1 (ET-1) have been observed after pulmonary air and thrombo-embolism. The role of ET-1 in the development of acute cardiovascular deterioration as a result of bone marrow fat embolization during vertebroplasty was therefore investigated. METHODS: Bone cement was injected into three lumbar vertebrae of six sheep in order to force bone marrow fat into the circulation. Invasive blood pressures and heart rate were recorded continuously until 60 min after the last injection. Cardiac output, arterial and mixed venous blood gas parameters and plasma ET-1 concentrations were measured at selected time points. Post-mortem, lung biopsies were taken for analysis of intravascular fat. RESULTS: Cement injections resulted in a sudden (within 1 min) and severe increase in pulmonary arterial pressure (>100%). Plasma concentrations of ET-1 started to increase after the second injection, but no significant changes were observed. Intravascular fat and bone marrow cells were present in all lung lobes. CONCLUSION: Cement injections into vertebral bodies elicited fat embolism resulting in subsequent cardiovascular changes that were characterized by an increase in pulmonary arterial pressure. Cardiovascular complications as a result of bone marrow fat embolism should thus be considered in patients undergoing vertebroplasty. No significant changes in ET-1 plasma values were observed. Thus, ET-1 did not contribute to the acute cardiovascular changes after fat embolism.

C��digo h��brido avanzado de motores de plasma de efecto Hall

La propulsi��n el��ctrica constituye hoy una tecnolog��a muy competitiva y de gran proyecci��n de futuro. Dentro de los diversos motores de plasma existentes, el motor de efecto Hall ha adquirido una gran madurez y constituye un medio de propulsi��n id��neo para un rango amplio de misiones. En la presente Tesis se estudian los motores Hall con geometr��a convencional y paredes diel��ctricas. La compleja interacci��n entre los m��ltiples fen��menos f��sicos presentes hace que sea dif��cil la simulaci��n del plasma en estos motores. Los modelos h��bridos son los que representan un mejor compromiso entre precisi��n y tiempo de c��lculo. Se basan en utilizar un modelo fluido para los electrones y algoritmos de din��mica de part��culas PIC (Particle-In- Cell) para los iones y los neutros. Permiten hacer uso de la hip��tesis de cuasineutralidad del plasma, a cambio de resolver separadamente las capas l��mite (o vainas) que se forman en torno a las paredes de la c��mara. Partiendo de un c��digo h��brido existente, llamado HPHall-2, el objetivo de la Tesis doctoral ha sido el desarrollo de un c��digo h��brido avanzado que mejorara la simulaci��n de la descarga de plasma en un motor de efecto Hall. Las actualizaciones y mejoras realizadas en las diferentes partes que componen el c��digo comprenden tanto aspectos te��ricos como num��ricos. Fruto de la extensa revisi��n de la algoritmia del c��digo HPHall-2 se han conseguido reducir los errores de precisi��n un orden de magnitud, y se ha incrementado notablemente su consistencia y robustez, permitiendo la simulaci��n del motor en un amplio rango de condiciones. Algunos aspectos relevantes a destacar en el subc��digo de part��culas son: la implementaci��n de un nuevo algoritmo de pesado que permite determinar de forma m��s precisa el flujo de las magnitudes del plasma; la implementaci��n de un nuevo algoritmo de control de poblaci��n, que permite tener suficiente n��mero de part��culas cerca de las paredes de la c��mara, donde los gradientes son mayores y las condiciones de c��lculo son m��s cr��ticas; las mejoras en los balances de masa y energ��a; y un mejor c��lculo del campo el��ctrico en una malla no uniforme. Merece especial atenci��n el cumplimiento de la condici��n de Bohm en el borde de vaina, que en los c��digos h��bridos representa una condici��n de contorno necesaria para obtener una soluci��n consistente con el modelo de interacci��n plasma-pared, y que en HPHall-2 a��n no se hab��a resuelto satisfactoriamente. En esta Tesis se ha implementado el criterio cin��tico de Bohm para una poblaci��n de iones con diferentes cargas el��ctricas y una gran dispersi��n de velocidades. En el c��digo, el cumplimiento de la condici��n cin��tica de Bohm se consigue por medio de un algoritmo que introduce una fina capa de aceleraci��n nocolisional adyacente a la vaina y mide adecuadamente el flujo de part��culas en el espacio y en el tiempo. Las mejoras realizadas en el subc��digo de electrones incrementan la capacidad de simulaci��n del c��digo, especialmente en la regi��n aguas abajo del motor, donde se simula la neutralizaci��n del chorro del plasma por medio de un modelo de c��todo volum��trico. Sin abordar el estudio detallado de la turbulencia del plasma, se implementan modelos sencillos de ajuste de la difusi��n an��mala de Bohm, que permiten reproducir los valores experimentales del potencial y la temperatura del plasma, as�� como la corriente de descarga del motor. En cuanto a los aspectos te��ricos, se hace especial ��nfasis en la interacci��n plasma-pared y en la din��mica de los electrones secundarios libres en el interior del plasma, cuestiones que representan hoy en d��a problemas abiertos en la simulaci��n de los motores Hall. Los nuevos modelos desarrollados buscan una imagen m��s fiel a la realidad. As��, se implementa el modelo de vaina de termalizaci��n parcial, que considera una funci��n de distribuci��n no-Maxwelliana para los electrones primarios y contabiliza unas p��rdidas energ��ticas m��s cercanas a la realidad. Respecto a los electrones secundarios, se realiza un estudio cin��tico simplificado para evaluar su grado de confinamiento en el plasma, y mediante un modelo fluido en el l��mite no-colisional, se determinan las densidades y energ��as de los electrones secundarios libres, as�� como su posible efecto en la ionizaci��n. El resultado obtenido muestra que los electrones secundarios se pierden en las paredes r��pidamente, por lo que su efecto en el plasma es despreciable, no as�� en las vainas, donde determinan el salto de potencial. Por ��ltimo, el trabajo te��rico y de simulaci��n num��rica se complementa con el trabajo experimental realizado en el Pnnceton Plasma Physics Laboratory, en el que se analiza el interesante transitorio inicial que experimenta el motor en el proceso de arranque. Del estudio se extrae que la presencia de gases residuales adheridos a las paredes juegan un papel relevante, y se recomienda, en general, la purga completa del motor antes del modo normal de operaci��n. El resultado final de la investigaci��n muestra que el c��digo h��brido desarrollado representa una buena herramienta de simulaci��n de un motor Hall. Reproduce adecuadamente la f��sica del motor, proporcionando resultados similares a los experimentales, y demuestra ser un buen laboratorio num��rico para estudiar el plasma en el interior del motor. Abstract Electric propulsion is today a very competitive technology and has a great projection into the future. Among the various existing plasma thrusters, the Hall effect thruster has acquired a considerable maturity and constitutes an ideal means of propulsion for a wide range of missions. In the present Thesis only Hall thrusters with conventional geometry and dielectric walls are studied. The complex interaction between multiple physical phenomena makes difficult the plasma simulation in these engines. Hybrid models are those representing a better compromise between precision and computational cost. They use a fluid model for electrons and Particle-In-Cell (PIC) algorithms for ions and neutrals. The hypothesis of plasma quasineutrality is invoked, which requires to solve separately the sheaths formed around the chamber walls. On the basis of an existing hybrid code, called HPHall-2, the aim of this doctoral Thesis is to develop an advanced hybrid code that better simulates the plasma discharge in a Hall effect thruster. Updates and improvements of the code include both theoretical and numerical issues. The extensive revision of the algorithms has succeeded in reducing the accuracy errors in one order of magnitude, and the consistency and robustness of the code have been notably increased, allowing the simulation of the thruster in a wide range of conditions. The most relevant achievements related to the particle subcode are: the implementation of a new weighing algorithm that determines more accurately the plasma flux magnitudes; the implementation of a new algorithm to control the particle population, assuring enough number of particles near the chamber walls, where there are strong gradients and the conditions to perform good computations are more critical; improvements in the mass and energy balances; and a new algorithm to compute the electric field in a non-uniform mesh. It deserves special attention the fulfilment of the Bohm condition at the edge of the sheath, which represents a boundary condition necessary to match consistently the hybrid code solution with the plasma-wall interaction, and remained as a question unsatisfactory solved in the HPHall-2 code. In this Thesis, the kinetic Bohm criterion has been implemented for an ion particle population with different electric charges and a large dispersion in their velocities. In the code, the fulfilment of the kinetic Bohm condition is accomplished by an algorithm that introduces a thin non-collisional layer next to the sheaths, producing the ion acceleration, and measures properly the flux of particles in time and space. The improvements made in the electron subcode increase the code simulation capabilities, specially in the region downstream of the thruster, where the neutralization of the plasma jet is simulated using a volumetric cathode model. Without addressing the detailed study of the plasma turbulence, simple models for a parametric adjustment of the anomalous Bohm difussion are implemented in the code. They allow to reproduce the experimental values of the plasma potential and the electron temperature, as well as the discharge current of the thruster. Regarding the theoretical issues, special emphasis has been made in the plasma-wall interaction of the thruster and in the dynamics of free secondary electrons within the plasma, questions that still remain unsolved in the simulation of Hall thrusters. The new developed models look for results closer to reality, such as the partial thermalization sheath model, that assumes a non-Maxwellian distribution functions for primary electrons, and better computes the energy losses at the walls. The evaluation of secondary electrons confinement within the chamber is addressed by a simplified kinetic study; and using a collisionless fluid model, the densities and energies of free secondary electrons are computed, as well as their effect on the plasma ionization. Simulations show that secondary electrons are quickly lost at walls, with a negligible effect in the bulk of the plasma, but they determine the potential fall at sheaths. Finally, numerical simulation and theoretical work is complemented by the experimental work carried out at the Princeton Plasma Physics Laboratory, devoted to analyze the interesting transitional regime experienced by the thruster in the startup process. It is concluded that the gas impurities adhered to the thruster walls play a relevant role in the transitional regime and, as a general recomendation, a complete purge of the thruster before starting its normal mode of operation it is suggested. The final result of the research conducted in this Thesis shows that the developed code represents a good tool for the simulation of Hall thrusters. The code reproduces properly the physics of the thruster, with results similar to the experimental ones, and represents a good numerical laboratory to study the plasma inside the thruster.

Transition from isentropic to isothermal expansion in laser produced plasma

The transition that the expansion flow of laser-produced plasmas experiences when one moves from long, low intensity pulses (temperature vanishing at the isentropic plasma-vacuum front,lying at finite distance) to short, intense ones (non-zero, uniform temperature at the plasma-vacuum front, lying at infinity) is studied. For plznar geometry and lqge ion number Z, the transition occurs for dq5/dt=0.14(27/8)k712Z���1zn$/m4f, 12nK,,; mi, and K are laser intensity, critical density,ion mass, and Spitzer���s heat conduction coefficient. This result remains valid for finite Zit,h ough the numerical factor in d$/dt is different. Shorter wavelength lasers and higher 4 plasmas allow faster rising pulses below transition.

Resonant absorption in a plasma step profile

Resonant absorption of p-polarized light shined on a plane-layered plasma with a step profile, is discussed as a function of wavelength (or critical density n,) of the light: for simplicity the incidence angle is assumed small. If n, lies within or above the step, the absorption A is given by Ginzburg���s result modified by strong reflections at the foot and top of the step. The absorption above is total for particular values of nc and U. For n, crossing the top of the density step the absorption is not monotonical: it exhibits a minimum that vanishes for zero radius of curvature U there and zero collision frequency 1��� (A - Iln VI-���). The results are applied to the profile produced by irradiating a solid target with a high-intensity pulse that steepens the plasma by radiation pressure.

Plasma kinetics issues in an ESA study for a plasma laboratory in space

A study supported by the European Space Agency (ESA), in the context of its General Studies Programme, performed an investigation of the possible use of space for studies in pure and applied plasma physics, in areas not traditionally covered by ���space plasma physics���. A set of experiments have been identified that can potentially provide access to new phenomena and to allow advances in several fields of plasma science. These experiments concern phenomena on a spatial scale (101���104 m) intermediate between what is achievable on the ground and the usual solar system plasma observations. Detailed feasibility studies have been performed for three experiments: active magnetic experiments, largescale discharges and long tether���plasma interactions. The perspectives opened by these experiments are discussed for magnetic reconnection, instabilities, MHD turbulence, atomic excited states kinetics, weakly ionized plasmas,plasma diagnostics, artificial auroras and atmospheric studies. The discussion is also supported by results of numerical simulations and estimates.

The ESA "Plasma Laboratory in Space" study

The European Space Agency has initiated, in the context of its General Studies Programme, a study of the possible use of space for studies in pure and applied plasma physics, in areas not traditionally covered by ���space plasma physics���. A team of experts has been set-up to review a broad range of area including industrial plasma physics and pure plasma physics, astrophysical and solar-terrestrial areas. A set of experiments have been identified that can potentially provide access to new phenomena and to allow advances in several fields of plasma science. These experiments concern phenomena on spatial scale (102 to104 m) intermediate between what is achievable on ground experiment and usual solar system plasma observations.

Plasma Heme Oxygenase-1 in Patients Resuscitated from out-of-Hospital Cardiac Arrest

Heme oxygenase-1 (HO-1) is an enzyme induced by hypoxia and reperfusion injury, and is associated with organ dysfunction in critically ill patients. Patients resuscitated from out-of-hospital cardiac arrest (OHCA) are subjected to hypoxemia, brain injury, and organ dysfunction. Accordingly, we studied HO-1 among these patients. A total of 143 OHCA patients resuscitated from a shockable initial rhythm and admitted to an ICU were included, with plasma HO-1 measured at ICU admission and at 24���h. We analyzed the associations between plasma HO-1 and time to return of spontaneous circulation (ROSC), 90-day mortality, and 12-month Cerebral Performance Category (CPC). HO-1 plasma concentrations were higher after OHCA compared with controls. HO-1 concentrations at admission and on day 1 associated with ROSC (P���=���0.002 to P���=���0.003). Admission and day 1 HO-1 plasma concentrations were higher in 90-day non-survivors than in survivors (P���=���0.017, 0.026). In addition, poor neurological outcome (CPC 3-5) was associated with higher HO-1 plasma levels at admission (P���=���0.024). Admission plasma HO-1 levels had an AUC of 0.623 to predict 90-day mortality and an AUC of 0.611 to predict CPC 3 to 5. In conclusion, we found that higher HO-1 plasma levels are associated with longer ROSC and poor long-term outcome.

A review of plasma endothelin-1 levels in CABG patient group

Introduction: Endothelin-1 is a potent vasoconstricting growth peptide. In physiologic conditions basal levels maintain vascular homeostasis, conversely in pathological situations it may be expressed in response to chronic and acute vascular injury. Elevated levels of plasma ET-1 have been identified in sub-populations at risk of ischaemic heart disease (IHD) including smokers, diabetics and hyerlipidaemic subjects and in patients with atherosclerotic disease. This peptide may be chronically expressed, such as in congestive heart failure where it has been used as a prognostic marker of disease severity and also acutely, after cardiac revascularisation surgery, possibly as a result of endothelial injury and ischaemia. Aims: The objectives of this study were to (1) identify basal endothelin-1 concentrations in a young healthy control group with no risk factors for IHD (control group 1); (2) to compare; (1) venous plasma ET-1 levels preoperatively and post-operatively in patients undergoing CABG surgery, (3) to compare pre-operative plasma ET-1 levels from the CABG group with an age and gender matched control group (control group 2) and (4) combine all three groups to assess correlations between plasma ET-1 and the various risk factors for IHD, including smoking, hypertension, hyperlipidemia, diabetes and family history. Methods: Venous specimens were collected in chilled EDTA tubes and samples measured using an ELISA assay (Biomedica), following the standard protocol for human EDTA plasma. Results: Forty CABG patients (5F, 35M, mean age 66 yrs), 15 control group 1 subjects (8F, 7M, mean age 29 yrs) and 30 control group 2 subjects (5F, 25M, mean age 61 yrs) participated in the study. No significant difference was detected in plasma ET-1 levels between the controls (1) and (2), and the CABG group, where plasma ET-1 levels were 3.37+/ 5.19 pmol/L, 1.99+/3.74 pmol/L and 1.28+/1.27 pmol/L, respectively. There was a non-significant elevation in post-op ET-1 plasma in comparison with the pre-op levels (2.50+/0.51 Vs 1.45+/6.44). There were also no statistical correlation between risk factors for IHD including smoking, hypertension, NIDDM, hyperlipidemia or family history when data from both patient and controls groups was merged. Conclusion: Contrary to other findings, plasma ET-1 does not appear to a valid marker for IHD or factors which are strongly associated with the pathogenesis of this disease.

Modernizing Legacy Physics Applications for Reuse in Web and SOA

This paper concerns the application of recent information technologies for creating a software system for numerical simulations in the domain of plasma physics and in particular metal vapor lasers. The presented work is connected with performing modernization of legacy physics software for reuse on the web and inside a Service-Oriented Architecture environment. Applied and described is the creation of Java front-ends of legacy C++ and FORTRAN codes. Then the transformation of some of the scientific components into web services, as well as the creation of a web interface to the legacy application, is presented. The use of the BPEL language for managing scientific workflows is also considered.

Magnetic field generation during intense laser channelling in underdense plasma

Channel formation during the propagation of a high-energy (120 J) and long duration (30 ps) laser pulse through an underdense deuterium plasma has been spatially and temporally resolved via means of a proton imaging technique, with intrinsic resolutions of a few micron and a few ps, respectively. Conclusive proof is provided that strong azimuthally symmetric magnetic fields with a strength of around 0.5 MG are created inside the channel, consistent with the generation of a collimated beam of<br/>relativistic electrons. The inferred electron beam characteristics may have implications for the cone-free fast-ignition scheme of inertial confinement fusion

Ion-acoustic envelope modes in a degenerate relativistic electron-ion plasma

<p>A self-consistent relativistic two-fluid model is proposed for one-dimensional electron-ion plasma dynamics. A multiple scales perturbation technique is employed, leading to an evolution equation for the wave envelope, in the form of a nonlinear Schr��dinger type equation (NLSE). The inclusion of relativistic effects is shown to introduce density-dependent factors, not present in the non-relativistic case - in the conditions for modulational instability. The role of relativistic effects on the linear dispersion laws and on envelope soliton solutions of the NLSE is discussed.</p>