Bioimpedance as a predictor of survival in renal failure and associated comorbidities.

Background: Renal failure requiring dialysis is associated with a high mortality. One of the contributing causes is overhydration. Overhydration can be assessed by bioimpedance analysis (BIA)– the non-invasive electrical measure of small current through the tissues that estimates the proportion of fluid that is intracellular water (ICW, typically muscle which is healthy) and extracellular (ECW, which in excess causes tissue oedema and is potentially dangerous). Several studies indicate that a extracellular water to total body water (TBW) ratio is associated with increased risk of death in dialysis patients but it is not clear if this is independent of other risk factors for death, namely comorbidity. Aims and objectives: To establish the prognostic value of BIA in the prediction of survival on dialysis in the context of other known predictors of survival or hospitalisation. With further analysis of the applicability of the same scenario to heart failure patients. Methodology: To conduct a systematic review using a standardised approach including a prespecified research question, search terms and criteria for study inclusion. With independent selection for inclusion in the study and quality appraisal by multiple authors with different backgrounds and experience. Results: 2701 studies identified by literature search, plus an additional 4 through reference checking. 38 papers included in final analysis, 4 of which were regarding heart failure cohorts. Analysis of the research shows that BIA is an independent predictor of mortality. Conclusion: BIA shown to be an independent predictor of mortality in dialysis patients, further research needed to extrapolate to heart failure (HF) populations

Energy dynamics in a simulation of LAPD turbulence

Energy dynamics calculations in a 3D fluid simulation of drift wave turbulence in the linear Large Plasma Device (LAPD) [W. Gekelman et al., Rev. Sci. Inst. 62, 2875 (1991)] illuminate processes that drive and dissipate the turbulence. These calculations reveal that a nonlinear instability dominates the injection of energy into the turbulence by overtaking the linear drift wave instability that dominates when fluctuations about the equilibrium are small. The nonlinear instability drives flute-like ($k_\parallel = 0$) density fluctuations using free energy from the background density gradient. Through nonlinear axial wavenumber transfer to $k_\parallel \ne 0$ fluctuations, the nonlinear instability accesses the adiabatic response, which provides the requisite energy transfer channel from density to potential fluctuations as well as the phase shift that causes instability. The turbulence characteristics in the simulations agree remarkably well with experiment. When the nonlinear instability is artificially removed from the system through suppressing $k_\parallel=0$ modes, the turbulence develops a coherent frequency spectrum which is inconsistent with experimental data

Blob dynamics in TORPEX poloidal null configurations

Three dimensional blob dynamics are simulated in X-point magnetic configurations in the TORPEX device via a non-field-aligned coordinate system, using an isothermal model which evolves density, vorticity, parallel velocity and parallel current density. By modifying the parallel gradient operator to include perpendicular perturbations from poloidal field coils, numerical singularities associated with field aligned coordinates are avoided. A comparison with a previously developed analytical model is performed and an agreement is found with minimal modification. Experimental comparison determines that the null region can cause an acceleration of filaments due to increasing connection length, but this acceleration is small relative to other effects, which we quantify. Experimental measurements are reproduced, and the dominant acceleration mechanism is identified as that of a developing dipole in a moving background. Contributions from increasing connection length close to the null point are a small correction