Aspects on measuring electrical current utilizing magnetic zero-flux technique

The utilization of high accuracy measurements of electrical quantities is a prerequisite for the development of modern society. Generally, measurements serve different purposes and hence the criteria for the measurement equipment and method are different. For example, the demands are mild if the application is the continuous monitoring of the power grid, more finely tuned for measuring methods used in research and development, and often challenging in the case of certified measuring methods adequate for calibration and accreditation. RISE Research Institutes of Sweden (former SP Technical Research Institute of Sweden) is appointed the National Metrology Institute by the Swedish government for electrical quantities and continuously develops and provides measurement technology for the different needs governed by application.The magnetic zero-flux technique is a non-contact measurement method for electrical AC and DC current and its design principle enables accurate measurements over a large current range. Its advantages come however with the price of a complex but sophisticated design. The zero-flux technique has been utilized for many decades, and there are a number of manufacturers providing commercial systems with somewhat different features.This project is devoted to the further investigation and advancement of some metrological aspects of the magnetic zero-flux technique for AC. Practical laboratory tests on a state-of-the-art zero-flux system are used to create a picture of its properties at higher frequencies than its manufacturer has provided detailed specifications for. Focus is to determine how sensitive the measurement results are to practical arrangements and limitations of the measurement setup. A method and guide to how different configurations of the measurement setup affect the measured results in different frequency ranges is provided. Utilizing this characterization, practical set-ups can be made, as optimal as possible for the frequency range of interest, avoiding time-consuming focus on aspects not relevant for the specific application.The identified aspects of interest are: (i) identifying the source of the measurement error in the zero-flux system’s design and, if possible, minimizing this error by design adjustments, (ii) measurement error and measurement uncertainty of a zero-flux system in presence of geometric asymmetry and disturbance from return or nearby conductors, (iii) simultaneous measurements of sinusoidal signals of different amplitudes, frequencies and phase angles, (iiii) detection of sub-synchronous events, and (v) non-steady state phenomena, like for example transients in the drive line of electrical vehicles. In this thesis, aspects (i) and (ii) above are in focus. Some conclusions can be drawn based on the performed study concerning aspect (iiii), whereas aspects (iii) and (v) remain out of its scope.The initial step of this project was the choice of a generally applicable method for characterization and evaluation of a zero-flux system. The method chosen is the combination of a coaxial primary current path, or as near coaxial as was practically convenient, and a Digital Sampling Watt Meter (DSWM). The method can be utilized for the characterization and evaluation of other zero-flux systems. An investigation was performed to decide from which part of the construction the phase angle error stems. The performed characterization allowed compensating for the errors, making the measurement accuracy greatly improved. Two modifications to the circuitry of the zero-flux systems were introduced and evaluated, both of which yielded improvement of its high frequency characteristics up to 100 kHz. Also the accuracy within the low frequency range (from 10 – 50 Hz) was improved by one of the modifications.The error of a zero-flux measuring system depends on the positioning of its sensor around the conductor carrying the measured current and the geometry of the primary current path. The total error increases with frequency, but which geometric factor that is the most important one varies with frequency. In this study, utilizing sinusoidal primary current, it was found that for 50 Hz, tilt of the sensor and positioning of the connection point for the measurement and zero-flux control cable (rotation) caused the largest effects on the scale factor. De-centring and the distances to different parts of the return conductor were less important in the 50 Hz case. For 25 kHz, de-centring and rotation were the main contributors to scale factor change, while tilt had the smallest measured effect. The total contribution from sensor positioning in the magnetic field to the expanded measurement uncertainty was estimated to 0.0024 % in the 50 Hz case, to 0.0040 % for 1 kHz, to 0.14 % for 10 kHz, and to 0.41 % for 25 kHz

Effects of Growth Hormone and Insulin-Like Growth Factor-1 on Postoperative Muscle and Substrate Metabolism

This study explored if a combined supplementation of GH and IGF-1 had an additive effect on whole body nitrogen economy, energy, substrate and skeletal muscle metabolism following surgical trauma. Patients were randomized to controls (C; n = 10), to GH (0.15 IU/kg/injection) (GH; n = 7) or GH combined with IGF-1 (40 μg/kg/injection) subcutaneously twice a day (GH-IGF-1; n = 9) together with standardized parenteral nutrition. Muscle amino acids, glutathione and the ribosomal pattern reflecting protein synthesis, and nitrogen balance were measured. GH- and GH-IGF-1 groups showed lower urea and higher plasma glucose concentrations. Energy expenditure increased in the GH-group. GH-IGF-1 prevented a decrease in muscle polyribosomes indicating a preserved muscle protein synthesis. In the GH group unaltered BCAA and AAA levels were seen in muscle indicating an unchanged protein breakdown, while the other groups showed increased muscle concentrations postoperatively. Without statistically difference GH marginally improved the nitrogen balance, in terms of higher values, and growth factors improved the nitrogen balance when the shift in urea was taken into account. To conclude, growth factors influences urea metabolism, protein degradation and protein synthesis. There was no clearcut additional effect when combining GH and IGF-1 but the study was probably underpowered to outrule this and effects on nitrogen balance

Early enteral nutrition compared to outcome in critically ill trauma patients at a level one trauma centre

Objectives: The benefit of an early enteral nutrition start in critical ill patients is widely accepted. However, limited published data focus on trauma patients. This study aimed to investigate the effect of early enteral nutrition initiation on length of stay and mortality in an intensive care unit (ICU), as well as explore if enteral nutrition initiation could serve as a prognostic marker in trauma patients.Design: This was a retrospective audit of a prospective ethics-approved database (University of KwaZulu-Natal Biomedical Research Ethics Committee No BE207-09) which compared enteral nutrition to outcome.Setting: The setting was a level 1 trauma ICU in Durban, South Africa.Subjects: The subjects were critically ill trauma patients.Outcome measures: Demographic data, enteral nutrition timing, feed tolerance, and the outcome of early versus late initiation of enteral feeding were the outcome measures.Results: Nine hundred and fifty-two patients were included. Eight hundred and ninety-eight received enteral nutrition and were divided into three subgroups (tertiles T1-T3) according to their Injury Severity Score (ISS). The statistical analysis demonstrated that an early enteral nutrition start had a significant positive effect on both length of stay (13.7 vs. 16.4 days, p-value 0.00315) and mortality (9.5 % vs. 20.7 % p-value 0.0062). A multiple logistic regression model was developed, using multiple variables, to test the factors that affected the outcome. There was a significant effect on length of stay with an early enteral nutrition start in patients with a low to medium ISS (T1), and a highly significant effect on mortality in patients with a low to medium, and high, ISS (T1 and T2). Early initiation of enteral nutrition is strongly favoured in regression analyses.Conclusion: Patients in the trauma ICU benefit from an early enteral nutrition. The model used featuring the three independent variables, i.e. the day on which enteral nutrition is commenced, age and ISS, may serve as a prognostic marker with regard to length of stay and mortality in the ICU.Keywords: enteral nutrition, early initiation, outcome predictio

Complications relating to enteral and parenteral nutrition in trauma patients: a retrospective study at a level one trauma centre in South Africa

Objectives: The aim of the study was to compare the incidence of complications in patients receiving enteral and parenteral nutrition (PN), and review how the early initiation of enteral feeding and early achievement of caloric goal would affect the incidence of complications.Design: The design was a retrospective audit of an ethics-approved prospective trauma registry and electronic medical record.Setting: The setting was a level one trauma centre intensive care unit.Subjects: One thousand and two consecutively treated patients were selected from 1 096 in the database.Outcome measures: Demographic data, nutrition, route of administration, time of initiation and complications in the form of sepsis, pneumonia and feed intolerance, were determined.Results: Patients receiving total PN (TPN) during their length of stay had a hazard ratio of 9.11 for the development of sepsis, compared to patients who were solely fed via the enteral route (p-value <0.001). The patients who reached their nutritional goal late showed a hazard ratio of 2.67 for the development of sepsis, compared to patients who reached the goal early (p-value < 0.001). Patients with late initiation of feeding also had a greater risk of developing sepsis, with a hazard ratio of 2.41, compared to patients with early initiation (p-value < 0.001). Patients achieving the nutritional goal late had a 17.9% increased risk of developing pneumonia (p-value < 0.001).Conclusion: This study confirms previous findings that the use of TPN is a strong predictor of the development of sepsis, compared to enteral nutrition. Causality linkage should be made with caution owing to the study design.Keywords: complications, critical illness, nutrition, trauma, outcom

Randomised trial of glutamine and selenium supplemented parenteral nutrition for critically ill patients

Background: Mortality rates in the Intensive Care Unit and subsequent hospital mortality rates in the UK remain high. Infections in Intensive Care are associated with a 2–3 times increased risk of death. It is thought that under conditions of severe metabolic stress glutamine becomes "conditionally essential". Selenium is an essential trace element that has antioxidant and anti-inflammatory properties. Approximately 23% of patients in Intensive Care require parenteral nutrition and glutamine and selenium are either absent or present in low amounts. Both glutamine and selenium have the potential to influence the immune system through independent biochemical pathways. Systematic reviews suggest that supplementing parenteral nutrition in critical illness with glutamine or selenium may reduce infections and mortality. Pilot data has shown that more than 50% of participants developed infections, typically resistant organisms. We are powered to show definitively whether supplementation of PN with either glutamine or selenium is effective at reducing new infections in critically ill patients. Methods/design: 2 × 2 factorial, pragmatic, multicentre, double-blind, randomised controlled trial. The trial has an enrolment target of 500 patients. Inclusion criteria include: expected to be in critical care for at least 48 hours, aged 16 years or over, patients who require parenteral nutrition and are expected to have at least half their daily nutritional requirements given by that route. Allocation is to one of four iso-caloric, iso-nitrogenous groups: glutamine, selenium, both glutamine & selenium or no additional glutamine or selenium. Trial supplementation is given for up to seven days on the Intensive Care Unit and subsequent wards if practicable. The primary outcomes are episodes of infection in the 14 days after starting trial nutrition and mortality. Secondary outcomes include antibiotic usage, length of hospital stay, quality of life and cost-effectiveness. Discussion: To date more than 285 patients have been recruited to the trial from 10 sites in Scotland. Recruitment is due to finish in August 2008 with a further six months follow up. We expect to report the results of the trial in summer 2009. Trial registration: This trial is registered with the International Standard Randomised Controlled Trial Number system. ISRCTN87144826Not peer reviewedPublisher PD

The etiology and prevention of feeding intolerance paralytic ileus – revisiting an old concept

Gastro-intestinal (G-I) motility is impaired ("paralytic ileus") after abdominal surgery. Premature feeding attempts delay recovery by inducing "feeding intolerance," especially abdominal distention that compromises respiration. Controlled studies (e.g., from Sloan-Kettering Memorial Hospital) have lead to recommendations that patients not be fed soon after major abdominal surgery to avoid this complication

Mechanisms of Endothelial Dysfunction in Resistance Arteries from Patients with End-Stage Renal Disease

The study focuses on the mechanisms of endothelial dysfunction in the uremic milieu. Subcutaneous resistance arteries from 35 end-stage renal disease (ESRD) patients and 28 matched controls were studied ex-vivo. Basal and receptor-dependent effects of endothelium-derived factors, expression of endothelial NO synthase (eNOS), prerequisites for myoendothelial gap junctions (MEGJ), and associations between endothelium-dependent responses and plasma levels of endothelial dysfunction markers were assessed. The contribution of endothelium-derived hyperpolarizing factor (EDHF) to endothelium-dependent relaxation was impaired in uremic arteries after stimulation with bradykinin, but not acetylcholine, reflecting the agonist-specific differences. Diminished vasodilator influences of the endothelium on basal tone and enhanced plasma levels of asymmetrical dimethyl L-arginine (ADMA) suggest impairment in NO-mediated regulation of uremic arteries. eNOS expression and contribution of MEGJs to EDHF type responses were unaltered. Plasma levels of ADMA were negatively associated with endothelium-dependent responses in uremic arteries. Preserved responses of smooth muscle to pinacidil and NO-donor indicate alterations within the endothelium and tolerance of vasodilator mechanisms to the uremic retention products at the level of smooth muscle. We conclude that both EDHF and NO pathways that control resistance artery tone are impaired in the uremic milieu. For the first time, we validate the alterations in EDHF type responses linked to kinin receptors in ESRD patients. The association between plasma ADMA concentrations and endothelial function in uremic resistance vasculature may have diagnostic and future therapeutic implications

Glutamine supplementation

Intravenous glutamine supplementation is standard care when parenteral nutrition is given for critical illness. There are data of a reduced mortality when glutamine supplementation is given. In addition, standard commercial products for parenteral nutrition do not contain any glutamine due to glutamine instability in aqueous solutions. For the majority of critical ill patients who are fed enterally, the available evidence is insufficient to recommend glutamine supplementation. Standard formulation of enteral nutrition contains some glutamine: 2-4 g/L. However, this dose is insufficient to normalize glutamine plasma concentration

Guidelines for Perioperative Care for Emergency Laparotomy Enhanced Recovery After Surgery (ERAS) Society Recommendations: Part 1—Preoperative: Diagnosis, Rapid Assessment and Optimization

BackgroundEnhanced Recovery After Surgery (ERAS) protocols reduce length of stay, complications and costs fora large number of elective surgical procedures. A similar, structured approach appears to improve outcomes, including mortality, for patients undergoing high-risk emergency general surgery, and specifically emergency laparotomy. These are the first consensus guidelines for optimal care of these patients using an ERAS approach.MethodsExperts in aspects of management of the high-risk and emergency general surgical patient were invited to contribute by the International ERAS Society. Pubmed, Cochrane, Embase, and MEDLINE database searches on English language publications were performed for ERAS elements and relevant specific topics. Studies on each item were selected with particular attention to randomized controlled trials, systematic reviews, meta-analyses and large cohort studies, and reviewed and graded using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) system. Recommendations were made on the best level of evidence, or extrapolation from studies on non-emergency patients when appropriate. The Delphi method was used to validate final recommendations. The guideline has been divided into two parts: Part 1—Preoperative Care and Part 2—Intraoperative and Postoperative management. This paper provides guidelines for Part 1.ResultsTwelve components of preoperative care were considered. Consensus was reached after three rounds.ConclusionsThese guidelines are based on the best available evidence for an ERAS approach to patients undergoing emergency laparotomy. Initial management is particularly important for patients with sepsis and physiological derangement. These guidelines should be used to improve outcomes for these high-risk patients

ISSN exercise & sport nutrition review: research & recommendations

Sports nutrition is a constantly evolving field with hundreds of research papers published annually. For this reason, keeping up to date with the literature is often difficult. This paper is a five year update of the sports nutrition review article published as the lead paper to launch the JISSN in 2004 and presents a well-referenced overview of the current state of the science related to how to optimize training and athletic performance through nutrition. More specifically, this paper provides an overview of: 1.) The definitional category of ergogenic aids and dietary supplements; 2.) How dietary supplements are legally regulated; 3.) How to evaluate the scientific merit of nutritional supplements; 4.) General nutritional strategies to optimize performance and enhance recovery; and, 5.) An overview of our current understanding of the ergogenic value of nutrition and dietary supplementation in regards to weight gain, weight loss, and performance enhancement. Our hope is that ISSN members and individuals interested in sports nutrition find this review useful in their daily practice and consultation with their clients