The rabbit blood shunt subarachnoid haemorrhage model.

The recently introduced rabbit blood shunt subarachnoid haemorrhage model is based on the two standard procedures of subclavian artery cannulation and transcutaneous cisterna magna puncture. An extracorporeal shunt placed in between the arterial system and the subarachnoid space allows examiner-independent SAH in a closed cranium. Despite its straightforwardness, it is worth examining some specific features and characteristics of the model. We outline technical considerations to successfully perform the model with minimal mortality and morbidity. In addition, we discuss outcome measures, advantages and limitations, and the applicability of the model for the study of early brain injury and delayed cerebral vasospasm after SAH.

Laparoscopically assisted ventriculoperitoneal shunt placement: a prospective randomized controlled trial

OBJECT In ventriculoperitoneal (VP) shunt surgery, laparoscopic assistance can be used for placement of the peritoneal catheter. Until now, the efficacy of laparoscopic shunt placement has been investigated only in retrospective and nonrandomized prospective studies, which have reported decreased distal shunt dysfunction rates in patients undergoing laparascopic placement compared with mini-laparotomy cohorts. In this randomized controlled trial the authors compared rates of shunt failure in patients who underwent laparoscopic surgery for peritoneal catheter placement with rates in patients who underwent traditional mini-laparotomy. METHODS One hundred twenty patients scheduled for VP shunt surgery were randomized to laparoscopic surgery or mini-laparotomy for insertion of the peritoneal catheter. The primary endpoint was the rate of overall shunt complication or failure within the first 12 months after surgery. Secondary endpoints were distal shunt failure, overall complication/ failure, duration of surgery and hospitalization, and morbidity. RESULTS The overall shunt complication/failure rate was 15% (9 of 60 cases) in the laparoscopic group and 18.3% (11 of 60 cases) in the mini-laparotomy group (p = 0.404). Patients in the laparoscopic group had no distal shunt failures; in contrast, 5 (8%) of 60 patients in the mini-laparotomy group experienced distal shunt failure (p = 0.029). Intraoperative complications occurred in 2 patients (both in the laparoscopic group), and abdominal pain led to catheter removal in 1 patient per group. Infections occurred in 1 patient in the laparoscopic group and 3 in the mini-laparotomy group. The mean durations of surgery and hospitalization were similar in the 2 groups. CONCLUSIONS While overall shunt failure rates were similar in the 2 groups, the use of laparoscopic shunt placement significantly reduced the rate of distal shunt failure compared with mini-laparotomy.

Interventional Laser-assisted Extraction of an Infected Trapped Ventriculoatrial Shunt Based on Techniques for Pacemaker Lead Explantation.

We present a case of successful interventional laser-assisted extraction of an endovascularly trapped long-term implanted ventriculoatrial shunt in a patient with shunt-associated septicemia. This approach is based on modified techniques for explantation of pacemaker leads and might be considered an additional option for extraction of otherwise nonremovable trapped endovascular catheters in experienced centers.

High isolation series-shunt photoconductive microwave switch

This article presents a wide band compact high isolation photoconductive switch, which is based on the series-shunt switch design with three photoconductive switches made of diced high-resistivity silicon wafer placed over a microstrip gap and activated by 808-nm near-infrared laser diodes. The switch shows an insertion loss of 1.2 dB and an isolation of 44.8 dB at 2 GHz. It is easy to operate and control by light, high-speed, electromagnetically transparent and it does not require any biasing circuits.

Cerebral energetics and the glycogen shunt: Neurochemical basis of functional imaging

Positron-emission tomography and functional MRS imaging signals can be analyzed to derive neurophysiological values of cerebral blood flow or volume and cerebral metabolic consumption rates of glucose (CMRGlc) or oxygen (CMRO2). Under basal physiological conditions in the adult mammalian brain, glucose oxidation is nearly complete so that the oxygen-to-glucose index (OGI), given by the ratio of CMRO2/CMRGlc, is close to the stoichiometric value of 6. However, a survey of functional imaging data suggests that the OGI is activity dependent, moving further below the oxidative value of 6 as activity is increased. Brain lactate concentrations also increase with stimulation. These results had led to the concept that brain activation is supported by anaerobic glucose metabolism, which was inconsistent with basal glucose oxidation. These differences are resolved here by a proposed model of glucose energetics, in which a fraction of glucose is cycled through the cerebral glycogen pool, a fraction that increases with degree of brain activation. The “glycogen shunt,” although energetically less efficient than glycolysis, is followed because of its ability to supply glial energy in milliseconds for rapid neurotransmitter clearance, as a consequence of which OGI is lowered and lactate is increased. The value of OGI observed is consistent with passive lactate efflux, driven by the observed lactate concentration, for the few experiments with complete data. Although the OGI changes during activation, the energies required per neurotransmitter release (neuronal) and clearance (glial) are constant over a wide range of brain activity.

Preliminary study of shunt related death in paediatric patients

Hydrocephalus is a condition commonly encountered in paediatric and adult neurosurgery and cerebrospinal fluid (CSF) shunting remains the treatment of choice for many cases. Despite improvements in shunt technology and technique, morbidity and mortality remain. The incidence of early shunt obstruction is high with later failures seen less frequently. This review aims to examine mortality associated with mechanical failure of CSF shunts within Queensland. Neurosurgical and Intensive Care databases were reviewed for cases of mortality associated with shunt failure. Eight cases were identified between the years of 1992 and 2002 with the average age at death 7.7 years. Deaths occurred on average 2 years after last shunt revision. Seven of the eight patients lived outside the metropolitan area. Shunting remains an imperfect means of treating hydrocephalus. Mortality may be encountered at any time post surgery and delays to surgical intervention influence this. Alternative measures such as third ventriculostomy or the placement of a separate access device should be considered. In the event of emergency, a spinal needle could be used to access the ventricle along the course of the ventricular catheter. (C) 2004 Elsevier Ltd. All rights reserved.

Exit ventriculoperitoneal shunt; enter endoscopic third ventriculostomy (ETV): contemporary views on hydrocephalus and their implications on management

Hydrocephalus has been known to affect humans since the birth of human medicine as it is described by Hippocrates. The management of this condition is however still dodged by challenges due to a poor understanding of its pathophysiology. The ventriculoperitoneal shunt presents considerable problems especially with respect to infection and shunt malfunction. Low income countries, that currently face the greater burden of paediatric hydrocephalus. experience an increased challenge with ventriculoperitoneal shunts due to a shortage of qualified personnel to handle shunt complications. Recent advances in neuro-endoscopic surgery have presented opportunities for alternative treatment options for hydrocephalus such as endoscopic third ventriculostomy (ETV). This paper explores the alternative views in the pathophysiology of hydrocephalus and how they explain the effectiveness of ETV in treating hydrocephalus arising from a variety of causes.

Development of diagnostic and prognostic algorithms for SF6 puffer circuit breakers from transient waveforms : a validation proposal

- This paper presents a validation proposal for development of diagnostic and prognostic algorithms for SF6 puffer circuit-breakers reproduced from actual site waveforms. The re-ignition/restriking rates are duplicated in given circuits and the cumulative energy dissipated in interrupters by the restriking currents. The targeted objective is to provide a simulated database for diagnosis of re-ignition/restrikes relating to the phase to earth voltage and the number of re-ignition/restrikes as well as estimating the remaining life of SF6 circuit-breakers. The model-based diagnosis of a tool will be useful in monitoring re-ignition/restrikes as well as predicting a nozzle’s lifetime. This will help ATP users with practical study cases and component data compilation for shunt reactor switching and capacitor switching. This method can be easily applied with different data for the different dielectric curves of circuit breakers and networks. This paper presents modelling details and some of the available cases, required project support, the validation proposal, the specific plan for implementation and the propsed main contributions.

Performance study of two different compensating devices in a custom power park

Simulation study of a custom power park (CPP) is presented. It is assumed that the park contains unbalanced and nonlinear loads in addition to a sensitive load. Two different types of compensators are used separately to protect the sensitive load against unbalance and distortion caused by the other loads. It has been shown that a shunt compensator can regulate the voltage of the CPP bus, whereas the series compensator can only regulate the sensitive load terminal voltage. Additional issues such as the load transfer through a static transfer switch, detection of sag/fault etc. are also discussed. The concepts are validated through PSCAD/EMTDC simulation studies on a sample distribution system.

Power Quality Improvement Using Interline Voltage Controller

The concept of an interline voltage controller (IVOLCON) to improve the power quality in a power distribution system is discussed. An IVOLCON consists of two shunt voltage source converters (VSCs) that are joined through a common dc bus. The VSCs are connected to two different feeders. The main aim of the IVOLCON is to control the PCC (Point of Common Coupling) bus voltages of the two feeders to pre-specified magnitudes. The phase angles of the PCC bus voltages are obtained such that the voltage across the common dc link remains constant. The structure, control and capability of the IVOLCON are described. The efficacy of the proposed configuration has been verified through simulation studies using PSCAD/EMTDC for voltage sags and feeder outage

Thermal studies of D.C. traction motors

This paper describes a thorough thermal study on a fleet of DC traction motors which were found to suffer from overheating after 3 years of full operation. Overheating of these traction motors is attributed partly because of the higher than expected number of starts and stops between train terminals. Another probable cause of overheating is the design of the traction motor and/or its control strategy. According to the motor manufacturer, a current shunt is permanently connected across the motor field winding. Hence, some of the armature current is bypassed into the current shunt. The motor then runs above its rated speed in the field weakening mode. In this study, a finite difference model has been developed to simulate the temperature profile at different parts inside the traction motor. In order to validate the simulation result, an empty vehicle loaded with drums of water was also used to simulate the full pay-load of a light rail vehicle experimentally. The authors report that the simulation results agree reasonably well with experimental data, and it is likely that the armature of the traction motor will run cooler if its field shunt is disconnected at low speeds