Glucose, lactate, and shuttling of metabolites in vertebrate retinas.

The vertebrate retina has specific functions and structures that give it a unique set of constraints on the way in which it can produce and use metabolic energy. The retina's response to illumination influences its energy requirements, and the retina's laminated structure influences the extent to which neurons and glia can access metabolic fuels. There are fundamental differences between energy metabolism in retina and that in brain. The retina relies on aerobic glycolysis much more than the brain does, and morphological differences between retina and brain limit the types of metabolic relationships that are possible between neurons and glia. This Mini-Review summarizes the unique metabolic features of the retina with a focus on the role of lactate shuttling.

Re-evaluating the National Subarachnoid Haemorrhage study (2006) from a Patient-Related-Outcome-Measure perspective: comparing fiscal outcomes of Treatment-as-Usual with an enhanced service.

BACKGROUND: Subarachnoid haemorrhage (SAH) is neurological catastrophe, creating major disruption for patient and family, hence the importance of considering Patient-Related-Outcome-Measures (PROM). This study uses the National Study of SAH (2006) to explore any fiscal benefits to patients and NHS if they had an enhanced Neuro-Vascular-Specialist-Nurse (NVSN) service compared to Treatment-as-Usual (TAU). METHOD: Ensuring total confidentiality, clinical data from the National Study (n=2397) were matched with regional clinical data of a TAU (n=137) and prospective NVSN service (n=184) patients. The TAU and NVSN fiscal outcomes were projected onto the National Study patients to provide estimates of the potential benefits that could accrue nationally from a NVSN service based upon length of stay and earlier return to work of patients and carers. RESULTS: There were substantial benefits for NVSN cohort related to shorter time in hospital, reduced family disruption, earlier return to work and fiscal benefits to family and the NHS. NVSN patients and carers potential savings were estimated at £ 8.097 million and £ 2.492 million to the service, £ 10.497 million overall. PRACTICE IMPLICATIONS: This PROM approach allows the 'patient's voice' to be heard, which facilitates speedier patient and family recovery, showing that an integrated treatment approach in 'high tech' neuro-surgery is cost-effective.

Variation in outcome after subarachnoid hemorrhage: a study of neurosurgical units in UK and Ireland.

BACKGROUNDS AND PURPOSE: The purpose of the study was to describe the characteristics, management, and outcomes of patients with confirmed aneurysmal subarachnoid hemorrhage and to compare outcomes across neurosurgical units (NSUs) in the UK and Ireland. METHODS: A cohort of patients admitted to NSUs with subarachnoid hemorrhage between September 14, 2001 and September 13, 2002 was studied longitudinally. Information was collected to characterize clinical condition on admission and treatment. Death or severe disability, defined by the Glasgow Outcome Score-Extended, was ascertained at 6 months. RESULTS: Data for 2397 patients with a confirmed aneurysm and no coexisting neurological pathology were collected by all 34 NSUs in the UK and Ireland. Aneurysm repair was attempted in 2198 (91.7%) patients (surgical clipping, 57.7%; endovascular coiling, 41.2%; other repair, 1.0%). Most patients (65.0%) were admitted to the NSU on the same day or the day after their hemorrhage; 32.0% of treated patients had the aneurysm repaired on the day of admission to the NSU (day 0), day 1 or day 2 and a further 39.3% by day 7. Glasgow Outcome Score-Extended at 6 months was obtained for 90.6% of patients (2172), of whom 38.5% had an unfavorable outcome. The median risk of an unfavorable outcome for all patients was 31% (5(th) and 95(th) percentiles, 12% and 83%), depending on prerepair prognostic factors. After adjustment for case-mix, the percentage of patients with an unfavorable outcome in each NSU did not differ significantly from the overall mean. CONCLUSIONS: In this study that collected representative data from the UK and Ireland, there was no evidence that the performance of any NSU differed from the average.

Horizontal stent-assisted coil embolisation of wide-necked intracranial aneurysms with the Enterprise stent--a case series with early angiographic follow-up.

INTRODUCTION: The purpose of the study is to describe our experience in eight cases of horizontal stenting across the circle of Willis in patients with terminal aneurysms. METHODS: Eight patients were treated with horizontal stent placement and aneurysm coiling. All aneurysms had highly unfavourable dome to neck ratios. All patients were followed up with digital subtraction angiography at 3-12 months following treatment. RESULTS: The Enterprise stent was successfully deployed horizontally in vessels of less than 2-mm diameter with no stent occlusion. Neurological complications occurred in one patient. Immediate and follow-up angiographic results were encouraging with six stable occlusions at 6 months. There was one asymptomatic case of in-stent stenosis and one case of late organised in-stent thrombus. CONCLUSIONS: Horizontal deployment of the Enterprise stent to assist coil embolisation of wide-necked terminal aneurysms is feasible. This device can be navigated via relatively small communicating arteries, in cases with favourable anatomy. Early angiographic results were favourable; however, longer-term follow-up will be required.

Spine surgery training and competence of European neurosurgical trainees.

BACKGROUND: Little is known about the nature of spine surgery training received by European neurosurgical trainees during their residency and the level of competence they acquire in dealing with spinal disorders. METHODS: A three-part questionnaire entailing 32 questions was devised and distributed to the neurosurgical trainees attending the EANS (European Association of Neurosurgical Societies) training courses of 2004. RESULTS: Of 126 questionnaires, 32% were returned. The majority of trainees responding to the questionnaire were in their final (6(th)) year of training or had completed their training (60.3% of total). Spinal surgery training in European residency programs has clear strengths in the traditional areas of microsurgical decompression for spinal stenosis and disc herniation (77-90% competence in senior trainees). Deficits are revealed in the management of spinal trauma (34-48% competence in senior trainees) and spinal conditions requiring the use of implants and anterior approaches, with the exception of anterior cervical stabilisation. CONCLUSIONS: European neurosurgical trainees possess incomplete competence in dealing with spinal disorders. EANS trainees advocate the development of a postresidency spine subspecialty training program.

Biomechanical efficiency is impaired in patients with chronic heart failure.

INTRODUCTION: Patients with chronic heart failure (CHF) have a lower peak oxygen consumption (pVO2) than normal subjects, and for a given quantity of work, have a lower total oxygen consumption (VO2) than controls. This apparent increase in biomechanical efficiency (BE) might be due to a higher proportion of anaerobic metabolism which, although leading to lower VO2 during steady state exercise, must be compensated for during recovery. METHODS: 13 patients with stable CHF and 12 controls underwent peak cycle exercise testing followed by three separate steady state exercise tests at 15%, 25% and 50% of the peak workload in random order. Oxygen consumption at steady state, deficit (during onset) and debt (during recovery) were calculated. BE was estimated as the total oxygen required to perform a given quantity of work. RESULTS: Patients had lower pVO2 and peak workload than control subjects. Absolute oxygen deficit and debt as a percentage of total oxygen consumed during the steady state tests was the same in both groups. However, once controlled for workload, VO2 deficit, debt and uptake at steady state were greater in patients than controls for the tests at 15% and 25% of peak. BE was inversely related to peak oxygen consumption in controls and patients. CONCLUSIONS: Patients with CHF have impaired BE at low work loads when compared with normal subjects.

A new approach to reconstruction models of dendritic branching patterns.

Quantitative models for characterising the detailed branching patterns of dendritic trees aim to explain these patterns either in terms of growth models based on principles of dendritic development or reconstruction models that describe an existing structure by means of a canonical set of elementary properties of dendritic morphology, which when incorporated into an algorithmic procedure will generate samples of dendrites that are statistically indistinguishable in both canonical and emergent features from those of the original sample of real neurons. This article introduces a conceptually new approach to reconstruction modelling based on the single assumption that dendritic segments are built from sequences of units of constant diameter, and that the distribution of the lengths of units of similar diameter is independent of location within a dendritic tree. This assumption in combination with non-parametric methods for estimating univariate and multivariate probability densities leads to an algorithm that significantly reduces the number of basic parameters required to simulate dendritic morphology. It is not necessary to distinguish between stem and terminal segments or to specify daughter branch ratios or dendritic taper. The procedure of sampling probability densities conditioned on local morphological features eliminates the need, for example, to specify daughter branch ratios and dendritic taper since these emerge naturally as a consequence of the conditioning process. Thus several basic parameters of previous reconstruction algorithms become emergent parameters of the new reconstruction process. The new procedure was applied successfully to a sample of 51 interneurons from lamina II/III of the spinal dorsal horn.

Metabolic gas kinetics depend upon the level of exercise performed.

BACKGROUND: The kinetics of oxygen and carbon dioxide at the onset of and recovery from exercise are slowed in patients with chronic heart failure (CHF). The aim of the present study was to establish whether the kinetics of O2 are influenced by the work rate. METHODS: Thirteen CHF patients and 12 control subjects underwent bicycle-based peak exercise testing with metabolic gas exchange analysis. Each subject then exercised at 15%, 25% and 50% of the maximal workload achieved until reaching steady state. Time constants for onset (T(onset)) and offset (T(offset)) for O2 uptake and CO2 output were correlated to the workload and the percentage of peak V(O2) performed during the steady state tests. RESULTS: Patients had lower peak oxygen uptake (pV(O2)) and the relation between ventilation and carbon dioxide output was steeper in patients than controls. T(offset) for both oxygen (O2) and carbon dioxide (CO(2)) from peak exercise was significantly greater in the patients than the controls and correlated with peak V(O2) (r=0.56, p<0.005 and r=0.58, p<0.005). T(onset) and T(offset) for O2 were increased in patients for each of the steady state tests and peak V(O2) correlated with T for recovery of O2 (r=0.44; p<0.05 from 15%, r=0.35; p= or <0.05 from 25%, and r=0.54; p<0.01 from 50%). There was a correlation between the T(onset) (r=0.42; p<0.0005 for O2 and r=0.23; p<0.05 for CO2) and T(offset) (r=0.49; p<0.0001 for O2 and r=0.42; p<0.0005 for CO2) and oxygen uptake as a percentage of peak exercise. CONCLUSIONS: This study demonstrates that the time constants of onset and offset for oxygen are dependent upon the degree of exertion performed relative to the individual's peak capacity.

Neurosurgical training in the United kingdom and ireland: assessing progress and attainment.

OBJECTIVE: To review neurosurgical training in the United Kingdom and Ireland in the past decade and the methods used to monitor training and assess trainee competence. METHODS: A database was compiled with data from 1990 to 2000 on behalf of the Specialist Advisory Committee in Neurosurgery from trainee logbook operative totals submitted on achieving accreditation or receiving the Certificate of Completion of Surgical Training. RESULTS: During the 11-year period, 109 trainees achieved accreditation or Certificate of Completion of Surgical Training. The median duration of training, including research, was 6.1 years. The total training duration per year did not change overall, although results suggested an increasing trend in the duration of clinical training (excluding research) from 4.8 to 5.6 years since 1997. The median age at accreditation or at receipt of Certificate of Completion of Surgical Training was 35 years 7 months. At completion of training, the Specialist Advisory Committee used operative totals in addition to reports from trainers to analyze the trainees' competence. Despite changes to the training system and a reduction in hours of work, the quality of training, as reflected by median operative totals, did not change during the decade. The database also permitted assessment of operative experience gained within each training program. CONCLUSION: The duration of training and training standards in terms of operative experience have remained constant during the past decade. Operative totals provide an objective method of assessing trainee progress and attainment and enable a comparison of experience offered by different training programs. An alternative method of assessing trainee operative competence that can be used in conjunction with median operative totals is proposed.

Perimesencephalic nonaneurysmal subarachnoid hemorrhage caused by jugular venous occlusion: case report.

OBJECTIVE: The cause of perimesencephalic nonaneurysmal subarachnoid hemorrhage remains unknown. We describe a patient in whom jugular venous occlusion preceded the occurrence of perimesencephalic nonaneurysmal subarachnoid hemorrhage. This finding supports the theory that the source of the hemorrhage is venous in origin. CLINICAL PRESENTATION: A 25-year-old man presented with sudden onset of headache after his head was held in a headlock during a playful fight 48 hours before the ictus. His computed tomographic (CT) scan on admission demonstrated a perimesencephalic pattern of subarachnoid hemorrhage. CT angiography excluded the presence of an underlying aneurysm or vascular malformation but showed bilateral jugular venous obstruction with hematoma surrounding the right internal jugular vein. Magnetic resonance imaging and a 4-vessel cerebral angiogram confirmed the CT angiographic findings. INTERVENTION: The patient was observed as an inpatient and had no complication of his hemorrhage. Follow-up at 5 months with CT angiography showed resolution of his neck hematoma and reopening of his internal jugular veins. CONCLUSION: The presence of acute jugular venous occlusion as a cause of perimesencephalic nonaneurysmal subarachnoid hemorrhage supports a venous origin of hemorrhage.

Evaluation of the use of the X-ray department with regard to plain chest radiography on acute general medical admissions in the context of recently introduced UK guidelines.

All requests for radiographs in the United Kingdom should comply with Royal College of Radiologists (RCR) guidelines, which aim to encourage more appropriate use of diagnostic radiology and so reduce the number of clinically unhelpful radiographic examinations. The aim of this study was to evaluate the use of the X-ray department during the normal working day and out of hours with regard to plain chest radiography on acute general medical admissions. A prospective study was performed using a questionnaire filled in by the requesting clinician, radiographer, and ward staff. Of 265 forms were used in a 1-month period, 221 were completed satisfactorily, and the data from these were used in the study. The median time taken for the chest X-ray to be performed was 80 min; once performed it took a median of 9 min to be returned to the ward. The requesting clinician took a median of 25 min to review the chest X-ray. However, the most striking statistic is that only 22% of the chest X-ray taken were reviewed by the junior doctors; the other 78% were looked at for the first time on the "post-take" ward rounds. The questionnaire form allowed requests to be graded as urgent, "soon," and nonurgent. There was very little difference in how long it took X-rays in these categories to be performed. This study shows that requests for the chest X-rays on acute medical admissions are more or less routine. Even though many are requested and performed as urgent examinations, 78% of all chest X-rays on these patients are not reviewed until the following morning. While many of these examinations may be deemed necessary, it is unlikely that all will comply with the RCR guidelines.

Investigation into the mechanisms of vagus nerve stimulation for the treatment of intractable epilepsy, using 99mTc-HMPAO SPET brain images.

Vagus nerve stimulation (VNS) has gained recognition as a treatment for refractory epilepsies where surgical treatment is not possible. While it appears that this treatment is effective in some patients, the mechanism of action is not clearly understood. The purpose of this study was to clarify findings of other positron emission tomography and single-photon emission tomography (SPET) investigations by measuring the acute effect of VNS on patients who have normal cerebral anatomy on magnetic resonance imaging and who have not previously been exposed to VNS. We investigated six subjects (two males and four females, mean age 29.5 years, range 21-39 years) with intractable epilepsy. One patient had primary generalised epilepsy causing generalised tonic-clonic seizures; the remaining five patients had localisation-related epilepsy causing complex partial seizures. SPET imaging was performed using 250 MBq of (99m)Tc-HMPAO and a four-scan paradigm - two with and two without stimulation. The stimulation began at VNS current levels of 0.25 mA and was increased according to the limit of patients' tolerance, usually defined by coughing or discomfort. The stimulating waveform was of continuous square wave pulses of 500 micro s duration at 30 Hz. Image analysis was by SPM99. Reduced perfusion during stimulation was observed in the ipsilateral brain stem, cingulate, amygdala and hippocampus and contralateral thalamus and cingulate. The study provides further evidence of the involvement of the limbic system in the action of vagal nerve stimulation.

The non-invasive detection of intracranial aneurysms: are neuroradiologists any better than other observers?

Can non-neuroradiologists detect intracranial aneurysms as well as neuroradiologists, using CT and MR angiography? Sixty patients undergoing intra-arterial digital subtraction angiography (IADSA) to detect aneurysms also underwent computed tomographic angiography (CTA) and time-of-flight magnetic resonance angiography (MRA). Consensus review of IADSA by two neuroradiologists was the reference standard. Two neuroradiologists, a neurosurgeon, a neuroradiographer and a general radiologist blinded to IADSA, plain CT and clinical data, independently reviewed hard-copy base and reconstructed maximum intensity projection images of the CTA and MRA studies. Thirty patients had a total of 63 aneurysms, 71.4% were