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Biomedical subjects

J D Pickard

Publications and source records attributed to J D Pickard.

At least 19 recordsLinked to original sources
PubMed2006

Intracortically distributed neurovascular coupling relationships within and between human somatosensory cortices.

The coupling of neuronal cellular activity to its blood supply is of critical importance to the physiology of the human brain and has been under discussion for more than a century. Linearity in this relationship has been demonstrated in some animal studies, but evidence is lacking in humans. In this study, we compared scalp evoked potentials and the functional magnetic resonance imaging (fMRI) blood oxygen level-dependent (BOLD) signal from healthy human volunteers with changes in the intensity of a somatosensory stimulus. By weighting the fMRI images according to the evoked potential amplitude at corresponding intensities, we tested for positive and negative covariation between these 2 data sets and the extent to which these were linear. Hemodynamic changes in primary somatosensory cortex covaried positively with neuronal activity in a predominantly linear manner, with a small quadratic contribution. Simultaneously, other cortical areas corresponding to the nonstimulated limbs were found to covary negatively and linearly in the hemispheres ipsilateral and contralateral to the stimulus. These concurrent and bilateral cortical dynamics, as well as the intraregional features of this neurovascular coupling, are both more complex than had been considered to date, with considerable implications.

Adult↗
PubMed2006

Changes over time in cognitive and structural profiles of head injury survivors.

Survivors of traumatic head injury often suffer chronic cognitive deficits. Considerable evidence implicates the cholinergic system in these deficits. Recently, we reported cognitive and structural abnormalities in a cohort of head injured survivors consistent with this hypothesis [see Salmond, C. H., Chatfield, D. A., Menon, D. K., Pickard, J. D., & Sahakian, B. J. (2005). Cognitive Sequelae of Head Injury: Involvement of Basal Forebrain and associated structures. Brain, 128(1), 189-200]. The stability of the cognitive and structural MRI profiles was investigated in a longitudinal study. Twenty-one survivors of moderate-severe head injury completed two comprehensive neuropsychological assessments and two structural MRI scans at least six months apart. A cohort of controls also completed these investigations. The results revealed that the cognitive and structural profiles are relatively stable from six months post-injury forward up to 3 years post-injury. Deficits in memory, attention and reaction time were found, with relative preservation of working memory, consistent with abnormalities in the cholinergic system. These findings suggest that cholinergic enhancers may be an effective treatment for cognitive deficits post-head injury in survivors up to three years post-injury.

Adolescent↗
PubMed2006

Intracranial pressure monitoring: modeling cerebrovascular pressure transmission.

OBJECTIVES: To examine changes in cerebrovascular pressure transmission derived from arterial blood pressure (ABP) and intracranial pressure (ICP) recordings by autoregressive moving average modeling technique. METHODS: Digitized ICP and ABP recordings were obtained from patients with brain injury. Two groups were defined: Group A with 4 patients who demonstrated plateau waves, and Group B with 4 intracranial hypertensive, hypoperfused patients. For each 16.5 s interval, mean values of ICP, ABP, cerebral perfusion pressure (CPP), and corresponding highest modal frequency (HMF) of cerebrovascular pressure transmission were computed. RESULTS: Mean values of CPP and HMF of 56.2 mmHg and 2.0 Hz for Group A were significantly higher (p < 0.005) than corresponding mean values of 31.9 mmHg and 0.744 Hz for Group B. The mean value of the slope of the regression line between HMF and CPP for group A of -0.034 Hz/mmHg was significantly different (p < 0.025) than the mean value of 0.0077 Hz/mmHg for Group B. Computations of HMF, pressure reactivity, and correlation pressure reactivity index on continuous pressure recordings are illustrated. CONCLUSIONS: Values of HMF of cerebrovascular pressure transmission are inversely related to CPP when pressure regulation is thought to be intact, and directly related when regulation is likely lost.

Algorithms↗
PubMed2006

Use of ICM+ software for on-line analysis of intracranial and arterial pressures in head-injured patients.

OBJECTIVE: To summarize our experience from the first 2 years of use of the ICM+ software in our Neurocritical Care Unit (NCCU). MATERIALS AND METHODS: Ninety-five head-injured patients (74 males, 21 females), average age 36 years, were managed in the NCCU. Intracranial pressure (ICP) was monitored using Codman intraparenchymal probes and arterial blood pressure (ABP) was measured from the radial artery. Signals were monitored by ICM+ software calculating mean values of ICP, ABP, cerebral perfusion pressure (CPP) and various indices describing pressure reactivity, compensation and vascular waveforms of ICP (pulse amplitude, respiratory, and slow waves), etc. RESULTS: Mean ICP was 17 mmHg, mean CPP was 73 mmHg. Seven patients showed permanent disturbance of cerebral autoregulation (mean pressure reactivity index above 0.3). Pressure reactivity index demonstrated significant U-shape relationship with CPP, suggesting loss of pressure reactivity at too low (CPP < 55 mmHg) and too high CPPs (CPP > 95 mmHg). Mean ICP was inversely correlated with respiratory rate (R = 0.46; p < 0.0001; reciprocal model). CONCLUSION: The new version of ICM+ software proved to be useful clinically in the NCCU. It allows continuous monitoring of pressure reactivity and exploratory analysis of factors implicating intracranial hypertension.

Adult↗
PubMed2006

Monitoring and interpretation of intracranial pressure after head injury.

OBJECTIVE: To investigate the relationships between long-term computer-assisted monitoring of intracranial pressure (ICP) and indices derived from its waveform versus outcome, age, and sex. MATERIALS AND METHODS: From 1992 to 2002, 429 sedated and ventilated head-injured patients were continuously monitored. ICP and arterial blood pressure (ABP) were recorded directly and stored in bedside computers. Additional calculated variables included: 1) Cerebral perfusion pressure (CPP) = ABP - ICP; 2) a PRx calculated as a moving correlation coefficient between slow waves (of periods from 20 seconds to 3 minutes) of ICP and ABP. RESULTS: Fatal outcome was associated with higher ICP (p < 0.000002), worse PRx (p < 0.0006), and lower CPP (p < 0.001). None of these parameters differentiated severely disabled patients from patients with a favorable outcome. Higher average ICP, lower CPP, worse outcome, and worse pressure reactivity were observed in females than in males (age-matched). Worse outcome, lower mean ICP, worse PRx, and higher CPP were significantly associated with the older age of patients. CONCLUSION: High ICP and low PRx are strongly associated with fatal outcome. There is a considerable heterogeneity amongst patients; optimization of care depends upon observing the time-trends for the individual patient.

Algorithms↗
PubMed2006

Decompressive craniectomy in traumatic brain injury: outcome following protocol-driven therapy.

Although decompressive craniectomy following traumatic brain injury is an option in patients with raised intracranial pressure (ICP) refractory to medical measures, its effect on clinical outcome remains unclear. The aim of this study was to evaluate the outcome of patients undergoing this procedure as part of protocol-driven therapy between 2000-2003. This was an observational study combining case note analysis and follow-up. Outcome was assessed at an interval of at least 6 months following injury using the Glasgow Outcome Scale (GOS) score and the SF-36 quality of life questionnaire. Forty-nine patients underwent decompressive craniectomy for raised and refractory ICP (41 [83.7%] bilateral craniectomy and 8 [16.3%] unilateral). Using the Glasgow Coma Scale (GCS), the presenting head injury grade was severe (GCS 3-8) in 40 (81.6%) patients, moderate (GCS 9-12) in 8 (16.3%) patients, and initially mild (GCS 13-15) in 1 (2.0%) patient. At follow-up, 30 (61.2%) patients had a favorable outcome (good recovery or moderate disability), 10 (20.48) remained severely disabled, and 9 (18.4%) died. No patients were left in a vegetative state. Overall the results demonstrated that decompressive craniectomy, when applied as part of protocol-driven therapy, yields a satisfactory rate of favorable outcome. Formal prospective randomized studies of decompressive craniectomy are now indicated.

Adolescent↗
PubMed2006

Decompressive craniectomy in traumatic brain injury: the randomized multicenter RESCUEicp study (www.RESCUEicp.com).

The RESCUEicp (Randomized Evaluation of Surgery with Craniectomy for Uncontrollable Elevation of intracranial pressure) study has been established to determine whether decompressive craniectomy has a role in the management of patients with traumatic brain injury and raised intracranial pressure that does not respond to initial treatment measures. We describe the concept of decompressive craniectomy in traumatic brain injury and the rationale and protocol of the RESCUEicp study.

Biomedical Research↗
PubMed2006

Inappropriate acute neurosurgical bed occupancy and short falls in rehabilitation: implications for the National Service Framework.

Patients undergoing neurosurgical intervention may require different types of organized rehabilitation. A prospective study was performed of the care needs of neurosurgical inpatients between the ages of 16 and 70 years who were in acute wards for more than 2 weeks. Only 58% of bed occupancy days were devoted to essential acute neurosurgical ward management. This figure was even lower for patients admitted with subarachnoid haemorrhage (36%) or traumatic brain injury (38%). Overall, 21% of bed days would have more appropriately spent in 'rapid access'/acute rehabilitation beds, 13% in 'active participation' rehabilitation beds and 5% in cognitive/behavioural rehabilitation units. Addressing this unmet need would increase the availability of acute neurosurgery beds, without needing to build and staff more neurosurgery wards.

Adolescent↗
PubMed2006

National Service Framework for long-term conditions--Quo vadis.

There is widespread dismay over the fate of the NSF for Long-term Conditions after all the efforts by so many people in securing its publication only one year ago in March 2005. In order to help to avoid its premature demise, the British Journal of Neurosurgery is pleased to provide a forum for the rapid publication of original papers and reviews that might help to catalyse the NSF's rational implementation. The first two of such papers are published in this Volume.

Delivery of Health Care↗
PubMed2006

Diffusion tensor imaging of benign intracranial hypertension: absence of cerebral oedema.

Cerebral oedema, it has been suggested, may have a role in the pathophysiology of benign intracranial hypertension (BIH). We applied diffusion tensor MR imaging (DTI), a technique able to detect cerebral oedema, to the study of patients with BIH. A quantitative regional analysis of diffusion parameters (trace and relative anisotropy) was conducted by comparing five BIH patients and six healthy controls. A small but significant increase in anisotropy accompanied by a small but significant decrease in trace was found in the putamen and head of the caudate nucleus. No significant changes were demonstrated in the thalamus, cerebral white matter or cortical regions. Our findings support other recent work that suggests cerebral oedema is not a factor in the pathogenesis of BIH.

Adult↗
PubMed2006

Standards for head injury management in acute hospitals: evidence from the six million population of the Eastern region.

OBJECTIVES: To develop standards of care for head injury and thereby identify and prioritize areas of the service needing development; to report the findings from a survey of compliance with such standards in the Eastern region of UK. METHODS: The standards were collaboratively developed through an inclusive and iterative process of regional surveys, multidisciplinary conferences, and working groups, following a method similar to that used by the Society of British Neurological Surgeons. The standards cover seven topics relating to all aspects of service delivery, with standards within each objective. Each standard has been designated a priority level (A, B, or C). The standards were piloted using a self-assessment questionnaire, completed by all 20 hospitals of the Eastern region. RESULTS: Full compliance was 36% and a further 30% of standards were partially met across the region, with some areas of service delivery better than others. Seventy eight per cent of level A standards were either fully or partially met. Results were better in the north of the region compared with the south. CONCLUSION: A survey of compliance with the head injury standards indicate that, with their whole systems approach and subject to further refinement, they are a useful method for identifying deficiencies in service provision and monitoring for quality of care both within organisations and regionally.

Craniocerebral Trauma↗
PubMed2006

Enhanced visualization and quantification of magnetic resonance diffusion tensor imaging using the p:q tensor decomposition.

Many scalar measures have been proposed to quantify magnetic resonance diffusion tensor imaging (MR DTI) data in the brain. However, only two parameters are commonly used in the literature: mean diffusion (D) and fractional anisotropy (FA). We introduce a visualization technique which permits the simultaneous analysis of an additional five scalar measures. This enhanced diversity is important, as it is not known a priori which of these measures best describes pathological changes for brain tissue. The proposed technique is based on a tensor transformation, which decomposes the diffusion tensor into its isotropic (p) and anisotropic (q) components. To illustrate the use of this technique, diffusion tensor imaging was performed on a healthy volunteer, a sequential study in a patient with recent stroke, a patient with hydrocephalus and a patient with an intracranial tumour. Our results demonstrate a clear distinction between different anatomical regions in the normal volunteer and the evolution of the pathology in the patients. In the normal volunteer, the brain parenchyma values for p and q fell into a narrow band with 0.976<p<1.063 x 10(-3) mm2 s(-1) and 0.15<q<1.08 x 10(-3) mm2 s(-1). The noise appeared as a compact cluster with (p,q) components (0.011, 0.141) x 10(-3) mm2 s(-1), while the cerebrospinal fluid was (3.320, 0.330) x 10(-3) mm2 s(-1). In the stroke patient, the ischaemic area demonstrated a trajectory composed of acute, sub-acute and chronic phases. The components of the lesion were (0.824, 0.420), (0.884, 0.254), (2.624, 0.325) at 37 h, 1 week and 1 month, respectively. The internal capsule of the hydrocephalus patient demonstrated a larger dispersion in the p:q plane suggesting disruption. Finally, there was clear white matter tissue destruction in the tumour patient. In summary, the p:q decomposition enhances the visualization and quantification of MR DTI data in both normal and pathological conditions.

Algorithms↗
PubMed2006

Improved delineation of glioma margins and regions of infiltration with the use of diffusion tensor imaging: an image-guided biopsy study.

BACKGROUND AND PURPOSE: The efficacy of radiation therapy, the mainstay of treatment for malignant gliomas, is limited by our inability to accurately determine tumor margins. As a result, despite recent advances, the prognosis remains appalling. Because gliomas preferentially infiltrate along white matter tracks, methods that show white matter disruption should improve this delineation. In this study, results of histologic examination from samples obtained from image-guided brain biopsies were correlated with diffusion tensor images. METHODS: Twenty patients requiring image-guided biopsies for presumed gliomas were imaged preoperatively. Patients underwent image-guided biopsies with multiple biopsies taken along a single track that went into normal-appearing brain. Regions of interest were determined from the sites of the biopsies, and diffusion tensor imaging findings were compared with glioma histology. RESULTS: Using diffusion tissue signatures, it was possible to differentiate gross tumor (reduction of the anisotropic component, q > 12% from contralateral region), from tumor infiltration (increase in the isotropic component, p > 10% from contralateral region). This technique has a sensitivity of 98% and specificity of 81%. T2-weighted abnormalities failed to identify the margin in half of all specimens. CONCLUSION: Diffusion tensor imaging can better delineate the tumor margin in gliomas. Such techniques can improve the delineation of the radiation therapy target volume for gliomas and potentially can direct local therapies for tumor infiltration.

Adolescent↗
PubMed2005

Diffusion tensor imaging in chronic head injury survivors: correlations with learning and memory indices.

Diffusion tensor imaging (DTI) provides a unique insight into the cellular integrity of the brain. While conventional magnetic resonance imaging underestimates the extent of pathology following closed head injury, diffusion-weighted imaging has been shown to more accurately delineate the extent of cerebral damage. There have only been a few case studies of DTI in chronic head injury survivors. This study used DTI to investigate changes in anisotropy and diffusivity in survivors of head injury at least 6 months after their injury. The relationship between cognition and diffusion abnormality was also investigated. The voxel-based analysis revealed significant bilateral decreases in anisotropy, in major white matter tracts and association fibers in the temporal, frontal, parietal and occipital lobes. Statistically significant increases in diffusivity were also found in widespread areas of the cortex. A significant positive correlation was found between diffusivity and impairment of learning and memory in the left posterior cingulate, left hippocampal formation and left temporal, frontal and occipital cortex. The common pattern of abnormality despite heterogeneous injury mechanism and lesion location in the group suggests that these cellular changes reflect secondary insults. The importance of diffusion abnormalities in head injury outcome is emphasized by the significant correlation between a learning and memory index and diffusivity in areas known to subserve this cognitive function.

Adolescent↗
PubMed2005

Physiological thresholds for irreversible tissue damage in contusional regions following traumatic brain injury.

Cerebral ischaemia appears to be an important mechanism of secondary neuronal injury in traumatic brain injury (TBI) and is an important predictor of outcome. To date, the thresholds of cerebral blood flow (CBF) and cerebral oxygen utilization (CMRO(2)) for irreversible tissue damage used in TBI studies have been adopted from experimental and clinical ischaemic stroke studies. Identification of irreversibly damaged tissue in the acute phase following TBI could have considerable therapeutic and prognostic implications. However, it is questionable whether stroke thresholds are applicable to TBI. Therefore, the aim of this study was to determine physiological thresholds for the development of irreversible tissue damage in contusional and pericontusional regions in TBI, and to determine the ability of such thresholds to accurately differentiate irreversibly damaged tissue. This study involved 14 patients with structural abnormalities on late-stage MRI, all of whom had been studied with (15)O PET within 72 h of TBI. Lesion regions of interest (ROI) and non-lesion ROIs were constructed on late-stage MRIs and applied to co-registered PET maps of CBF, CMRO(2) and oxygen extraction fraction (OEF). From the entire population of voxels in non-lesion ROIs, we determined thresholds for the development of irreversible tissue damage as the lower limit of the 95% confidence interval for CBF, CMRO(2) and OEF. To test the ability of a physiological variable to differentiate lesion and non-lesion tissue, we constructed probability curves, demonstrating the ability of a physiological variable to predict lesion and non-lesion outcomes. The lower limits of the 95% confidence interval for CBF, CMRO(2) and OEF in non-lesion tissue were 15.0 ml/100 ml/min, 36.7 mumol/100 ml/min and 25.9% respectively. Voxels below these values were significantly more frequent in lesion tissue (all P < 0.005, Mann-Whitney U-test). However, a significant proportion of lesion voxels had values above these thresholds, so that definition of the full extent of irreversible tissue damage would not be possible based upon single physiological thresholds. We conclude that, in TBI, the threshold of CBF below which irreversible tissue damage consistently occurs differs from the classical CBF threshold for stroke (where similar methodology is used to define such thresholds). The CMRO(2) threshold is comparable to that reported in the stroke literature. At a voxel-based level, however (and in common with ischaemic stroke), the extent of irreversible tissue damage cannot be accurately predicted by early abnormalities of any single physiological variable.

Adolescent↗
PubMed2005

Cerebral microdialysis methodology--evaluation of 20 kDa and 100 kDa catheters.

Microdialysis monitoring of cerebral metabolism is now performed in several neuro-intensive care units. Conventional microdialysis utilizes CMA70 catheters with 20 kDa molecular weight cut-off membranes enabling the measurement of small molecules such as glucose, lactate, pyruvate and glutamate. The CMA71 100 kDa molecular weight cut-off microdialysis catheter has recently been introduced to allow detection of larger molecules such as cytokines. The objective of this study was to perform in vitro and in vivo testing of the CMA71 microdialysis catheter, comparing its performance with the CMA70. In vitro comparison studies of three of each catheter using reference analyte solutions, demonstrated equivalent recovery for glucose, lactate, pyruvate and glutamate (range 94-97% for CMA70 and 88-103% for CMA71). In vivo comparison involved intracranial placement of paired CMA70 and CMA71 catheters (through the same cranial access device) in six patients with severe traumatic brain injury. Both catheters were perfused with CNS Perfusion Fluid without dextran at 0.3 microl min-1 with hourly sampling and bedside analysis on a CMA600 microdialysis analyser. The two catheters yielded equivalent results for glucose, lactate, pyruvate, glutamate and lactate/pyruvate ratio. CMA71 microdialysis catheters can, therefore, be used for routine clinical monitoring of extracellular substances, as well as for their intended research role of larger molecular weight protein sampling.

Adolescent↗