Biomedical subjects

John D Pickard

Publications and source records attributed to John D Pickard.

At least 19 recordsLinked to original sources

PubMed2003

Assessment of cerebrovascular autoregulation in head-injured patients: a validation study.

BACKGROUND AND PURPOSE: Cerebrovascular autoregulation is frequently measured in head-injured patients. We attempted to validate 4 bedside methods used for assessment of autoregulation. METHODS: PET was performed at a cerebral perfusion pressure (CPP) of 70 and 90 mm Hg in 20 patients. Cerebral blood flow (CBF) and cerebral metabolic rate for oxygen (CMRo2) were determined at each CPP level. Patients were sedated with propofol and fentanyl. Norepinephrine was used to control CPP. During PET scanning, transcranial Doppler (TCD) flow velocity in the middle cerebral artery was monitored, and the arterio-jugular oxygen content difference (AJDo2) was measured at each CPP. Autoregulation was determined as the static rate of autoregulation based on PET (SROR(PET)) and TCD (SROR(TCD)) data, based on changes in AJDo2, and with 2 indexes based on the relationship between slow waves of CPP and flow velocity (mean velocity index, Mx) and between arterial blood pressure and intracranial pressure (pressure reactivity index, PRx) RESULTS: We found significant correlations between SROR(PET) and SROR(TCD) (r2=0.32; P<0.01) and between SROR(PET) and PRx (r2=0.31; P<0.05). There were no significant associations between PET data and autoregulation as assessed by changes in AJDo2. Global CMRo2 was significantly lower at the higher CPP (P<0.01). CONCLUSIONS: Despite some variability, SROR(TCD) and PRx may provide useful approximations of autoregulation in head-injured patients. At least with our methods, CMRo2 changes with the increase in CPP; hence, flow-metabolism coupling may affect the results of autoregulation testing.

Adolescent↗

PubMed2003

Effect of hypertonic saline on cerebral blood flow in poor-grade patients with subarachnoid hemorrhage.

BACKGROUND AND PURPOSE: The goal of this study was to examine the effects of hypertonic saline on cerebral blood flow (CBF) in poor-grade patients with subarachnoid hemorrhage. METHODS: We administered 23.5% hypertonic saline (2 mL/kg IV) 1 time to 10 patients, 2 times to 7 patients, and 3 times to 1 patient. All patients had transcranial Doppler (TCD), intracranial pressure (ICP) monitoring, and analysis of serum sodium and osmolality; 6 had xenon CT (XeCT). Data were used to characterize the changes in CBF, cerebral vascular resistance (CVR), ICP, cerebral perfusion pressure (CPP), and potential rheological mechanisms of action. RESULTS: In the first treatment episode, CPP increased 26.8% (P=0.0003, at 28.3 minutes) from a rise in mean arterial blood pressure (ABP) of 10.5% (P=0.02, at 22.2 minutes) and a fall in ICP (-74.7%, P=0.002, at 60.0 minutes). Flow velocity (FV) of the middle cerebral artery increased 70.8% (P=0.00005, at 20.0 minutes), resulting in a corresponding fall in estimated CVR (-26.6%, P=0.01, at 16.3 minutes). The half-lives of effects on ABP, CPP, ICP, FV, and estimated CVR were 20.0, 53.6, 139.1, 42.7, and 27.1 minutes, respectively. In the second treatment episode, all these parameters had the same response except estimated CVR, which did not reach statistical significance. XeCT confirmed the increase in CBF (22.9%, P=0.02) without regional differences. A fall in CBF after hypertonic saline was identified in only a single region of interest in a patient in whom baseline flow was low but not infarcted. Serum sodium rose by 11.4 and 8.8 mmol/L, and osmolality rose by 26.7 and 16.3 mosm/L in the first and second treatment episodes, respectively. Hemoglobin decreased by 0.7 and 0.6 g/L and hematocrit decreased by 1.9% and 2.4% in the first and second treatment episodes, respectively. CONCLUSIONS: We found that 23.5% hypertonic saline increases CBF in poor-grade patients with subarachnoid hemorrhage. These effects are associated with improved indexes of blood rheology. Potential therapeutic benefits are discussed.

Adult↗

PubMed2003

The effects of large-dose propofol on cerebrovascular pressure autoregulation in head-injured patients.

UNLABELLED: In healthy individuals, cerebrovascular pressure autoregulation is preserved or even improved when propofol is infused. We examined the effect of an increase in propofol plasma concentration on pressure autoregulation in 10 head-injured patients. Using target-controlled infusions, the static rate of autoregulation was determined at a moderate (2.3 +/- 0.4 microg/mL) and a large (4.3 +/- 0.04 microg/mL) plasma target concentration of propofol. Using norepinephrine to control cerebral perfusion pressure, transcranial Doppler measurements from the middle cerebral artery were made at a cerebral perfusion pressure of 70 and 85 mm Hg at each propofol concentration. Middle cerebral artery flow velocities at the large propofol concentration were significantly lower than at the moderate concentration, without any concurrent increase in arterio-jugular difference in oxygen content, a finding compatible with maintained flow-metabolism coupling. Despite this, static rate of autoregulation decreased significantly from 54% +/- 36% to 28% +/- 35% (P = 0.029). Our data suggest that after head injury, the cerebrovascular effects of propofol are different from those observed in healthy individuals. We propose that large doses of propofol should be used cautiously in head-injured patients, because there is the potential to increase the injured brain's vulnerability to secondary insults. IMPLICATIONS: Propofol is used for sedation and control of intracranial pressure in head-injured patients. In contrast to previous data from healthy individuals, we show a deterioration of cerebrovascular pressure autoregulation with fast propofol infusion rates after head injury. Large propofol doses may increase the injured brain's vulnerability to secondary insults.

Adult↗

PubMed2003

Hydrodynamic properties of extraventricular drainage systems.

OBJECTIVE: Extraventricular drains (EVDs) are intended to control intracranial pressure for patients with acute disorders of the cerebrospinal fluid circulation. We tested five commercially available EVDs to assess their fundamental hydrodynamic properties, which determine the quality of this control. METHODS: The five most frequently used drainage systems were tested. The pressure responses to water flow from a computer-controlled infusion pump were studied in the rig constructed in the UK Shunt Evaluation Laboratory (Cambridge, England). EVDs were studied under normal conditions and after brief (20-s) contact of the vent located in the drip chamber with the test reagent. Pure water and water with 10% rat blood content were used for testing. RESULTS: All of the tested EVDs demonstrated low hydrodynamic resistance [<3.5 mm Hg/(ml/min)], indicating their ability to control intracranial pressure. When the drip chamber vents were in brief contact with the reagent, the hydrodynamic properties of two models were unaffected. For the three other EVDs, blockage of the drip chamber was observed, leading to increases in the inlet pressure to more than 150 mm Hg. All three models that demonstrated obstruction have the same vent configuration, which allows cerebrospinal fluid to accumulate close to the filter when the drip chamber is held horizontally. This feature was confirmed to be the cause of the blockage. CONCLUSION: In clinical practice, special care should be taken to avoid contact of the drip chamber vents with cerebrospinal fluid, which causes obstruction and may lead to the development of gross intracranial hypertension. Specific configurations, as identified in this testing program, are safer than others in this respect.

Animals↗

PubMed2003

The efficacy and safety of aprotinin for hemostasis during intracranial surgery.

OBJECT: The aim of this study was to determine the safety and efficacy of prophylactic high-dose intravenous aprotinin in reducing intraoperative blood loss in the neurosurgical population. METHODS: A randomized, double-blind, placebo-controlled trial was conducted in parallel groups in two regional neurosurgical departments. One hundred patients with a preoperative diagnosis of intracranial meningioma or vestibular schwannoma subsequently confirmed on histological studies were included. All patients were older than 18 years of age, pregnancy had been excluded, there was no history of bleeding diathesis, no previous exposure to aprotinin, and no ingestion of antiplatelet or anticoagulant medications within the 2 weeks preceding surgery. Aprotinin was administered in doses of 30,000 kallikrein-inhibiting units (KIU)/kg body weight on induction of anesthesia and was continued as an infusion of 10,000 KIU/kg/hr until surgery was complete, or for a maximum of 8 hours. Intraoperative blood loss, blood transfusion, the Glasgow Outcome Scale score, and the Index of Independence were measured, and screening for deep vein thrombosis and the Mini-Mental State Examination were performed. CONCLUSIONS: Intraoperative blood loss was reduced from 1014 ml (geometric mean) to 508 ml (p = 0.028). Although this study was not designed to evaluate the need for blood transfusion, 37 U of blood was used in 11 patients in the aprotinin group and 58 U in 13 patients in the placebo group (not significant). There were no significant differences in postoperative thrombotic risk or other outcome measures between treatment groups. Aprotinin therefore can be safely used to reduce intraoperative blood loss in patients who are not receiving anticoagulation therapy.

Aprotinin↗

PubMed2003

Positron emission tomographic cerebral perfusion disturbances and transcranial Doppler findings among patients with neurological deterioration after subarachnoid hemorrhage.

OBJECTIVE: After aneurysmal subarachnoid hemorrhage, approximately 30% of patients experience delayed neurological deficits, related in part to arterial vasospasm and dysautoregulation. Transcranial Doppler (TCD) ultrasonography is commonly used to noninvasively detect arterial vasospasm. We studied cerebral perfusion patterns and associated TCD indices for 25 patients who developed clinical signs of delayed neurological deficits. METHODS: Patients were treated in a neurosurgical intensive care unit and were studied if they exhibited delayed focal or global neurological deterioration. Positron emission tomographic cerebral blood flow (CBF) studies and TCD studies measuring the mean flow velocity (FV) of the middle cerebral artery and the middle cerebral artery FV/internal carotid artery FV ratio (with the internal carotid artery FV being measured extracranially at the cranial base) were performed. Glasgow Outcome Scale scores were assessed at 6 months. RESULTS: A markedly heterogeneous pattern of CBF distribution was observed, with hyperemia, normal CBF values, and reduced flow being observed among patients with delayed neurological deficits. TCD indices were not indicative of the cerebral perfusion findings. The mean CBF value was slightly lower for patients who did not survive (32.3 ml/100 g/min), compared with those who did survive (36.0 ml/100 g/min, P = 0.05). CONCLUSION: Among patients who developed delayed neurological deficits after aneurysmal subarachnoid hemorrhage, a wide range of cerebral perfusion disturbances was observed, calling into question the traditional concept of large-vessel vasospasm. Commonly used TCD indices do not reflect cerebral perfusion values.

Adult↗

PubMed2002

Venous sinus stenting for refractory benign intracranial hypertension.

Similarities between benign intracranial hypertension and cerebral venous sinus thrombosis are well recognised and the importance of excluding the latter-especially sagittal sinus thrombosis-is understood. Some have suggested that all benign intracranial hypertension is caused by venous hypertension, mostly from stenoses or occlusions of the lateral sinuses. We describe a woman with refractory benign intracranial hypertension. With venography and manometry we showed partial obstruction of both transverse venous sinuses, with raised pressures proximal to the obstructions. Dilation of one of the sinuses with a stent reduced the pressure gradient, with striking symptomatic improvement. Investigation and treatment of benign intracranial hypertension should be revisited in view of these findings.

Adult↗

PubMed2002

(18)F-Endothelin-1, a positron emission tomography (PET) radioligand for the endothelin receptor system: radiosynthesis and in vivo imaging using microPET.

Positron emission tomography (PET) is a powerful technique with the sensitivity to image and quantify receptor-bound radioligands in vivo. Recent progress in PET scanner technology has resulted in the development of dedicated tomographs designed for small animals, with resolution that allows the delineation of discrete organs and their larger substructures in rats and mice. Our aim was to determine whether endothelin-1 (ET-1) could be labelled with (18)F, and whether the resulting (18)F-ET-1 would have the required pharmacokinetic properties to permit binding and imaging of ET receptors in vivo. (18)F-ET-1 could be produced in a total radiochemical yield of 5.9+/-0.7% in 207+/-3 min (n=20). Specific radioactivities were in the range 220-370 GBq/micromol, and the radiochemical purity of the isolated (18)F-ET-1 was >95%. In vivo distribution in the rat was studied using microPET. High levels of (18)F-ET-1 uptake were found in lung and kidney, whereas liver showed moderate levels of uptake. The resolution of the microPET scanner was sufficient to differentiate heterogeneous uptake in subrenal structures in the rat.

Animals↗

PubMed2002

Detecting residual cognitive function in persistent vegetative state.

Despite converging agreement about the definition of persistent vegetative state, recent reports have raised concerns about the accuracy of diagnosis in some patients, and the extent to which, in a selection of cases, residual cognitive functions may remain undetected. Objective assessment of residual cognitive function can be extremely difficult as motor responses may be minimal, inconsistent, and difficult to document in many patients, or may be undetectable in others because no cognitive output is possible. Here we describe strategies for using H(2)(15)O positron emission tomography activation studies to study covert cognitive processing in patients with a clinical diagnosis of persistent vegetative state. Three cases are described in detail. Of these, two exhibited clear and predicted regional cerebral blood flow responses during well-documented activation paradigms (face recognition and speech perception) which have been shown to produce specific, robust and reproducible activation patterns in normal volunteers. Some months after scanning, both patients made a significant recovery. In a third case, blood flow data were acquired during a speech perception task, although methodological difficulties precluded any systematic interpretation of the results. In spite of the multiple logistic and procedural problems involved, these results have major clinical and scientific implications and provide a strong basis for the systematic study of possible residual cognitive function in patients diagnosed as being in a persistent vegetative state.

Adult↗

PubMed2002

Continuous monitoring of cerebrovascular pressure reactivity allows determination of optimal cerebral perfusion pressure in patients with traumatic brain injury.

OBJECTIVES: To define optimal cerebral perfusion pressure (CPPOPT) in individual head-injured patients using continuous monitoring of cerebrovascular pressure reactivity. To test the hypothesis that patients with poor outcome were managed at a cerebral perfusion pressure (CPP) differing more from their CPPOPT than were patients with good outcome. DESIGN: Retrospective analysis of prospectively collected data. SETTING: Neurosciences critical care unit of a university hospital. PATIENTS: A total of 114 head-injured patients admitted between January 1997 and August 2000 with continuous monitoring of mean arterial blood pressure (MAP) and intracranial pressure (ICP). MEASUREMENTS AND MAIN RESULTS: MAP, ICP, and CPP were continuously recorded and a pressure reactivity index (PRx) was calculated online. PRx is the moving correlation coefficient recorded over 4-min periods between averaged values (6-sec periods) of MAP and ICP representing cerebrovascular pressure reactivity. When cerebrovascular reactivity is intact, PRx has negative or zero values, otherwise PRx is positive. Outcome was assessed at 6 months using the Glasgow Outcome Scale. A total of 13,633 hrs of data were recorded. CPPOPT was defined as the CPP where PRx reaches its minimum value when plotted against CPP. Identification of CPPOPT was possible in 68 patients (60%). In 22 patients (27%), CPPOPT was not found because it presumably lay outside the studied range of CPP. Patients' outcome correlated with the difference between CPP and CPPOPT for patients who were managed on average below CPPOPT (r =.53, p <.001) and for patients whose mean CPP was above CPPOPT (r = -.40, p <.05). CONCLUSIONS: CPPOPT could be identified in a majority of patients. Patients with a mean CPP close to CPPOPT were more likely to have a favorable outcome than those whose mean CPP was more different from CPPOPT. We propose use of the criterion of minimal achievable PRx to guide future trials of CPP oriented treatment in head injured patients.

Adolescent↗

PubMed2002

Effect of hyperventilation on cerebral blood flow in traumatic head injury: clinical relevance and monitoring correlates.

OBJECTIVE: To investigate the effect of hyperventilation on cerebral blood flow in traumatic brain injury. DESIGN: A prospective interventional study. SETTING: A specialist neurocritical care unit. PATIENTS: Fourteen healthy volunteers and 33 patients within 7 days of closed head injury. INTERVENTIONS: All subjects underwent positron emission tomography imaging of cerebral blood flow. In patients, PaCO2 was reduced from 36 +/- 1 to 29 +/- 1 torr (4.8 +/- 0.1 to 3.9 +/- 0.1 kPa) and measurements repeated. Jugular venous saturation (SjvO2 ) and arteriovenous oxygen content differences (AVDO2 ) were monitored in 25 patients and values related to positron emission tomography variables. MEASUREMENTS AND MAIN RESULTS: The volumes of critically hypoperfused and hyperperfused brain (HypoBV and HyperBV, in milliliters) were calculated based on thresholds of 10 and 55 mL.100g(-1).min(-1), respectively. Whereas baseline HypoBV was significantly higher in patients ( p<.05), baseline HyperBV was similar to values in healthy volunteers. Hyperventilation resulted in increases in cerebral perfusion pressure (p <.0001) and reductions in intracranial pressure (p <.001), whereas SjvO2 (>50%) and AVDO2 (<9 mL/mL) did not exceed global ischemic thresholds. However, despite these beneficial effects, hyperventilation shifted the cerebral blood flow distribution curve toward the hypoperfused range, with a decrease in global cerebral blood flow (31 +/- 1 to 23 +/- 1 mL.100g(-1).min(-1); p<.0001) and an increase in HypoBV (22 [1-141] to 51 [2-428] mL; p<.0001). Hyperventilation-induced increases in HypoBV were apparently nonlinear, with a threshold value between 34 and 38 torr (4.5-5 kPa). CONCLUSIONS: Hyperventilation increases the volume of severely hypoperfused tissue within the injured brain, despite improvements in cerebral perfusion pressure and intracranial pressure. Significant hyperperfusion is uncommon, even at a time when conventional clinical management includes a role for modest hyperventilation. These reductions in regional cerebral perfusion are not associated with ischemia, as defined by global monitors of oxygenation, but may represent regions of potentially ischemic brain tissue.

Adolescent↗

PubMed2002

Immunohistochemical localization of calcitonin receptor-like receptor and receptor activity-modifying proteins in the human cerebral vasculature.

Calcitonin gene-related peptide and adrenomedullin belong to a structurally related neuropeptide family and are potent vasodilators expressed in the trigeminovascular system. The molecular identity of receptors for these proteins has only recently been elucidated. Central to functional binding of these neuropeptides is the G-protein-coupled receptor, the calcitonin receptor-like receptor (CRLR), whose cell surface expression and pharmacology is determined by coexpression of a receptor activity-modifying protein (RAMP). CRLR combined with RAMP binds calcitonin gene-related peptide with high affinity, whereas CRLR coexpression with RAMP2 or -3 confers high-affinity binding of adrenomedullin. The authors investigated the expression of these receptor components in human cerebral vasculature to further characterize neuropeptide receptor content and the potential functions of these receptors. Localization has been carried out using specific antisera raised against immunogenic peptide sequences that were subsequently applied using modern immunohistochemical techniques and confocal microscopy. The results are the first to show the presence of these receptor component proteins in human middle meningeal, middle cerebral, pial, and superficial temporal vessels, and confirm that both calcitonin gene-related peptide and adrenomedullin receptors may arise from the coassembly of RAMPs with CRLR in these vessel types. These novel data advance the understanding of the molecular function of the trigeminovascular system, its potential role in vascular headache disorders such as migraine, and may lead to possible ways in which future synthetic ligands may be applied to manage these disorders.

Autoradiography↗

PubMed2002

Correlation between cerebral blood flow, substrate delivery, and metabolism in head injury: a combined microdialysis and triple oxygen positron emission tomography study.

Microdialysis continuously monitors the chemistry of a small focal volume of the cerebral extracellular space. Conversely, positron emission tomography (PET) establishes metabolism of the whole brain, but only for the duration of the scan. The objective of this study was to apply both techniques to head-injured patients simultaneously to assess the relation between microdialysis (glucose, lactate, lactate/pyruvate [L/P] ratio, and glutamate) and PET (cerebral blood flow [CBF], cerebral blood volume, oxygen extraction fraction (OEF), and cerebral metabolic rate of oxygen) parameters. Microdialysis catheters were inserted into the frontal cerebral cortex and adipose tissue of the anterior abdominal wall of 17 severely head-injured patients. Microdialysis was performed during PET scans, with regions of interest defined by the location of the microdialysis catheter membrane. An intervention (hyperventilation) was performed in 13 patients. The results showed that combining PET and microdialysis to monitor metabolism in ventilated patients is feasible and safe, although logistically complex. There was a significant relation between the L/P ratio and the OEF (Spearman r = 0.69, P = 0.002). There was no significant relation between CBF and the microdialysis parameters. Moderate short-term hyperventilation appeared to be tolerated in terms of brain chemistry, although no areas were sampled by microdialysis where the OEF exceeded 70%. Hyperventilation causing a reduction of the arterial carbon dioxide tension by 0.9 kPa resulted in a significant elevation of the OEF, in association with a reduction in glucose, but no significant elevation in the L/P ratio or glutamate.

Adolescent↗

PubMed2002

Cerebral autoregulation among patients with symptoms of hydrocephalus.

OBJECTIVE: To study the relationship between the resistance to cerebrospinal fluid (CSF) outflow and cerebral autoregulation. METHODS: We examined 35 patients who presented with ventricular dilation and clinical symptoms of communicating hydrocephalus. For all of these patients, CSF compensatory reserve was investigated by using a computerized infusion test, with simultaneous recording of blood flow velocity wave forms (by using transcranial Doppler ultrasonography) and arterial blood pressure (with a Finapress finger cuff). The resistance to CSF outflow was calculated as the absolute increase in intracranial pressure (interpolated over vasogenic waves) divided by the infusion rate (1.5 ml/min in most cases). The index of autoregulation was assessed as a correlation coefficient (moving time window of 5 min) between slow waves (with periods of 20 s to 2 min) in mean blood flow velocity and cerebral perfusion pressure. RESULTS: The mean intracranial pressure increased during the test, from 6 mm Hg (standard deviation, 6 mm Hg) to 20 mm Hg (standard deviation, 10 mm Hg) (P < 0.0001). The index of autoregulation was significantly correlated with the resistance to CSF outflow (r = -0.41, P < 0.03), indicating better autoregulation with greater resistance to CSF outflow. CONCLUSION: Patients presenting with ventricular dilation may exhibit either decreased (atrophy) or increased (normal-pressure hydrocephalus) resistance to CSF outflow. Increased resistance is correlated with preserved autoregulation. Patients with low resistance, suggesting brain atrophy, more often have disturbed autoregulation in the middle cerebral artery territory, as assessed by transcranial Doppler ultrasonography.

Adult↗

PubMed2002

Adverse cerebral events detected after subarachnoid hemorrhage using brain oxygen and microdialysis probes.

OBJECTIVE: A prospective observational study was conducted to investigate whether episodes of ischemia are detected by continuous cerebral monitoring and whether such episodes are related to clinical outcome. METHODS: Forty patients (35 after subarachnoid hemorrhage and 5 after complex aneurysm surgery) were monitored for a total of 174 days (mean, 4 d; range, 1-12 d). Brain tissue partial pressures of oxygen and carbon dioxide, pH, and temperature were measured continuously using Neurotrend sensors (Codman, Bracknell, England). Bedside analysis of extracellular chemistry was performed hourly using microdialysis. Glasgow Outcome Scale score was assessed at 3 to 6 months. RESULTS: Patients with poor World Federation of Neurosurgical Societies grades (4 and 5) or an unfavorable outcome (severe disability or death) had, on average, higher lactate and lactate/pyruvate ratio but lower glucose/lactate ratio (P < or = 0.05). Brain tissue partial pressure of oxygen decreased to below 1.1 kPa in 78% of the patients for 18% (95% confidence interval, 12-24%) of time monitored. There were 197 episodes in which brain tissue partial pressures of oxygen decreased to below 1.1 kPa for at least 30 minutes. Unfavorable outcome was associated with more of these episodes (8.8 episodes; 95% confidence interval, 4.4-13.2 episodes) than favorable outcome (2.2 episodes; 95% confidence interval, 1.1-3.3 episodes), as well as an episode of glutamate levels of more than 10 micromol/L or lactate/pyruvate ratio more than 40 (P < 0.05, chi(2) test). CONCLUSION: Intraparenchymal oximetry and microdialysis can detect but fail to predict the development of delayed cerebral ischemia. There were associations between episodes of low brain oxygen, abnormal microdialysis, and unfavorable outcome, but these associations were weak.

Brain↗

PubMed2002

A case study of hemispatial neglect using finite element analysis and positron emission tomography.

BACKGROUND: The authors present a patient who developed transient hemispatial neglect following surgical drainage of a large right frontotemporal arachnoid cyst. As symptoms evolved in parallel with brain shift over the subsequent months, the authors hypothesized that the disorder was associated with the appearance of mechanical stresses in the cerebral mantle. METHODS: To map tissue stress at the various stages of deformation, a finite element computer simulation was conducted on the basis of computed tomography scans of the patient. RESULTS: The authors' results demonstrate substantial shear and compressive stress concentrations in the parietal lobe, a region commonly associated with neglect, and where positron emission tomography confirmed hypoperfusion in this patient. Treatment with combined ventricular-peritoneal and cystoperitoneal shunts was accompanied by clinical recovery and improvement of right parietal lobe cerebral blood flow. CONCLUSIONS: The authors conclude that brain deformation was a contributing factor in the reversible neglect syndrome by compromising the normal flow of blood and/or the deactivation of subcortical circuits of the parietal lobe.

Aged↗

PubMed2002

Increased anisotropy in acute stroke: a possible explanation.

BACKGROUND AND PURPOSE: The increase in fractional anisotropy (FA) in acute stroke has yet to be explained. Using an engineering methodology known as pq diagrams, we sought to explain the increase in FA by describing changes in the total magnitude of the diffusion tensor (L) as well as the isotropic (p) and anisotropic (q) components. METHODS: Diffusion tensor imaging was performed in 10 patients with stroke <27 hours old. The diffusion tensor was decomposed into the p and q components and plotted to describe the diffusion trajectories. FA was also calculated and compared. RESULTS: There was significant and consistent reduction in p, q, and L (p: mean, -50.0%; range, -36.6% to -64.5%; q: mean, -50.8%; range, -30.8% to -72.8%; L: mean, -50.3%; range, -37.0% to -65.1%). There were inconsistent changes in FA (mean, -0.5%; range, -44.9% to +45.0%). Five patients had elevated FA due to proportionately higher loss of L than q. CONCLUSIONS: Changes in FA only occur when there is a change in the ratio of q/L. Acute elevation of FA occurred in the context of a larger reduction in L than q. The elevation in FA occurs in the context of a reduction in the anisotropic tensor and therefore is a consequence of ratio-metric measurement. This appears to clarify the reported increase in FA in terms of alterations in the shape of the apparent diffusion tensor. pq diagrams appear to offer improved resolution of acute diffusion changes in ischemia.

Aged↗

PubMed2002

Measurement of brain tissue oxygenation performed using positron emission tomography scanning to validate a novel monitoring method.

OBJECT: The benefits of measuring cerebral oxygenation in patients with brain injury are well accepted; however, jugular bulb oximetry, which is currently the most popular monitoring technique used has several shortcomings. The goal of this study was to validate the use of a new multiparameter sensor that measures brain tissue oxygenation and metabolism (Neurotrend) by comparing it with positron emission tomography (PET) scanning. METHODS: A Neurotrend sensor was inserted into the frontal region of the brain in 19 patients admitted to the neurointensive care unit. After a period of stabilization, the patients were transferred to the PET scanner suite where C15O, 15O2, and H2(15)O PET scans were obtained to facilitate calculation of regional cerebral blood volume, O2 metabolism, blood flow, and O2 extraction fraction (OEF). Patients were given hyperventilation therapy to decrease arterial CO2 by approximately 1 kPa (7.5 mm Hg) and the same sequence of PET scans was repeated. For each scanning sequence, end-capillary O2 tension (PvO2) was calculated from the OEF and compared with the reading of brain tissue O2 pressure (PbO2) provided by the sensor. In three patients the sensor was inserted into areas of contusion and these patients were eliminated from the analysis. In the subset of 16 patients in whom the sensor was placed in healthy brain, no correlation was found between the absolute values of PbO2 and PvO2 (r = 0.2, p = 0.29); however a significant correlation was obtained between the change in PbO2 (deltaPbO2) and the change in PvO2 (deltaPvO2) produced by hyperventilation in a 20-mm region of interest around the sensor (p = 0.78, p = 0.0035). CONCLUSIONS: The lack of correlation between the absolute values of PbO2 and PvO2 indicates that PbO2 cannot be used as a substitute for PvO2. Nevertheless, the positive correlation between deltaPbO2 and deltaPvO2 when the sensor had been inserted into healthy brain suggests that tissue PO2 monitoring may provide a useful tool to assess the effect of therapeutic interventions in brain injury.

Adult↗