Real-Time Non-Invasive Imaging and Detection of Spreading Depolarizations through EEG: An Ultra-Light Explainable Deep Learning Approach.

A core aim of neurocritical care is to prevent secondary brain injury. Spreading depolarizations (SDs) have been identified as an important independent cause of secondary brain injury. SDs are usually detected using invasive electrocorticography recorded at high sampling frequency. Recent pilot studies suggest a possible utility of scalp electrodes generated electroencephalogram (EEG) for non-invasive SD detection. However, noise and attenuation of EEG signals makes this detection task extremely challenging. Previous methods focus on detecting temporal power change of EEG over a fixed high-density map of scalp electrodes, which is not always clinically feasible. Having a specialized spectrogram as an input to the automatic SD detection model, this study is the first to transform SD identification problem from a detection task on a 1-D time-series wave to a task on a sequential 2-D rendered imaging. This study presented a novel ultra-light-weight multi-modal deep-learning network to fuse EEG spectrogram imaging and temporal power vectors to enhance SD identification accuracy over each single electrode, allowing flexible EEG map and paving the way for SD detection on ultra-low-density EEG with variable electrode positioning. Our proposed model has an ultra-fast processing speed (<0.3 sec). Compared to the conventional methods (2 hours), this is a huge advancement towards early SD detection and to facilitate instant brain injury prognosis. Seeing SDs with a new dimension - frequency on spectrograms, we demonstrated that such additional dimension could improve SD detection accuracy, providing preliminary evidence to support the hypothesis that SDs may show implicit features over the frequency profile.

The Relationship Between Seizures and Spreading Depolarizations in Patients with Severe Traumatic Brain Injury.

BACKGROUND: Both seizures and spreading depolarizations (SDs) are commonly detected using electrocorticography (ECoG) after severe traumatic brain injury (TBI). A close relationship between seizures and SDs has been described, but the implications of detecting either or both remain unclear. We sought to characterize the relationship between these two phenomena and their clinical significance. METHODS: We performed a post hoc analysis of a prospective observational clinical study of patients with severe TBI requiring neurosurgery at five academic neurotrauma centers. A subdural electrode array was placed intraoperatively and ECoG was recorded during intensive care. SDs, seizures, and high-frequency background characteristics were quantified offline using published standards and terminology. The primary outcome was the Glasgow Outcome Scale-Extended score at 6 months post injury. RESULTS: There were 138 patients with valid ECoG recordings; the mean age was 47 ± 19 years, and 104 (75%) were men. Overall, 2,219 ECoG-detected seizures occurred in 38 of 138 (28%) patients in a bimodal pattern, with peak incidences at 1.7-1.8 days and 3.8-4.0 days post injury. Seizures detected on scalp electroencephalography (EEG) were diagnosed by standard clinical care in only 18 of 138 (13%). Of 15 patients with ECoG-detected seizures and contemporaneous scalp EEG, seven (47%) had no definite scalp EEG correlate. ECoG-detected seizures were significantly associated with the severity and number of SDs, which occurred in 83 of 138 (60%) of patients. Temporal interactions were observed in 17 of 24 (70.8%) patients with both ECoG-detected seizures and SDs. After controlling for known prognostic covariates and the presence of SDs, seizures detected on either ECoG or scalp EEG did not have an independent association with 6-month functional outcome but portended worse outcome among those with clustered or isoelectric SDs. CONCLUSIONS: In patients with severe TBI requiring neurosurgery, seizures were half as common as SDs. Seizures would have gone undetected without ECoG monitoring in 20% of patients. Although seizures alone did not influence 6-month functional outcomes in this cohort, they were independently associated with electrographic worsening and a lack of motor improvement following surgery. Temporal interactions between ECoG-detected seizures and SDs were common and held prognostic implications. Together, seizures and SDs may occur along a dynamic continuum of factors critical to the development of secondary brain injury. ECoG provides information integral to the clinical management of patients with TBI.

Development and Evaluation of a Method for Automated Detection of Spreading Depolarizations in the Injured Human Brain.

BACKGROUND: Spreading depolarizations (SDs) occur in some 60% of patients receiving intensive care following severe traumatic brain injury and often occur at a higher incidence following serious subarachnoid hemorrhage and malignant hemisphere stroke (MHS); they are independently associated with worse clinical outcome. Detection of SDs to guide clinical management, as is now being advocated, currently requires continuous and skilled monitoring of the electrocorticogram (ECoG), frequently extending over many days. METHODS: We developed and evaluated in two clinical intensive care units (ICU) a software routine capable of detecting SDs both in real time at the bedside and retrospectively and also capable of displaying patterns of their occurrence with time. We tested this prototype software in 91 data files, each of approximately 24 h, from 18 patients, and the results were compared with those of manual assessment ("ground truth") by an experienced assessor blind to the software outputs. RESULTS: The software successfully detected SDs in real time at the bedside, including in patients with clusters of SDs. Counts of SDs by software (dependent variable) were compared with ground truth by the investigator (independent) using linear regression. The slope of the regression was 0.7855 (95% confidence interval 0.7149-0.8561); a slope value of 1.0 lies outside the 95% confidence interval of the slope, representing significant undersensitivity of 79%. R2 was 0.8415. CONCLUSIONS: Despite significant undersensitivity, there was no additional loss of sensitivity at high SD counts, thus ensuring that dense clusters of depolarizations of particular pathogenic potential can be detected by software and depicted to clinicians in real time and also be archived.

Prognostic Value of Spreading Depolarizations in Patients With Severe Traumatic Brain Injury.

Importance: Advances in treatment of traumatic brain injury are hindered by the inability to monitor pathological mechanisms in individual patients for targeted neuroprotective treatment. Spreading depolarizations, a mechanism of lesion development in animal models, are a novel candidate for clinical monitoring in patients with brain trauma who need surgery. Objective: To test the null hypothesis that spreading depolarizations are not associated with worse neurologic outcomes. Design, Setting, and Participants: This prospective, observational, multicenter cohort study was conducted from February 2009 to August 2013 in 5 level 1 trauma centers. Consecutive patients who required neurological surgery for treatment of acute brain trauma and for whom research consent could be obtained were enrolled; participants were excluded because of technical problems in data quality, patient withdrawal, or loss to follow-up. Primary statistical analysis took place from April to December 2018. Evaluators of outcome assessments were blinded to other measures. Interventions: A 6-contact electrode strip was placed on the brain surface during surgery for continuous electrocorticography during intensive care. Main Outcomes and Measures: Electrocorticography was scored for depolarizations, following international consensus procedures. Six-month outcomes were assessed by the Glasgow Outcome Scale-Extended score. Results: A total of 157 patients were initially enrolled; 19 were subsequently excluded. The 138 remaining patients (104 men [75%]; median [interquartile range] age, 45 [29-64] years) underwent a median (interquartile range) of 75.5 (42.2-117.1) hours of electrocorticography. A total of 2837 spreading depolarizations occurred in 83 of 138 patients (60.1% incidence) who, compared with patients who did not have spreading depolarizations, had lower prehospital systolic blood pressure levels (mean [SD], 133 [31] mm Hg vs 146 [33] mm Hg; P = .03), more traumatic subarachnoid hemorrhage (depolarization incidences of 17 of 37 [46%], 18 of 32 [56%], 22 of 33 [67%], and 23 of 30 patients [77%] for Morris-Marshall Grades 0, 1, 2, and 3/4, respectively; P = .047), and worse radiographic pathology (in 38 of 73 patients [52%] and 42 of 60 patients [70%] for Rotterdam Scores 2-4 vs 5-6, respectively; P = .04). Of patients with depolarizations, 32 of 83 (39%) had only sporadic events that induced cortical spreading depression of spontaneous electrical activity, whereas 51 of 83 patients (61%) exhibited temporal clusters of depolarizations (≥3 in a 2-hour span). Nearly half of those with clusters (23 of 51 [45%]) also had depolarizations in an electrically silent area of the cortex (isoelectric spreading depolarization). Patients with clusters did not improve in motor neurologic examinations from presurgery to postelectrocorticography, while other patients did improve. In multivariate ordinal regression adjusting for baseline prognostic variables, the occurrence of depolarization clusters had an odds ratio of 2.29 (95% CI, 1.13-4.65; P = .02) for worse outcomes. Conclusions and Relevance: In this cohort study of patients with acute brain trauma, spreading depolarizations were predominant but heterogeneous and independently associated with poor neurologic recovery. Monitoring the occurrence of spreading depolarizations may identify patients most likely to benefit from targeted management strategies.

Clinical translation of microfluidic sensor devices: focus on calibration and analytical robustness.

We present approaches to facilitate the use of microfluidics outside of the laboratory, in our case within a clinical setting and monitoring from human subjects, where the complexity of microfluidic devices requires high skill and expertise and would otherwise limit translation. Microfluidic devices show great potential for converting complex laboratory protocols into on-chip processes. We demonstrate a flexible microfluidic platform can be coupled to microfluidic biosensors and used in conjunction with clinical microdialysis. The versatility is demonstrated through a series of examples of increasing complexity including analytical processes relevant to a clinical environment such as automatic calibration, standard addition, and more general processes including system optimisation, reagent addition and homogenous enzyme reactions. The precision and control offered by this set-up enables the use of microfluidics by non-experts in clinical settings, increasing uptake and usage in real-world scenarios. We demonstrate how this type of system is helpful in guiding physicians in real-time clinical decision-making.

3D printed microfluidic device for online detection of neurochemical changes with high temporal resolution in human brain microdialysate.

This paper presents the design, optimisation and fabrication of a mechanically robust 3D printed microfluidic device for the high time resolution online analysis of biomarkers in a microdialysate stream at microlitre per minute flow rates. The device consists of a microfluidic channel with secure low volume connections that easily integrates electrochemical biosensors for biomarkers such as glutamate, glucose and lactate. The optimisation process of the microfluidic channel fabrication, including for different types of 3D printer, is explained and the resulting improvement in sensor response time is quantified. The time resolution of the device is characterised by recording short lactate concentration pulses. The device is employed to record simultaneous glutamate, glucose and lactate concentration changes simulating the physiological response to spreading depolarisation events in cerebrospinal fluid dialysate. As a proof-of-concept study, the device is then used in the intensive care unit for online monitoring of a brain injury patient, demonstrating its capabilities for clinical monitoring.

Neurostereologic Lesion Volumes and Spreading Depolarizations in Severe Traumatic Brain Injury Patients: A Pilot Study.

BACKGROUND: Spreading depolarizations (SDs) occur in 50-60% of patients after surgical treatment of severe traumatic brain injury (TBI) and are independently associated with unfavorable outcomes. Here we performed a pilot study to examine the relationship between SDs and various types of intracranial lesions, progression of parenchymal damage, and outcomes. METHODS: In a multicenter study, fifty patients (76% male; median age 40) were monitored for SD by continuous electrocorticography (ECoG; median duration 79 h) following surgical treatment of severe TBI. Volumes of hemorrhage and parenchymal damage were estimated using unbiased stereologic assessment of preoperative, postoperative, and post-ECoG serial computed tomography (CT) studies. Neurologic outcomes were assessed at 6 months by the Glasgow Outcome Scale-Extended. RESULTS: Preoperative volumes of subdural and subarachnoid hemorrhage, but not parenchymal damage, were significantly associated with the occurrence of SDs (P's < 0.05). Parenchymal damage increased significantly (median 34 ml [Interquartile range (IQR) - 2, 74]) over 7 (5, 8) days from preoperative to post-ECoG CT studies. Patients with and without SDs did not differ in extent of parenchymal damage increase [47 ml (3, 101) vs. 30 ml (- 2, 50), P = 0.27], but those exhibiting the isoelectric subtype of SDs had greater initial parenchymal damage and greater increases than other patients (P's < 0.05). Patients with temporal clusters of SDs (≥ 3 in 2 h; n = 10 patients), which included those with isoelectric SDs, had worse outcomes than those without clusters (P = 0.03), and parenchymal damage expansion also correlated with worse outcomes (P = 0.01). In multivariate regression with imputation, both clusters and lesion expansion were significant outcome predictors. CONCLUSIONS: These results suggest that subarachnoid and subdural blood are important primary injury factors in provoking SDs and that clustered SDs and parenchymal lesion expansion contribute independently to worse patient outcomes. These results warrant future prospective studies using detailed quantification of TBI lesion types to better understand the relationship between anatomic and physiologic measures of secondary injury.

The continuum of spreading depolarizations in acute cortical lesion development: Examining Leão's legacy.

A modern understanding of how cerebral cortical lesions develop after acute brain injury is based on Aristides Leão's historic discoveries of spreading depression and asphyxial/anoxic depolarization. Treated as separate entities for decades, we now appreciate that these events define a continuum of spreading mass depolarizations, a concept that is central to understanding their pathologic effects. Within minutes of acute severe ischemia, the onset of persistent depolarization triggers the breakdown of ion homeostasis and development of cytotoxic edema. These persistent changes are diagnosed as diffusion restriction in magnetic resonance imaging and define the ischemic core. In delayed lesion growth, transient spreading depolarizations arise spontaneously in the ischemic penumbra and induce further persistent depolarization and excitotoxic damage, progressively expanding the ischemic core. The causal role of these waves in lesion development has been proven by real-time monitoring of electrophysiology, blood flow, and cytotoxic edema. The spreading depolarization continuum further applies to other models of acute cortical lesions, suggesting that it is a universal principle of cortical lesion development. These pathophysiologic concepts establish a working hypothesis for translation to human disease, where complex patterns of depolarizations are observed in acute brain injury and appear to mediate and signal ongoing secondary damage.

'Spreading depression of Leão' and its emerging relevance to acute brain injury in humans.

A new research field in translational neuroscience has opened as a result of the recognition since 2002 that "spreading depression of Leão" can be detected in many patients with acute brain injury, whether vascular and spontaneous, or traumatic in origin, as well as in those many individuals experiencing the visual (or sensorimotor) aura of migraine. In this review, we trace from their first description in rabbits through to their detection and study in migraine and the injured human brain, and from our personal perspectives, the evolution of understanding of the importance of spread of mass depolarisations in cerebral grey matter. Detection of spontaneous depolarisations occurring and spreading in the periphery or penumbra of experimental focal cortical ischemic lesions and of their adverse effects on the cerebral cortical microcirculation and on the tissue glucose and oxygen pools has led to clearer concepts of how ischaemic and traumatic lesions evolve in the injured human brain, and of how to seek to improve clinical management and outcome. Recognition of the likely fundamental significance of spreading depolarisations for this wide range of serious acute encephalopathies in humans provides a powerful case for a fresh examination of neuroprotection strategies.

Simultaneous monitoring of potassium, glucose and lactate during spreading depolarization in the injured human brain - Proof of principle of a novel real-time neurochemical analysis system, continuous online microdialysis.

Spreading depolarizations occur spontaneously and frequently in injured human brain. They propagate slowly through injured tissue often cycling around a local area of damage. Tissue recovery after an spreading depolarization requires greatly augmented energy utilisation to normalise ionic gradients from a virtually complete loss of membrane potential. In the injured brain, this is difficult because local blood flow is often low and unreactive. In this study, we use a new variant of microdialysis, continuous on-line microdialysis, to observe the effects of spreading depolarizations on brain metabolism. The neurochemical changes are dynamic and take place on the timescale of the passage of an spreading depolarization past the microdialysis probe. Dialysate potassium levels provide an ionic correlate of cellular depolarization and show a clear transient increase. Dialysate glucose levels reflect a balance between local tissue glucose supply and utilisation. These show a clear transient decrease of variable magnitude and duration. Dialysate lactate levels indicate non-oxidative metabolism of glucose and show a transient increase. Preliminary data suggest that the transient changes recover more slowly after the passage of a sequence of multiple spreading depolarizations giving rise to a decrease in basal dialysate glucose and an increase in basal dialysate potassium and lactate levels.

Inverse neurovascular coupling to cortical spreading depolarizations in severe brain trauma.

Cortical spreading depolarization causes a breakdown of electrochemical gradients following acute brain injury, and also elicits dynamic changes in regional cerebral blood flow that range from physiological neurovascular coupling (hyperaemia) to pathological inverse coupling (hypoperfusion). In this study, we determined whether pathological inverse neurovascular coupling occurred as a mechanism of secondary brain injury in 24 patients who underwent craniotomy for severe traumatic brain injury. After surgery, spreading depolarizations were monitored with subdural electrode strips and regional cerebral blood flow was measured with a parenchymal thermal diffusion probe. The status of cerebrovascular autoregulation was monitored as a correlation between blood pressure and regional cerebral blood flow. A total of 876 spreading depolarizations were recorded in 17 of 24 patients, but blood flow measurements were obtained for only 196 events because of technical limitations. Transient haemodynamic responses were observed in time-locked association with 82 of 196 (42%) spreading depolarizations in five patients. Spreading depolarizations induced only hyperaemic responses (794% increase) in one patient with intact cerebrovascular autoregulation; and only inverse responses (-24% decrease) in another patient with impaired autoregulation. In contrast, three patients exhibited dynamic changes in neurovascular coupling to depolarizations throughout the course of recordings. Severity of the pathological inverse response progressively increased (-14%, -29%, -79% decrease, P < 0.05) during progressive worsening of cerebrovascular autoregulation in one patient (Pearson coefficient 0.04, 0.14, 0.28, P < 0.05). A second patient showed transformation from physiological hyperaemic coupling (44% increase) to pathological inverse coupling (-30% decrease) (P < 0.05) coinciding with loss of autoregulation (Pearson coefficient 0.19 → 0.32, P < 0.05). The third patient exhibited a similar transformation in brain tissue oxygenation, a surrogate of blood flow, from physiologic hyperoxic responses (20% increase) to pathological hypoxic responses (-14% decrease, P < 0.05). Pathological inverse coupling was only observed with electrodes placed in or adjacent to evolving lesions. Overall, 31% of the pathological inverse responses occurred during ischaemia (<18 ml/100 g/min) thus exacerbating perfusion deficits. Average perfusion was significantly higher in patients with good 6-month outcomes (46.8 ± 6.5 ml/100 g/min) than those with poor outcomes (32.2 ± 3.7 ml/100 g/min, P < 0.05). These results establish inverse neurovascular coupling to spreading depolarization as a novel mechanism of secondary brain injury and suggest that cortical spreading depolarization, the neurovascular response, cerebrovascular autoregulation, and ischaemia are critical processes to monitor and target therapeutically in the management of acute brain injury.

Surgical management of traumatic brain injury: a comparative-effectiveness study of 2 centers.

OBJECT: Mass lesions from traumatic brain injury (TBI) often require surgical evacuation as a life-saving measure and to improve outcomes, but optimal timing and surgical technique, including decompressive craniectomy, have not been fully defined. The authors compared neurosurgical approaches in the treatment of TBI at 2 academic medical centers to document variations in real-world practice and evaluate the efficacies of different approaches on postsurgical course and long-term outcome. METHODS: Patients 18 years of age or older who required neurosurgical lesion evacuation or decompression for TBI were enrolled in the Co-Operative Studies on Brain Injury Depolarizations (COSBID) at King's College Hospital (KCH, n = 27) and Virginia Commonwealth University (VCU, n = 24) from July 2004 to March 2010. Subdural electrode strips were placed at the time of surgery for subsequent electrocorticographic monitoring of spreading depolarizations; injury characteristics, physiological monitoring data, and 6-month outcomes were collected prospectively. CT scans and medical records were reviewed retrospectively to determine lesion characteristics, surgical indications, and procedures performed. RESULTS: Patients enrolled at KCH were significantly older than those enrolled at VCU (48 vs 34 years, p < 0.01) and falls were more commonly the cause of TBI in the KCH group than in the VCU group. Otherwise, KCH and VCU patients had similar prognoses, lesion types (subdural hematomas: 30%-35%; parenchymal contusions: 48%-52%), signs of mass effect (midline shift ≥ 5 mm: 43%-52%), and preoperative intracranial pressure (ICP). At VCU, however, surgeries were performed earlier (median 0.51 vs 0.83 days posttrauma, p < 0.05), bone flaps were larger (mean 82 vs 53 cm(2), p < 0.001), and craniectomies were more common (performed in 75% vs 44% of cases, p < 0.05). Postoperatively, maximum ICP values were lower at VCU (mean 22.5 vs 31.4 mm Hg, p < 0.01). Differences in incidence of spreading depolarizations (KCH: 63%, VCU: 42%, p = 0.13) and poor outcomes (KCH: 54%, VCU: 33%, p = 0.14) were not significant. In a subgroup analysis of only those patients who underwent early (< 24 hours) lesion evacuation (KCH: n = 14; VCU: n = 16), however, VCU patients fared significantly better. In the VCU patients, bone flaps were larger (mean 85 vs 48 cm(2) at KCH, p < 0.001), spreading depolarizations were less common (31% vs 86% at KCH, p < 0.01), postoperative ICP values were lower (mean: 20.8 vs 30.2 mm Hg at KCH, p < 0.05), and good outcomes were more common (69% vs 29% at KCH, p < 0.05). Spreading depolarizations were the only significant predictor of outcome in multivariate analysis. CONCLUSIONS: This comparative-effectiveness study provides evidence for major practice variation in surgical management of severe TBI. Although ages differed between the 2 cohorts, the results suggest that a more aggressive approach, including earlier surgery, larger craniotomy, and removal of bone flap, may reduce ICP, prevent cortical spreading depolarizations, and improve outcomes. In particular, patients requiring evacuation of subdural hematomas and contusions may benefit from decompressive craniectomy in conjunction with lesion evacuation, even when elevated ICP is not a factor in the decision to perform surgery.

Detection of spreading depolarization with intraparenchymal electrodes in the injured human brain.

BACKGROUND: Spreading depolarization events following ischemic and traumatic brain injury are associated with poor patient outcome. Currently, monitoring these events is limited to patients in whom subdural electrodes can be placed at open craniotomy. This study examined whether these events can be detected using intra-cortical electrodes, opening the way for electrode insertion via burr hole. METHODS: Animal work was carried out on adult Sprague-Dawley rats in a laboratory setting to investigate the feasibility of recording depolarization events. Subsequently, 8 human patients requiring craniotomy for traumatic brain injury or aneurysmal subarachnoid hemorrhage were monitored for depolarization events in an intensive care setting with concurrent strip (subdural) and depth (intra-parenchymal) electrode recordings. RESULTS: (1) Depolarization events can be reliably detected from intra-cortically placed electrodes. (2) A reproducible slow potential change (SPC) waveform morphology was identified from intra-cortical electrodes on the depth array. (3) The depression of cortical activity known to follow depolarization events was identified consistently from both intra-cortical and sub-cortical electrodes on the depth array. CONCLUSIONS: Intra-parenchymally sited electrodes can be used to consistently identify depolarization events in humans. This technique greatly extends the capability of monitoring for spreading depolarization events in injured patients, as electrodes can be sited without the need for craniotomy. The method provides a new investigative tool for the evaluation of the contribution of these events to secondary brain injury in human patients.

Propagation of cortical spreading depolarization in the human cortex after malignant stroke.

OBJECTIVE: To investigate hemodynamic response pattern and spatiotemporal propagation of cortical spreading depolarization in the peri-infarct region of malignant hemispheric stroke. METHODS: In this prospective observational case study we used intraoperative laser speckle technology to measure cerebral blood flow in patients with malignant hemispheric stroke. Additionally, postoperative occurrence of cortical spreading depolarization was monitored using a subdural recording strip for electrocorticography and infarct progression was assessed by serial MRI. RESULTS: In 7 of 20 patients, 19 blood flow changes typical of cortical spreading depolarizations occurred during a 20-minute period. Thirteen events were characterized by increase, 2 by biphasic response, and 4 by decrease of blood flow. Propagation velocity ranged from 1.7 to 9.2 mm/min and propagation area from 0.1 to 4.8 cm(2). Intrinsic optical signal alterations preceded and low-frequency vascular fluctuations were suppressed during the hemodynamic responses. A mean number of 56 ± 82 cortical spreading depolarizations per patient was recorded and a mean infarct progression of 30 ± 13 cm(3) was detected in 5 of 7 patients. CONCLUSIONS: We visualize the spatiotemporal propagation of spreading depolarizations in the human cerebral cortex intraoperatively. In patients with focal ischemia, multiple cortical spreading depolarizations with either hyperemic or hypoemic flow responses occurred. Our data suggest that, in patients with focal ischemia, cortical spreading depolarizations are associated with both unfavorable and protective hemodynamic responses.

Spreading ischemia after aneurysmal subarachnoid hemorrhage.

Spreading depolarization (SD) is a wave of mass neuronal and glial depolarization associated with net influx of cations and water. Prolonged SDs facilitate neuronal death. SD induces tone alterations in cerebral resistance arterioles, leading to either transient hyperperfusion (physiological neurovascular coupling) in healthy tissue or hypoperfusion (inverse neurovascular coupling = spreading ischemia) in tissue at risk for progressive damage. Spreading ischemia has been shown experimentally in an animal model replicating the conditions present following aneurysmal subarachnoid hemorrhage (aSAH), in animal models of the ischemic core and penumbra following middle cerebral artery occlusion, and in patients with aSAH. In animals, spreading ischemia produced widespread cortical necrosis. In patients, spreading ischemia occurred in temporal correlation with ischemic lesion development early and late after aSAH. We briefly review important features of SD and spreading ischemia following aSAH.

Effect of analgesics and sedatives on the occurrence of spreading depolarizations accompanying acute brain injury.

Spreading depolarizations are waves of mass neuronal and glial depolarization that propagate across the injured human cortex. They can occur with depression of neuronal activity as spreading depressions or isoelectric spreading depolarizations on a background of absent or minimal electroencephalogram activity. Spreading depolarizations are characterized by the loss of neuronal ion homeostasis and are believed to damage functional neurons, leading to neuronal necrosis or neurological degeneration and poor outcome. Analgesics and sedatives influence activity-dependent neuronal ion homeostasis and therefore represent potential modulators of spreading depolarizations. In this exploratory retrospective international multicentre analysis, we investigated the influence of midazolam, propofol, fentanyl, sufentanil, ketamine and morphine on the occurrence of spreading depolarizations in 115 brain-injured patients. A surface electrode strip was placed on the cortex, and continuous electrocorticographical recordings were obtained. We used multivariable binary logistic regression to quantify associations between the investigated drugs and the hours of electrocorticographical recordings with and without spreading depolarizations or clusters of spreading depolarizations. We found that administration of ketamine was associated with a reduction of spreading depolarizations and spreading depolarization clusters (P < 0.05). Midazolam anaesthesia, in contrast, was associated with an increased number of spreading depolarization clusters (P < 0.05). By using a univariate odds ratio analysis, we also found a significant association between ketamine administration and reduced occurrence of isoelectric spreading depolarizations in patients suffering from traumatic brain injury, subarachnoid haemorrhage and malignant hemispheric stroke (P < 0.05). Our findings suggest that ketamine-or another N-methyl-d-aspartate receptor antagonist-may represent a viable treatment for patients at risk for spreading depolarizations. This hypothesis will be tested in a prospective study.

Cortical spreading ischemia in the absence of proximal vasospasm after aneurysmal subarachnoid hemorrhage: evidence for a dual mechanism of delayed cerebral ischemia.

There are longstanding inconsistencies in the evidence thought to link vasospasm in the major branches of the Circle of Willis with delayed cerebral ischemia and poor outcome from aneurysmal subarachnoid hemorrhage (aSAH). The demonstrations, first in the laboratory, and more recently in patients with aSAH, of cortical spreading ischemia based on an abnormal response of the cerebral microcirculation to spreading depolarization offer an additional possible mechanism for delayed ischemia. That such events can occur in the substantial absence of proximal vasospasm is compatible with this concept, but the preliminary evidence needs support from more extensive studies.

Spreading depolarisations and outcome after traumatic brain injury: a prospective observational study.

BACKGROUND: Pathological waves of spreading mass neuronal depolarisation arise repeatedly in injured, but potentially salvageable, grey matter in 50-60% of patients after traumatic brain injury (TBI). We aimed to ascertain whether spreading depolarisations are independently associated with unfavourable neurological outcome. METHODS: We did a prospective, observational, multicentre study at seven neurological centres. We enrolled 109 adults who needed neurosurgery for acute TBI. Spreading depolarisations were monitored by electrocorticography during intensive care and were classified as cortical spreading depression (CSD) if they took place in spontaneously active cortex or as isoelectric spreading depolarisation (ISD) if they took place in isoelectric cortex. Investigators who treated patients and assessed outcome were masked to electrocorticographic results. Scores on the extended Glasgow outcome scale at 6 months were fitted to a multivariate model by ordinal regression. Prognostic score (based on variables at admission, as validated by the IMPACT studies) and spreading depolarisation category (none, CSD only, or at least one ISD) were assessed as outcome predictors. FINDINGS: Six individuals were excluded because of poor-quality electrocorticography. A total of 1328 spreading depolarisations arose in 58 (56%) patients. In 38 participants, all spreading depolarisations were classified as CSD; 20 patients had at least one ISD. By multivariate analysis, both prognostic score (p=0·0009) and spreading depolarisation category (p=0·0008) were significant predictors of neurological outcome. CSD and ISD were associated with an increased risk of unfavourable outcome (common odds ratios 1·56 [95% CI 0·72-3·37] and 7·58 [2·64-21·8], respectively). Addition of depolarisation category to the regression model increased the proportion of variance in outcome that could be attributed to predictors from 9% to 22%, compared with the prognostic score alone. INTERPRETATION: Spreading depolarisations were associated with unfavourable outcome, after controlling for conventional prognostic variables. The possibility that spreading depolarisations have adverse effects on the traumatically injured brain, and therefore might be a target in the treatment of TBI, deserves further research. FUNDING: US Army CDMRP PH/TBI research programme.

Chain length-dependent cooperativity in fatty acid binding and oxidation by cytochrome P450BM3 (CYP102A1).

Fatty acid binding and oxidation kinetics for wild type P450(BM3) (CYP102A1) from Bacillus megaterium have been found to display chain length-dependent homotropic behavior. Laurate and 13-methyl-myristate display Michaelis-Menten behavior while there are slight deviations with myristate at low ionic strengths. Palmitate shows Michaelis-Menten kinetics and hyperbolic binding behavior in 100 mmol/L phosphate, pH 7.4, but sigmoidal kinetics (with an apparent intercept) in low ionic strength buffers and at physiological phosphate concentrations. In low ionic strength buffers both the heme domain and the full-length enzyme show complex palmitate binding behavior that indicates a minimum of four fatty acid binding sites, with high cooperativity for the binding of the fourth palmitate molecule, and the full-length enzyme showing tighter palmitate binding than the heme domain. The first flavin-to-heme electron transfer is faster for laurate, myristate and palmitate in 100 mmol/L phosphate than in 50 mmol/L Tris (pH 7.4), yet each substrate induces similar high-spin heme content. For palmitate in low phosphate buffer concentrations, the rate constant of the first electron transfer is much larger than k (cat). The results suggest that phosphate has a specific effect in promoting the first electron transfer step, and that P450(BM3) could modulate Bacillus membrane morphology and fluidity via palmitate oxidation in response to the external phosphate concentration.

Spreading depolarizations have prolonged direct current shifts and are associated with poor outcome in brain trauma.

Cortical spreading depolarizations occur spontaneously after ischaemic, haemorrhagic and traumatic brain injury. Their effects vary spatially and temporally as graded phenomena, from infarction to complete recovery, and are reflected in the duration of depolarization measured by the negative direct current shift of electrocorticographic recordings. In the focal ischaemic penumbra, peri-infarct depolarizations have prolonged direct current shifts and cause progressive recruitment of the penumbra into the core infarct. In traumatic brain injury, the effects of spreading depolarizations are unknown, although prolonged events have not been observed in animal models. To determine whether detrimental penumbral-type depolarizations occur in human brain trauma, we analysed electrocorticographic recordings obtained by subdural electrode-strip monitoring during intensive care. Of 53 patients studied, 10 exhibited spreading depolarizations in an electrophysiologic penumbra (i.e. isoelectric cortex with no spontaneous activity). All 10 patients (100%) with isoelectric spreading depolarizations had poor outcomes, defined as death, vegetative state, or severe disability at 6 months. In contrast, poor outcomes were observed in 60% of patients (12/20) who had spreading depolarizations with depression of spontaneous activity and only 26% of patients (6/23) who had no depolarizations (χ2, P<0.001). Spontaneous electrocorticographic activity and direct current shifts of depolarizations were further examined in nine patients. Direct current shift durations (n=295) were distributed with a significant positive skew (range 0:51-16:19 min:s), evidencing a normally distributed group of short events and a sub-group of prolonged events. Prolonged direct current shifts were more commonly associated with isoelectric depolarizations (median 2 min 36 s), whereas shorter depolarizations occurred with depression of spontaneous activity (median 2 min 10 s; P<0.001). In the latter group, direct current shift durations correlated with electrocorticographic depression periods, and were longer when preceded by periodic epileptiform discharges than by continuous delta (0.5-4.0 Hz) or higher frequency activity. Prolonged direct current shifts (>3 min) also occurred mainly within temporal clusters of events. Our results show for the first time that spreading depolarizations are associated with worse clinical outcome after traumatic brain injury. Furthermore, based on animal models of brain injury, the prolonged durations of depolarizations raise the possibility that these events may contribute to maturation of cortical lesions. Prolonged depolarizations, measured by negative direct current shifts, were associated with (i) isoelectricity or periodic epileptiform discharges; (ii) prolonged depression of spontaneous activity and (iii) occurrence in temporal clusters. Depolarizations with these characteristics are likely to reflect a worse prognosis.