Recovery of the cortical evoked response following temporary middle cerebral artery occlusion in baboons: relation to local blood flow and PO2

Predictive Value of Multimodality Intraoperative Neurophysiological Monitoring During Cardiac Surgery

INTRODUCTION

This study aimed to determine the ability of multimodality intraoperative neurophysiologic monitoring, including somatosensory evoked potentials (SSEP) and EEG, to predict perioperative clinical stroke and stroke-related mortality after open-heart surgery in high-risk patients.

METHODS

The records of all consecutive patients who underwent coronary artery bypass grafting, and cardiac valve repair/replacement with high risk for stroke who underwent both SSEP and EEG recording at the University of Pittsburgh Medical Center between 2009 and 2015 were reviewed. Sensitivity and specificity of these modalities to predict in-hospital clinical strokes and stroke-related mortality were calculated.

RESULTS

A total of 531 patients underwent open cardiac procedures monitored using SSEP and EEG. One hundred thirty-one patients (24.67%) experienced significant changes in either modality. Fourteen patients (2.64%) suffered clinical strokes within 24 hours after surgery, and eight patients (1.50%) died during their hospitalization. The incidence of in-hospital clinical stroke and stroke-related mortality among patients who experienced a significant change in monitoring compared with those with no significant change was 11.45% versus 1.75%. The sensitivity and specificity of significant changes in either SSEP or EEG to predict in-hospital major stroke and stroke-related mortality were 0.93 and 0.77, respectively.

CONCLUSIONS

Intraoperative neurophysiologic monitoring with SSEP and EEG has high sensitivity and specificity in predicting perioperative stroke and stroke-related mortality after open cardiac procedures. These results support the benefits of multimodality neuromonitoring during cardiac surgery.

The core/penumbra model: implications for acute stroke treatment and patient selection in 2021

Despite major advances in prevention, ischaemic stroke remains one of the leading causes of death and disability worldwide. After centuries of nihilism and decades of failed neuroprotection trials, the discovery, initially in non-human primates and subsequently in man, that ischaemic brain tissue termed the ischaemic penumbra can be salvaged from infarction up to and perhaps beyond 24 h after stroke onset has underpinned the development of highly efficient reperfusion therapies, namely intravenous thrombolysis and endovascular thrombectomy, which have revolutionized the management of the acute stroke patient. Animal experiments have documented that how long the penumbra can survive depends not only on time elapsed since arterial occlusion ('time is brain'), but also on how severely perfusion is reduced. Novel imaging techniques allowing the penumbra and the already irreversibly damaged core in the individual subject to be mapped have documented that the time course of core growth at the expense of the penumbra widely differs from patient to patient, and hence that individual physiology should be considered in addition to time since stroke onset for decision-making. This concept has been implemented to optimize patient selection in pivotal trials of reperfusion therapies beyond 3 h after stroke onset and is now routinely applied in clinical practice, using computed tomography or magnetic resonance imaging. The notion that, in order to be both efficient and harmless, treatment should be tailored to each patient's physiological characteristics represents a radical move towards precision medicine.

Normobaric hyperoxia retards the evolution of ischemic brain tissue toward infarction in a rat model of transient focal cerebral ischemia

OBJECTIVES

Oxygen therapy has been long considered a logical therapy for ischemic stroke. Our previous studies showed that normobaric hyperoxia (normobaric hyperoxia (NBO), 95% O2 with 5% CO2) treatment during ischemia reduced ischemic neuronal death and cerebromicrovascular injury in animal stroke models. In this study, we studied the effects of NBO on the evolution of ischemic brain tissue to infarction in a rat model of transient focal cerebral ischemia.

METHODS

Male Sprague-Dawley rats were given NBO (95% O2) or normoxia (21% O2) during 90-min filament occlusion of the middle cerebral artery (MCAO), followed by 3 or 22.5 h of reperfusion. 2,3,5-triphenyltetrazolium chloride (TTC) staining was used to evaluate the longitudinal evolution of tissue infarction. Results： In normoxic rats, MCA-supplied cortical and striatal tissue was infarcted after 90-min MCAO with 22.5 h of reperfusion. NBO-treated rats showed a 61.4% reduction in infarct size and tissue infarction mainly occurred in the ischemic striatum. When infarction was assessed at an earlier time point, i.e. at 3 h of reperfusion, normoxic rats showed significantly smaller but mature infarction (no TTC staining, white color), with the infarction mainly occurring in the striatum. Unexpectedly, NBO-treated rats only showed immature lesion (partially stained by TTC, light white color) in the ischemic striatum, indicating that NBO treatment also retarded the process of neuronal death in the ischemic core. Of note, NBO-preserved striatal tissue underwent infarction after prolonged reperfusion. Conclusions： Our results demonstrate that NBO treatment given during cerebral ischemia retards the evolution of ischemic brain tissue toward infarction and NBO-preserved cortical tissue survives better than NBO-preserved striatal tissue during the phase of reperfusion.

Endothelial dysfunction abrogates the efficacy of normobaric hyperoxia in stroke

Hyperoxia has been uniformly efficacious in experimental focal cerebral ischemia. However, pilot clinical trials have showed mixed results slowing its translation in patient care. To explain the discordance between experimental and clinical outcomes, we tested the impact of endothelial dysfunction, exceedingly common in stroke patients but under-represented in experimental studies, on the neuroprotective efficacy of normobaric hyperoxia. We used hyperlipidemic apolipoprotein E knock-out and endothelial nitric oxide synthase knock-out mice as models of endothelial dysfunction, and examined the effects of normobaric hyperoxia on tissue perfusion and oxygenation using high-resolution combined laser speckle and multispectral reflectance imaging during distal middle cerebral artery occlusion. In normal wild-type mice, normobaric hyperoxia rapidly and significantly improved tissue perfusion and oxygenation, suppressed peri-infarct depolarizations, reduced infarct volumes, and improved neurological function. In contrast, normobaric hyperoxia worsened perfusion in ischemic brain and failed to reduce infarct volumes or improve neurological function in mice with endothelial dysfunction. These data suggest that the beneficial effects of hyperoxia on ischemic tissue oxygenation, perfusion, and outcome are critically dependent on endothelial nitric oxide synthase function. Therefore, vascular risk factors associated with endothelial dysfunction may predict normobaric hyperoxia nonresponders in ischemic stroke. These data may have implications for myocardial and systemic circulation as well.

Hypoxia-inducible factor signalling mechanisms in the central nervous system

In the CNS, neurones are highly sensitive to the availability of oxygen. In conditions where oxygen availability is decreased, neuronal function can be altered, leading to injury and cell death. Hypoxia has been implicated in a number of central nervous system pathologies including stroke, head trauma and neurodegenerative diseases. Cellular responses to oxygen deprivation are complex and result in activation of short- and long-term mechanisms to conserve energy and protect cells. Failure of synaptic transmission can be observed within minutes following this hypoxia. The acute effects of hypoxia on synaptic transmission are primarily mediated by altering ion fluxes across membranes, pre-synaptic effects of adenosine and other actions at glutamatergic receptors. A more long-term feature of the response of neurones to hypoxia is the activation of transcription factors such as hypoxia-inducible factor. The activation of hypoxia-inducible factor is governed by a family of dioxygenases called hypoxia-inducible factor prolyl 4 hydroxylases (PHDs). Under hypoxic conditions, PHD activity is inhibited, thereby allowing hypoxia-inducible factor to accumulate and translocate to the nucleus, where it binds to the hypoxia-responsive element sequences of target gene promoters. Inhibition of PHD activity stabilizes hypoxia-inducible factor and other proteins thus acting as a neuroprotective agent. This review will focus on the response of neuronal cells to hypoxia-inducible factor and its targets, including the prolyl hydroxylases. We also present evidence for acute effects of PHD inhibition on synaptic transmission and plasticity in the hippocampus.

Toward the Neurovascular Unit A Journey in Clinical Translation

The Nobel laureate Max Delbrück often said that it is the crossover between disciplines where advances are possible in science. This certainly has been true for our understanding of the vascular biology of the central nervous system in the setting of ischemic stroke. The ability to cross the boundaries of hemostasis, neurology, hematology, and neuroscience has facilitated our research direction to define the relation of the microvasculature to neuron function. Work begun with the clinical scientific exploration of the contributions of arterial thrombosis to the acute injury processes initiated by focal cerebral ischemia has led to an increased understanding of the effects of ischemia on microvessel integrity.

Normobaric hyperoximia increases hypoxia-induced cerebral injury: DTI study in rats

Perinatal hypoxia affects normal neurological development and can lead to motor, behavioral and cognitive deficits. A common acute treatment for perinatal hypoxia is oxygen resuscitation (hyperoximia), a controversial treatment. Magnetic resonance imaging (MRI), including diffusion tensor imaging (DTI), was performed in a P7 rat model of perinatal hypoxia to determine the effect of hyperoximia. These studies were performed on two groups of animals: 1) animals which were subjected to ischemia followed by hypoxia (HI), and 2) HI followed by hyperoximic treatment (HHI). Lesion volumes on high resolution MRI and DTI derived measures, fractional anisotropy (FA), mean diffusivity (MD), and axial and radial diffusivities (lambda(l) and lambda(t), respectively) were measured in vivo one day, one week, and three weeks after injury. Most significant differences in the MRI and DTI measures were found at three weeks after injury. Specifically, three weeks after HHI injury resulted in significantly larger hyperintense lesion volumes (95.26 +/- 50.42 mm(3)) compared to HI (22.25 +/- 17.62 mm(3)). The radial diffusivity lambda(t) of the genu of corpus callosum was significantly larger in HHI (681 +/- 330 x 10(-6) mm(2)/sec) than in HI (486 +/- 96 x 10(-6) mm(2)/sec). Over all, most significant differences in all the DTI metrics (FA, MD, lambda(t), lambda(l)) at all time points were found in the corpus callosum. Our results suggest that treatment of perinatal hypoxia with normobaric oxygen does not ameliorate, but exacerbates damage.

Inhibition of gp91(phox) contributes towards normobaric hyperoxia afforded neuroprotection in focal cerebral ischemia

Oxygen therapy is a promising treatment strategy for ischemic stroke. One potential safety concern with oxygen therapy, however, is the possibility of increased generation of reactive oxygen species (ROS), which could exacerbate ischemic brain injury. Our previous study indicated that normobaric hyperoxia (NBO, 95% O(2) with 5% CO(2)) treatment during ischemia salvaged ischemic brain tissue and significantly reduced ROS generation in transient experimental stroke. In this follow-up study, we tested the hypothesis that suppression of NADPH oxidase is an important mechanism for NBO-induced reduction of ROS generation in focal cerebral ischemia. Male Sprague-Dawley rats were given NBO (95% O(2)) or normoxia (21% O(2)) during 90-min filament occlusion of the middle cerebral artery, followed by 22.5-hour reperfusion. NBO treatment increased the tissue oxygen partial pressure (pO(2)) level in the ischemic penumbra close to the pre-ischemic value, as measured by electronic paramagnetic resonance (EPR), and led to a 30.2% reduction in magnetic resonance imaging (MRI) apparent diffusion coefficients (ADC) lesion volume. Real time PCR and western blot analyses showed that the mRNA and protein expression of NADPH oxidase catalytic subunit gp91(phox) were upregulated in the ischemic brain, which was significantly inhibited by NBO. As a consequence of gp91(phox) inhibition, NBO treatment reduced NADPH oxidase activity in the ischemic brain. Our results suggest that NBO treatment given during ischemia reduces ROS generation via inhibiting NADPH oxidase, which may serve as an important mechanism underlying NBO's neuroprotection in acute ischemic stroke.

The rapid decrease in astrocyte-associated dystroglycan expression by focal cerebral ischemia is protease-dependent

During focal cerebral ischemia, the detachment of astrocytes from the microvascular basal lamina is not completely explained by known integrin receptor expression changes. Here, the impact of experimental ischemia (oxygen-glucose deprivation (OGD)) on dystroglycan expression by murine endothelial cells and astrocytes grown on vascular matrix laminin, perlecan, or collagen and the impact of middle cerebral artery occlusion on alphabeta-dystroglycan within cerebral microvessels of the nonhuman primate were examined. Dystroglycan was expressed on all cerebral microvessels in cortical gray and white matter, and the striatum. Astrocyte adhesion to basal lamina proteins was managed in part by alpha-dystroglycan, while ischemia significantly reduced expression of dystroglycan both in vivo and in vitro. Furthermore, dystroglycan and integrin alpha6beta4 expressions on astrocyte end-feet decreased in parallel both in vivo and in vitro. The rapid loss of astrocyte dystroglycan during OGD appears protease-dependent, involving an matrix metalloproteinase-like activity. This may explain the rapid detachment of astrocytes from the microvascular basal lamina during ischemic injury, which could contribute to significant changes in microvascular integrity.

Normobaric hyperoxia improves cerebral blood flow and oxygenation, and inhibits peri-infarct depolarizations in experimental focal ischaemia

Normobaric hyperoxia is under investigation as a treatment for acute ischaemic stroke. In experimental models, normobaric hyperoxia reduces cerebral ischaemic injury and improves functional outcome. The mechanisms of neuroprotection are still debated because, (i) inhalation of 100% O2 does not significantly increase total blood O2 content; (ii) it is not known whether normobaric hyperoxia increases O2 delivery to the severely ischaemic cortex because of its short diffusion distance; and (iii) hyperoxia may reduce collateral cerebral blood flow (CBF) to ischaemic penumbra because it can cause vasoconstriction. We addressed these issues using real-time two-dimensional multispectral reflectance imaging and laser speckle flowmetry to simultaneously and non-invasively determine the impact of normobaric hyperoxia on CBF and oxygenation in ischaemic cortex. Ischaemia was induced by distal middle cerebral artery occlusion (dMCAO) in normoxic (30% inhaled O2, arterial pO2 134 +/- 9 mmHg), or hyperoxic mice (100% inhaled O2 starting 15 min after dMCAO, arterial pO2 312 +/- 10 mmHg). Post-ischaemic normobaric hyperoxia caused an immediate and progressive increase in oxyhaemoglobin (oxyHb) concentration, nearly doubling it in ischaemic core within 60 min. In addition, hyperoxia improved CBF so that the area of cortex with < or =20% residual CBF was decreased by 45% 60 min after dMCAO. Furthermore, hyperoxia reduced the frequency of peri-infarct depolarizations (PIDs) by more than 60%, and diminished their deleterious effects on CBF and metabolic load. Consistent with these findings, infarct size was reduced by 45% in the hyperoxia group 2 days after 75 min transient dMCAO. Our data show that normobaric hyperoxia increases tissue O2 delivery, and that novel mechanisms such as CBF augmentation, and suppression of PIDs may afford neuroprotection during hyperoxia.

Stroke Research in the Modern Era: Images versus Dogmas

Recovery of function following ischaemic stroke is a fascinating clinical observation. It comprises several modes, e.g. spectacular recovery in a matter of hours or days and gradual recovery over months or even years. That a non-functioning neural system can regain its function, even partially so, is challenging because of the obvious therapeutic implications. Until the mid-70s, however, dogmas largely prevailed which underpinned the then nihilistic approach to stroke patients. Proving these dogmas wrong has been a major achievement of modern stroke research. Thanks particularly to physiological imaging, key observations from the basic neurosciences have translated into the clinical realm in ways immediately understandable to the clinician, allowing the emergence of pathophysiology-based management.

Models of focal cerebral ischemia in the nonhuman primate

Ischemic stroke is a uniquely human disease syndrome. Models of focal cerebral ischemia developed in nonhuman primates provide clinically relevant platforms for investigating pathophysiological alterations associated with ischemic brain injury, microvascular responses, treatment responses, and clinically relevant outcomes that may be appropriate for ischemic stroke patients. A considerable number of advantages attend the use of nonhuman primate models in cerebral vascular research. Appropriate development of such models requires neurosurgical expertise to produce single or multiple vascular occlusions. A number of experimentally and clinically accessible outcomes can be measured, including neurological deficits, neuron injury, evidence of non-neuronal cell injury, infarction volume, real-time imaging of injury development, vascular responses, regional cerebral blood flow, microvascular events, the relation between neuron and vascular events, and behavioral outcomes. Nonhuman primate models of focal cerebral ischemia provide excellent opportunities for understanding the vascular and cellular pathophysiology of cerebral ischemic injury, which resembles human ischemic stroke, and the appropriate study of pharmacological interventions in a human relevant setting.

Brain tissue oxygenation monitoring supplementary to somatosensory evoked potential monitoring for aneurysm surgery. Initial clinical experience

The object of the study was to evaluate brain tissue oxygenation (p(ti)O2) for intra-operative monitoring of critical ischemic events during early cerebral aneurysm surgery of the anterior circulation supplementary to somatosensory evoked potentials (SEPs). P(ti)O2 was continuously evaluated during surgery for an intracranial aneurysm in 28 patients. Standard cortical SEP monitoring was simultaneously performed. The two monitoring methods were compared by evaluating their respective responses to intra-operative events (particularly temporary vessel occlusion), clinical and neuroradiological outcome. P(ti)O2 and SEPs were reliably used for monitoring in 16 patients. Seven patients were excluded due to too high or too low p(ti)O2 readings or initial absence of SEPs (six patients). Of 64 intra-operative events 19 events (eight patients) were associated with a significant decrease in p(ti)O2 (below 10 mmHg), 22 events (13 patients) were associated with a significant change in SEP amplitude (< 50% decrease related to baseline). Temporary vessel occlusion (six SEP andp(ti)O2 changes each in eightpatients) and surgical dissection were most likely to be followed by significant changes in a monitoring method. Intra-operative p(ti)O2 was found to be a safe, rapid method for documenting ischemic events. P(ti)O2 was found to supplement SEP monitoring. The use of p(ti)O2 measurement as a routine monitoring method in aneurysm surgery is limited by its focal spatial resolution. Nevertheless, it might be helpful as an adjunct in situations when SEPs are absent at baseline, in aneurysms when parent vessel anatomy is complex or if temporary vessel occlusion is planned.

Correlation between central somatosensory conduction time, blood flow velocity, and delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage

In this retrospective study of 67 aneurysmal patients, the predictive role of central conduction time (CCT) on vasospasm occurrence evaluated by means of transcranial Doppler sonography (TCD) and the correlation of CCT to blood flow velocity measured simultaneously in postoperative course were studied. Data about the clinical state of patients at the time of admission (Hunt Hess scale), severity of subarachnoidal hemorrhage on initial CT scan (Fisher grade), timing of surgery (acute or delayed), outcome (Glasgow Outcome Scale), severity of vasospasm graded by highest mean blood flow velocity (BFV) during the entire clinical course and CCT values measured at admission (preoperatively), then postoperatively (one day after surgery) and simultaneously with later TCD investigations were collected from the files. Interhemispheric difference of CCT was also calculated. The results showed that CCT at admission was not predictive for vasospasm. CCT measured either at admission or on the first postoperative day did not differ significantly in the different grades of vasospasm. Similar results were obtained in the acute and in the late operated group of patients. The results also suggest that increased CCT and interhemispheric difference at the time of admission indicate a worse prognosis, but this can be related to higher surgical risk rather than to a higher incidence of late ischemic deterioration. Simultaneous CCT and TCD examinations demonstrated that coincident and statistically significant (p < 0.01) increase of actual CCT (6.7 msec) was found only in the severe grade of vasospasm (BFV 200 cm/s). The authors discuss the role of CCT and TCD monitoring in the management of aneurysmal subarachnoid hemorrhage.

Neurophysiologic effects of retrograde cerebral perfusion used for aortic reconstruction

OBJECTIVE

The results of neurophysiologic monitoring using somatosensory evoked potentials (SSEPs) and electroencephalography (EEG) were analyzed to determine if retrograde cerebral perfusion (RCP) supported central nervous system electrical function during surgery that required temporary interruption of antegrade cerebral perfusion (IACP).

DESIGN

A prospective, observational study.

SETTING

A university hospital.

PARTICIPANTS

Fifteen adult patients who underwent aortic reconstruction using RCP and three patients who underwent thoracic aortic operations using hypothermic circulatory arrest without RCP.

INTERVENTIONS

SSEPs and EEG were monitored continuously throughout the operation. Regression analysis was performed to determine the factors that affected the rate of decrease in SSEP amplitudes during IACP and the time required for SSEP and EEG activity to recover after antegrade cerebral perfusion (ACP) was restored.

MEASUREMENTS AND MAIN RESULTS

The amplitude of SSEPs that were elicited decreased over time after IACP. The mean +/- standard deviation (SD) time required for the brachial plexus (Erb's point), cervicomedullary junction (N13), and brainstem (N18) SSEPs to decrease to 0.5 of their original amplitude after IACP were 30 +/- 2, 19 +/- 2, and 16 +/- 2 minutes, respectively. The rate of decrease in the N18 SSEP amplitude after IACP correlated positively to the fraction of no-flow time (p = 0.01).

CONCLUSION

RCP attenuated the rate of decay in SSEP amplitudes during IACP. This suggested that RCP had a measurable physiologic effect on central nervous system function and may increase the time that ACP can be safely interrupted.

Why do all drugs work in animals but none in stroke patients? 1. Drugs promoting cerebral blood flow

Medical treatments which presumably alter cerebral blood flow (CBF) have been quite unimpressive in their effect on stroke outcome. In considering experimental and clinical data from the use of haemodilution and of the antiplatelet agent prostacyclin in focal cerebral ischaemia, and the current work with fibrinolytic agents in acute stroke, several lessons are apparent. Often agents hypothesized to affect CBF receive an underserved reputation based on sparse experimental evidence. Significant even unsuspected differences between species limit application to the clinical setting. Limitations of CBF measurements in experimental models and in humans raise questions about apparent responses to those agents. The failure to confirm a relationship between CBF enhancement and reduction in infarct development experimentally has plagued these approaches. The need for early application of agents which may modulate CBF during cerebral ischaemia is critical. Attention to these general issues and careful application of appropriate models are necessary so that a potentially useful therapeutic intervention is not overlooked.

Chronic cerebral hypoperfusion and impaired neuronal function in rats

BACKGROUND AND PURPOSE

Studies in acute cerebral ischemia have shown that reductions in cerebral blood flow of up to 50% do not lead to infarction or alterations in neuronal electric activity. Little is known about the effects of chronic reductions in cerebral blood flow. The purpose of this study was to evaluate neuronal electrophysiological function in brain that had been subjected to a chronic reduction of cerebral blood flow of less than 50%. Based on existing knowledge of thresholds of cerebral ischemia, neuronal electrophysiological function should be unaffected by hypoperfusion of this magnitude.

METHODS

An arteriovenous fistula model in the rat was used to induce chronic cerebral hypoperfusion with reductions of cerebral blood flow of 25% to 50% as measured previously by 14C-labeled autoradiography. Using in vitro electrophysiological brain slice techniques, long-term potentiation in hippocampal CA1 neurons was examined extracellularly after 6 months of chronic noninfarctional cerebral hypoperfusion. Brains were also examined histologically at this time for evidence of cerebral infarction.

RESULTS

There was no evidence of cerebral infarction. Long-term potentiation was produced in 9 of 12 control animals and only 2 of 8 hypoperfused animals. This difference was significant (P < .05) and demonstrated that long-term potentiation was impaired in animals with chronic hypoperfusion.

CONCLUSIONS

Noninfarctional reductions in cerebral blood flow of up to 50% do impair neuronal function in chronic cerebral ischemia, a result quite distinct from that seen in acute ischemia. The threshold for neuronal dysfunction in chronic cerebral hypoperfusion is lower than that found in acute cerebral ischemia, suggesting that duration as well as severity of ischemic insult determines cellular viability. Chronic hypoperfusion may lead to a noninfarctional state with impaired neuronal function, a category of chronic cerebral ischemia not previously identified.

Differential effects of transient occlusion of common carotid arteries in normotensive rats on the somatosensory and visual system

The effect of transient occlusion of both carotid arteries in normotensive rats (BCCA) on the electrical function of the central nervous system was monitored by recording somatosensory evoked potentials (SEPs), visual evoked potentials (VEPs) and electroretinogram (ERG). The amplitude and latency of cortical SEPs were not affected by BCCA. In contrast, the latency of P1 and N1 of VEPs were increased and the peak-to-peak amplitude (P1-N1) decreased. The amplitude of the b-wave of the ERG was reduced and its latency increased during BCCA. These changes in VEPs and ERG were limited to the period of BCCA. During the first hour of reperfusion VEPs and the b-wave of the ERG revealed no differences between former occluded animals and sham-operated controls. The present results suggest that both sensory pathways display a different susceptibility to BCCA.

Augmented efficacy of external CPR by intermittent occlusion of the ascending aorta

BACKGROUND

After prolonged cardiac arrest, conventional methods of closed-chest cardiac compression are ineffective. This is primarily because of failure to generate minimal threshold levels of coronary perfusion pressure for cardiac resuscitation. This report introduces a new option for cardiac resuscitation by use of a combination of intermittent ascending aortic balloon occlusion, aortic infusion, and precordial compression to increase the pressure gradient for coronary perfusion.

METHODS AND RESULTS

Twenty anesthetized, mechanically ventilated, normovolemic domestic pigs were investigated. A 10F balloon catheter was advanced from the left femoral artery into the ascending aorta. Ventricular fibrillation was induced with an AC current delivered through an electrode catheter advanced into the right ventricle. Precordial compression was initiated after 7 minutes of untreated ventricular fibrillation. The animals were randomized to one of four groups: (1) balloon occlusion with proximal infusion of oxygenated saline, (2) balloon occlusion alone, (3) proximal aortic infusion together with epinephrine without balloon occlusion, and (4) injection of epinephrine without balloon occlusion or proximal infusion. For balloon occlusion, the balloon was inflated for 30 seconds during each minute of cardiopulmonary resuscitation. In the subsets of animals that received infusions, oxygenated saline (30 mL) was injected into the proximal aorta immediately after balloon occlusion. Epinephrine was used in two subsets: It was injected as a bolus in amounts of 30 micrograms/kg into the right atrium at 30 seconds after start of precordial compression and repeated as required to maintain coronary perfusion pressure within the range of 25 to 30 mm Hg. Defibrillation was attempted at 1 minute after start of precordial compression and at 1-minute intervals thereafter. Resuscitation attempts were continued until there was return of spontaneous circulation or for a total of 30 minutes after start of precordial compression. Coronary perfusion pressure generated by precordial compression was significantly increased after balloon occlusion. Each of 10 animals was successfully resuscitated and survived for 48 hours after balloon occlusion whether or not it was combined with infusion. Three of five animals were resuscitated by a combination of infusion and epinephrine in the absence of aortic occlusion, but none survived for 48 hours (P = .02). Only one epinephrine-treated animal was successfully resuscitated and survived for 48 hours in the absence of balloon occlusion or infusion (P < .05).

CONCLUSIONS

Ascending aortic balloon occlusion with or without proximal aortic infusion strikingly increased resuscitability and 48-hour survival after cardiac arrest under conditions when conventional methods failed.

Current role of electroencephalography in cerebral ischemia

BACKGROUND

The electroencephalogram has been largely supplanted by neuroimaging techniques for the diagnosis and localization of ischemic stroke. However, because of its close correlation with cerebral metabolism and its ability to detect brief transient alterations in cortical function, the electroencephalogram may still be useful for certain diagnostic applications in stroke.

SUMMARY OF REVIEW

The relation of electroencephalographic phenomena to cerebral blood flow and metabolism is reviewed. Ten clinical questions that can be addressed by the electroencephalogram in patients with stroke are posed. The presence of seizures, confirmation of diagnosis, intraoperative monitoring, and level of consciousness are areas of proven usefulness. The electroencephalogram provides less worthwhile information about the time course, prognosis, and localization of strokes. Computerized techniques are of potential but unproven value.

CONCLUSIONS

The electroencephalogram retains a worthwhile place in the evaluation of patients with cerebral ischemia when it is used to answer specific questions. All patients with strokes do not need electroencephalograms, but the test can provide uniquely useful data in some.

Differences in carotid shunt flow rates and implications for cerebral blood flow

A wide variety of carotid shunts are available for use in extracranial carotid surgery. Since it is commonly assumed that when properly positioned all shunts are equal in ability to protect the brain from cerebral ischemia, the choice of shunt is usually based on handling characteristics. However, after an intraoperative stroke occurred in a patient, we compared shunt flow rates using a simple and reproducible method of measurement. A mock circuit was created using a saline-filled fluid reservoir connected to the particular shunt being tested via 1/2-inch tubing. Hydrostatic pressure across the shunt was varied by changing the height of the reservoir, and the flow was collected over 30-second intervals. Multiple flow rate measurements were performed for each shunt with pressure gradients varying from 25 to 150 cm H2O. The data show significant hemodynamic differences among commercially available carotid shunts. A pressure gradient of 75 cm H2O produced a 2.8-fold variation in the amount of fluid delivered by various shunts. Minimal cerebral blood flow requirements and the possibility of underperfusion require that the surgeon consider such data in choosing an appropriate carotid shunt.

Diffusion-weighted imaging studies of cerebral ischemia in gerbils. Potential relevance to energy failure

BACKGROUND AND PURPOSE

Diffusion-weighted magnetic resonance imaging has been shown to be particularly suited to the study of the acute phase of cerebral ischemia in animal models. The studies reported in this paper were undertaken to determine whether this technique is sensitive to the known ischemic thresholds for cerebral tissue energy failure and disturbance of membrane ion gradients.

METHODS

Diffusion-weighted images of the gerbil brain were acquired under two sets of experimental conditions: as a function of cerebral blood flow after controlled graded occlusion of the common carotid arteries (partial ischemia), as a function of time following complete bilateral carotid artery occlusion (severe global ischemia), and on deocclusion after 60 minutes of ischemia.

RESULTS

During partial cerebral ischemia, the diffusion-weighted images remained unchanged until the cerebral blood flow was reduced to 15-20 ml.100 g-1.min-1 and below, when image intensity increased as the cerebral blood flow was lowered further. This is similar to the critical flow threshold for maintenance of tissue high-energy metabolites and ion homeostasis. After the onset of severe global cerebral ischemia, diffusion-weighted image intensity increased gradually after a delay of approximately 2.5 minutes, consistent with complete loss of tissue adenosine triphosphate and with the time course of increase in extracellular potassium. This hyperintensity decreased on deocclusion following 60 minutes of ischemia.

CONCLUSIONS

The data suggest that diffusion-weighted imaging is sensitive to the disruption of tissue energy metabolism or a consequence of this disruption. This raises the possibility of imaging energy failure noninvasively. In humans, this could have potential in visualizing brain regions where energy metabolism is impaired, particularly during the acute phase following stroke.

Management of giant intracranial aneurysms

Based on an own material of 64 cases a survey is given on the management of giant intracranial aneurysms. Essential investigations are as well CT and Magnetic Resonance Scanning as detailed angiographic studies. With regard to the operative handling the following questions are discussed: approach; use of temporary vascular occlusion and related monitoring; preparation of the aneurysm neck for occlusion. In cases without recent subarachnoid haemorrhage morbidity and mortality were less than 10%. It was 15% in cases where recent haemorrhage had occurred.

Effects of nilvadipine on neuronal function in the ischemic cat brain

The effect of nilvadipine, a dihydropyridine-type calcium entry blocker, on neuronal function during and following ischemia was investigated with a model of focal cerebral ischemia in cats and was compared with that of nicardipine. Drugs were given intravenously 30 minutes before occlusion of the left middle cerebral artery (MCA). Occlusion of the left MCA for 60 minutes was followed by reperfusion for 90 minutes. The amplitude of the somatosensory evoked potentials (SEPs), and the residual relative regional cortical blood flow in the left ectosylvian gyrus and the left posterior sigmoid gyrus, were higher or had a tendency toward higher values in the nilvadipine-treated (32 micrograms/kg) group than in other groups. After reperfusion, the amplitude of SEPs rapidly recovered in the nilvadipine-treated groups. When administered before MCA occlusion, nilvadipine improved neuronal function measured by SEPs both during and following the ischemic period. Thus, nilvadipine is effective against neuronal dysfunction in focal cerebral ischemia.

Effect of ischemia and reperfusion on lambda of the lumped constant of the [14C]deoxyglucose technique

We measured the parameter lambda, which is the ratio of the distribution spaces of 2-deoxy-D-glucose (DG) and glucose in the brain, in a model of focal cerebral ischemia in the cat. lambda is the parameter in the lumped constant of the [14C]DG technique most susceptible to changes in ischemia. Cats were subjected to occlusion of the middle cerebral artery for a period of 2 h. During the last 60 min of occlusion, [14C]DG was infused in a programmed fashion so as to obtain a stable arterial blood [14C]DG concentration. The brain was funnel-frozen to preserve tissue metabolites and the frozen brain was sampled regionally (4 to 7-mg samples) for local concentrations of glucose, ATP, phosphocreatine (PCr), and lactate. In a separate series of cats, the infusion of [14C]DG was started after 2 h of occlusion and 3 h of recirculation. In both series, lambda declined slightly for increased levels of tissue glucose and increased appreciably as tissue glucose decreased. A similar relationship was observed between lambda and ATP and PCr, although the correlation was not as clear. Since lambda, and hence the lumped constant, increases in ischemia as well as in postischemic tissue, it is important to measure tissue glucose concentration if quantitative values of local cerebral glucose metabolism are desired in this condition.

Lidocaine accelerates neuroelectrical recovery after incomplete global ischemia in rabbits

The use of high-dose lidocaine for cerebral protection during ischemia has produced varied results. Our study uses a new, single carotid artery preparation in the rabbit to produce incomplete global ischemia by graded carotid occlusion; specific electroencephalographic changes are used as the end point for the extent of blood flow reduction sustained during 20 minutes. We monitored arterial pressure, intracranial pressure, and internal carotid blood flow that were recorded with an electromagnetic flowmeter after surgical ligation of the opposite internal and the two vertebral arteries, and we studied the electroencephalogram and somatosensory-evoked potentials elicited by stimulation of the sciatic nerve. Low-dose lidocaine (0.2 mg/kg/min) infused throughout the experiment significantly accelerated the time course of the return of electroencephalographic and evoked-potential amplitudes toward control. Deep halothane anesthesia alone elicited the slowest recovery, suggesting that the action of lidocaine was independent of its general anesthetic effect. There were very small differences among the groups in the measured arterial pressure, intracranial pressure, and cerebral blood flow, suggesting that lidocaine changed recovery rate without markedly modifying any characteristic of the postischemic cerebral perfusion. The protective effect of lidocaine may be the result of a specific blockade of Na+ channels or a decrease in excitatory neurotransmitter release, either of which would cause a delay in the onset of the events that lead to neuronal damage during ischemia.

Brain stem auditory-evoked potentials in different strains of rodents

This study was conducted to evaluate variations in brain stem auditory-evoked potentials (BAEPs) among different strains of rodents. BAEPs were recorded by routine procedures from rodents of different strains or species. These included 22 Long-Evans, 28 Wistar and 28 Sprague-Dawley rats, and six hamsters. Within the first 10 ms, there were five consistent and reproducible positive waves of BAEPs in each rodent, named I, II, III, IV and V in correspondence with the nomenclature of waves I-VII in human BAEPs. These BAEPs were also similar to those observed in other vertebrates and in human controls. However, there were variations in waveforms and peak latencies among rodents, even in the rats of the same strain that came from different laboratory centres. At optimal stimulation intensity, usually around 90 dB, the mean latencies of the waves varied as follows: I, 1.23-1.53 ms; II, 1.88-2.28 ms; III, 2.62-2.94 ms; IV, 3.49-3.97 ms; and V, 4.47-5.14 ms. They were significantly different between species, but not in different strains of rats if they came from the same animal centre. The conduction time in the central portion illustrated by interpeak latencies between I and III, III and V, and I and V was dependent on the species (P less than 0.05). When recorded in a soundproof incubator, the minimal hearing threshold showed a significant species difference. The animal BAEP model can be employed for evaluating the physiological function or the pathological conditions of the brain stem. The confirmation of BAEP variations among different species or strains will be helpful in deciding which kind of rodents will be appropriate to serve as animal models for the various purposes of BAEP studies.

Continuous lidocaine infusion and focal feline cerebral ischemia

We measured somatosensory evoked potentials, infarct size, and cerebral blood flow in 20 cats subjected to occlusion of the middle cerebral artery for 3 hours, followed by an equal period of reperfusion. The cats were randomized into a treatment group that received a continuous infusion of 2 mg/kg lidocaine hydrochloride or a control group that received an equivalent volume of normal saline. All 10 treated cats retained measurable evoked potentials throughout the experiment. In five control cats, evoked potentials disappeared completely at some point during the occlusion (difference between groups significant at p less than 0.001). Mean amplitude of the major cortical wave in the nine treated cats with cerebral infarcts was higher than that of the nine corresponding controls (p less than 0.05). Lidocaine reduced the mean +/- SEM size of the infarcts from 30.1 +/- 6.0% in the control group to 14.7 +/- 4.9% in the treated group (p less than 0.05). As blood flow was reduced in the infarct and peri-infarct zones in the control but not the treated cats, our results suggest that the beneficial effects of lidocaine may be due to preservation of blood flow in the ischemic zone.

Effect of lidocaine after experimental cerebral ischemia induced by air embolism

To investigate possible approaches to the treatment of neural damage induced by air embolism and other forms of acute cerebral ischemia, somatosensory evoked potentials (SEP's) were measured after cerebral air embolism in the anesthetized cat. Air was introduced into the carotid artery in increments of 0.08 ml until the SEP amplitude was reduced to approximately 10% or less of baseline values. Either a saline or lidocaine infusion was begun 5 minutes after inducing cerebral ischemia. In the saline-treated group, SEP amplitude was reduced to 6.7% +/- 1.6% (mean +/- standard error of the mean) of baseline, with a return to 32.6% +/- 4.7% of baseline over a 2-hour period. In the lidocaine-treated group, SEP amplitude was reduced to 5.9% +/- 1.5%, with a return to 77.3% +/- 6.2% over a 2-hour period. The results suggest that lidocaine administration facilitates the return of neural function after acute cerebral ischemia induced by air embolism.

Effects of a new Ca2+ antagonist, KB-2796, on the regional cerebral blood flow and somatosensory evoked potentials in the ischemic brain in cats

Effects of a new Ca2+ antagonist, 1-[bis(4-fluorophenyl) methyl]-4-(2,3,4-trimethoxybenzyl) piperazine dihydrochloride (KB-2796), on the regional cerebral blood flow (rCBF) and somatosensory evoked potentials (SEPs) were investigated using a model of focal cerebral ischemia in cats. In experiment 1, an occlusion of the middle cerebral artery for 4 hours persistently reduced the ipsilateral rCBF in both the control and the KB-2796-treated groups. However, the flow reduction was much milder in the treatment group than in the control group. Amplitudes of the SEPs diminished in both groups but the rate of deterioration was much slower in the treatment group than in the control group. In experiment 2, an occlusion of the middle cerebral artery for 1 hour was followed by reperfusion for 3 hours. The ipsilateral rCBF decreased during occlusion in both the control and the treatment groups. In the control group, postischemic hyperperfusion was seen in the ectosylvian gyrus after reperfusion, whereas the ipsilateral rCBF recovered rapidly to the control values without showing a phase of hyperperfusion in the treatment group. The rate of recovery of the SEPs was also much more rapid in the treatment group.

Evoked potential monitoring and temporary clipping in cerebral aneurysm surgery

Temporary occlusion of the parent artery greatly facilitates the dissection of large cerebral aneurysms, while much reducing the risk of intraoperative rupture and avoiding the use of profound arterial hypotension. Intraoperative somatosensory evoked potential (SEP) monitoring was carried out in 25 aneurysm cases where temporary clipping was employed electively under moderate hypothermia. Occlusion times ranged from 6.3 to 52 minutes at 28.7 degrees C to 32.5 degrees C. Among 15 middle cerebral artery (MCA) occlusion cases the SEP was lost within 5 or 6 minutes in two cases undergoing early surgery and in one case with marked vasospasm and was lost within 9 minutes in one case with pre-existing infarction in the territory of the MCA. The SEP persisted throughout MCA occlusion periods of 6.3 to 52 minutes in 8 cases. Occlusion of parent arteries of unruptured aneurysms was well tolerated. At least 2 minutes of MCA occlusion after loss of the SEP were tolerated without neurological sequelae, while transient new deficits were seen when MCA occlusion was continued for 4 and for 4 + 11 minutes and an increased deficit was seen when occlusion was continued for 7 minutes after loss of the SEP. In each of the internal carotid artery (ICA) occlusion and bilateral anterior cerebral artery occlusion groups the SEP was lost in one case and was absent for about one minute before reperfusion was instituted. The ICA case had a transient deficit lasting about 4 hours; no other complications were seen in these two groups. Complications were not seen in any case where the SEP was not lost during the occlusion period. Factors affecting collateral perfusion and possible means of increasing tolerance to ischaemia in this situation are discussed.(ABSTRACT TRUNCATED AT 250 WORDS)

Extended latency of the cortical component of the somatosensory-evoked potential accompanying moderate increases in cerebral blood flow during systemic hypoxia in cats

In 24 adult cats, the somatosensory-evoked potential (SEP) and cerebral blood flow (CBF) were measured under paralyzed, anesthetized conditions during exposure to two different ventilatory regimens. Group I cats (ventilated from 20 to 2% oxygen) responded with a significant increase in white matter blood flow from 25.0 +/- 7.8 to 43.8 +/- 10.5 ml/100 g/min recorded at 7% O2. Gray matter blood flows in these animals increased but not to significant levels above the control blood flow measured at 20%. No significant changes in blood flow were observed in group II animals ventilated over the range of 25-3% oxygen as gray matter rose slightly (but not significantly) with hypoxia and white matter flows remained at levels of 25-30 ml/100 g/min. The latency of the cortical component of the SEP was related to the degree of hypoxia. For both groups, significant extensions in the latency to the occurrence of the cortical component of the SEP (normalized to the % of control SEP) occurred in each case (P less than 0.05). An inverse, linear relationship existed between the latency to the appearance of cortical component (ms) and the percentage oxygen concentration of the ventilatory mixture. No significant changes in thalamocortical conduction times were found, which indicates that hypoxia may have generalized effects on the synaptic pathways supporting the conduction of the SEP. The variation in blood flow and the latency of the cortical component observed between groups I and II may reflect the oxygen concentration used at the beginning of the experiment (25 vs 20%) and the gradations between them vs 3 and 2%.(ABSTRACT TRUNCATED AT 250 WORDS)

Loss of the somatosensory evoked response as an indicator of reversible cerebral ischemia during hypothermic, low-flow cardiopulmonary bypass

We assessed somatosensory evoked response (SSER) as a monitor of cerebral protection during nonpulsatile, hypothermic cardiopulmonary bypass (CPB). In 13 dogs under CPB, extracorporeal flow rate (EFR) thresholds for loss of SSER were determined by stepwise reduction of the EFR from 2.0 to 0.25 L/min/m2 at perfusion temperatures of 35 degrees C, 30 degrees C, 25 degrees C, and 20 degrees C. Testing began at 35 degrees C in Group 1 (N = 6) and at 20 degrees C in Group 2 (N = 7). Immediately on loss of SSER (denoted as a decrease of 80% or more in the amplitude of the somatosensory evoked potentials), EFR was restored to 2.0 L/min/m. Thresholds for loss of SSER ranged between 0.75 and 0.25 L/min/m2. SSER was always restored on return of EFR to 2.0 L/min/m2; thus loss of SSER was a reversible ischemic change. Both groups had similar threshold values at 35 degrees C, but at lower temperatures, Group 1 thresholds were significantly higher than those in Group 2. Since 35 degrees C was the first test temperature for Group 1 but the last for Group 2, EFR reduction at 35 degrees C apparently caused neurophysiological changes (depletion of cortical energy reserves), which diminished subsequent tolerance to ischemia, but EFR reduction at 20 degrees C did not. Our findings show that loss of SSER warns of reversible cerebral ischemia, and support SSER monitoring as a useful measure of cerebral function during low-flow, hypothermic CPB.

Clinical evidence supporting a subthalamic origin of the P15 wave of the somatosensory evoked potentials to median nerve stimulation

Both somatosensory (SSEPs) and brain-stem auditory evoked potentials (BAEPs) were recorded in 3 patients with localized lesions in the thalamus or brain-stem. In one patient with a right thalamic cystic tumour there was a significant interhemispheric difference in the central conduction time (CCT), but the N14-P15 interval was not affected on either side and BAEPs showed normal wave latencies and interpeak latencies (IPLs). The second patient had a colloid cyst of the third ventricle in which central herniation had occurred resulting in 'locked-in' syndrome. The P15 peak was absent on one side and markedly prolonged in latency on the other. BAEPs showed neither wave IV nor V on either side. The third patient had compression of the right posterior rostral pons by a metastatic tumour, resulting in significant prolongation of the CCT on the side of the tumour because of increase in the N14-P15 interval. Both I-V and III-V interpeak latencies were significantly prolonged bilaterally without prolongation in I-III IPL in this case. There was a correlation between the electrophysiological abnormalities of P15 and of BAEP wave V. These results suggest that the origin of the P15, which is usually recorded as a far-field potential, may be in the subthalamus or the upper part of the brain-stem.

Effects of temporary arterial occlusion on somatosensory evoked responses in aneurysm surgery

Changes in the central conduction time (CCT) during the application of temporary clips were studied in 40 patients who had undergone operations for intracranial aneurysms in relation to postoperative neurological outcome. Ten of these 40 patients (25%) showed postoperative morbidity, although promptly recoverable in 5. None of the patients whose CCTs did not change following temporary occlusion of major vessels showed any postoperative morbidity, except in one case of anterior cerebral artery aneurysm. In 6 patients, temporary vascular occlusion caused a considerable transient prolongation in CCT of up to 10 msec. Two of these 6 patients were associated with postoperative neurological deficit (which was recoverable in 1). The cortical response became flat in 15 patients. Seven of these 15 patients showed hemispheric deficits postoperatively, although recoverable in 4. There was a correlation between the change in the somatosensory evoked response and postoperative outcome. Disappearance of the N20 potential following occlusion is regarded as a danger signal, but postoperative, irrecoverable neurological deficit seems to be unlikely if its disappearance takes more than 3-4 minutes. Even if the cortical response disappears, the clinical outcome is expected to be good if the N20 potential recovers within 20 minutes after recirculation.

Acute cerebral ischaemia: concurrent changes in cerebral blood flow, energy metabolites, pH, and lactate measured with hydrogen clearance and 31P and 1H nuclear magnetic resonance spectroscopy. I. Methodology

CBF has been measured with the hydrogen clearance technique in the two cerebral hemispheres of the gerbil under halothane anaesthesia. This has been correlated with changes in local pH, tissue lactate, and phosphorus energy metabolites measured in the same animals with 1H and 31P nuclear magnetic resonance (NMR) spectroscopy. The NMR measurements were made with two surface coils, one on each hemisphere. This article describes the experimental details and shows that in acute unilateral or bilateral forebrain ischaemia metabolic changes can be monitored by NMR with no significant interhemispheric cross talk. The metabolic effects of reperfusion are also shown. The model allows the definition of the time course of the metabolic consequences of regional ischaemia and reperfusion in individual laboratory animals.

Plasticity of the brain in respect of functional restoration after subarachnoid haemorrhage

Subarachnoid haemorrhage caused by aneurysmal rupture constitutes a great impact on the brain and on the intracranial content as a whole, with emphasis on the subarachnoid spaces and arteries. The rupture is followed by a wide range of pathological alterations in the neural function and an outcome varying from neglected signs subsiding in a few days to immediate death. Two main factors seem to influence the different events after subarachnoid bleeding. One is the rupture itself which can be extremely variable in severity and in its immediate as well as late consequences. The other is the ability of all parts of the intracranial content to recover. In order to understand either of both the other should also be looked at and both have to be dealt with if we are to treat patients with an aneurysmal rupture properly. For this reason a grading of rupture will be given in respect of some characteristic events in the light of neural restoration. Clearing of CSF, resolution of brain oedema, restoration of impaired CBF, absorption of cisternal and parenchymal haematoma are all of importance. The majority of lesions which developed after the rupture are not fatal or irreversible and even the neural tissue destroyed by the impact or late ischaemia can be functionally replaced. Possible methods of treatment for attaining this functional restoration will be discussed.

Evaluation of brain dysfunction in hypertensive putaminal hemorrhage with multimodality evoked potentials

Changes in multimodality evoked potentials (MEP's), consisting of somatosensory evoked potentials (SEP's), visual evoked potentials (VEP's), and auditory evoked brainstem responses (AEBR's), were studied in 36 patients with hypertensive putaminal hemorrhage to ascertain the relation among areas and distribution of brain dysfunction, the size of hemorrhage on computerized tomographic scan, and the clinical outcome. Among MEP's, SEP's were most significantly involved in all patients. Abnormalities in VEP's and AEBR's remained mild or moderate when the hemorrhage did not extend to the diencephalon. If SEP's were normal or mildly abnormal, they improved early the ictus. These patients did well clinically. If SEP's were absent, the patients had poor outcome even when the hemorrhage was small and located outside the internal capsule. In contrast, deterioration or persistence of MEP's indicated secondary insult to the brain and poor patient outcome. Early and serial MEP studies are useful in evaluating primary and secondary brain dysfunction and in predicting patient outcome in hypertensive putaminal hemorrhage.

Cerebral blood flows and tissue oxygen levels associated with maintenance of the somatosensory evoked potential and cortical neuronal activity in focal ischemia

The middle cerebral artery was occluded in 18 cats to evaluate the physiological consequences of cerebral blood flow reductions on the somatosensory evoked potential, spontaneous neuronal activity, and oxygen availability in the ipsilateral and contralateral hemispheres. In the ipsilateral ectosylvian gyrus high-grade ischemia was produced as blood flow in the gray matter was reduced from 52.1 +/- 8.6 (mean +/- SE) to 13.3 +/- 9.0 ml/100 g/min and in the white matter from 33.8 +/- 5.6 to 6.1 +/- 6.4 ml/100 g/min. This significant reduction (p less than 0.05) was associated with abolition of the cortical component of the somatosensory evoked potentials. In all animals occlusion resulted in a predictable extended latency change and a variable amplitude response of the cortical component of the contralaterally recorded somatosensory evoked potentials. In 5 animals, oxygen availability was measured and spontaneous neuronal activity in the contralateral hemisphere was recorded. Volume expansion and hemodilution with either dextran or saline infusions elevated cerebral blood flow in the contralateral gray matter significantly (p less than 0.05) compared with the control and clip values. Ipsilateral spontaneous activity stopped within 4-12 minutes of occlusion, while contralateral spike activity persisted at rates at least equal to those recorded immediately following occlusion.

Comparison of the somatosensory evoked potential and the direct cortical response following severe incomplete global ischemia: selective vulnerability of the white matter conduction pathways

Eight cats were subjected to graded hemorrhagic hypotension following bilateral carotid ligation to produce incomplete global cerebral ischemia. Three additional cats served as controls. The somatosensory evoked potential (SEP) and direct cortical response (DCR) were monitored in all animals and in each case, the cortical component of the SEP was abolished during progressive ischemia while the morphology of the DCR was well-preserved but with reduced amplitude. Determinations of adenosine triphosphate (ATP), phosphocreatine (PCr), and lactate levels in cerebral cortex and white matter were made in five experimental cats and the three controls. At the time of failure of the cortical SEP, PCr was dramatically reduced and lactate moderately elevated in the white matter while ATP remained unchanged. Cortical lactate was only mildly elevated and PCr and ATP were unchanged accounting for preservation of the DCR. In this model of global ischemia, abolition of the cortical SEP is due to a block of stimulus conduction in white matter projection pathways. A hypothesis to explain the observed metabolic changes is presented and correlation is made to clinical situations.

Effect of transient cerebral ischemia on metabolic activation of a somatosensory circuit

The effects of transient ischemia on the metabolic responsiveness of a well-defined brain circuit were investigated with [14C]2-deoxyglucose autoradiography. Rats underwent 30 min of severe forebrain ischemia followed by postischemic recirculation periods of 1, 2, 3, 5, and 10 days. At these times, unilateral whisker stimulation was carried out, resulting in the metabolic activation of the whisker barrel circuit. An altered pattern of glucose utilization within both stimulated and nonstimulated circuit relay stations was observed at 1, 2, and 3 days following ischemia. At 1 day, stimulus-evoked increases in metabolic activity were severely depressed within both the ventrobasal thalamus and layer IV of the cortical barrel field region. Baseline metabolic rate within nonstimulated relay areas was also severely depressed at this time. At postischemic days 2 and 3, moderate levels of increased glucose utilization were apparent overlying cortical layer IV and the superficial half of layer VI, while layers I, II, III, and V appeared less responsive to metabolic activation. By day 5, whisker stimulation resulted in normal levels of increased glucose utilization within the activated ventrobasal thalamus and layer IV of the cortical barrel field region. Glucose utilization within nonactivated relay stations, depressed at earlier time periods, had also returned to control levels by day 5. At both 5 and 10 days, an altered laminar pattern of elevated glucose utilization was apparent within the activated barrel field region, with local CMRglu being depressed in layer V compared with control values. These results demonstrate that periods of transient ischemia produce both reversible and longer-lasting effects on the ability of the CNS to respond to peripheral activation.(ABSTRACT TRUNCATED AT 250 WORDS)