CBF and time thresholds for the formation of ischemic cerebral edema, and effect of reperfusion in baboons

Focal cerebral ischemia in rats: effects of induced hypertension, during reperfusion, on CBF

The effect of phenylephrine-induced hypertension on CBF was investigated after 120 min of middle cerebral artery occlusion in rats. Blood pressure was manipulated by one of the following schedules during a 90-min period of reperfusion: 90/NORM, 90 min of normotensive reperfusion; 90/HTN, 90 min of hypertensive reperfusion (MABP increased by 30 mm Hg); or 15/HTN, the 90-min period of reperfusion was divided into 30 min of normotension, followed by 15 min of hypertension and 45 min of normotension. At the end of reperfusion, 100 microCi kg-1 of [14C]iodoantipyrine was given and an autoradiographic analysis of CBF performed. In the coronal brain section at the center of middle cerebral artery distribution, the area (percentage of hemisphere, mean +/- SD) with a CBF of 0-20 or 21-40 ml 100 g-1 min-1 was less (p less than 0.05) in the 15/HTN group (1 +/- 2 and 5 +/- 3%, respectively) versus the 90/HTN group (12 +/- 4 and 10 +/- 4%), which was in turn less than in the 90/NORM group (18 +/- 5 and 22 +/- 6%). These data are consistent with the hypothesis that during reperfusion a short interval of hypertension effectively augments CBF via an abrupt opening of collapsed vessels and that a more sustained interval of hypertension conveys no added benefit.

Computed tomographic-angiographic findings within the first five hours of cerebral infarction

BACKGROUND AND PURPOSE

Modern management of acute stroke necessitates early diagnosis. To this end, we sought to delineate the radiographic features of focal hemispheric infarction within 5 hours of ictus.

METHODS

Fifty patients, ages 54-79, with ischemic strokes productive of at least hemiparesis underwent computed tomographic scanning and cerebral angiography (n = 38) or carotid ultrasound (n = 12). Radiographic lesions were characterized for location, size, and pathophysiology.

RESULTS

Acute abnormalities, hypodensity, and mass effect were seen in 56% of scans and confirmed on a second scan 5-7 days later. Intracranial angiographic abnormalities occurred in 61% of patients: arterial occlusions in 45% and delayed arterial filling in 16%. Hemorrhagic infarctions occurred in 26% of second scans and were associated with mass effect (100%) and arterial occlusions (89%). Infarcts with hemorrhagic transformation were larger on both scans than those without (p = 0.001). Of four patients with infarctions in watershed territories on the scans, two had middle cerebral artery occlusions on angiography, thereby questioning the specificity of such scan lesions to low-flow states.

CONCLUSIONS

We conclude that cerebral infarctions are often visible on early scans, but their locations may not be etiologically determinative. The infarcts associated with intracranial arterial occlusions (45%) were of thromboembolic origin, but, given current controversies as to the pathophysiology of lacunar and watershed infarctions, we cannot ascertain the etiology in the remainder. These findings are relevant to the new stroke therapies that require administration in the first hours after infarction.

Time- and pressure-dependent changes in blood-brain barrier permeability after temporary middle cerebral artery occlusion in rats

After 180 min of temporary middle cerebral artery occlusion in rats, the affect of phenylephrine-induced hypertension on blood-brain barrier permeability was assessed. One of the following blood-pressure regimens was maintained during either a 30- or 120-min period of reperfusion: (a) 30/Norm, 30 min of normotensive reperfusion was allowed; (b) 30/HTN, mean arterial blood pressure was increased by 35 mm Hg during 30 min of reperfusion; (c) 120/Norm, 120 min of normotensive reperfusion was allowed; or (d) 120/HTN, mean arterial blood pressure was increased by 35 mm Hg during 120 min of reperfusion. Evans blue (30 mg/kg) was given, and brains were analyzed for Evans blue by spectrophotometry. Evans blue (microgram/g brain tissue, mean +/- SD) was greater (P less than 0.05) in both hypertensive groups versus their time matched normotensive groups (30/HTN: 80 +/- 16 versus 18 +/- 6 in the 30/Norm group; 120/HTN: 17 +/- 6 versus 8 +/- 3 in the 120/Norm group). In addition, Evans blue was greater (P less than 0.05) in both 30-min groups versus their pressure matched 120-min groups (30/Norm: 18 +/- 6 versus 8 +/- 3 in the 120/Norm group; 30/HTN: 80 +/- 16 versus 17 +/- 6 in the 120/HTN group). The data are consistent with previous studies which have demonstrated an opening of the blood-brain barrier at the onset of reperfusion. In addition, the data support a hypothesis that changes in blood-brain barrier permeability are more sensitive to hypertension in the early period of reperfusion.

Serial changes in somatosensory evoked potentials following cerebral infarction

The relationship between somatosensory evoked potentials (SEPs) and recovery from stroke was investigated in 12 patients. All had suffered recent cerebral infarction. SEPs were performed within the first week, 6 weeks, 3 months and 6 months after stroke onset. Improvement of initially abnormal SEPs was maximal in the first 6 weeks and this correlated closely with the period of maximum clinical improvement. The results of this study suggest that the major effect of stroke on SEPs occurs acutely and is little affected by secondary degenerative processes.

Haemodynamic considerations in the management of patients with subarachnoid haemorrhage

Cerebral vasospasm occurs, following subarachnoid haemorrhage, in the majority of patients and is accompanied by cerebral ischaemia in 30%. The objectives of this article are to review (1) the effects of subarachnoid haemorrhage and vasospasm on cerebral blood flow (CBF); (2) the effects of induced hypotension and hypocapnia on CBF in these patients; (3) current therapy for cerebral ischaemia from vasospasm. The medical literature was searched using Index Medicus; for the period 1983-90 this search was done on a computer with the CD-ROM version of Index Medicus, Silver Platter. Papers were selected on the basis of validity and applicability to clinical practice; animal studies are included when human data is lacking. Cerebral vasospasm may decrease cerebral blood flow, disturb autoregulation and place the patient at risk for delayed cerebral ischaemia. Intraoperative induced hypotension and hypocapnia can decrease CBF further, although effects of either on outcome have not been evaluated. Calcium antagonists are effective for both the prevention and the treatment of delayed cerebral ischaemia. Of the mechanical treatments, systemic-arterial hypertension has the firmest scientific foundation, although this is frequently combined with haemodilution and blood volume expansion. There is a need for randomized clinical trials to assess the efficacy of these latter treatments.

Comparison of diffusion- and T2-weighted MRI for the early detection of cerebral ischemia and reperfusion in rats

The sensitivity of diffusion-weighted MRI was compared to that of T2-weighted MRI following temporary middle cerebral artery occlusion (MCA-O) for 33 min followed by 4 h of reperfusion in rats. Diffusion-weighted spin-echo images using strong gradients (b value of 1413 s/mm2) demonstrated a significant increase in signal intensity in ischemic regions as early as 14 min after onset of ischemia in comparison to the normal, contralateral hemisphere (p less than 0.05). This hyperintensity returned to baseline levels during reperfusion. T2-weighted images showed no evidence of brain injury during the temporary occlusion. In three rats subjected to permanent MCA-O, diffusion-weighted MRI demonstrated an increased signal intensity on the first image following occlusion and continued to increase during the 4-h observation period. T2-weighted images failed to demonstrate significant injury until approximately 2 h after MCA-O. Signal intensity ratios of ischemic to normal tissues were greater in the diffusion-weighted images than in the T2-weighted MR images at all time points (p less than 0.05). Close anatomical correlation was found between the early and sustained increase in diffusion-weighted MRI signal intensity and localization of infarcts seen on post-mortem histopathology.

Quantitative proton magnetic resonance imaging in focal cerebral ischemia in rat brain

Proton magnetic resonance (MR) imaging has been recommended as a diagnostic tool for the detection of focal cerebral ischemia. We compared microscopic MR images of rat brains after focal cerebral ischemia with evidence of histological damage found on corresponding silver-impregnated or cresyl violet-stained brain sections. Ten male Wistar rats were subjected to permanent unilateral occlusions of the right middle cerebral and common carotid arteries under halothane anesthesia. Twenty-four hours later the area of injury on MR images amounted to 26% of the total slice area, whereas only 9% of the total slice area was necrotic on histological sections from the same animals. The infarcted areas on tissue sections were surrounded by regions of selective neuronal injury in the cerebral cortex and occasionally in the hippocampus. The area of injury on MR images was larger than the combined areas of infarction and selective neuronal injury on histological sections. Areas of increased T2 values on MR images extended medially into noninfarcted striatum and laterally and dorsally into noninfarcted cortex. The lateral and dorsal areas on MR images frequently coincided with cortical areas in which considerable selective neuronal injury was present in the upper cortical layers. We hypothesize that the abnormal areas on MR images above histologically normal brain tissue represent the ischemic penumbra. If true, this is the first demonstration of the ischemic penumbra by MR imaging and may reflect our use of Wistar rats, a new image analysis technique, and ultra-high resolution MR imaging.

Hypervolemic-hemodilution and hypertension during temporary middle cerebral artery occlusion in rats: the effect on blood-brain barrier permeability

The effect of hypervolemic-hemodilution, with and without hypertension, on blood-brain barrier permeability was investigated in rats, after 180 minutes of middle cerebral artery occlusion (MCAo), and 60 minutes of reperfusion. One of the following conditions was maintained during MCAo: 1) Control--hematocrit and blood pressure were not manipulated; 2) Hypervolemic-Hemodilution/Normotension--the hematocrit was decreased to 30%; 3) Hypervolemic-Hemodilution/Hypertension--the hematocrit was decreased to 30% and mean arterial pressure increased by 30 mmHg with phenylphrine. In all groups, Evans Blue was administered, and its concentration determined by spectrophotometric assay. Evans Blue (micrograms (g-1 of brain tissue [mean +/- SD]) was greater in the Hypervolemic-Hemodilution/Hypertension group (71 +/- 20) versus the Control (13 +/- 9) and Hypervolemic-Hemodilution/Normotension (17 +/- 10) groups (p less than 0.05). No other differences were present. These results support the hypothesis that during MCAo, hypervolemic-hemodilution/hypertensive therapy effects an increase in blood-brain barrier permeability in the early period of reperfusion.

Stable xenon-enhanced CT measurement of cerebral blood flow in reversible focal ischemia in baboons

When the lateral striate arteries of the baboon are temporarily occluded for either 20 or 60 minutes, a near-cessation of blood flow is followed by a dramatic, transient local increase in blood flow values. These findings are evident from serial xenon (Xe)-computerized tomography (CT) measurement of cerebral blood flow (CBF). In this study, 20 minutes of vessel occlusion resulted in brief (less than 1 hour) hyperemia, with no subsequent CT alteration and minimal random neuronal injury. Sixty minutes of occlusion resulted in a more prolonged hyperemia, a low-density area on CT images within 3 hours of reperfusion, and infarction of all cellular elements within the anterior lentiform nucleus. The Xe-CT method provides a sensitive, noninvasive technique for examining sequential alterations of CBF in small regions deep within the brain. This method of recording CBF also permits correlative studies of cerebral infarction, both clinically and experimentally, and allows reasonable inference about the probabilities of neuronal tissue damage with or without reperfusion.

An RSPCA/FRAME Survey of the Use of Non-human Primates as Laboratory Animals in Great Britain, 1984–1988

A literature-based survey of the use of non-human primates as laboratory animals in Great Britain in 1984–1988 was carried out as a background to extending debate about the ethical and practical issues involved. The 289 publications considered were grouped in 15 subject areas and reviewed in terms of scientific purpose, methods employed, numbers and species of animals used, and their source, care and ultimate fate. In addition, the Association of the British Pharmaceutical Industry provided a comment on the use of non-human primates by pharmaceutical companies. Specific causes for concern were identified, and future prospects considered.

An intravascular technique to occlude the middle cerebral artery in baboons

A technique is described for occlusion of the middle cerebral artery in the baboon by an intravascular approach. A torque catheter is introduced under fluroscopic control into the internal carotid artery by transfemoral catheterization. In conjunction with a guide wire an infusion microcatheter with increasing stiffness from the distal tip to the proximal shaft is positioned in the proximal part of the middle cerebral artery via the introducer system. N-Butyl-2-cyanoacrylate-monomers are injected into the microcatheter for permanent occlusion of the middle cerebral artery. The procedure was successfully completed in 21 out of 24 baboons. In 3 baboons the occlusion could not be achieved since the torque catheter could not pass proximal extreme tortuosities of possibly arterisclerotic internal carotid arteries. Infarcts in the 21 animals were confirmed by computerized tomography and/or autopsies in all animals.

Pial arterial pressure contribution to early ischemic brain edema

The effect of pial arterial pressure (PAP) on brain edema was examined in cats with middle cerebral artery (MCA) occlusion. Measurements of PAP and regional CBF (rCBF) were collected in the central core and the peripheral margin of the MCA territory over 180 min post MCA occlusion. Brain water content in each region was determined at the end of the experiment. MCA occlusion resulted in decreased PAP and rCBF in both the core (PAP = 13 mm Hg, rCBF = 9 ml/100 g/min) and the peripheral region (PAP = 15 mm Hg, rCBF = 18 ml/100 g/min). Brain edema developed in both the core and the peripheral region. Brain water content was correlated inversely with PAP in the core region and positively in the peripheral region. The results indicate that decreased blood flow contributes to cytotoxic edema in the core, and a hydrostatic pressure gradient preferentially enhances edema formation in the peripheral region. Maintenance of high perfusion pressure early after ischemia onset may suppress brain edema in the core region.

Cerebral blood flow determination within the first 8 hours of cerebral infarction using stable xenon-enhanced computed tomography

Cerebral blood flow mapping with stable xenon-enhanced computed tomography (Xe/CT) was performed in conjunction with conventional computed tomography (CT) within the first 8 hours after the onset of symptoms in seven patients with cerebral infarction. Six patients had hemispheric infarctions, and one had a progressive brainstem infarction. Three patients with very low (less than 10 ml/100 g/min) blood flow in an anatomic area appropriate for the neurologic deficit had no clinical improvement by the time of discharge from the hospital; follow-up CT scans of these three patients confirmed infarction in the area of very low blood flow. Three patients with moderate blood flow reductions (15-45 ml/100 g/min) in the appropriate anatomic area had significant clinical improvement from their initial deficits and had normal follow-up CT scans. One patient studied 8 hours after stroke had increased blood flow (hyperemia) in the appropriate anatomic area and made no clinical recovery.

Effect of indomethacin and a free radical scavenger on cerebral blood flow and edema after cerebral artery occlusion in cats

Using the middle cerebral artery occlusion model in cats, we evaluated the possible role of the cyclooxygenase pathway in alterations of local cerebral blood flow and the development of cortical edema following prolonged ischemia or recirculation. We divided 57 cats into three groups, and each cat received saline (control), indomethacin, or the free radical scavenger ONO-3144. Each group was subdivided into prolonged ischemia (4 hours of occlusion: PI) and recirculation (2 hours of occlusion followed by 2 hours of recirculation: RC) subgroups. We compared local cerebral blood flow and cortical specific gravity between the PI and RC subgroups of the control and drug-treated groups. In the PI subgroup, indomethacin did not influence the time course of local cerebral blood flow but significantly worsened the decrease in cortical specific gravity. On the other hand, indomethacin significantly improved postischemic hypoperfusion and ameliorated the decrease in cortical specific gravity in the RC subgroup. The effects of ONO-3144 were similar to those of indomethacin, except that ONO-3144 did not affect cortical specific gravity in the PI subgroup. Indomethacin inhibits cyclooxygenase activity, whereas ONO-3144 scavenges the oxygen-centered radical released in the conversion of prostaglandin G2 to prostaglandin H2. Thus, prostaglandins do not seem to play a major role in the occurrence of brain edema due to prolonged regional ischemia. By contrast, oxygen-centered radicals released from the cyclooxygenase pathway appear to be at least partially responsible for the occurrence of recirculation-induced edema and postischemic hypoperfusion.

Magnetic resonance imaging and 31P magnetic resonance spectroscopy for evaluating focal cerebral ischemia

Recent advances in magnetic resonance (MR) imaging and MR spectroscopy (MRS) allow the noninvasive in vivo study of a variety of anatomical, physiological, and biochemical alterations that may occur in different cerebral pathologies. The authors have investigated the use of MR imaging and MRS to monitor the evolution of experimental focal cerebral ischemia in rats. Permanent focal cerebral ischemia was induced in 36 rats, and 12 normal rats were used as a control group. Changes in high-energy phosphate metabolites were followed in vivo using MRS during the 1st hour and at 3 and 6 hours after ischemic insult. Changes in vivo MR images were evaluated at 1, 3, 6, 12, and 24 hours after ischemic insult. Significant decreases (p less than 0.05) in phosphocreatine/inorganic phosphate ratios and intracellular pH values occurred immediately after the induction of ischemia. The presence of an infarcted area seen on MR images was a constant finding at 3 hours after ischemic insult, and was well defined and localized at 12 and 24 hours. The location of areas of infarction seen on MR images correlated well with areas identified histopathologically. The T1 and T2 MR relaxation times were significantly increased 3 hours after ischemic insult and remained prolonged for at least 24 hours. The results show that MR imaging is a sensitive method to measure cerebral infarction, and that MRS is a sensitive measure of changes that occur in the early phases of ischemia, perhaps when cellular changes may still be reversible. At 3 and 6 hours after the ischemic insult, however, 31P-MRS spectra may appear to be "normal" despite the presence of well-documented areas of infarction.

The risk of ischaemic brain damage during the use of self-retaining brain retractors

Self-retaining brain retractors (SRBR) are commonly used during intracranial surgery and they are indispensable during microneurosurgery. To evaluate limitations in the employment of SRBR, as well animal as human studies have been performed. In the animal studies, male Wistar rats were used for measurements of regional cerebral blood flow (rCBF) changes during brain retractor pressure (BRP) provided by lead weights. These weights, corresponding to different levels of mm Hg, were applicated for different periods of time on the parietal cortex after craniotomy. In one part of the animal studies different profiles of the application surface of the weights were evaluated. For measurement of the rCBF (n = 41) autoradiography with carbon-14(14C)iodoantipyrine was used as described by Gjedde et al (1980). A neuropathological method (n = 30) was used to reveal possible brain damage after graded BRP. In the rats the thresholds of rCBF, regional cerebral perfusion pressure (rCPP) and time were 20-25 ml/100 g/min, 20 mm Hg and 7-10 minutes respectively. In the human studies only alert patients without neurological deficits (except defects of the visual fields) and in whom preoperative CT-scans did not disclose any sign of infarction were included. BRP beneath as well the tip as the centre of the SRBR and the MABP were recorded continuously. Patients with peroperative complications were excluded. During the operations induced hypotension (n = 20) and mannitol (n = 6) were administrated. The patients (n = 23) had a 3-month follow-up examination. In man the thresholds of rCPP and time were found to be 10 mm Hg and 6-8 minutes, respectively. Other authors have found a rCBF threshold of 10-13 ml/100 g/min (Astrup 1982, Iannotti & Hoff 1983). It is concluded that the results obtained in the rat studies are comparable to the human situation if reservations are made concerning the differences in the thresholds of rCBF and rCPP. The time threshold of cerebral ischaemia seems to be rather equal in rat and in man. If these thresholds are reached, intermittent BRP is absolutely recommendable. It was also found that the most easily-handled retractors, those with a flat profile, did not decrease the rCBF further than other types of retractors.

The vulnerability of gerbils to focal cerebral ischemia. Neurological signs and regional biochemical changes after ischemia and recirculation

Gerbils of both sexes were used to study the effects of 30-min ischemia and subsequent recirculation for 4 and 8 days. The mortality rate was 9% during ischemia and 34% in the recirculation period. No close correlation was found between the extent of metabolic changes and the severity of clinical signs after ischemia. Gerbils exhibited severe clinical signs with metabolic patterns of severe hypoxic damage, but with only slight biochemical changes as well, stressing the necessity of detailed examination in regional metabolic studies. According to planimetrical evaluation the most sensitive indicator of ischemic damage was alteration in pH. Decrease in pH without changes in ATP and NADH was associated with severe clinical signs. Biochemical changes were demonstrated after recirculation in some gerbils having severe clinical signs at the end of the ischemic period. The changes in pH and potassium found 8 days after the ischemic insult stress that a 30-min focal ischemia might have long lasting, perhaps irreversible consequences.

Is postischaemic water accumulation related to delayed postischaemic hypoperfusion in rat brain?

The effect of reversible cerebral ischaemia on brain oedema development was studied with a gravimetric method. Cerebral blood flow changes after ischaemia were correlated with alterations in brain specific gravity. Forebrain ischaemia (15 min) was induced in rats by reversible bilateral ligation of both carotid arteries plus induction of controlled hypotension to 50 mm Hg. The specific gravity of different brain structures was determined in a Percoll column up to 24 h after ischaemia. In addition, regional cerebral blood flow was measured by 14C-iodoantipyrine autoradiography. Cerebral ischaemia resulted in reduction of cerebral blood flow to less than 1% of normal in cortical structures and the caudatoputamen. One hour after the end of ischaemia blood flows were still reduced to 30-50% of the control level indicative of delayed postischaemic hypoperfusion. Specific gravity in cortex and hypothalamus reached a maximal decrease 10 min after the end of the ischaemia, and was still significantly reduced at 1 h, while it was normal again 6 hrs later. Regression analysis between regional cerebral blood flows and the corresponding specific gravities were made at various time points, but no significant correlations could be established. Other mechanisms, like vasoconstriction, rheologic or metabolic factors may be causative for the delayed postischaemic hypoperfusion.

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.

Ischemic brain edema and the osmotic gradient between blood and brain

The relationship of the osmotic pressure gradient between blood and brain, and the development of ischemic brain edema was studied. Focal cerebral ischemia was produced by left middle cerebral artery occlusion in rats. Brain osmolality was determined with a vapor pressure osmometer, brain water content by wet-dry weight, and tissue sodium and potassium contents by flame photometry. Permeability of the BBB was tested by Evans blue. Measurements were made from the ischemic cortex within 14 days of occlusion. Brain osmolality increased from 311 +/- 2 to 329 +/- 2 mOsm/kg by 6 h after occlusion. Serum osmolality did not change significantly. The osmotic gradient between blood and brain peaked at approximately 26 mOsm/kg. Brain osmolality then decreased to 310 +/- 2 mOsm/kg by 12 h after occlusion and remained at about that same level. Water content increased progressively within 1 day of occlusion, then gradually decreased by 14 days. Brain tissue sodium plus potassium content did not increase within 6 h of occlusion, and Evans blue extravasation was not seen within that time. These findings indicate that an osmotic pressure gradient contributes to the formation of edema only during the early stage of cerebral ischemia. Furthermore, the increase in brain osmolality is not related to tissue electrolyte change or BBB disruption to protein.

Intracerebral hemorrhage in a primate model: effect on regional cerebral blood flow

The dynamic changes in regional cerebral blood flow (rCBF), induced by a developing intracerebral hematoma, were studied in eight anesthetized monkeys. Hematomas were generated by allowing femoral arterial blood to enter the caudate nucleus via a stereotactically implanted needle. Intracranial pressure peaked at 51 +/- 8 mmHg at 3 minutes after the ictus, and remained high throughout the 3-hour procedure. Cerebral blood flow was significantly reduced in all brain regions for 1 hour after the ictus. The lowest rCBF values were recorded in the immediate clot penumbra and were below threshold levels for ischemic neuronal damage for 90 minutes after the hemorrhage.

Proton magnetic resonance imaging in experimental cerebral ischaemia

MRI was performed on 11 primates, 7 with a proximal and 4 with a distal MCA occlusion. Chronic implanted electrodes created only minor image disturbances. The development of oedema formation was visualised in repetitive imaging. The site of the MCA occlusion determined the infarct-size.

Experimental intracerebral mass: time-related effects on local cerebral blood flow

Cerebral blood flow (CBF) was measured at different times during the first 150 minutes following an experimental space-occupying lesion produced with a 50-microliter microballoon in rats. Local CBF was measured with the carbon-14-labeled iodoantipyrine quantitative autoradiographic technique. A region of local ischemia developed around the mass, while the remote effects of the mass were minimal. The focal ischemic lesion enlarged with time, and simulated removal of the lesion within this design did not alleviate the ischemia.

Experimental intracerebral hemorrhage: effects of a temporary mass lesion

Late pathophysiological events after the production and subsequent removal of an intracerebral mass were investigated using a mechanical microballoon model to simulate intracerebral hemorrhage. Immediately following balloon inflation in the caudate nucleus of rats, there was a significant increase in intracranial pressure to 14 +/- 1 mm Hg (mean +/- standard error of the mean), accompanied by a reduction in cerebral blood flow (CBF) in the ipsilateral frontal cortex, as measured by the hydrogen-clearance technique. Carbon-14-iodoantipyrine autoradiography revealed a significant reduction in the CBF of the ipsilateral caudate nucleus 4 hours after balloon inflation: 31% of the caudate nucleus had a CBF of less than 20 ml X 100 gm-1 X min-1 compared to only 1% in the sham-treated control group (balloon insertion without inflation). The rats with an intracerebral mass exhibited a significant increase in the volume of ischemic damage in the ipsilateral caudate nucleus (17.1% of total volume) compared to only 1.7% in the sham-treated group; however, there was no evidence of cerebral edema. Ischemic damage and reduced CBF persisted for 4 hours after transient inflation of a microballoon in the caudate nucleus. This suggests that ischemic damage occurs at the time of formation of the lesion and is not prevented by its early removal.

Experimental focal ischemia in cats: changes in multimodality evoked potentials as related to local cerebral blood flow and ischemic brain edema

Somatosensory and auditory evoked cortical potentials (SEP's and AEP's), regional cerebral blood flow, regional brain water content, and alteration of the blood-brain barrier were investigated in 3 cortical areas during permanent and 1- and 2-hour transient occlusion of the left middle cerebral artery and after restoration of blood flow in cats. During occlusion, blood flow in the auditory cortex was severely suppressed. In the fore limb projection area of the somatosensory cortex, blood flow was moderately reduced while it was nearly unaffected in the hind limb projection area. Despite different degrees of ischemia in the 3 cortical areas, all evoked responses were completely abolished within 10 minutes after occlusion. During permanent occlusion, the pattern of blood flow reduction persisted, and all evoked potentials stayed abolished. Recirculation after occlusion restored blood flow rapidly. AEP's recovered poorly after both 1 and 2 hours of ischemia. SEP's regained normal amplitudes soon after recirculation in the group with 1-hour occlusion. After 2 hours of ischemia, the recovery of SEP's was variable but better than that of the AEP's. Remarkable water accumulation was observed in the auditory cortex of all 3 groups and was accompanied in the 2-hour ischemia group by a disruption of the blood-brain barrier. In the 2-hour group, water accumulation was also found in the subcortical white matter radiation, whereas significant changes in regional water content were not observed in the somatosensory areas. The present study indicates that abolition of SEP's during middle cerebral artery occlusion in cats is caused by lesions in the afferent pathway leading to cortical deafferentation rather than by cortical ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Recirculation after cerebral ischemia. Simultaneous measurement of cerebral bloodflow, brain edema, cerebrovascular permeability and cortical EEG in the rat

The 4-vessel occlusion rat model of cerebral ischemia was modified to permit the simultaneous measurement of cerebral blood flow (hydrogen clearance), brain edema (specific gravity), cerebrovascular permeability (14C-AIB) and electrocardiogram. Surgery was performed in one stage in the anesthetised, paralysed and ventilated rat and severe hemispheric ischemia was produced in all animals. Electrode implantation did not alter cortical specific gravity or Ki for 14C-AIB. During 4-vessel occlusion mean cortical CBF was 5.8 +/- 1.4 ml-1 100 g-1 min. and this was associated with an isoelectric ECoG; 15 min of ischemia produced a significant reduction in mean cortical specific gravity (increase in brain edema). Following 15 min ischemia, 180 min of recirculation were permitted. Post-ischemic blood flow showed an immediate hyperemia (CBF = 202 +/- 12 ml-1 100 g-1 min.) followed by hypoperfusion (CBF = 58 +/- 8 ml-1 100 g-1 min). There was an early further decrease in cortical specific gravity. Further recirculation led to a significant increase in cortical specific gravity (resolution of brain edema). The transfer constant (Ki) for 14C-AIB was not altered at any stage in recirculation. This appears to be a model of pure cytotoxic edema until 180 min recirculation after 15 min cerebral ischemia. Recirculation permitted return of cortical electrical activity.

Role of a hydrostatic pressure gradient in the formation of early ischemic brain edema

We studied whether a hydrostatic pressure gradient between arterial blood and brain tissue plays a role in the formation of early ischemic cerebral edema after middle cerebral artery (MCA) occlusion in cats. Tissue pressure, regional CBF, and water content were measured from the cortex in the core and the peripheral zone of brain normally perfused by the MCA. Intraluminal arterial pressure was altered at intervals by inflation of an aortic balloon to vary the blood-tissue pressure gradient in the ischemic zone. Brain water content in the ischemic core, where flow fell to 5.5 ml/100 g/min, increased within 1 h of occlusion. After occlusion tissue pressure rose from 7.95 +/- 0.72 mm Hg at 1 h to 13.16 +/- 1.13 mm Hg at 3 h. When intraluminal pressure was increased, water content increased further, but only at 1 h after occlusion. In the periphery where flow was 18.9 ml/100 g/min during normotension, neither water content nor tissue pressure rose within 3 h of occlusion. Increased intraluminal pressure was accompanied by increased water content only at 3 h. This study indicates that a hydrostatic pressure gradient is an important element in the development of ischemic brain edema, exerting its major effect during the initial phase of the edema process.

The association of hyperglycemia with cerebral edema in stroke

A retrospective review of stroke patients admitted to our hospital revealed 39 patients diagnosed as suffering an acute completed ischemic stroke who also had had fasting (AC) serum glucose determinations and sequential computer tomography (CT) studies. The patients were divided into three groups on the basis of mean AC serum glucose: Group 1 (n = 12) mean serum AC glucose greater than 150 mg/dl; Group 2 (n = 13) mean serum AC glucose 100-150 mg/dl; and Group 3 (n = 14) mean serum AC glucose less than 100 mg/dl. CT scans performed on each patient were studied for the presence of midline shift and/or ventricular compression, which were interpreted as evidence of cerebral edema. The three groups were comparable with respect to mean age, average mean arterial blood pressure and initial infarct size. Our results show that in Group 1, 42% of the patients died within the first week following their CVA with clinical evidence of transtentorial herniation confirmed by CT or autopsy. In contrast, none of the Group 3 patients died and only one showed radiological evidence for cerebral edema. Group 2 patients showed intermediate mortality and evidence of cerebral edema. These trends were statistically significant at p less than 0.005. In addition, the combined hyperglycemic group (1 and 2) had a significantly higher rate of development of hypodensity on CT (p less than 0.05) than the normoglycemic group. Our findings suggest that patients with hyperglycemia in association with their CVA develop more pronounced cerebral edema and have a worse clinical outcome. Possible pathophysiological mechanisms that may underlie this observation are discussed.

Cortical tissue pressure gradients in early ischemic brain edema

We examined the role of ischemic brain edema, tissue pressure gradients, and regional CBF (rCBF) in adjacent regions of cerebral cortex in cats with middle cerebral artery (MCA) occlusion (MCAO). Tissue pressure, rCBF, and water content were measured from gray matter in the central core and the peripheral margin of the MCA territory over 6 h after MCAO. Ventricular fluid pressure and CSF pressure were recorded. Tissue pressure in the ischemic core, with a flow of approximately 5 ml/100 g/min, increased more than that in the periphery where flow was approximately 19 ml/100 g/min. Tissue pressure rose progressively to 14.8 +/- 1.0 mm Hg in the core over 6 h after MCAO, establishing a significant pressure gradient between that tissue and the lateral ventricle nearby or the subarachnoid space in the middle fossa within the first 3 h. The increase in tissue pressure was linearly related to the amount of edema fluid that developed until the edema reached a severe degree. This study shows that a hydrostatic tissue pressure gradient within ischemic cortex is associated with ischemic brain edema. The magnitude of the gradient that develops is related to the severity of ischemic edema in that tissue.