Experimental ischemic brain swelling

Attenuation of decompressive hypoperfusion and cerebral edema by superoxide dismutase

This study tested the hypothesis that ischemia-reperfusion injury initiated by the superoxide anion radical is a major component of postdecompression hypoperfusion and cerebral edema, and could be attenuated by superoxide dismutase (SOD). A supratentorial extradural balloon was placed in 20 fasting, lightly anesthetized, mechanically ventilated dogs and inflated in 0.5-ml increments (0.07 ml/sec) at 15-minute intervals. The end-point of balloon expansion was the onset of an isoelectric electroencephalogram, near-arrest of hemispheric cerebral blood flow (CBF) (measured by H2 clearance), and the appearance of a suprainfratentorial intracranial pressure gradient, which was held for 15 minutes. The in vivo development of brain edema was detected by measuring brain elastic response (BER) extradurally, and was correlated with postmortem measurement of brain water content (gravimetry); blood-brain barrier integrity was tested by Evans blue dye given after the insult. After decompression, the dogs were randomly assigned to one of four treatment groups: Group I received hyperventilation (PaCO2 28 +/- 1 mm Hg, mean +/- standard deviation); Group II received furosemide (2.4 mg/kg) and pentobarbital (10 mg/kg) every 8 hours; Group III received 20% mannitol in a 1.4-gm/kg bolus plus furosemide, 0.5 mg/kg; and Group IV received SOD, 15,000 U/kg every 15 minutes for 3 hours. At 4 hours of decompression Group IV had significantly greater recovery in local CBF and BER than Groups I, II, and III (p less than 0.05). The 24-hour survival rate was 20% for Group I, 60% for Group II, 80% for Group III, and 100% for Group IV. The survival rate appeared to correlate with a variable degree of postmortem intraparenchymal hemorrhages, blood-brain barrier disruption, and moderate to severe brain edema for Groups I, II, and III. In contrast, Group IV had the least brain edema (p less than 0.05) and Evans blue dye extravasation (p less than 0.05) and the fewest intraparenchymal hemorrhages. These data support the hypothesis that, under the experimental conditions described here, the superoxide anion plays a major role in the pathophysiology of postdecompression ischemic edema.

Effect of common carotid occlusion on beta-adrenergic receptor function in cerebral microvessels

beta-adrenergic receptors were measured in cerebral microvessels of gerbils and rats after ligature of the right or left common carotid artery. The results indicate a decrease in the number of beta-adrenergic receptors in brain microvessels of both ipsilateral and contralateral hemispheres. This event may reflect altered patterns of the neuronal regulation of brain microvasculature and may be related to cerebrovascular alterations which are concomitant with ischemia. Furthermore, the results show that the decrease in beta-receptor density is more pronounced in the left hemisphere, independently on the side of carotid occlusion. This finding suggests that microvessel function in the left side of the brain is more vulnerable to hypoxia effects.

Neuronal control of brain microvessel function

Cerebral capillary endothelium forms a barrier limiting and controlling the movement of ions and solutes between blood and brain. Recent anatomical, physiological and biochemical studies have suggested the possibility that capillary function may be directly controlled by neuronal structures. Alterations in neuronal systems involved in the regulation of microcirculation may account for microvascular dysfunctions which occur in different pathologic conditions.

Brain free fatty acids, edema, and mortality in gerbils subjected to transient, bilateral ischemia, and effect of barbiturate anesthesia

Brain free fatty acids (FFAs) and brain water content were measured in gerbils subjected to transient, bilateral cerebral ischemia under brief halothane anesthesia (nontreated group) and pentobarbital anesthesia (treated group). Mortality in the two groups was also evaluated. In nontreated animals, both saturated and mono- and polyunsaturated FFAs increased approximately 12-fold in total at the end of a 30-min period of ischemia; during recirculation, the level of free arachidonic acid dropped rapidly, while other FFAs gradually decreased to their preischemic levels in 90 min. In treated animals, the levels of total FFAs were lower than the nontreated group during ischemia, but higher at 90 min of reflow, and the decrease in the rate of free arachidonic acid was slower in the early period of reflow. Water content increased progressively during ischemia and recirculation with no extravasation of serum protein, but the values were consistently lower in the treated group. None of the nontreated animals survived for 2 weeks; in contrast, survival was 37.5% in the treated group. It is suggested that barbiturate protection from transient cerebral ischemia may be mediated by the attenuation of both membrane phospholipid hydrolysis during ischemia and postischemic peroxidation of accumulated free arachidonic acid.

Reperfusion of focal ischemia of varying duration: postischemic hyper- and hypo-perfusion

Reperfusion into focal ischemia was studied in 25 cats after middle cerebral artery (mca) occlusion of 15 min to 2 hours duration. Changes in cerebral blood flow (CBF) were followed with the hydrogen clearance method in the center and periphery of the ischemic lesion expected. Postischemic hyperperfusion was found often after 15 and 30 min ischemia and regularly after 60 min mca occlusion. It was followed by normal flow after 15 and 30 min occlusion and by postischemic hypoperfusion after 1 hour ischemia. After 2 hours occlusion hypoperfusion generally was not preceded by hyperperfusion. After 60 min ischemia hyperperfusion could not prevent the development of severe hypoperfusion, but often was accompanied by a marked flow reduction in the periphery of the mca territory. The data indicate that hyperperfusion after ischemic periods lasting 60 min and more induces hypoperfusion in the area itself and in neighbouring regions by affecting perfusion pressure and thereby may enlarge ischemic damage.

Barbiturate effects on acute experimental intracranial hypertension

Acute intracranial hypertension was induced in cats by progressive inflation of an epidural balloon. Changes in intracranial pressure (ICP), mean arterial pressure (MAP), cerebral perfusion pressure (CPP), heart rate (HR), electroencephalogram (EEG), and pupil size were studied in untreated animals and in animals that had received barbiturates at different stages during the experiment. In animals pretreated with barbiturates, the increase in ICP during balloon expansion was significantly less than in untreated animals (p less than 0.001). The CPP, initially higher in untreated animals, was not significantly different (P less than 0.05) as the mass lesion pressure-volume curve exceeded the inflection point. In the postdeflation period, the untreated animals developed a significant increase in ICP, whereas, in the barbiturate-pretreated group, the ICP returned to preinflation values, suggesting a protective effect of barbiturates against postcompression brain swelling. Barbiturates affected ICP and CPP differently in animals with intracranial hypertension due to the presence of an epidural balloon that was maintained inflated compared to those with postdeflation brain swelling. In the latter group, pentobarbital reduced ICP (p less than 0.05) without significantly decreasing the CPP, whereas, in the mass lesion group, barbiturates failed to reduce the ICP and caused a deterioration in CPP (p less than 0.025). Brain gross pathological changes were significantly less in the pretreated animals as compared with all other groups. The results suggest that if barbiturate treatment is to have therapeutic value, the timing of the therapy and the criteria for its initiation should be determined.

Local cerebral blood flow following transient cerebral ischemia. I. Onset of impaired reperfusion within the first hour following global ischemia

Using the hydrogen clearance technique, local cerebral blood flow (LCBF) in 22 dogs was estimated at 6 parietal sites prior to and following 5 min of total global ischemia. Ischemia was immediately followed by an initial reactive hyperemia during which the electrocorticogram (ECoG) usually began to recover, and within the first 30 min, most of the LCBF's decreased to subnormal values. This onset of hypoperfusion was accompanied by a concomitant decrease in ECoG activity. Two animals that maintained normal local perfusion after the initial hyperemia recovered ECoG activity quickly. These results suggest that the subsequent poor reperfusion was caused by an increased microvascular resistance rather than by blood aggregates, increased blood viscosity, or a variety of other mechanism which have been proposed. Increased vascular tonus was, at least, partly responsible for the increased vascular resistance. This report supports the hypothesis that impaired reperfusion (which occurs some time after an initial hyperemia) may be responsible for ultimate neuronal death, rather than the period of global ischemic hypoxia per se.

Production of various models of cerebral infarction in the dog by means of occlusion of intracranial trunk arteries

Using the dog, which has been believed unsuitable for research on brain infarction because of an extensive collateral cerebral circulation, we have succeeded in producing at will ischemic foci, as determined from post-occlusion carbon perfusion, in the thalamus, cerebral mantle or entire cerebral hemisphere. This has been achieved by occlusion of various combinations of cerebral vessels at the base of the brain. A unilateral temporal approach has been used in identifying and occluding all of the bilateral trunk arteries. The following models of cerebral infarction have been made: 1) unilateral or bilateral complete cerebral hemisphere infarction, 2) unilateral or bilateral cerebral mantle infarction, 3) unilateral or bilateral thalamic infarction, 4) unilateral hemispheric and contralateral cerebral mantle infarction, 5) unilateral cerebral mantle and contralateral thalamic infarction, and 6) unilateral complete cerebral hemisphere and contralateral cerebral mantle infarction. These models of infarction in the dog can be produced with a high degree of success, and the amount of infarction can be controlled by the duration of vessel occlusion. The pathophysiology of brain infarction and brain edema following recirculation can be hemodynamically, electroencephalographically and biochemically studied using these models of cerebral infarction.

Experimental brain injury in the dog. The pharmacological effects of pentobarbital and sodium nitroprusside

✓ Brain injury was created in anesthetized dogs by the inflation and subsequent deflation of an epidural balloon. Animals in which intracranial pressure (ICP) increased to 40 torr within 3 hours after balloon removal were included in a randomized treatment protocol that included three treatment groups. Group I (control animals) received no additional treatment. Group II animals received 40 mg/kg pentobarbital initially, plus hourly doses. Group III animals received sufficient sodium nitroprusside to reduce systemic arterial pressure (SAP) to 80 to 90 torr. Pentobarbital reduced ICP compared to control animals, but cerebral perfusion pressure (CPP) was also reduced. Barbiturate treatment also prevented plateau waves. Progressive parallel deterioration in CPP occurred with time in control and pentobarbital-treated animals. The viability of the central nervous system was not improved by pentobarbital. Profound systemic hypotension, a major complication of pentobarbital treatment, required mephentermine to reverse it. Sodium nitroprusside failed to reduce ICP and caused a rapid, profound deterioration in CPP which far exceeded that observed in control or barbiturate-treated animals. Plateau waves were not prevented by nitroprusside. Barbiturates were more potent than nitroprusside in combatting systemic hypertension caused by elevated ICP. Pentobarbital may act by suppression of a central neurogenic mechanism for systemic hypertension and cerebral vasoparalysis. As a cerebral vasodilator, nitroprusside when used in the presence of an intracranial mass, brain edema, or cerebral vasoparalysis, will cause a rise in ICP and a fall in SAP, as well as a drastic reduction in CPP. Its use is probably contraindicated in these situations. Furthermore, it is inferior to barbiturates in reducing ICP and SAP and in preventing plateau waves.

Intracranial pressure in patients with diffuse cerebral arterial spasm following ruptured intracranial aneurysms

Intracranial pressure (ICP) was recorded continuously in 12 pre-operative patients with angiographic evidence of diffuse cerebral arterial spasm due to a ruptured intracranial aneurysm. Recordings were made for 1 to 7 days, starting within 13 days after the haemorrhage. 1. An increased ICP was observed in the first week after subarachnoid haemorrhage (SAH) in 4 of the patients without any signs of angiographic arterial spasm. 2. This initial increase was regularly followed by a depression of ICP in between 7--12 days after SAH. In 11 out of 12 patients such a depression was concomitant with the beginning of arterial spasm. During the period of depressed ICP pattern, 6 patients showed little or no neurological deterioration, whereas 5 patients showed impaired consciousness or neurological deficits. 3. A secondary rise of ICP thereafter always followed due to ischaemic brain swelling or infarction, and was usually associated with a serious neurological deterioration. 4. Continuous ventricular drainage was performed to control the secondary increased ICP in 7 patients who survived, 4 of them with good clinical improvement and 3 with severe neurological deficits. 5. In the stage of depressed ICP, the administration of isoproterenol and steroids is recommended in order to try to alleviate the secondary rise of ICP.

Report of Joint Committee for Stroke Resources. IV. Brain edema in stroke

A classification of brain edema is provided as well as an extensive review of the animal models from which we have derived most of the basic information we have about the formation and resolution of edema. The clinical aspects of cerebral edema in stroke are discussed and also modern methods for identifying cerebral edema in the human. Attention is given to computed tomography and enhanced CT and advances in their application to this condition. Treatment of cerebral edema in the stroke patient using glycerol, dextran 40, mannitol, steroids, and other drugs is discussed and the need pointed out for controlled clinical trials of the therapeutic effectiveness of these agents.

Effect of cardiac arrest on cerebral circulation. An experimental investigation

The effect of 2 to 15 min of cardiac arrest on cerebral circulation was investigated in dogs and Rhesus monkeys. When circulatory arrest lasted longer than 5 minutes, angiographic changes of the no-reflow phenomenon were observed between 3 and 4 h after resuscitation in dogs but not in monkeys. These findings were (1) marked prolongation of the arterial phase in both intracranial and extracranial arteries; followed by (2) occasional evidence of dilatation of the proximal intracranial arteries with non-filling of the distal intracranial arteries; and (3) faint demonstration of the venous phase. Carbon black perfusion results were (1) diffuse lack of perfusion at the arteriolar-capillary level and (2) multifocal areas of filling defects. Regional cortical blood flow measurement in monkeys disclosed a significant decrease in flow starting from 3 h after re-establishment of circulation for those in which longer than 5 min of arrest was induced.

Resuscitation of the monkey brain after one hour's complete ischemia. II. Brain water and electrolytes

Adult normothermic rhesus monkeys were submitted to one hour's complete cerebral ischemia, followed by periods of blood recirculation varying from 45 min to 24 h. The functional impact of ischemia and the subsequent recovery was monitored by electrophysiological recording and a distinction was made between animals with signs of functional recovery and animals without recovery. Prior to ischemia the water content of the gray matter was 81.1 plus or minus 0.3% (mean plus or minus S.D.) and of the white matter 68.9 plus or minus 0.8%. The sodium-potassium ratio in the gray matter was 0.43 plus or minus 0.02 and in the white matter 0.62 plus or minus 0.06. During one hour's ischemia brain water did not change significantly, but the differences in the sodium-potassium ratio in white and gray matter were reduced. Blood recirculation of the brain after ischemia caused a considerable increase in brain water content and a shift in the sodium-potassium ratio up to 1.0. Calculated brain swelling was maximal after 45 min when it reached 11.1% of the total brain volume in an animal with recovery and 12.2% in another one without recovery. In animals with signs of functional recovery brain swelling rapidly diminished, followed by a more gradual normalization of brain electrolytes within 24 h. In animals without functional recovery electrolyte shifts were irreversible or even progressed further. It is concluded that brain swelling and electrolyte derangements following one hour's cerebral ischemia are fully reversible when signs of functional recovery appear and brain metabolism returns.

Cerebral apoplexy (stroke) treated with or without prolonged artificial hyperventilation. 1. Cerebral circulation, clinical course, and cause of death

Fifty patients with severe cerebral apoplexy were treated with artificial hyperventilation of three days' duration facilitated by general anesthesia (barbiturates and muscle relaxants) and instituted within the first day after onset of the attack. After a classification according to carotid angiographical findings, degree of consciousness and focal symptoms, a random allocation was performed so that 24 patients were subjected to moderate hypocapnia (Pa CO CO 2 about 25 mm Hg) and 26 patients to normocapnia (Pa CO CO 2 about 40 mm Hg). Afterward, 21 comparable patients not receiving ventilatory treatment were studied. The clinical course and the mortality rate showed no statistically significant differences between the three groups. All patients studied disclosed a longstanding (12 days) spontaneous hyperventilation.

The ventilation treatment was followed by a low cerebral perfusion pressure and a high rate of pulmonary complications. Autopsies from all groups studied typically showed tentorial herniation and pathological lung changes.

In 32 of the patients without occlusion of the carotid artery the regional cerebral blood flow was measured before hyperventilation treatment was applied. A low mean flow and focal abnormalities (ischemia, hyperemia, vasoparalysis) typically were found and in good correlation to the autopsy findings. In six of 13 patients tested an "inverse steal syndrome" following aminophylline was disclosed.

Hemodynamic and metabolic concomitants of brain swelling and cerebral edema due to experimental cerebral infarction

✓ Severe cerebral ischemia was produced in 25 baboons by clamping the carotid and vertebral arteries bilaterally for 10 minutes. Cerebral hemodynamics and metabolism were monitored throughout. Cerebral anoxia was less severe in animals in which a marked pressor response occurred due to ischemia of the vasomotor center, and a reversible type of brain swelling was usual. In those with more severe ischemic anoxia, progressive cerebral edema was a pathological entity. Evidence is presented that cerebral edema was caused by loss of autoregulation of cerebral blood flow (CBF) concomitant with hyperemia and an increase of water and chloride content of brain tissue. Cerebral edema began when CBF was reduced during occlusion and progressed for several hours after termination of occlusion. Evidence is adduced that uncoupling of oxidative phosphorylation may be an important concomitant of cerebral edema.

Intracranial pressure in patients with ruptured saccular aneurysm

✓ Intracranial pressure was recorded in 21 patients with subarachnoid hemorrhage due to rupture of a saccular aneurysm. Two different pressure patterns were found in nine patients who had verified recurrent hemorrhages while awaiting clinical improvement. One was associated with massive hematoma while the other occurred with edema but only minimal hematoma; the terms “hemorrhagic-compressive lesion” and “ischemic-edematous lesion” have been used for these two conditions. Four patients showed transient deterioration concomitant with marked pressure peaks in the continuous record. Although there was no evidence of fresh hemorrhage, three of these episodes were followed by a verified hemorrhage within 24 hours. Since no such “warning episode” was seen after the aneurysm had been clipped, the authors consider this pressure peak and concomitant clinical deterioration to be related to the mechanism of aneurysm rupture and possibly a forerunner of a life-threatening hemorrhage. These three pressure patterns showed the whole range from full spatial compensation to total decompensation. The determining factors are considered to be the volume of extravasated blood, the vasomoter reaction, and the intracranial spatial buffering capacity.