Changes of epidural pressures after experimental occlusion of one middle cerebral artery in cats

Liposome-encapsulated hemoglobin alleviates brain edema after permanent occlusion of the middle cerebral artery in rats

Liposome-encapsulated hemoglobin (LEH) was proven to be protective in cerebral ischemia/reperfusion injury. The present study evaluated LEH in a rat model of permanent middle cerebral artery (MCA) occlusion to clarify its effect during ischemia and reperfusion. Five minutes after thread occlusion of the MCA, rats were infused with 10 mL/kg of LEH (LEH, n = 13), and compared with normal controls (n = 11). Additional animals received the same MCA occlusion with no treatment (CT, n = 11), saline (saline, n = 10), empty liposome solution (EL, n = 13), or washed red blood cells (RBC, n = 7). Severity of brain edema was determined 24 h later by signal strength in T2-weighted magnetic resonance imaging of the cortex, striatum, hippocampus, and pyriform lobe. The results showed that brain edema/infarction observed in any vehicle-infused control was significantly more severe than in LEH-treated rats. There was a tendency toward aggravated edema in rats receiving ELs. LEH infusion at a dose of 10 mL/kg significantly reduced edema formation as compared to other treatments in a wide area of the brain 24 h after permanent occlusion of the MCA. Low oncotic pressure of EL and LEH solution (vehicle solution) appeared to cause nonsignificant aggravation of edema and reduced protective effects of LEH.

Acute Carotid Artery Thrombosis: Description of 12 Surgically Treated Cases

The morbidity and mortality of stroke secondary to acute internal carotid artery thrombosis range from 40 to 69% and from 15 to 55%, respectively, after purely medical treatment. This report describes a series of 12 patients who underwent urgent surgical treatment for primary acute carotid artery thrombosis between January 1999 and December 2002. Upon admission, all patients had severe neurologic deficits contralateral to carotid artery thrombosis. One patient experienced ongoing changes in the level of consciousness. The interval between the onset of symptoms and admission was less than 6 hr in all cases. Initial work-up in all patients included a brain computed tomographic scan with contrast injection and carotid duplex scan. The operative procedure consisted of carotid thomboemdarterectomy after shunt placement with prosthetic patch closure. Intraoperative angiography was performed in all cases. Following treatment, we observed deterioration of neurologic status leading to death in one case; improvement with partial regression of initial neurologic deficit in two cases, including one patient who died from causes unrelated to carotid artery disease; and full neurologic recovery in nine cases. The delay to revascularization was longer than 6 hr in both patients who died. These data support surgical intervention for carotid artery thrombosis in selected patients without major disturbances of consciousness or hemorrhagic infarction, provided that the delay to revascularization is less than 6 hr.

Repeat positron emission tomographic studies in transient middle cerebral artery occlusion in cats: residual perfusion and efficacy of postischemic reperfusion

The wider clinical acceptance of thrombolytic therapy for ischemic stroke has focused more attention on experimental models of reversible focal ischemia. Such models enable the study of the effect of ischemia of various durations and of reperfusion on the development of infarctions. We used high-resolution positron emission tomography (PET) to assess cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO2), oxygen extraction fraction (OEF), and cerebral metabolic rate of glucose (CMRglc) before, during, and up to 24 h after middle cerebral artery occlusion (MCAO) in cats. After determination of resting values, the MCA was occluded by a transorbital device. The MCA was reopened after 30 min in five, after 60 min in 11, and after 120 min in two cats. Whereas all cats survived 30-min MCAO, six died after 60-min and one after 120-min MCAO during 6-20 h of reperfusion. In those cats surviving the first day, infarct size was determined on serial histologic sections. The arterial occlusion immediately reduced CBF in the MCA territory to < 40% of control, while CMRO2 was less affected, causing an increase in OEF. Whereas in the cats surviving 24 h of reperfusion after 60- and 120-min MCAO, OEF remained elevated throughout the ischemic episode, the initial OEF increase had already disappeared during the later period of ischemia in those cats that died during the reperfusion period. After 30-min MCAO, the reperfusion period was characterized by a transient reactive hyperemia and fast normalization of CBF, CMRO2, and CMRglc, and no or only small infarcts in the deep nuclei were found in histology. After 60- and 120-min MCAO, the extent of hyperperfusion was related to the severity of ischemia, decreased CMRO2 and CMRglc persisted, and cortical/subcortical infarcts of varying sizes developed. A clear difference was found in the flow/metabolic pattern between surviving and dying cats: In cats dying during the observation period, extended postischemic hyperperfusion accompanied large defects in CMRO2 and CMRglc, large infarcts developed, and intracranial pressure increased fatally. In those surviving the day after MCAO, increased OEF persisted over the ischemic episode, postischemic hyperperfusion was less severe and shorter, and the perfusional and metabolic defects as well as the final infarcts were smaller. These results stress the importance of the severity of ischemia for the further course after reperfusion and help to explain the diverging outcome after thrombolysis, where a relation between the residual flow and the effectiveness of reperfusion was also observed.

Dynamic penumbra demonstrated by sequential multitracer PET after middle cerebral artery occlusion in cats

Experimental models of focal cerebral ischemia have provided important data on early circulatory and biochemical changes, but typically their correspondence with metabolic and hemodynamic findings in stroke patients has been poor. To fill the gap between experimental studies at early time points and rather late clinical studies, we repeatedly measured CBF, CMRO2, oxygen extraction fraction (OEF), cerebral blood volume (CBV), and CMRglc in six cats before and up to 24 h after permanent middle cerebral artery (MCA) occlusion (MCAO), using the 15O steady state and [18F]fluorodeoxy-glucose methods and a high-resolution positron emission tomography (PET) scanner. Likewise, three sham-operated control cats were studied during the same period. Final infarct size was determined on serial histologic sections. In the areas of final glucose metabolic depression that were slightly larger than the histologic infarcts, mean CBF dropped to approximately 40% of control values immediately on arterial occlusion. If further decreased to < 20% during the course of the experiment. This progressive ischemia was most conspicuous in border zones. CMRO2 fell to a lesser degree (55%), eventually reaching approximately 25% of its control level. At early stages, OEF increased mainly in the center of ischemia. With time, areas of increased OEF moved from the center to the periphery of the MCA territory. Concurrently, progressive secondary decreases in OEF in conjunction with further reductions of CBF and CMRO2 indicated the development of central necrosis. The findings are highly suggestive of a dynamic penumbra. In five cats with complete MCA infarcts, CBF decreased and OEF increased in the contralateral hemisphere after 24 h, suggesting whole-brain damage. This effect may be explained by the widespread brain edema found histologically in addition to the nonspecific CBF reductions and OEF elevations observed also in the sham-operated controls after 1 day in the experimental condition. In one cat, cortical OEF increased only transiently. Normal CMRO2 and CMRglc were eventually restored, and the final infarct was small. This study demonstrates that acute regional pathophysiologic changes can be repeatedly assessed by multivariate PET in cats. Viable tissue can be detected up to several hours after MCA occlusion, and the transition of misery-perfused regions into necrosis or preserved tissue can be followed over time. The present results support the concept of a dynamic penumbra, in which for up to 24 h tissue damage spreads progressively from the center to the periphery of ischemia. Sequential high-resolution PET provides insight into the dynamics of regional pathophysiology and may thus further the development of rational therapeutic strategies.

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.

Photochemically induced cerebral infarction. II. Edema and blood-brain barrier disruption

Alterations in the blood-brain barrier to proteins, and regional water and electrolyte content were documented in a rat model of photochemically induced small-vessel thrombosis leading to infarction. Horseradish peroxidase (HRP) or Evans blue was given immediately following a 2-min photochemical sensitization period. At 5 min following irradiation, multifocal sites of peroxidase extravasation were noted within the irradiated area. Ultrastructural examination revealed endothelial cells filled with HRP which in some cases extended into the basal lamina and extracellular spaces. At 15 min, protein leakage was more pronounced within the irradiated zone and reaction product was also apparent within the subarachnoid and perivascular spaces of brain regions remote from the site of irradiation. Widespread staining on the surface of the irradiated hemisphere was apparent in rats perfused 8 h following Evans blue infusion. Water content increased significantly by 15 min within the irradiated zone but not in brain regions remote from this site. Although vasogenic edema is an early event in this stroke model, increases in water content are restricted to the irreversibly damaged site. In contrast, protein tracer escaping from microvessels coursing within the irradiated zone was widely distributed. These findings implicate endothelial barrier dysfunction in the genesis of tissue injury in this model. Morphological evidence for the capability of macromolecules to escape from a site of evolving infarction and to migrate to distances remote from the area of primary microvascular damage is also discussed.

Selective functional vulnerability of cortical neurons following transient MCA-occlusion in the cat

Simultaneous recordings of several cortical neurons were obtained before, during and after transient 15 min occlusion of the middle cerebral artery in cats. With the use of a multiple electrode array consisting of 4-7 platinum/iridium microelectrodes, the cortical pericellular blood flow was concurrently measured by means of the hydrogen clearance technique. Hydrogen clearance measurements revealed a homogeneous blood flow distribution throughout all phases of the experiment in the area covered by the different microelectrodes. Considering only the results of experiments with low residual blood flow during ischemia (less than 0.1 ml/g/min), single unit activity ceased immediately after occlusion and remained so during the ischemic period. The recovery time of action potentials after reperfusion ranged from 10 min to 3 hours depending on the examined neuron. Lower values for discharge rates of the individual cells were generally observed after reoccurrence, although some units exhibited temporarily an even higher spike frequency. Furthermore, the spike form usually changed in that the hyperpolarizing afterpotentials were enlarged after recirculation. However, some cells with a nearly unchanged spike form were found as well. The results indicate that the recovery of cell function largely depends on the individual neuron which supports the idea of a selective functional vulnerability of cortical neurons in response to ischemia.

Neurologic deficit, blood flow and biochemical sequelae of reversible focal cerebral ischemia in cats

Temporary focal cerebral ischemia was induced in 23 cats by occluding the left middle cerebral artery (MCA) for 2 h. Animals then were divided into groups for unforced reperfusion of varying duration ranging from 2 to 48 h. Regional blood flow (rCBF) at the borders of the ischemic area was measured repeatedly using the hydrogen clearance technique, and neurological ratings were obtained, both during ischemia and reperfusion. At the scheduled end of reperfusion brains were frozen in situ with liquid nitrogen, and regional distributions of biochemical substrate contents as well as tissue pH were visualized using bioluminescence and fluorescence techniques. During focal ischemia collateral flow in the border zone dropped to 55 +/- 20.3% of control level, and all animals developed a neurologic deficit with a median of 6 points on a disability scale from 0 to 10, rCBF and functional impairment being closely correlated (tau = -0.47, P1 less than 0.005). After reopening of the MCA there was an immediate and rather uniform increase in border zone flow to 105 +/- 25.7% of control level, while neurologic recovery was quite variable. In all but one animal reversible ischemia led to persistent disturbances in the energy-producing metabolism as demonstrated by the low regional ATP content, which in part was accompanied by a diminished NADH fluorescence and an alkaline pH shift at high tissue glucose levels. These findings suggest that disturbances in cerebral energy metabolism induced by temporary ischemia may be caused by inhibition of the glycolytic pathway that is hardly reversed by unforced reperfusion and, therefore, results in permanent damage.

Neurologic deficit and cerebral ATP depletion after temporary focal ischemia in cats

Focal ischemia was induced in 23 cats by occluding the left middle cerebral artery for 2 h. The animals were then divided into groups for unforced reperfusion of variable duration ranging from 2 to 48 h. Neurological ratings were obtained during both ischemia and reperfusion. Following planned sacrifice the regional ATP content was assessed by means of a bioluminescence method showing spatial distribution and degree of ATP depletion. All the animals developed a neurologic deficit, with a median of 6 points on a disability scale of 0-10. After reopening of the middle cerebral artery, neurologic recovery was quite variable depending on the initial neurologic deficit (partial phi = 0.67, p1 less than 0.05): Animals with mild initial functional impairment improved and those with severe neurologic disturbances either died early or developed a more severe neurologic deficit, irrespective of the duration of reperfusion. The degree of ATP depletion and the amount of brain tissue involved exhibited a significant correlation with the neurological outcome (tau = 0.50, p1 less than 0.05), but they were even more closely related to the initial neurologic deficit (partial phi = 1.00, p1 less than 0.001), suggesting an early definitive manifestation of deficiencies in regional energy metabolism.

Flow and neuronal density in tissue surrounding chronic infarction

In 6 cats, cerebral infarction was produced by transorbital occlusion of the left middle cerebral artery (MCA). Five animals developed typical cortical infarcts. Eight weeks later, cerebral blood flow (CBF) was determined by 14C-iodoantipyrine autoradiography and the number of intact neurons was counted histologically. Two non-operated cats served as controls. Cortical blood flow in the infarcted hemisphere was reduced by 24.6-74.4% when compared to the flow in the contralateral cortex and in controls. Averaged white matter flow was decreased by 39.1%. Regional cortical flow was gradually reduced from parasagittal regions towards the infarct. In the surrounding of the infarct, cortical perfusion was decreased to 24.8 +/- 9.7 ml/100 g/min, i.e. 19.7% of contralateral flow. Although the infarcts were sharply demarcated macroscopically, the number of cortical neurons decreased gradually from the midline to the peri-infarct zone. A significant linear correlation was found between absolute CBF-values and the number of neurons in areas of the infarcted hemisphere. The homolateral gyrus lateralis had normal neuronal density but flow was reduced by 20%. These findings suggest that the blood flow reduction in tissue surrounding chronic infarcts is due to neuronal cell loss and to functional inactivation caused by damage of afferent fibers.

Pentobarbital protection from cerebral infarction without suppression of edema

We studied the mechanism of barbiturate protection from focal cerebral infarction in cats by examining in detail edema formation 72 hours after acute, permanent occlusion of the left middle cerebral artery (LMCA). Neurological function, gas exchange, vital signs, and intracranial pressure (ICP) were observed during the post-occlusion period, and infarct size and cerebral edema were measured after sacrifice. Infarct size was reduced only when pentobarbital was given before occlusion and continued for 24 hours. Edema formation was not suppressed even though the extent of infarction was. Clinical evidence of stroke developed and ICP rose in most cats after occlusion despite the presence of pentobarbital sufficient to reduce infarct size. Elevated ICP accounted for most premature deaths despite intensive cardiopulmonary support. Water and electrolyte changes in the ischemic hemisphere continued to develop throughout the 72 hour post-occlusion period in pentobarbital-treated cats, suggesting that resolution of edema was delayed by the drug. We conclude that pentobarbital reduces infarct size and attenuates the expected time course of ischemic edema in cats, but that the drug has little effect on the severity of edema that develops after arterial occlusion.

Protective effect of Fluosol-DA in acute cerebral ischemia

Fluosol-DA (Perfluorochemical Blood Substitutes) are small particle fluorocarbons suspended in an emulsion and have a high propensity for carrying oxygen and carbon dioxide. Fluosol-DA was investigated for the modification of acute focal cerebral ischemia and compared to mannitol. A total of 36 adult cats were divided into 3 groups and had transorbital microtourniquet ligation of the middle cerebral artery (MCA). Control animals were given intravenous isotonic saline. Animals in the experimental groups were treated with either intravenous Fluosol-DA or mannitol. All animals were nursed in an oxygen chamber and 4 cats from each group were sacrificed at 1, 3 and 6 hours after MCA occlusion. The results of macroscopic and histological examination of the brain suggested Fluosol-DA had a definite protective effect on acute focal cerebral ischemia which was in keeping with the observed neurological outcome. It is suggested that Fluosol-DA may support flow in the microcirculation and that the small particles of Fluosol-DA may be able to reach the area of ischemia via collaterals by decreasing blood viscosity, preventing narrowing of the arteriolar and capillary lumen and increasing the cerebral blood flow.

Some principles of postoperative epidural pressure monitoring

A retrospective analysis is presented of 115 cerebral tumour cases where continuous epidural pressure (EDP) monitoring was carried out postoperatively using an implantable transducer constructed on a coplanar principle. Correct implantation of the transducer is crucial to reliable measurement. The influence of transducer location on EDP is highly significant and can be accounted for at least partly by hydrostatic forces. The effect of postural changes similarly has a hydrostatic component. Clinically complicated cases were usually easily distinguishable from uncomplicated cases with a similar transducer location. EDP is usually low in the absence of complications during the first 6 to 12 hours postoperatively. For postoperative monitoring, an EDP transducer should be placed as near to the site of surgery as possible for maximum sensitivity to local pressure changes and the earliest detection of complications.

Thresholds of focal cerebral ischemia in awake monkeys

An awake-primate model has been developed which permits reversible middle cerebral artery (MCA) occlusion during physiological monitoring. This method eliminates the ischemia-modifying effects of anesthesia, and permits correlation of neurological function with cerebral blood flow (CBF) and neuropathology. The model was used to assess the brain's tolerance to focal cerebral ischemia. The MCA was occluded for 15 or 30 minutes, 2 to 3 hours, or permanently. Serial monitoring evaluated neurological function, local CBF (hydrogen clearance), and other physiological parameters (blood pressure, blood gases, and intracranial pressure). After 2 weeks, neuropathological evaluation identified infarcts and their relation to blood flow recording sites. Middle cerebral artery occlusion usually caused substantial decreases in local CBF. Variable reduction in flow correlated directly with the variable severity of deficit. Release of occlusion at up to 3 hours led to clinical improvement. Pathological examination showed microscopic foci of infarction after 15 to 30 minutes of ischemia, moderate to large infarcts after 2 to 3 hours of ischemia, and in most cases large infarcts after permanent MCA occlusion. Local CBF appeared to define thresholds for paralysis and infarction. When local flow dropped below about 23 cc/100 gm/min, reversible paralysis occurred. When local flow fell below 10 to 12 cc/100 gm/min for 2 to 3 hours or below 17 to 18 cc/100 gm/min during permanent occlusion, irreversible local damage was observed. These studies imply that some cases of acute hemiplegia, with blood flow in the paralysis range, might be improved by surgical revascularization. Studies of local CBF might help identify suitable cases for emergency revascularization.

Hypertension and acute focal cerebral ischemia. Infarction and edema after occlusion of a middle cerebral artery in cats

Hypertension was produced in 8 cats by nephrectomy and wrapping the opposite kidney. Subsequent occlusion of one middle cerebral artery caused ischemic infarcts that were larger than those of 8 normotensive cats. The larger infarcts may have been caused by increases of ischemic cerebral edema resulting from changes in the cerebral endothelial barrier induced by hypertension. In addition to increasing the likelihood of strokes, hypertension in humans may predispose toward larger cerebral infarcts.

Protection from cerebral ischemia by a new imidazole derivative (Y-9179) and pentobarbital. A comparative study in chronic middle cerebral artery occlusion in cats

For the purpose of investigating the protective action against cerebral ischemia by a new imidazole derivative (Y-9179) and pentobarbital, regional cerebral ischemia was produced in 53 cats by permanent occlusion of the middle cerebral artery (MCA) via the transorbital approach. In 20 cats, the clips were applied at the origin of the right MCA whereas in the remaining 33 they were applied laterally. The administration of Y-9179 (6.25 and 12.5 mg/kg/day), pentobarbital (25 mg/kg/day) and saline was started 30 min after MCA occlusion and continued for 3 days. The cats were observed for 7 days and then sacrificed. Since there was a remarkable difference in mortality between the medial (65%) and the lateral occlusion groups (15%), the evaluation of drug effects was based only on the results obtained with the lateral occlusion group. The brains were sliced at 4 fixed coronal planes, in which the ratios of the infarcted area in the 2 hemispheres were obtained by planimetry. A statistically significant decrease in the infarction rate was found both in Y-9179 and pentobarbital-treated groups compared to the control group. Since the CNS depressant action of Y-9179 is far less potent than that of pentobarbital, the present results indicate the potential usefulness of Y-9179 in the management of strokes.

Modification of acute focal ischemia by treatment with mannitol

A simple implanted device was used to occlude acutely the left middle cerebral artery (MCA) of 16 conscious cats. Eight received no treatment and 8 were given intravenous mannitol (1.2 gm/kg) at the time of occlusion. The initial neurological findings in both groups were similar, that is, agitation, forced circling, and right hemiparesis. The treated cats remained alert but the untreated cats became lethargic and drowsy. Perfusion with a mixture of colloidal carbon and buffered paraformaldehyde was carried out from 30 minutes to 6 hours following MCA occlusion. Results of morphological examination of brains from the treated and untreated groups suggested that mannitol had a protective effect upon cerebral tissue during the primary phase of acute focal ischemia. Light microscopic analysis of neuronal alterations demonstrated considerable preservation of neurons in brains of treated cats. Beneficial effect of mannitol was attributed partly to prevention of capillary narrowing and suppression of ischemic cerebral edema.

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.

Relationships among intracranial pressure, blood pressure, and superficial cerebral vasculature after experimental occlusion of one middle cerebral artery

A cranial window conforming to the contours of the underlying cerebral cortical surface was implanted successfully in 18 cats. Subsequently the left middle cerebral artery (MCA) was occluded inside the sealed cranium and changes in the superficial cortical vasculature were related to measurements of intracranial pressure (ICP), measured extradurally, and to the resulting infarcts. Vascular changes early after MCA occlusion were not predictive of the outcome of the occlusion, except for aggregation of formed elements of the blood in arterioles, which was a bad prognostic sign. Secondary reactive hyperemia was not beneficial; increases of ICP suggested that hyperemia led to increased cerebral edema as well as to swelling.

Experimental subarachnoid hemorrhage from a middle cerebral artery. Neurologic deficits, intracranial pressures, blood pressures, and pulse rates

Devices to produce experimental subarachnoid hemorrhage (SAH) can be implanted in animals. After SAH is produced by the puncture of a middle cerebral artery (MCA) in awake cats, neurologic deficits develop that are not as severe as those caused by MCA occlusion. Biphasic increases of epidural pressure occur and are related to the extent and distribution of the hemorrhage. Ischemic changes are more severe if the flow of blood through the MCA is interrupted.

Implanted device for middle cerebral artery occlusion in conscious cats

A simple implantable device was applied to the left middle cerebral artery of adult cats. One week later the artery was occluded acutely while the animals were conscious. Forced circling and tonic deviation of the head and neck toward the left were noted within seconds of occlusion. A right hemiparesis developed one to two minutes later. Cerebral angiography confirmed the presence of the middle cerebral artery occlusion when the occluding stylet was inserted. Removal of the stylet resulted in reopening of the artery. Light microscopic examination of the brains revealed severe acute ischemic changes in a large left cortical and subcortical area. Partial loss of endothelial lining and thinning of the media were demonstrated in the compressed segment of the middle cerebral artery.