The blood-brain barrier following experimental subarachnoid hemorrhage. Part 1: Response to insult caused by arterial hypertension

In three groups of cats, the authors studied the effect of subarachnoid hemorrhage (SAH) on the permeability of the blood-brain barrier (BBB) to the penetration of Evans blue-protein complex. One group received arterial hypertension alone, one group SAH alone, and one group SAH followed by arterial hypertension. Animals subjected to arterial hypertension alone showed areas of BBB breakdown. However, when cats were rendered hypertensive after SAH, there were no demonstrable BBB lesions. The SAH was produced by intracisternal injection of whole blood and hypertension by the intravenous injection of metaraminol. The preservation of the BBB after SAH is discussed. Vasospasm is considered as a possible hemodynamic variable responsible for the protection of the BBB from hypertensive damage. The need for a new model is proposed to further investigate the state of the BBB after SAH.     

Barrier disruption in the major cerebral arteries after experimental subarachnoid hemorrhage in spontaneously hypertensive and normotensive rats

The effects of experimental subarachnoid hemorrhage (SAH) on the blood-arterial wall barrier in the major cerebral arteries were studied in 24 spontaneously hypertensive rats (SHR) and 13 Sprague-Dawley rats (SDR). Horseradish peroxidase (HRP) was given intravenously before killing the animals to assess the integrity of the barrier. In the acute experimental group, transient elevation of intracranial pressure (ICP) and systemic arterial pressure produced by cisternal injection of whole blood, saline solution, or Elliott's B solution resulted in extensive disturbance of the blood-arterial wall barrier. In the chronic group, only the cisternal injection of whole blood in SHR brought about an extensive and marked disturbance of the arterial permeability. These results suggest that: (a) early breakdown of the blood-arterial wall barrier seems to be due to a sudden rise in the ICP or arterial pressure; (b) in the chronic experiments, the subarachnoid clot is the most important factor responsible for the permeability changes; and (c) in the chronic SAH experiments, the blood-arterial wall barrier seems to be more vulnerable in SHR than in Sprague-Dawley rats. Due to the well-known similarities between SHRs and hypertensive human beings, patients with chronic hypertension should be considered at high risk after SAH for extensive blood-arterial wall barrier disturbances.     

短期应用高渗盐水对重症蛛网膜下腔出血患者颅内压、脑血流量的影响

目的 探讨23.4%高渗盐水(HTS)对重症蛛网膜下腔出血(SAH)患者颅内压、脑灌注压、脑血流量(CBF)的影响.方法 16例重症SAH患者(GCS≤8分)在颅压升高时接受静脉输注23.4%HTS,监测用药前及用药后30、60、90、120、150、180 min的颅内压(ICP),平均动脉压(MAP),脑灌注压(CPP)及脑血流速度(FV).结果 用药后30 min可见ICP显著降低,同时MAP、CPP及FV显著升高(P<0.05),ICP显著降低可持续180 min,CPP和FV的改善持续约90 min(P<0.05).结论 HTS能显著降低重症SAH患者的ICP,改善脑组织灌注,可用来纠正脑缺血引起的病生理变化.     

The blood-brain barrier following experimental subarachnoid hemorrhage. Part 2: Response to mercuric chloride infusion

Under controlled physiological conditions, fresh blood was injected into the cisterna magna of 10 adult cats to produce subarachnoid hemorrhage (SAH). Damage to the blood-brain barrier (BBB) was induced 30 minutes after SAH by the intracarotid injection of a 6 x 10(-5)M solution of mercuric chloride (HgCl2). A control series of five cats received the same injection of HgCl2. Intravenously injected Evans blue dye was used to indicate areas of BBB damage. The lesions were confirmed by fluorescence microscopy. All control animals showed BBB damage in the hemisphere injected with HgCl2. Of the animals in the test group with SAH, 90% were free from lesions. When lesions were present, the distribution differed from that in the control group. These results bear a similarity to the reported absence of HgCl2 lesions during the acute stages after total cerebral ischemia. This suggests that the cellular components of the BBB participate in a general metabolic inhibition following SAH.     

Induction of heat shock protein 70 in the rat brain following intracisternal infusion of autologous blood: evaluation of acute neuronal damage.

OBJECT: Investigation into a potential treatment for the acute period following onset of spontaneous subarachnoid hemorrhage (SAH) is hampered by the lack of a standardized experimental model. For that purpose the authors elaborated on a small-animal model in which computer-controlled intracisternal blood infusion is used and investigated whether this model can reliably reproduce acute neuronal injury after SAH. METHODS: Whole autologous blood (blood-infused group) or isotonic saline (control group) was infused into the cisterna magna or olfactory cistern of rats. The infusions decreased exponentially during a 5-minute period. Throughout the infusion period, intracranial pressure (ICP) was monitored. Neuronal injury was quantified by observing tissue immunoreactivity to a 70-kD heat shock protein (HSP70) and comparing this with the tissue's reaction to hematoxylin and eosin staining. On Days 1, 3, and 5, the CA1, CA3, and dentate gyrus regions of the hippocampus were analyzed, respectively. During saline infusion ICP increased within seconds beyond 80 mm Hg and afterward decreased in accordance with the infusion rate. During the infusion of blood, the same initial pressure peak was found, but the ICP remained increased beyond this pressure level throughout the 5-minute infusion period. The HSP70 immunoreactivity in the saline-infused group was found only on Day 1 in the CA1 region and the dentate gyrus, but not in the CA3. After injection of whole blood, there was HSP70-positive staining in the CA1, CA3, and dentate gyrus regions throughout the observation period. CONCLUSIONS: The controlled cisternal infusion of blood caused neuronal injury that resembled that of previous experimental models that produce SAH by rupture of intracranial vessels with endovascular techniques. Unlike those experiments, the intracisternal infusion technique presented by the authors provides more standardized bleeding with regard to ICP, the volume of subarachnoid blood, and the extent of acute cellular injury.     

Barrier disruption in the major cerebral arteries following experimental subarachnoid hemorrhage

The effects of experimental subarachnoid hemorrhage (SAH) on the blood-arterial wall barrier in the major cerebral arteries were studied in 20 normotensive dogs. Horseradish peroxidase (HRP) was given intravenously before the animals were sacrificed to assess the integrity of the barrier. Transient elevation of intracranial pressure (ICP) produced by cisternal injection of saline solution resulted in HRP leakage at the branching points of the major cerebral arteries. Extensive disturbance of the blood-arterial wall barrier was consistently observed in the major cerebral arteries after SAH, with or without elevation of ICP. These results suggest that both subarachnoid clot and a sudden rise in the ICP are important factors causing the breakdown of the blood-arterial wall barrier, but that the effect of the clot is the most profound. Electron microscopy revealed that opening of the interendothelial junctions is one of the important mechanisms responsible for the HRP leakage in the major cerebral arteries following SAH. Disturbance of arterial permeability in the major cerebral arteries following SAH probably accounts for the abnormal post-contrast enhancement that occurs in patients who are prone to develop vasospasm following aneurysm rupture, and is probably involved in the pathogenesis of vasospasm.     

Barrier disruption in the major cerebral arteries during the acute stage after experimental subarachnoid hemorrhage

The effects of experimental subarachnoid hemorrhage (SAH) on the blood-arterial wall barrier in the basilar arteries were studied during the acute stage after SAH. SAH was induced in rats by injecting fresh autologous blood into the cisterna magna. Horseradish peroxidase (HRP) was given intravenously before killing the animals to assess the integrity of the barrier. In the basilar arteries taken from the animals that were killed 30 minutes after the cisternal injection of either mock cerebrospinal fluid or arterial blood, HRP reaction products were diffusely observed in the subendothelial spaces and smooth muscle layers. At 5 hours after the blood injection, no permeation of HRP into the subendothelial space was observed. Endothelial cell transcytosis seemed to be the important mechanism for HRP permeation into the subendothelial space rather than the opening of interendothelial junctions. The disruption of the blood-arterial wall barrier in the major cerebral arteries after SAH may be involved in the pathogenesis of vasospasm.     

Subacute hydrocephalus after experimental subarachnoid hemorrhage: its prevention by intrathecal fibrinolysis with recombinant tissue plasminogen activator.

It is investigated whether intrathecal fibrinolysis may prevent subacute hydrocephalus after subarachnoid hemorrhage (SAH). In 19 cats, SAH was induced by the intracisternal infusion of 1 ml/kg body weight of fresh autologous blood at a rate of 0.6 ml/min. Eleven of those animals were treated by intrathecal fibrinolysis performed 24 hours after experimental SAH by intracisternal infusion of 3 mg of recombinant tissue plasminogen activator. Included were eight animals suffering from experimental SAH and four healthy animals retained for control. A computed tomographic scan performed 24 hours after the SAH displayed an acute hydrocephalus from the experimental procedure. Cerebrospinal fluid outflow resistance was 71 +/- 5.0 mm Hg/ml/min in the healthy animals, 265 +/- 19.8 mm Hg/ml/min in the nontreated animals 7 days after SAH, and 151 +/- 6.4 mm Hg/ml/min in the recombinant tissue plasminogen activator-treated animals 7 days after SAH (mean +/- standard deviation; changes significant with P less than 0.01). Postmortem planimetry of both lateral ventricles gives a mean of 3.7 +/- 2.7 mm2 in the healthy animals, 11.1 +/- 3.9 mm2 in the nontreated group after SAH (P less than 0.01), and 3.5 +/- 1.1 mm2 in the animals treated with recombinant tissue plasminogen activator. Intracranial pressure monitoring demonstrated marked intracranial pressure waves only in the nontreated animals after SAH. It is concluded that intrathecal fibrinolysis may prevent subacute hydrocephalus after experimental SAH.     

Physiological and electrophysiological consequences of etoposide-induced blood-brain barrier disruption

The present study investigates the effects of etoposide-induced blood-brain barrier (BBB) disruption on systemic blood pressure (SBP), intracranial pressure (ICP), and electroencephalographic (EEG) activity. A total of 29 rats were divided into two groups. In Group 1, 8 control animals received intracarotid normal saline; in Group 2, 21 animals received intracarotid etoposide. SBP, ICP, and EEG were monitored continuously under general anesthesia and controlled ventilation after tracheostomy. Intravenous Evans blue dye was used for determination of BBB disruption. Although none of the Group 1 animals showed BBB disruption, 57% of the animals in Group 2 showed marked BBB disruption (3+). A slight but statistically significant increase in ICP was noted in the Group 2 animals with 3+ BBB disruption, although lesser degrees of barrier disruption (1+ or 2+) resulted in no significant alteration in ICP. The amplitude and frequency of the EEG decreased significantly ipsilateral to the side of intracarotid infusion in all animals with 3+ barrier disruption with a tendency to return toward normal within 2 hours. The degree of transient EEG change observed correlates well with the degree of barrier disruption, potentially allowing clinical determination of BBB disruption by this method.     

Efficacy of single intracisternal bolus injection of recombinant tissue plasminogen activator to prevent delayed cerebral vasospasm after experimental subarachnoid hemorrhage

Premature lysis of subarachnoid blood clots by thrombolytic substances such as urokinase and plasmin has been shown to be efficacious in preventing cerebral vasospasm in clinical and experimental investigations. Recently, tissue plasminogen activator (rtPA) derived from recombinant deoxyribonucleic (DNA) technology has been introduced as a new thrombolytic substance. With its high affinity for fibrin-bound plasminogen and low affinity for circulating plasminogen by which a clot-selective fibrinolysis can be achieved without the danger of inducing systemic fibrinogenolysis, rtPA might be the ideal substance for the postoperative lysis of cisternal blood accumulations after subarachnoid hemorrhage. The efficacy of rtPA in preventing delayed cerebral vasospasm after experimental subarachnoid hemorrhage using a single intracisternal bolus injection of this agent was investigated. With a single injection of 25 micrograms of rtPA into the cisterna magna 48 hours after the first and 6 hours after the second injection of blood in the two-hemorrhage model of cerebral vasospasm, angiographic spasm of the basilar artery was completely prevented in all animals so treated whereas in the control group severe vasospasm occurred. Autopsy studies of the experimental animals demonstrated that the subarachnoid blood clots were almost completely removed by intracisternal rtPA application. Additionally the pathomorphological signs of proliferative vasculopathy present in all animals of the control group were not demonstrable in the rtPA group. As intracisternal bolus injection of rtPA is highly efficacious in preventing angiographic as well as pathomorphological vasospasm, it is concluded that use of this thrombolytic substance might be a promising approach for pharmacological blood clot removal.     

Pharmacological reversibility of experimental cerebral vasospasm

Using a morphometric technique, the pharmacological reversibility of luminal narrowing after experimental subarachnoid hemorrhage (SAH) was investigated. For vasodilation, a "cocktail" consisting of 10(-4) M papaverine, 2 x 10(-4) M sodium nitroprusside, and 10(-5) M adenosine was administered intra-arterially. Forty-two rabbits were divided into six groups: control (normal animals); control plus cocktail (normal animals perfused with the cocktail before fixation); SAH (animals sacrificed 48 hours subsequent to intracisternal injection of 1.5 ml/kg of arterial blood); SAH plus cocktail (SAH plus perfusion with the cocktail); BaCl2 (animals sacrificed 10 minutes after intracisternal injection of 2 ml of 3 x 10(-3) M BaCl2); and BaCl2 plus cocktail (BaCl2 animals perfused with the cocktail). The diameter of the basilar arteries in the control and the control plus cocktail groups was not significantly different. BaCl2 reduced the diameter 44% and SAH reduced the diameter 27%. There were no significant differences between the diameter of the BaCl2 plus cocktail group and SAH plus cocktail group when compared with the control or the control plus cocktail group. Morphological examination by light and transmission electron microscopy showed luminal narrowing and corrugation of the elastic lamina with few degenerative or proliferative changes of the vessel wall in animals with SAH. These results suggest that cerebral vasospasm is caused initially by smooth muscle contraction rather than by proliferative vasculopathy and that it is not an irreversible process.     

Acute changes in the dynamics of the cerebrospinal fluid system during experimental subarachnoid hemorrhage

Early changes in intracranial pressure (ICP), ICP volume index, and resistance to absorption of cerebrospinal fluid induced by experimental subarachnoid hemorrhage were studied in cats. After SAH, the ICP was slightly elevated, and there was a decrease in the buffering capacity of the intracranial space and a sharp rise in outflow resistance. During infusion of blood into the cisterna magna with a constant infusion rate, an extensive increase in ICP could be demonstrated in contrast to the infusion of saline, which caused only slight elevation of ICP. Furthermore, during blood infusion, the ICP level did not reach a plateau phase of pressure, as was demonstrated during infusion of saline. It is suggested that the marked increase in ICP during blood infusion into the subarachnoid space is caused by intracranial volume loading and the simultaneous increase in cerebrospinal fluid outflow resistance. It is concluded that the reported relationship between increased cerebrospinal fluid outflow resistance and increased ICP supports the hypothesis of a strong increase in ICP during subarachnoid hemorrhage in human subjects.     

An experimental study of the acute stage of subarachnoid hemorrhage

A baboon model of subarachnoid hemorrhage (SAH) has been developed to study the changes in cerebral blood flow (CBF), intracranial pressure (ICP), and cerebral edema associated with the acute stage of SAH. In this model, hemorrhage was caused by avulsion of the posterior communicating artery via a periorbital approach, with the orbit sealed and ICP restored to normal before SAH was produced. Local CBF was measured in six sites in the two hemispheres, and ICP monitored by an implanted extradural transducer. Following sacrifice of the animal, the effect of the induced SAH on ICP, CBF, autoregulation, and CO2 reactivity in the two hemispheres was assessed. Brain water measurements were also made in areas of gray and white matter corresponding to areas of blood flow measurements, and also in the deep nuclei. Two principal patterns of ICP change were found following SAH; one group of animals showed a return to baseline ICP quite quickly and the other maintained high ICP for over an hour. The CBF was reduced after SAH to nearly 20% of control values in all areas, and all areas showed impaired autoregulation. Variable changes in CO2 reactivity were evident, but on the side of the hemorrhage CO2 reactivity was predominantly reduced. Differential increase in pressure lasting for over 7 minutes was evident soon after SAH on the side of the ruptured vessel. There was a significant increase of water in all areas, and in cortex and deep nuclei as compared to control animals.     

Intracranial pressure levels and single wave amplitudes, Glasgow Coma Score and Glasgow Outcome Score after subarachnoid haemorrhage

Summary Object. To relate intracranial pressure (ICP) levels and single ICP wave amplitudes to the acute clinical state (Glasgow Coma Score, GCS) and final clinical outcome (Glasgow Outcome Score, GOS) in patients with subarachnoid haemorrhage (SAH). Methods. Twenty-seven consecutive patients with severe SAH had their ICP and arterial blood pressure (ABP) continuously monitored during days 1–6 after SAH. The acute clinical state could be assessed in 11 non-sedated cases using the Glasgow Coma Scale, while outcome was assessed in all cases after 6 months using the Glasgow Outcome Scale. The ICP/ABP recordings were stored as raw data files and analyzed retrospectively. For every consecutive 6 seconds time window, mean ICP, mean cerebral perfusion pressure (CPP) and the mean ICP wave amplitude were computed. Results. The GCS during days 1–6 after SAH was significantly related to the mean ICP wave amplitude, but not to the mean ICP or mean CPP. There was also a strong relationship between the mean ICP wave amplitude and GOS 6 months after SAH, with mean ICP wave amplitudes being significantly lower in those with moderate disability/good recovery, as compared with those with severe disability and death. Mean ICP was significantly higher in those who died than in the group with moderate disability/good recovery whereas mean CPP was not different between outcome groups. Conclusions. In this small patient group the mean ICP wave amplitude during days 1–6 after SAH was related to the acute clinical state (GCS) as well as to the clinical outcome (GOS) 6 months after SAH. Similar relationships were not found for mean ICP or the mean CPP, except for a higher mean ICP in those who died than in those with moderate disability/good recovery.     

Evidence for direct impairment of neuronal function by subarachnoid metabolites following SAH

Dysfunction of neuronal signal processing and transmission occurs after subarachnoid hemorrhage (SAH) and contributes to the high morbidity and mortality of this pathology. The underlying mechanisms include early brain injury due to elevation of the intracranial pressure, disruption of the blood–brain barrier, brain edema, reduction of cerebral blood flow, and neuronal cell death. Direct influence of subarachnoid blood metabolites on neuronal signaling should be considered. After SAH, some metabolites were shown to directly induce disruption of neuronal integrity and neuronal signaling, whereas the effects of other metabolites on neurotoxicity and neuronal signaling have not yet been investigated. Therefore, this mini-review will discuss recent evidence for a direct influence of subarachnoid blood and its metabolites on neuronal function.     

Cerebral arterial responses to induced hypertension following subarachnoid hemorrhage in the monkey.

Regional cerebral blood flow (rCBF), angiographic cerebral arterial caliber, and cerebrospinal fluid (CSF) pressure were measured in rhesus monkeys to determine the effect of experimentally induced subarachnoid hemorrhage (SAH) on cerebral arterial responses to graded increases in blood pressure. These measurements were also performed in a control group of monkeys subjected to a mock SAH by injection of artificial CSF into the cerebral space. Before subarachnoid injection of blood or artificial CSF, graded increases in mean arterial blood pressure (MABP) to a level 40% to 50% above baseline values had no effect on rCBF. The major cerebral arteries constricted and CSF pressure remained unchanged. Similar responses were observed after injections of artificial CSF. When MABP was increased in animals that had been subjected to subarachnoid injection of blood, rCBF increased and was associated with dilatation of the major cerebral arteries and moderate increases in CSF pressure. These results demonstrate that cerebral arterial responses to increases in blood pressure may be abnormal in the presence of subarachnoid blood. The manner in which abnormal cerebral arterial reactivity, changes in blood pressure, and vasospasm combine to determine the level of cerebral perfusion following SAH is postulated.     

Experimental subarachnoid hemorrhage: subarachnoid blood volume,mortality rate,neuronal death,cerebral blood flow,and perfusion pressure in three different rat models

OBJECTIVE: To investigate which of three subarachnoid hemorrhage (SAH) models is the most suitable for studies of pathological and pathophysiological processes after SAH. METHODS: SAH was induced in rats via intracranial endovascular perforation (perforation model), blood injection into the cisterna magna (300 microl), or blood injection into the prechiasmatic cistern (200 microl). The subarachnoid blood volume was quantitatively measured. Cerebral blood flow (CBF) (as assessed with laser Doppler flowmetry), intracranial pressure, and mean arterial blood pressure were recorded for 90 minutes after SAH. Mortality was recorded, and neuronal death was assessed in animals that survived 7 days after SAH. RESULTS: The subarachnoid blood volume was close to the injected amount after prechiasmatic SAH. In the other models, the volume varied between 40 and 480 microl. The mortality rates were 44% in the perforation SAH group, 25% in the prechiasmatic SAH group, and 0% in the cisterna magna SAH group; the corresponding values for neuronal death were 11, 44, and 28%. Cerebral perfusion pressure approached baseline values within 5 minutes after SAH in all three models. CBF decreased to approximately 35% of baseline values immediately after SAH in all groups; it gradually increased to normal values 15 minutes after SAH in the cisterna magna SAH group and to 60 and 89% of baseline values 90 minutes post-SAH in the perforation and prechiasmatic SAH groups. CBF was significantly correlated with the subarachnoid blood volume. CONCLUSION: The prechiasmatic SAH model seems to be the most suitable for study of the sequelae after SAH; it produces a significant decrease in CBF, an acceptable mortality rate, and substantial pathological lesions, with high reproducibility. The CBF reduction is predominantly dependent on the amount of subarachnoid blood.     

Positron emission tomography with 68-Ga-EDTA and computed tomography in patients with subarachnoid haemorrhage

Summary 26 patients with subarachnoid haemorrhage (SAH) were investigated with 68-Ga-EDTA and positron emission tomography (PET) in order to evaluate the presence of a blood brain barrier (BBB) disturbance. Only one patient showed a BBB disruption. It is suggested that increased levels of substances with higher molecular weight than 68-Ga-EDTA in the cerebrospinal fluid (CSF) are the result of a change in the metabolism of the CSF and the brain tissue caused by a SAH.     

Etiology of the disruption in blood-arterial wall barrier following experimental subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage is associated with a sudden rise in intracranial pressure, acute arterial hypertension, and subarachnoid blood. The role that each of these factors may play in the development of the acute barrier disruption of the major cerebral arteries following subarachnoid hemorrhage was investigated in 42 rabbits. Horseradish peroxidase was given intravenously to assess the integrity of the barrier by transmission electron microscopy. Permeation of the tracer into the vessel was noted only in animals with increased intracranial pressure. A sudden rise in intracranial pressure is suggested to trigger acute barrier disruption following subarachnoid hemorrhage.     

Limited role of inducible nitric oxide synthase in blood-brain barrier function after experimental subarachnoid hemorrhage

Excessive nitric oxide (NO) produced by inducible nitric oxide synthase (iNOS) may play a pivotal role in blood-brain barrier (BBB) breakdown following subarachnoid hemorrhage (SAH). We investigated if the inhibition of iNOS could reduce BBB breakdown and cerebral edema, thereby leading to improved outcome 24 h after SAH. Forty male rats were assigned to three groups: control, SAH, and treatment groups. SAH was induced by perforating the bifurcation of the internal carotid artery. The neurological score and the mortality were evaluated 24 h after the surgery. The expression of iNOS, the concentration of NO metabolites, morphological changes in neuronal cells, water content, and IgG leakage were also evaluated. The expression of iNOS, as well as the concentration of NO metabolites, was elevated after SAH. Treatment with p-Toluenesulfonate decreased both the expression of iNOS and the concentration of NO metabolites. However, there was no significant change in water content, BBB disruption, or morphological findings between the SAH group and the treatment group. Furthermore no significant differences in neurological score or mortality were observed. The iNOS inhibitor failed to reduce BBB breakdown, brain edema, and neuronal cell death and failed to improve the neurological score and the mortality 24 h after SAH.