Cerebral blood flow following induced subarachnoid hemorrhage in the monkey

Animal Welfare Aspects in Planning and Conducting Experiments on Rodent Models of Subarachnoid Hemorrhage

Subarachnoid hemorrhage is an acute life-threatening cerebrovascular disease with high socio-economic impact. The most frequent cause, the rupture of an intracerebral aneurysm, is accompanied by abrupt changes in intracerebral pressure, cerebral perfusion pressure and, consequently, cerebral blood flow. As aneurysms rupture spontaneously, monitoring of these parameters in patients is only possible with a time delay, upon hospitalization. To study alterations in cerebral perfusion immediately upon ictus, animal models are mandatory. This article addresses the points necessarily to be included in an animal project proposal according to EU directive 2010/63/EU for the protection of animals used for scientific purposes and herewith offers an insight into animal welfare aspects of using rodent models for the investigation of cerebral perfusion after subarachnoid hemorrhage. It compares surgeries, model characteristics, advantages, and drawbacks of the most-frequently used rodent models-the endovascular perforation model and the prechiasmatic and single or double cisterna magna injection model. The topics of discussing anesthesia, advice on peri- and postanesthetic handling of animals, assessing the severity of suffering the animals undergo during the procedure according to EU directive 2010/63/EU and weighing the use of these in vivo models for experimental research ethically are also presented. In conclusion, rodent models of subarachnoid hemorrhage display pathophysiological characteristics, including changes of cerebral perfusion similar to the clinical situation, rendering the models suited to study the sequelae of the bleeding. A current problem is low standardization of the models, wherefore reporting according to the ARRIVE guidelines is highly recommended. Animal welfare aspects of rodent models of subarachnoid hemorrhage. Rodent models for investigation of cerebral perfusion after subarachnoid hemorrhage are compared regarding surgeries and model characteristics, and 3R measures are suggested. Anesthesia is discussed, and advice given on peri- and postanesthetic handling. Severity of suffering according to 2010/63/EU is assessed and use of these in vivo models weighed ethically.

Experimental subarachnoid haemorrhage models in rats

There is no comprehensive and reliable model available in small animals that are suitable for the study of subarachnoid haemorrhage (SAH). In the study we reviewed the advantages and disadvantages of available SAH models in rats and presented our model. Experimental SAH was induced in a group of 350-450 g Sprague-Dawley rats. A 2 mm-diameter burr hole was drilled and, working under a microscope, haemorrhage was produced by transclival puncture of the basilar artery with a 20 microns thick piece of glass. The rats were assigned to either the experimental group (n: 7) or the control group (n: 7). Local cerebral blood flow (LCBF), intracranial pressure (ICP), and cerebral perfusion pressure (CPP) were measured for 60 min after SAH, after which the rats were decapitated. Microscopic examinations were done on three different segments of the basilar artery. There was a significant and sharp drop in LCBF just after SAH was induced (56.17 +/- 12.80 mlLD/min/100 g and 13.57 +/- 5.85 mlLD/min/100 g for baseline and post-SAH, respectively; p < 0.001), the flow slowly increased by the end of the experiment but never recovered to pre-SAH values (43.63 +/- 7.6 mlLD/min/100 g, p < 0.05). ICP (baseline 7.33 +/- 0.8 mmHg) increased acutely to 70.6 +/- 9.2 mmHg, and also returned to normal levels by 60 min after SAH. CPP (baseline 75.1 +/- 4.9 mmHg) dropped accordingly (to 21.0 +/- 6.3 mmHg) and then increased, reaching 70.1 +/- 4.9 mmHg at 60 min after SAH. Examinations of the arteries revealed decreased inner luminal diameter and distortion of the elastica layer. We present an inexpensive and reliable model of SAH in the rat that allows single and multiple haemorrhages and to study the early and late course of pathological changes.

Beneficial effect of renin-angiotensin system for maintaining blood pressure control following subarachnoid haemorrhage

Subarachnoid haemorrhage is a serious condition often accompanied by delayed cerebral ischaemia. Earlier reports have provided evidence suggesting a role for angiotensin II in the development of cerebral vasospasm following subarachnoid bleeding. We sought to examine the influence of angiotensin II blockade with losartan on blood pressure and survival in animals following experimental subarachnoid haemorrhage, induced in conscious rats by injecting homologous blood via a catheter placed along the surface of the brain. We combined measurements of plasma renin activity with blood pressure recording in order to examine renin-angiotensin system activation following experimental subarachnoid haemorrhage. Following subarachnoid injury an approximately three-fold increase in plasma renin activity occurred (3.4 +/- 1.0 vs. 10.1 +/- 1.8 ng angiotensin I produced/ml/h, p < 0.01). In animals treated with losartan (20 mg/kg) prior to the induction of subarachnoid haemorrhage blood pressure fell dramatically following the cerebral injury (124 +/- 5 vs. 94 +/- 7 mmHg, p < 0.001), whereas blood pressure remained unchanged in control animals. Survival was markedly reduced in those animals treated with losartan. Given the pronounced decrease in blood pressure and impaired survival following subarachnoid haemorrhage in animals treated with losartan, it would appear that the acute activation of the renin-angiotensin system following this insult is in fact a desirable, compensatory response.

Nitric oxide scavenging by hemoglobin or nitric oxide synthase inhibition by N-nitro-L-arginine induces cortical spreading ischemia when K+ is increased in the subarachnoid space

We investigated the combined effect of increased brain topical K+ concentration and reduction of the nitric oxide (NO.) level caused by nitric oxide scavenging or nitric oxide synthase (NOS) inhibition on regional cerebral blood flow and subarachnoid direct current (DC) potential. Using thiopental-anesthetized male Wistar rats with a closed cranial window preparation, brain topical superfusion of a combination of the NO. scavenger hemoglobin (Hb; 2 mmol/L) and increased K+ concentration in the artificial cerebrospinal fluid ([K+]ACSF) at 35 mmol/L led to sudden spontaneous transient ischemic events with a decrease of CBF to 14+/-7% (n=4) compared with the baseline (100%). The ischemic events lasted for 53+/-17 minutes and were associated with a negative subarachnoid DC shift of -7.3+/-0.6 mV of 49+/-12 minutes' duration. The combination of the NOS inhibitor N-nitro-L-arginine (L-NA, 1 mmol/L) with [K+]ACSF at 35 mmol/L caused similar spontaneous transient ischemic events in 13 rats. When cortical spreading depression was induced by KCl at a 5-mm distance, a typical cortical spreading hyperemia (CSH) and negative DC shift were measured at the closed cranial window during brain topical superfusion with either physiologic artificial CSF (n=5), or artificial CSF containing increased [K+]ACSF at 20 mmol/L (n=4), [K+]ACSF at 3 mmol/L combined with L-NA (n=10), [K+]ACSF at 10 mmol/L combined with L-NA (five of six animals) or [K+]ACSF at 3 mmol/L combined with Hb (three of four animals). Cortical spreading depression induced longlasting transient ischemia instead of CSH, when brain was superfused with either [K+]ACSF at 20 mmol/L combined with Hb (CBF decrease to 20+/-20% duration 25+/-21 minutes, n=4), or [K+]ACSF at 20 mmol/L combined with L-NA (n=19). Transient ischemia induced by NOS inhibition and [K],ACSF at 20 mmol/L propagated at a speed of 3.4+/-0.6 mm/min, indicating cortical spreading ischemia (CSI). Although CSH did not change oxygen free radical production, as measured on-line by in vivo lucigenin-enhanced chemiluminescence, CSI resulted in the typical radical production pattern of ischemia and reperfusion suggestive of brain damage (n=4). Nimodipine (2 microg/kg body weight/min intravenously) transformed CSI back to CSH (n=4). Vehicle had no effect on CSI (n=4). Our data suggest that the combination of decreased NO. levels and increased subarachnoid K+ levels induces spreading depression with acute ischemic CBF response. Thus, a disturbed coupling of metabolism and CBF can cause ischemia. We speculate that CSI may be related to delayed ischemic deficits after subarachnoid hemorrhage, a clinical condition in which the release of Hb and K+ from erythrocytes creates a microenvironment similar to the one investigated here.

Acute vasoconstriction after subarachnoid hemorrhage

OBJECTIVE

Decreased cerebral blood flow (CBF) and cerebral ischemia occurring immediately after subarachnoid hemorrhage (SAH) may be caused by acute microvascular constriction. However, CBF can also be influenced by changes in intracranial pressure (ICP) and cerebral perfusion pressure (CPP). The goal of these experiments was to assess the significance of acute vasoconstriction after SAH and its relationship to changes in CBF, ICP, CPP, and extracellular glutamate concentrations.

METHODS

Three experiments were performed using the endovascular filament technique to produce SAH. In the first experiment, CBF, ICP, and CPP were measured for 60 minutes after SAH (n = 21) and were correlated with the 24-hour mortality rate. In the second experiment, rats undergoing SAH (n = 23) or a sham procedure (n = 7) were perfused 60 minutes after SAH for measurement of the circumference and wall thickness of the internal carotid and anterior cerebral arteries and correlation with CBF, ICP, and CPP. In the third experiment (n = 11), extracellular glutamate concentrations determined by hippocampal and cortical microdialysis and high performance liquid chromatography were correlated with physiological changes.

RESULTS

CBF reductions to less than 40% of baseline for 60 minutes after SAH predicted 24-hour mortality with 100% accuracy and were used to define "lethal" SAH. In contrast, ICP and CPP 60 minutes after SAH were not correlated with the mortality rate. The vascular circumference was significantly smaller in lethal than in sublethal SAH or sham-operated rats (P < 0.001). Vessel measurements were correlated with both CBF and hemorrhage size (P < 0.01). Extracellular glutamate concentration increased to 600% of baseline after lethal SAH in both hippocampus and cortex and was inversely correlated with CBF (r = 0.9, P < 0.001) but did not increase after sublethal SAH.

CONCLUSION

Acute vasoconstriction after SAH occurs independently of changes in ICP and CPP and is associated with decreased CBF, larger hemorrhage size, persistent elevations of extracellular glutamate, and poor outcome. Acute vasoconstriction seems to contribute directly to ischemic brain injury after SAH. Further evaluations of pharmacological agents with the potential to reverse acute vasoconstriction may increase CBF and improve outcome.

Time-course alterations of monoamine levels and cerebral blood flow in brain regions after subarachnoid hemorrhage in rats

To investigate the possible correlation between changes in monoaminergic neuronal activity and cerebral blood flow (CBF) in the same brain region after subarachnoid hemorrhage (SAH), monoamine levels were analyzed by both HPLC-ECD and fluorohistochemistry techniques, and CBF was measured by using colored microspheres. At the second day of SAH, significant and nonsignificant reductions in blood flow were seen in the examined brain regions with a marked increase in CBF appearing in the telencephalon and hypothalamus on the third day. Significant reductions of monoamine levels in most brain regions were also observed on the second day after SAH, whereas norepinephrine (NE) levels in midbrain increased to 1.5 times compared to the normal level. These reductions were sustained until the fourth day of SAH, although at the third day, serotonin (5-HT) and dopamine levels in the hippocampus and 5-HT levels in the cerebelium were significantly elevated. In fluorohistochemical studies, the fluoro-intensities of monoamines, particularly catecholamines, in the midbrain dorsal NE bundle were enhanced at the second day after SAH. These NE neurons originated from the A5 cell group close to the area where homologous blood was applied through the cisterna magna. The results obtained after SAH show an apparent correlation between changes in monoamine levels and CBF in norepinephrine (NE)-rich areas. These results suggest that SAH-induced neuronal dysfunctions, particularly with NE neurons, are caused not only by reductions of blood flow but also by hemorrhage.

Acute Cerebral Artery Constriction in the Spontaneously Hypertensive Rat following Blood and Plasma Administration into the Subarachnoid Space

The purpose of the present study was to demonstrate, using a vascular casting technique, acute vasoconstrictive changes in the cerebral vasculature 1 h following whole-blood or plasma infusion into the subarachnoid space of conscious spontaneously hypertensive rats. Vascular casts from animals infused (over 20 min) with 0.45 ml of heparinized autologous arterial blood or plasma exhibited incomplete filling, while casts from saline-infused controls exhibited virtually no filling defects. Significant elevations in intracranial pressure were noted in blood, but not in plasma- or saline-infused rats. Two characteristic forms of constriction occurred, depending upon the vessel lumen diameter. Vessels with lumen diameters >100 &mgr;m were flattened longitudinally with deep endothelial nuclear imprints, while smaller vessels had focal circular constrictions resembling beads. Arterial cast filling terminated in vessels with lumen diameters from 70 to 120 &mgr;m with focal signs of constriction at or near the point of cast termination. The results indicate that the presence of both blood and plasma in the subarachnoid space produces acute small-artery constriction. This phenomenon is due to a noncellular blood component and does not correlate with increases in intracranial pressure. Copyright 1996 S. Karger AG, Basel

The Sheffield model of subarachnoid hemorrhage in rats

BACKGROUND AND PURPOSE

There is no comprehensive and reliable model available in small animals that is suitable for the study of subarachnoid hemorrhage (SAH). Most of the existing models either require extensive surgery to achieve SAH or neglect the importance of an injury to the vessel and the impact of suddenly raised intracranial pressure (ICP). The presented model is designed to overcome these shortcomings.

METHODS

Forty-three male Wistar rats were anesthetized. Regional cerebral blood flow was measured using the H2 clearance method bilaterally in the middle cerebral artery territory. ICP and blood pressure were continuously monitored. Blood gases were kept within physiological limits. SAH was produced by passing a nylon thread up through the right internal carotid artery and piercing a hole in the right anterior cerebral artery. The animals were divided into three experimental groups treated with varied operative techniques. After 3 hours the surviving animals were killed, and SAH was confirmed by postmortem examination.

RESULTS

The described method proved to be a reliable way of producing SAH in rats. The onset of SAH was characterized by a sudden increase in ICP. There were some differences in the reduction of regional cerebral blood flow and the survival rate in the experimental groups. This may represent differing degrees of severity of the produced SAH.

CONCLUSIONS

We present an inexpensive and reliable model of SAH in the rat that allows the early course of biochemical, physiological, and pathological changes to be studied.

Cerebral blood flow and glucose metabolism in the squirrel monkey during the late phase of cerebral vasospasm

A double-isotope autoradiography technique was used to evaluate cerebral blood flow (CBF) and cerebral glucose metabolism (CMRglu) during the late phase of vasospasm in a squirrel monkey subarachnoid haemorrhage (SAH) model. Cisternal blood injections induced both global and focal changes in CBF and CMRglu six days following SAH, the timepoint of maximal late spasm in this model. There was a global decrease in CBF of about 30% accompanied by an increase in deoxyglucose uptake of about 50%. Four of seven animals also had foci with flow decreased to 40% of control and deoxyglucose uptake increased to 300% of control. There was an altered but still present interdependence between flow and metabolism post SAH.

Cerebral blood flow changes induced by electrical stimulation of the Gasserian ganglion after experimentally induced subarachnoid haemorrhage in pigs

The effect of trigeminal electrical stimulation on cerebral blood flow has been studied in conditions of normal or reduced cerebral blood flow (CBF). Autologous blood was injected into the subarachnoid space of ten Pittmann-Moore pigs to induce subarachnoid haemorrhage (SAH) accompanied by cerebral blood flow (CBF) reduction. One week later, in six of ten animals, a considerable decrease of CBF was noted as evaluated by means of a recording-system monitoring over the right parieto-temporal calvarium the washout of 133Xenon injected into the internal carotid artery after the external carotid had been clamped. Continuous electrical stimulation of the Gasserian ganglion performed in the six animals with severely induced CBF reduction produced a remarkable cerebrovascular dilation and increase of CBF lasting over 3 h. Electrical stimulation of the Gasserian ganglion produced a similar pattern of vasodilation in six pigs in which no blood was injected and no reduction of CBF was evident. The mechanisms and the anatomical pathways which underlie these results are discussed.

Cerebral blood flow and intracranial pressure during experimental subarachnoid haemorrhage

The relationships of intracranial pressure (ICP), systemic blood pressure (SBP) and cerebral blood flow (CBF) during experimental subarachnoid haemorrhage were investigated in cats. Continuous monitoring of regional cerebral blood flow (rCBF) was done by a thermal diffusion method using a Peltier stack. During haemorrhage ICP rose within 5.4 +/- 0.97 minutes from 10.5 +/- 4.9 to 176.1 +/- 27.8 mmHg. This strong increase of ICP resulted in a temporary arrest of cerebral circulation. The Cushing response during the haemorrhage could not improve the cerebral circulation, but in contrast caused a further increase of ICP. After the haemorrhage the cerebral blood flow normalised within minutes. It is concluded, that the Cushing response during a subarachnoid haemorrhage should be regarded as a deleterious rather than a beneficial mechanism.

Effect of pre- and postganglionic lesioning of the trigeminal nerve on cerebral blood flow and glucose metabolism following a subarachnoid haemorrhage in the squirrel monkey

Simultaneous cerebral blood flow (CBF) and glucose metabolism (CMRglu) studies with a double isotope autoradiographic technique were applied to squirrel monkeys submitted to a unilateral pre- or postganglionic trigeminal lesion. The CBF values were not affected following a pre- or postganglionic lesion per se. In contrast, there was a global increase in the cerebral glucose uptake of about 50% as compared to controls following both kinds of lesions. Following a subarachnoid haemorrhage (SAH) 2-4 weeks after pre- or postganglionic trigeminal lesioning, there was a decrease in CBF similar to that seen in the control group. In the animals with a preganglionic lesion, the 50% increase in glucose uptake was not further augmented by a SAH and the increase in CMRglu was comparable to that found in control SAH animals. In the postganglionically lesioned monkeys, a SAH induced an additional increase in glucose uptake of about 50%. The findings suggest that the trigeminal system is involved in the regulation of cerebral metabolism via a brainstem centre.

Vasospasm due to massive subarachnoid haemorrhage--a rat model

Although the pathophysiology of chronic cerebral vasospasm following subarachnoid haemorrhage (SAH) is still unclear, it is certain that the amount of subarachnoid blood is predictive of the severity of cerebral vasospasm. Accordingly, massive subarachnoid haemorrhage (greater than 0.5 ml) was induced in adult rats via direct injection into the cisterna magna. Compared to other previously published models of experimental SAH in rats a much larger amount of blood was injected. The basilar artery was exposed 72 hours post subarachnoid haemorrhage and photographed under controlled conditions. The diameter of the artery was assessed by an image analyzer. A 50% reduction in diameter was found in 25 rats subjected to SAH as compared to 9 control rats and 4 rats with intracisternal saline injection. We conclude that when massive subarachnoid haemorrhage is induced, and direct measurements of the basilar artery are made, the rat can be used as a reliable model for investigation of SAH induced arterial vasospasm.

Experimental isobaric subarachnoid hemorrhage: regional mitochondrial function during the acute and late phase

Patients treated for aneurysmal subarachnoid hemorrhage show, in the long-term follow up, an elevated rate of cognitive disturbances that are mainly related to the impact of the initial bleeding: the neurotoxic effects of blood deposition in subarachnoidal spaces may result in a diffuse encephalopathy, but the intrinsic mechanism and the biochemical correlates are not known. In the present study we have evaluated mitochondrial function after experimental induction of subarachnoid hemorrhage. Mitochondrial function was evaluated in four different rat brain areas (frontal cortex, occipital cortex, hippocampus, and brain stem) after experimental isobaric subarachnoid hemorrhage in rats. Subarachnoid hemorrhage was induced by injecting 0.07 mL of arterial autologous blood into the cisterna magna. Intracranial pressure did not significantly increase. The nonsynaptic mitochondrial fraction was isolated from different rat brain areas, and the maximal rate of enzymatic reactions of some key enzymatic activities related to the Krebs cycle [nicotinamide adenine dinucleotide (oxidized form) (NAD+)-isocitrate dehydrogenase, citrate synthase, and succinate dehydrogenase] and of the electron transfer chain (cytochrome oxidase) were evaluated. The nonsynaptic mitochondrial fraction was utilized also to check parameters related to the mitochondrial respiration: state 3, state 4, uncoupled state, respiratory control ratio, and adenosine 5'-diphosphate/oxygen ratio. The biochemical parameters were measured at 1 and 72 hours after the subarachnoidal injection of blood. Subarachnoid hemorrhage did not affect the mitochondrial enzymatic activities both at 1 and 72 hours, while the mitochondrial enzymatic activities parameters were significantly affected: in particular, a significant decrease of respiratory control ratio in all tested brain areas was demonstrated. The increased mitochondrial vulnerability in the delayed phases could be one of the biochemical correlates of post-hemorrhagic encephalopathy.

The time course of intracranial pathophysiological changes following experimental subarachnoid haemorrhage in the rat

The rat subarachnoid haemorrhage (SAH) model was further studied to establish the precise time course of the globally reduced CBF that follows and to ascertain whether temporally related changes in cerebral perfusion pressure (CPP) and intracranial pressure (ICP) take place. Parallel ultrastructural studies were performed upon cerebral arteries and their adjacent perivascular subarachnoid spaces. SAH was induced by a single intracisternal injection of autologous arterial blood. Serial measurements of regional cortical CBF by hydrogen clearance revealed that experimental SAH resulted in an immediate 50% global reduction in cortical flows that persisted for up to 3 h post SAH. At 24 h, flows were still significantly reduced at 85% of control values (p less than 0.05), but by 48 h had regained normal values and were maintained up to 5 days post SAH. ICP rose acutely after haemorrhage to nearly 50 mm Hg with C-type pressure waves being present. ICP then fell slowly, only fully returning to control levels at 72 h. Acute hydrocephalus was observed on autopsy examination of SAH animals but not in controls. Reductions in CPP occurred post SAH, but only in the order of 15%, which could not alone account for the fall in CBF that took place. At 48 and, to a lesser extent, 24 h post SAH, myonecrosis confined largely to smooth muscle cells of the immediately subintimal media was observed. No significant changes in the intima or perivascular nerve plexus were seen. Within 24 h of haemorrhage, a limited degree of phagocytosis of erythrocytes by pial lining cells took place. However, early on the second day post SAH, a dramatic increase in the numbers of subarachnoid macrophages arose from a transformation of cells of the pia-arachnoid. This period was characterised by intense phagocytic activity, erythrocytes, fibrin, and other debris being largely cleared over the next 24 h. At 5 days post SAH the subarachnoid macrophage population declined, cells losing their mobile active features to assume a more typical pia-arachnoid cell appearance once more. Our studies indicate that this increasingly utilised small animal model of SAH develops global cortical flow changes only acutely, and it is likely that early vasospasm, secondary to released blood products rather than pressure changes per se, is responsible for the initial cerebral ischaemia that develops. Interestingly, both cerebral arterial vasculopathy and perivascular macrophage phagocytic activity are most marked at approximately 48 h following SAH in the rat, a time at which a phase of delayed cerebral arterial narrowing has previously been documented.

Chronic cerebral blood flow changes following experimental subarachnoid hemorrhage in rats

Experimental subarachnoid hemorrhage was induced in 52 adult male Wistar rats by microsurgical transclival basilar artery puncture. Telencephalic blood flow measured in 24 rats with subarachnoid hemorrhage was compared with that in 23 sham-operated rats and 10 unoperated control rats using the [14C]butanol indicator fractionation technique. Telencephalic blood flow was significantly less in the rats with subarachnoid hemorrhage than in the sham-operated rats 3 (78.7 +/- 6.9 [n = 7] and 112.0 +/- 8.5 [n = 8] ml/100 g/min, respectively; p less than 0.01), 7 (74.9 +/- 5.1 [n = 9] and 112.6 +/- 4.6 [n = 8] ml/100 g/min, p less than 0.001), and 14 (81.9 +/- 6.0 [n = 8] and 104.1 +/- 5.4 [n = 7] ml/100 g/min, p less than 0.01) days after surgery. Telencephalic blood flow in unoperated controls (114.7 +/- 4.9 ml/100 g/min) did not differ significantly from sham-operated rats. Clinically, the 52 rats with subarachnoid hemorrhage were indistinguishable from 32 sham-operated rats. Postmortem examinations in 10 rats used in a preliminary investigation demonstrated significant blood clot in the basal cisterns 2 hours after basilar artery puncture. Intracranial pressure was slightly elevated (2.3 mm Hg over baseline) 30 minutes after the hemorrhage (n = 7), but when measured 3 (n = 3) or 7 (n = 3) days after surgery it had returned to baseline. Histologic examination of the brains from 10 rats subjected to subarachnoid hemorrhage 7 (n = 5) or 14 (n = 5) days before sacrifice revealed no evidence of cerebral ischemia or vasculopathic changes in the cerebral arteries.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in serotonin and neuropeptide Y content of cerebrovascular sympathetic nerves following experimental subarachnoid hemorrhage

The effect of an experimental subarachnoid hemorrhage (SAH) upon neurotransmitter content in sympathetic nerves supplying the major cerebral arteries of the rat has been examined by immunohistochemical analysis and high performance liquid chromatography with electrochemical detection (HPLC-ECD). In particular, changes that occur in sympathetic nerve content of the vasoconstrictor agents serotonin (5-HT) and neuropeptide Y (NPY), which are colocalized with noradrenaline, were assessed. Subarachnoid hemorrhage was induced by a single injection of autologous arterial blood into the cerebrospinal fluid (CSF) space of the cisterna magna. The density of 5-HT-containing and NPY-containing perivascular nerve fibers per unit area of vessels was measured at defined intervals from 15 min to 5 days post-SAH. In addition, an HPLC study was performed to quantify the actual amounts of 5-HT and noradrenaline present in circle of Willis vessels at 3 h post-SAH. Comparison was made with sham-operated animals and animals that received a cisternal injection of buffered saline in place of blood. Our results reveal a major increase in cerebrovascular sympathetic nerve content of serotonin, arising by uptake, presumably from subarachnoid blood clot, within the first 3 h post-SAH. Neuropeptide Y content, however, decreased from 3 up to 48 h posthemorrhage. By 3 days post-SAH, when the majority of subarachnoid clot had resorbed, the sympathetic nerve content of both NPY and 5-HT was restored to normal. This pattern of change was not observed in either sham-operated or saline-injected controls.

Effect of subarachnoid hemorrhage on intracranial pulse waves in cats

The influence of vasoconstrictors of intracranial arteries on the amplitude and configuration of the intracranial pulse wave (ICPW) was investigated. Continuous pressure recordings from the descending aorta (systemic arterial pressure) and the third cerebral ventricle (intracranial pressure) were obtained from anesthetized cats. Computerized analysis of the configuration, amplitude, and frequency spectrum of ventricular wave (ICPW) and aortic pulse wave (SAPW) was performed. Artificial cerebrospinal fluid (CSF), blood, or 5-hydroxytryptamine (5-HT) was injected intracisternally. In 24 control cats, 2 ml artificial CSF was injected into the cisterna magna. This produced a significant increase in amplitude of the ICPW but no change in the SAPW. Ten animals received 14 intracisternal injections of 2 ml autologous blood which caused narrowing of the amplitude of the ICPW as well as of all its components (P1, P2, and P3), with no significant change in the SAPW's. Eight animals were also subjected to cisternal injection of 2 ml of a 10(-4)-M solution of 5-HT, resulting in findings similar to those produced by autologous blood. Frequency spectrum of the intracranial and aortic pulse waves showed a high degree of correlation between wave amplitudes and height of the fundamental wave in the FFT record. These results suggest that the cerebral vasospasm that follows cisternal injections of blood and 5-HT in cats can be diagnosed by analysis of the ICPW. This method may allow early diagnosis and continuous monitoring of cerebral vasospasm in humans.

Subarachnoid hemorrhage fails to produce vasculopathy or chronic blood flow changes in rats

Cerebral blood flow was measured by a [14C]butanol indicator fractionation technique in rats subjected to subarachnoid hemorrhage, in control rats, and in rats given injections of buffered saline into the subarachnoid space (sham hemorrhage). Cerebral blood flow was significantly decreased in both the subarachnoid hemorrhage and sham hemorrhage rats 3 hours after injection. However, blood flow returned to control levels by 24 hours, and measurement for 14 days after subarachnoid hemorrhage failed to show any delayed decrease in cerebral blood flow. Electron microscopic studies of basilar arteries from rats subjected to subarachnoid hemorrhage 72 hours before killing failed to show any of the morphologic changes that have been associated with vasospasm in humans or in higher animal models. Our studies indicate that the rat model of subarachnoid hemorrhage has limited applicability to the study of subarachnoid hemorrhage following ruptured cerebral aneurysms in humans. However, although rats are not a perfect model of this clinical condition, some pathophysiologic changes similar to those observed in human subarachnoid hemorrhage have been demonstrated in this model and deserve further investigation.

Regional cerebral metabolic activity in the rat following experimental subarachnoid hemorrhage

A new experimental model was employed to investigate alterations of cerebral metabolic activity in rats subjected to extensive subarachnoid hemorrhage (SAH). The hemorrhages were produced in anesthetized animals by inserting 0.37 ml fresh autologous arterial blood into the subarachnoid space. Rats that underwent sham operations received subarachnoid injections of mock CSF to study the effects of sudden raised intracranial pressure (ICP). Forty-eight hours after subarachnoid injection, the unanesthetized rats were given intravenous injections of [14C]2-deoxyglucose. Experiments were terminated 45 min later by decapitation, and the brains were removed and frozen. Regional brain metabolic activity was studied employing quantitative autoradiography. In comparison with control animals, cerebral metabolic activity was diffusely decreased following SAH. Statistically significant decreases in metabolic activity of less than 34% were observed in 17 of 30 brain regions studied. The largest percentage reductions were in regions displaying the highest basal metabolic rates. Subarachnoid injections of mock CSF also produced depression of cerebral metabolic activity, but quantitatively these changes were not as pronounced as in the hemorrhage group. These studies demonstrate regional changes in brain function following SAH. The data relate these changes to both the presence of blood in the subarachnoid space and sudden raised ICP.

Cerebrovascular and metabolic changes during the delayed vasospasm following experimental subarachnoid hemorrhage in baboons, and treatment with a calcium antagonist

A model has been designed in baboons for simulating the clinical situation during the late phase of vasospasm in patients with subarachnoid hemorrhage (SAH). A total amount of 14-33 ml autologous blood was injected into the cisternal system on 3 occasions in the course of 4 days. Neurological symptoms were seen, and the mortality rate was 29%. Angiography 3 days after the last injection showed arterial vasoconstriction amounting to 23% in the vertebro-basilar system, and 11% (right) and 18% (left) in the carotid system. Cerebral blood flow (CBF) measured by the intra-arterial 133Xe technique and the cerebral metabolic rate of oxygen (CMRO2) were reduced by 18% and 11%, respectively. The hypercapnic CBF response was significantly impaired, from a mean of 3.90 ml/100 g/min to 1.72 ml/100 g/min of flow increase for each mm Hg elevation of paCO2. Autoregulation, tested by administration of angiotensin II, was also significantly affected as evidenced by a pressure-dependent increment of CBF during hypertension in 5 out of 7 animals tested. The impaired autoregulation was reflected in the autoregulatory index, which in the whole group increased from 0.06 ml/100 g/min for each mm Hg increase in MABP in the pre-SAH animals to 0.29 ml/100 g/min per mm Hg post-SAH. Treatment with the calcium antagonist, nimodipine (0.5 microgram/kg/min i.v. during 45 min), enhanced CBF significantly by 17% before experimental SAH, whereas after SAH the effect was slight and did not reach statistical significance; CMRO2 was not significantly affected in either group. Intravenous nimodipine combined with hypertension resulted in a marked increase in the autoregulatory index to 1.58 ml/100 g/min per mm Hg in pre-SAH animals and a less pronounced increment to 0.58 ml/100 g/min per mm Hg following experimental SAH. The beneficial effect of nimodipine reported in SAH patients is therefore, in view of our findings, more likely due primarily to a protective mechanism at the cellular level than to an influence on the vascular bed.

Subarachnoid hemorrhage in the rat: cerebral blood flow and glucose metabolism during the late phase of cerebral vasospasm

A double-isotope technique for the simultaneous measurement of CBF and CMRglu was applied to a subarachnoid hemorrhage (SAH) model in the rat. Cisternal injection of 0.07 ml blood caused a rather uniform 20% reduction in CBF together with an increase in glucose utilization of 30% during the late phase of vasospasm. In one-third of the SAH animals, there were focal areas where the flow was lowered to 30% of the control values and the glucose uptake increased to approximately 250% of control. We suggest that blood in the subarachnoid space via a neural mechanism induces the global flow and metabolic changes, and that the foci are caused by vasospasm superimposed on the global flow and metabolic changes. In the double-isotope autoradiographic technique, [14C]iodoantipyrine and [3H]deoxyglucose were used for CBF and CMRglu measurements, respectively, in the same animal. In half of the sections, the [14C]iodoantipyrine was extracted using 2,2-dimethoxypropane before the section was placed on a 3H- and 14C-sensitive film. The other sections were placed on x-ray film with an emulsion insensitive to 3H. The validity of the double-isotope method was tested by comparing the data with those obtained in animals receiving a single isotope. The CBF and metabolic values obtained in the two groups were similar.

Altered membrane properties of cerebral vascular smooth muscle following subarachnoid hemorrhage: an electrophysiological study. I. Changes in resting membrane potential (Em) and effect on the electrogenic pump potential contribution to Em

Subarachnoid hemorrhage was produced experimentally in cats by intracisternal injection of non-heparinized autologous arterial blood obtained by cardiac puncture under ketamine and xylazine anesthesia. Cats were sacrificed at varying time intervals between 30 min and 7 days post ictus. Measurements of resting membrane potential were recorded from smooth muscle cells of the basilar artery. These measurements were obtained by impalement from the adventitial surface of isolated but otherwise intact segments of the artery using glass microelectrodes with tip sizes less than 0.1 micron. The resting membrane potential recorded in vitro from animals previously subjected to subarachnoid hemorrhage in vivo was consistently and significantly depolarized when compared to normal controls. This depolarization was present as early as 30 min post ictus. Addition of the cardiac glycoside, ouabain, in a concentration of 10(-5)M depolarized cells from both control and experimental animals. There is a significant electrogenic pump potential contribution to the resting membrane potential of vascular smooth muscle cells. Ouabain is a potent blocker of Na+, K+-ATPase, the enzyme responsible for maintaining the cation electrochemical gradients. The depolarization recorded in these cells following subarachnoid hemorrhage is not, therefore, due to impairment of the electrogenic pump. The significance and implications of these findings are discussed.

A contribution to the pathogenesis of respiratory disturbances associated with subarachnoid haemorrhage; an experimental approach using an animal model

The present experimental work focuses on the mechanisms involved in respiratory distress observed in the course of subarachnoid haemorrhage. For this purpose, respiratory disturbances were induced in rabbits by injecting fresh autologous blood into the subarachnoid space. For six hours after this artificially induced SAH, blood PO2 and PCO2 as well as expiratory air CO2 were regularly determined, while during the same period cerebral blood flow and cerebrospinal fluid pressure measurements were recorded. The results of this study suggest that pressure effects acting the brain structures that support respiration are principally involved in the pathogenesis of respiratory disturbances following SAH. A decrease in CBF and hypoxia with hypercapnia play a contributing secondary role adding to a vicious cycle phenomenon.

Regional CBF, intraventricular pressure, and cerebral metabolism in patients with ruptured intracranial aneurysms

Regional cerebral blood flow (rCBF), cerebral metabolic rate of oxygen (CMRO2), intraventricular pressure, and lactate/pH levels in the cerebrospinal fluid (CSF) were measured in 38 patients with ruptured intracranial aneurysms between the 3rd and 13th day after subarachnoid hemorrhage (SAH). Angiography was performed following the rCBF study and the degree of vasospasm was measured on the angiograms. The patients were graded clinically according to the system of Hunt and Hess. Cerebral vasospasm significantly influenced rCBF: global reductions and focal changes (ischemia, hyperemia, and tissue peaks) were commonly associated with vasospasm. Patients with severe diffuse spasm always had global ischemia (21 +/- 5 ml/100 gm/min), and cerebral infarctions were demonstrated subsequently, The CMRO2 was more reduced than rCBF, indicating an uncoupling between flow and metabolism. This relative luxury perfusion was associated with CSF lactic acidosis and intracranial hypertension. The arteriovenous difference of oxygen was equally reduced in all categories of patients, probably due to the primary insult of SAH. The CMRO2 decreased concomitantly with arterial caliber, indicating a secondary impairment of cerebral metabolism due to vasospasm.

Decrease in cerebral blood flow in rats after experimental subarachnoid hemorrhage: a new animal model

There continues to be a need for good animal models of experimental subarachnoid hemorrhage (SAH). The rat would be an ideal subject in which to study SAH since it is inexpensive and easier to use than the larger laboratory animals. The present study was undertaken to determine if alterations of cerebral blood flow could be produced in the rat after experimental SAH, and thereby justify using the rat as a model for further study of SAH. Rats weighing between 450 and 500 grams underwent insertion of a cannula into the cisterna magna at least 5 days prior to physiological testing. One group of rats then received a 0.3 cc injection of fresh autologous arterial blood into the cisterna magna to simulate a SAH. Another group of rats received injection of an equal volume of mock CSF (buffered saline) into the cisterna magna. A third group of rats had no subarachnoid injections. In all three groups, blood flow to the cerebral hemispheres was measured with the labeled microsphere technique. Rats with experimental SAH showed a 40% decrease of cerebral blood flow, whereas rats with saline injections showed only a 15% decrease. Control rats had no changes of cerebral blood flow. These studies demonstrate that the rat is a potential experimental model for investigations into SAH.

The role of the prostacyclin-thromboxane system in cerebral vasospasm following induced subarachnoid hemorrhage in the rabbit

Subarachnoid hemorrhage (SAH) was induced in 50 rabbits by injecting 1.25 cc/kg of autologous, well heparinized, fresh arterial blood into the cisterna magna, followed by suspending the animals in a head-down position at 30 degrees for 15 minutes. The animals were evenly divided into five groups: a control group, or groups receiving post-SAH prostacyclin (PGI2), carbacyclin, thromboxane A2 (TXA2) synthetase inhibitor (OKY-1581), or nutralipid. Radiographic vertebrobasilar arterial spasm was demonstrated on the 3rd day post-SAH in the control animals. This was decreased in the prostacyclin and the carbacyclin groups and was absent in the OKY-1581 and the nutralipid groups. Cerebral blood flow (CBF) measurements on the 4th day post-SAH using the xenon-133 technique failed to reveal any significant difference between the prostacyclin, the carbacyclin, and the control groups, but flows in the nutralipid and the OKY-1581 groups were significantly higher. There was a good correlation between the clinical status and the CBF. Intracytoplasmic vacuolation and detachment of the vascular endothelium, seen ultrastructurally, may account for the impaired synthesis of prostacyclin. Exogenous prostacyclin and carbacyclin decreased vasospasm but failed to improve cerebral perfusion. OKY-1581 blocked the synthesis of the potent vasoconstrictor, TXA2, which is not only formed during platelet aggregation but also induces platelet aggregation. Nutralipid contains linolenic acid, a precursor of eicosapentaenoic acid (EPA), which is more potent in inhibiting platelet aggregation and in blocking TXA2 production. The various fatty acid constituents of nutralipid bind to albumin and thereby shorten the half-life of TXA2.

Early effects of experimental arterial subarachnoid haemorrhage on the cerebral circulation. Part I: Experimental subarachnoid haemorrhage in cat and its pathophysiological effects. Methods of regional cerebral blood flow measurement and evaluation of microcirculation

Studies of pathophysiological changes, regional cerebral blood flow (rCBF) and cerebral microcirculation were performed in cats subjected to arterial subarachnoid haemorrhage (SAH). An original method for SAH imitating aneurysm rupture was developed. The bleeding was induced by puncturing of the internal carotid artery approached tranpresphenoidally and followed by immediate closure of the skull opening. It was found, that arterial subarachnoid bleeding elevates intracranial pressure and results in a transitory fall in cerebral perfusion pressure which is not prevented by elevation of arterial blood pressure (Cushing reflex). A depression in brain electrical activity and respiration rate were present in the course of subarachnoid haemorrhage.

A new model of subarachnoid hemorrhage in experimental animals with the purpose to examine cerebral vasospasm

Using 20 rabbits, we tried to establish a new model of experimental subarachnoid hemorrhage (SAH) for examining both acute and chronic cerebral vasospasm. A cranial opening was drilled, and a puncture made on the posterior branch of the middle cerebral artery. A second puncture was made in the superior sagittal sinus for additional withdrawal of subarachnoid blood. The bleeding thus induced resulted in arterial spasm which was studied by using serial electrocorticograms, cerebral blood flow measurement with 133Xe, and videomicroscopy of the small pial vessels at various intervals. After death of the animals, the brains were observed to identify the extention of the bleeding. It was indeed obvious that large amounts of subarachnoid blood clots had accumulated. This investigation showed that the rabbit can be used as a new experimental model of SAH. With a two-puncture method, it is possible to simulate the clinical phenomenon of a ruptured aneurysm, that seems to produce acute and chronic cerebral vasospasm. For the latter, the accumulation of blood clots in the basal surfaces plays an important role. The three methods of observation, videomicroscopy, cerebral blood flow measurements, and electrocorticography appeared to provide useful information in the study of biphasic vasospasm in the rabbit.

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.

Regional cerebral blood flow in the acute stage of experimentally induced subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) was induced in 13 adult mongrel cats by a slow injection of fresh autogenous blood into the cisterna magna. Serial determinations of regional cerebral blood flow (rCBF) in the cortex and deep-seated areas (internal capsule, thalamus, and caudate nucleus) were made during the following 2 hours, while intracranial pressure (ICP) was maintained at normal values. A decrease in rCBF was observed in all the areas examined. This reduction followed a characteristic triphasic pattern with an initial steep decline immediately after the SAH. The clinical implications of these findings are discussed.

Experimental cerebral vasospasm: resolution by chlorpromazine

Vasospasm of the cat basilar artery was produced by electrical, mechanical, or chemical stimuli or by subarachnoid hemorrhage. The vasospasm induced by these stimuli was relieved by the topical application of chlorpromazine to the vascular wall. Chlorpromazine appears to be a nonspecific vasoparalytic agent. Unlike previously used substances, it is effective in resolving vasospasm caused by mechanical as well as chemical irritation.

Effect of subarachnoid hemorrhage on the extracellular microenvironment

Local experimental subarachnoid hemorrhage (SAH) was produced over the cerebral cortex in 15 cats. The cellular response was monitored using ion-specific electrodes for extracellular potassium (K+) and calcium (Ca++) activity, DC cortical potential, and electrocorticogram. The response was characterized by a profound cellular depolarization and extracellular calcium (Ca++) depletion which accompanied extracellular potassium (K+) accumulation. The prehemorrhage baseline calcium levels measured 1.14 +/- 0.11 mM, and were lowered to 0.4 to 0.7 mM/liter in different experiments. The K+ accumulation reached levels between 16 and 31 mM from a baseline of 3.17 +/- 0.52 mM and were cleared to normal or nearly normal within 5 minutes. The Ca++ levels also returned to normal within 5 minutes, but remained depressed for the duration of the experiment in two animals. These results confirm that blood extravasated into the subarachnoid space had a direct effect on parenchymal elements. The combination of transient K+ elevations and calcium depression may play an important role in the development of vascular spasm by inducing or facilitating a contraction in the muscular layer in the wall of major intracranial vessels.

Cerebrovascular reactivity and metabolism after subarachnoid hemorrhage in baboons

Subarachnoid hemorrhage (SAH) was induced in baboons by puncturing the middle cerebral artery. Four to seven days later cerebral blood flow (CBF) responses to changing PaCO2 and to intracarotid infusion of 1.0, 2.5 and 5.0 micrograms of 5-hydroxytryptamine (5-HT)/kg/min were studied using the intracarotid 133xenon clearance technique. Indices of cerebral metabolism were determined by measuring arterio-venous differences for oxygen, pyruvate, lactate and glucose. The results were compared with those from sham-operated baboons. In the sham-operated group normal CO2 reactivity was seen, and 5-HT infusion did not produce any significant change in CBF or cerebral metabolism. By contrast, the group in which SAH was induced showed a significant decrease in CBF and cerebral oxygen utilization, and attenuated CO2 reactivity.

Regional cerebral blood flow in patients with ruptured intracranial aneurysms

Eighty-five studies of regional cerebral blood flow (rCBF) were performed on 49 patients with ruptured intracranial aneurysms. The changes in rCBF were analyzed under various pathophysiological conditions, The degree of flow abnormalities correlated well with the clinical severity of neurological deficits. All of the patients with diffuse vasospasm of severe grade, to less than half of their control value, showed focal areas of decreased flow below 30 ml/100 gm/min, in addition to a reduction in mean CBF. The relief or disappearance of vasospasm in angiograms was followed by the increase of rCBF in the ischemic focus and mean CBF. Marked reduction in rCBF was found in patients with intracerebral hematoma and ventricular dilatation. Impaired CO2 response and autoregulation were found in patients with severe neurological deficits, a severe degree of vasospasm and marked depression of CBF. In this series direct operation was delayed in patients with impaired vascular reactivity as well as marked decrease of mean CBF below 30 ml/100 gm/min; good clinical results were obtained in thses patients.

Ultrastructural changes in feline arterial endothelium following subarachnoid hemorrhage

Scanning electron microscopy of feline basilar arterial endothelium 4 hours, and 1, 3,5, and 7 days after subarachnoid hemorrhage (SAH) showed longitudinal furrows that correlated with angiographically demonstrated vasospasm. These ridges persisted after fixation at physiological pressure, and probably reflected medial contraction with undulation of the underlying elastic lamina. No change in endothelial cell morphology or thrombogenesis was observed as long as 7 days after SAH. There is no evidence from this study to suggest that ischemia from vasospasm is a product of thromboembolism from damaged endothelial surfaces.

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.

Cerebrovascular response to infused 5-hydroxytryptamine in the baboon. Part 1. 5-Hydroxytryptamine infusion

Cerebral blood flow was measured in 17 baboons before and during infusion of 5-hydroxytryptamine (5-HT) into the internal carotid artery. The mean values for total cerebral blood flow, grey matter flow, and white matter flow before 5-HT infusion were 40.8, 59.2, and 12.7 ml/min/100 gm of tissue, respectively. There was no significant alteration in total blood flow or flow through grey matter when 5-HT was infused at dosages ranging from 0.5 to 10.0 microng/kg/min. A small but significant decrease in white matter blood flow was recorded when 5-HT was infused at a rate exceeding 2.5 microng/kg/min. The study indicates that in vivo, with the xenon clearance method, intra-arterial infusion of 5-HT does not significantly alter cerebral blood flow.

Cerebrovascular response to infused 5-hydroxytryptamine in the baboon. Part 2. 5 Hydroxytryptamine infusion in estrogen and progesterone treated animals

The effect of intracarotid infusion of 5-hydroxytryptamine (5-HT) on cerebral blood flow was studied in five female baboons 7 days after intramuscular injection of slow release estrogen and progesterone. The control values for total cerebral blood flow, grey matter flow, and white matter flow were 38.9, 57.5, and 11.0 ml/min/100 gm of tissue respectively. There was a statistically significant decrease in total, grey and white matter blood flow during infusion of 5-HT at dosages ranging from 0.5 to 10.0 microng/kg/min. The study indicates that in female baboons pretreated with estrogen and progesterone, intracarotid infusion of 5-HT produces a dose dependent decrease in cerebral blood flow, which did not occur in control animals.

Pathogenetic role of no-reflow phenomenon in experimental subarachnoid hemorrhage in dogs

The real pathogenetic role of no-reflow phenomenon in clinical situations such as the acute stage of subarachnoid hemorrhage (SAH) is not yet known. To study this problem, we carried out the following experiment in dogs: SAH was induced by withdrawing a needle previously inserted into the internal carotid artery through a small craniectomy in the lateral base of the skull. Complete dural repair and cranioplasty was done to avoid cerebrospinal fluid leakage. Cortical cerebral blood flow (CBF) changes, measured by a double-needle type thermocouple, intracranial pressure (ICP), electroencephalogram (EEG), and sensory evoked response were monitored under controlled ventilation of 3 hours after SAH. At the end of the experiment, the brain was perfused with carbon black solution at a pressure of 120mm Hg. The 32 episodes of SAH thus induced yielded two basic patterns of ICP changes which simulated those previously reported with human SAH. In the first pattern, reactive hyperemia was always observed, followed by complete or incomplete recovery of cerebral function. Perfusion defects were frequently seen in the thalamus, basal ganglia, and parietooccipital cortex symmetrically. In the second pattern, prolonged elevation of ICP resulted in failure of recovery of both CBF and EEG. Carbon black filled only the pial arteries and the rest of the brain was totally unperfused. From the results, the pathogenetic role of the no-flow phenomenon in the acute stage of SAH as influencing the prognosis is strongly suspected.

A model for spasm of the anterior cerebral artery

A model for production of spasm of the anterior cerebral artery in primates is presented. The model consists of injection of 0.35 cc of fresh blood into the chiasmatic cistern through the optic canal after orbital exenteration. Clinical and angiographical follow-up is possible. The clinical appraisal of acute and chronic changes can be accomplished in the awake animal.

Effect of intracisternal phentolamine on cerebral blood flow after subarachnoid injection of blood

The hydrogen clearance method was used to measure total and focal cerebral blood flow (CBF) in the monkey before and for 5 hours after a simulated subarachnoid hemorrhage (SAH). Some monkeys also received 0.2 to 1.0 mg/kg phentolamine intracisternally 3 hours after SAH. Results show that SAH did not change cerebrovascular resistance, but as cerebral perfusion pressure decreased, CBF fell transiently. Phentolamine injected intracisternally 3 hours after SAH produced a significant fall in arterial blood pressure; cerebrovascular resistance did not change but CBF decreased significantly. These data indicate that intracisternal phentolamine cannot be considered potentially useful to treat ischemic encephalopathy after SAH.

The effect of a simulated subarachnoid hemorrhage on cerebral blood flow in the monkey

The hydrogen clearance method was used to measure local and total cerebral blood flow (CBF) in the rhesus monkey before and for five hours after a simulated subarachnoid hemorrhage (SAH). CBF remained stable after SAH unless SAH was associated with a fall in cerebral perfusion pressure. In addition, cerebrovascular resistance did not increase after SAH. These results suggest that vasoactive agents in fresh whole blood, and the arterial spasm they produce when added to cerebrospinal fluid (CSF), play only a limited role in the pathogenesis of ischemic encephalopathy that follows an SAH.

Angiographic visualization of fatal hemorrhage from a cerebral arteriovenous malformation. Case report

✓ The authors report and discuss a rare angiographic demonstration of extravasation of contrast material from a ruptured arteriovenous malformation.

Experimental intracerebral hematoma. Reduction of oxygen tension in brain and cerebrospinal fluid

✓ Intracerebral hematoma was simulated in 16 dogs. Oxygen tension was measured in the adjacent cerebral parenchyma, fourth ventricle, and cervical subarachnoid space by both microelectrode and sampling techniques in the course of four different studies. Determinations of intracranial pressure and the pH, pO2, pCO2 of arterial blood and cerebrospinal fluid (CSF) were made. Reductions of oxygen tension were encountered uniformly, both in brain parenchyma and CSF, following the induction of intracerebral hematoma. There was an associated acidosis in the CSF compartment. The findings cannot be explained on the basis of increased intracranial pressure or reduced cerebral perfusion. The acidosis may be related to the metabolic effects of blood as well as tissue hypoxia. The changes suggest additional reasons for the evacuation of intracerebral hematomas in man.

Total cerebral blood flow in the monkey measured by hydrogen clearance

Simple hydrogen-sensitive polarographical electrodes of thin platinum wire were inserted into the torcular Herophili of Rhesus monkeys. Hydrogen was administered by inhalation for ten minutes, after which the hydrogen clearance was recorded from torcular blood. At a Paco 2 of 32 mm Hg (SD ± 2.3), flow in the fast flow compartment was 102 ml/100 gm per minute (SD ± 19.1), and flow in the slow flow compartment was 28 ml/100 gm per minute (SD ± 5.8). Mean total cerebral blood flow was 52 ml/100 gm per minute (SD ± 10.5). Coefficient of variation was less than 10%.

Our experience suggests that one may reliably measure average total cerebral blood flow in the experimental setting by following the clearance of hydrogen from torcular blood. The method is relatively simple, inexpensive and radiation-free. It can be easily combined with the standard hydrogen clearance technique for measuring local tissue blood flow, thereby permitting the simultaneous recording of both local and total brain blood flow.

The effect of graded hypocapnia and hypercapnia on regional cerebral blood flow and cerebral vessel caliber in the rhesus monkey: study of cerebral hemodynamics following subarachnoid hemorrhage and traumatic internal carotid spasm

Correlative cerebral blood flow (CBF) and vessel diameter studies were performed during graded Paco, change in control monkeys and in monkeys subjected to subarachnoid hemorrhage and internal carotid artery spasm.

In the control series CBF increased linearly between Pa CO CO2 values of 30 mm Hg and 60 mm Hg. An increase in Pa CO CO2 from 40 mm Hg to 62 mm Hg produced a mean CBF increase of 74% while a reduction of Pa CO CO2 to 25 mm Hg resulted in a decrease of 40%. Cerebral gray matter was more responsive to Pa CO CO2 change than white matter. Caliber of the larger capacitance vessels did not provide an adequate index of the status of cerebral circulation.

In the experimental series both SAH and traumatic internal carotid artery spasm caused a decreased hemodynamic responsiveness to Pa CO CO2 . However, when Pa CO CO2 was raised to 60 to 65 mm Hg, marked increases in cerebral perfusion occurred (breakthrough phenomenon). In general, a poor correlation between CBF and vessel diameter studies was found in the postinsult period.

The studies indicated: (1) SAH caused an increase in cerebrovascular resistance and a decrease in CBF, (2) hemodynamic responses to Pa CO CO2 change, although diminished, were not abolished in the acute period after SAH, (3) hypercapnia (Pa CO CO2 > 60 mm Hg) significantly increased cerebral perfusion whether or not vasospasm was alleviated, and (4) the small distal cerebral vessels were more reactive to Pa CO CO2 change and were more intimately associated with regulation of cerebral perfusion.