AUTHOR(S): Valtysson, Johann, M.D.; Jiang, Minghui, M.D.; Persson, Lennart, M.D., Ph.D.
Neurosurgery 30; 887-890, 1992 ABSTRACT: The objective of this study was to mimic in a simple experiment the two major brain insults sustained by the patient with a subarachnoid hemorrhage, that is, the ictus and the subsequent delayed reduction of focal cerebral blood flow caused by vasospasm without the interference of subarachnoid blood, to test the hypothesis that ictal events not related to the presence of blood in the subarachnoid space per se may be important for the development of ischemic deficits and cerebral infarction when vasospasm develops. Groups of rats were subjected to a sudden transient elevation of the intracranial pressure to a level causing a brief period of complete global ischemia by infusion of mock cerebrospinal fluid into the cisterna magna (this manipulation was designed to allow survival of the animal and recovery of consciousness). Two and onehalf hours later, a focal ischemic insult was induced by occlusion of the middle cerebral artery. Rats subjected to middle cerebral artery occlusion alone and sham operation served as controls. The infarct size was used as the end point and was calculated on brain slices stained with 2,3,5-triphenyltetrazolium chloride. The study demonstrates that a brief sudden elevation in intracranial pressure, in itself consistent with survival and recovery, increased the vulnerability of the brain to a subsequent focal ischemic insult. Thus the combination of insults resulted in significantly (P < 0.05) larger infarcts than did middle cerebral artery occlusion alone. Further, this combination of insults resulted in a disproportionate enlargement of the affected hemisphere, which could not be explained by the increased infarct size alone. KEY WORDS: Cerebral blood flow; Cerebral ischemia; Subarachnoid hemorrhage INTRODUCTION Rupture of an intracranial arterial aneurysm causing subarachnoid hemorrhage (SAH) initiates a complex pathophysiological process, which in many patients ultimately leads to permanent brain damage resulting in morbidity or death. In the individual patient, the extent of damage is obviously determined by the accumulated effects of sustained insults to the brain during this process. The two major insults are presumably those directly related to ictus and to the
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Department of Neurosurgery, Uppsala University Hospital, Uppsala, Sweden
delayed arterial narrowing (vasospasm). Other insults include such related to intracerebral hematoma, acute hydrocephalus, or surgical trauma. All involve cerebral hypoxia/ischemia, and complications such as hypoxemia, hypotension, hyperthermia, hyperglycemia, and epileptic seizures can therefore aggravate the insults. The direct effects of rupture of an aneurysm have been subjected to both experimental and clinical repeated bleeding studies (4,5,6,10,11,15,17). Rupture is often followed by an instant rise in intracranial pressure (ICP) to the level of the arterial blood pressure, thereby transiently stopping the cerebral perfusion and causing an episode of global ischemia of variable severity. In patients who regain consciousness, the ICP usually returns to normal or slightly higher. Such patients are generally supposed to be out of danger of the ictal effects of the hemorrhage and are considered to be at low risk for ischemic complications. The second major insult, delayed vasospasm, has been blamed for development of delayed ischemic deficits and infarction. Clinical and experimental studies have shown that blood in the subarachnoid space is necessary for the development of vasospasm (for review see ref. 9). Severe vasospasm without delayed ischemic deficits or infarction is seen; on the other hand, delayed ischemic deficits and infarction sometimes appear without signs of vasospasm seen on angiograms (14). Thus mechanisms other than vasospasm alone are apparently involved in the pathogenesis of the delayed ischemic deficits and cerebral infarction that follow SAH. In this study, we explore the hypothesis that events directly related to ictus, such as the instant increase in ICP and subsequent transient global ischemia, albeit consistent with clinical recovery after ictus, render the brain vulnerable to subsequent insults, for example reduction in focal blood flow caused by vasospasm, for a considerable time (6,15). Experimental models of SAH have usually involved the introduction of blood into the cerebrospinal fluid (CSF) compartment by some means, and variations of this manipulation are then studied by various techniques. In patients the amount of subarachnoid blood appears to correlate not only with vasospasm but also to the severity of ictus; this fact may confuse studies on the possible influence of ictal events on the development of cerebral infarction. The objective of the present experiment was to mimic in a simple fashion the two major insults sustained by the SAH patient: the ictus and the subsequent reduction of focal blood flow (vasospasm), without interference from subarachnoid blood, to test a basic prerequisite for our hypothesis, namely, that a transient increase in ICP renders the brain more vulnerable to a subsequent decrease in focal blood flow. Groups of rats were subjected to a sudden transient rise in ICP to a level causing a brief period of global ischemia (this manipulation was designed to allow survival of the animal and recovery of consciousness). A focal ischemic insult was then induced by occluding of the middle cerebral artery
Redistribution of this article permitted only in accordance with the publisher’s copyright provisions.
Neurosurgery 1992-98 June 1992, Volume 30, Number 6 887 Transient Elevation of the Intracranial Pressure Increases the Infarct Size and Perifocal Edema after Subsequent Middle Cerebral Artery Occlusion in the Rat Experimental and Clinical Study
Elevation of the intracranial pressure The complete compression ischemia model described by Ljunggren et al. (8) was used with minor modifications. Briefly, the ICP was instantly elevated by infusion of mock CSF through a needle (Periplex, Braun, Hannover, Germany) placed in the cisterna magna with the aid of a stereotactic instrument (Carnegie Medicine). The needle was connected to two catheters, one for the introduction of mock CSF and one for ICP registration (Grass Model 79D; Goldstath physiological pressure transducer). The position of the needle in the CSF compartment was checked continuously by following the ICP pulsations before and after the rise in ICP. During ICP elevation no pulsation was observed. The ICP was raised by opening the catheter to a reservoir containing mock CSF hanging above the rat's head. In this way the intracranial cavity was suddenly subjected to the hydrostatic pressure of the fluid column in the catheter and reservoir, resulting in instant elevation of the ICP to a level above the systemic blood pressure. The rise in ICP caused a reflex increase in arterial blood pressure, which was countered by adding more halothane to the gas mixture. In this way, the ICP was elevated to about 10% above the systemic blood pressure. After 2.5 or 5 minutes the ICP elevation was stopped by closing the catheter, and the ICP returned to slightly above normal almost immediately. Middle cerebral artery occlusion MCA occlusion was produced by bipolar coagulation of the left MCA as described elsewhere (16,18) . Care was taken to coagulate the vessel along a line from a point proximal to the olfactory tract to the inferior cerebral vein (1). Design of the experiment The protocol is shown in Table 2. Sixteen rats were subjected to elevation of ICP for 5 minutes or to a sham procedure in which cisterna magna was punctured and the ICP only registered for 5 minutes. The rats were then maintained on controlled ventilation for 2.5 hours and then subjected to MCA
Evaluation of brain damage The anesthetized rats were swiftly decapitated, and the brains were removed and cut into three 2-mm coronal slices centered at the level of the bregma. The slices were stained with 1% TTC for 60 minutes at 37 to 40°C and immersed in 4% buffered formaldehyde (3) . They were used for mapping the area of the ipsilateral (infarct-containing) and contralateral hemispheres and the area of the infarct, with the aid of a camera lucida. The area measurements obtained with the aid of a computer-based digitizing system (ABC 80, Luxor AB, Motala, Sweden) were used to calculate the infarct volume as described elsewhere (13) and modified by us (J. Valtysson, M. Jiang, and L. Persson, unpublished observations). For statistical analysis, commercial software (StatView SE+Graphic, Brain Power Inc.) on a personal computer (Macintosh, Apple Computer Inc.) was used. Student's t test was used, and a probability level of P < 0.05 was considered to be significant. RESULTS The sham procedures did not cause any additional changes in the TTC-stained brains. The clinical signs observed 24 and 48 hours after elevation in ICP alone were those of moderate lethargy; the rats moving around slowly but in an almost normal fashion. Some rats had a "hunchback" posture. The animals appeared to react normally to sound, touch, and pain. Vision was not specifically tested, but appeared to be abnormal. Comparison of infarct size in the different groups (Table 3) showed that rats subjected to a 5-minute elevation of ICP followed by MCA occlusion 2.5 hours later (Group I) had larger infarcts than those subjected to MCA occlusion alone (Group II). The difference is statistically significant (P < 0.05; Students t test). Also, the expansion of the hemisphere (ipsilateral minus contralateral hemispheres) harboring the infarct was significantly larger in Group I. The proportion between the volume of ipsilateral hemisphere expansion and the infarct volume differed between Groups I and II, the ipsilateral hemisphere expansion in Group I being greater than could be explained by increased infarct
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MATERIALS AND METHODS We used 21 male Sprague-Dawley rats weighing 350 to 450 g; they were allowed water and food ad libitum. They were anesthetized in a closed box with 4% halothane and intubated. Artificial ventilation was maintained (Harvard rodent respirator, Millis, Boston, MA) with a gas mixture of halothane (0.52%) and N2O/O2 (3:1). An arterial catheter was inserted into the tail artery for continuous registration of arterial blood pressure (Grass Model 79D; Goldstath physiological pressure transducer, Quincy, Boston, MA). Frequent checks of the blood gases were made throughout the experiment and the body temperature was maintained constant at ∼37.5°C using a thermal pad (CMA 150, Carnegie Medicine AB, Stockholm, Sweden). Blood samples were taken for determination of glucose concentration (Table 1).
occlusion or to a sham operation in which the MCA was exposed but not coagulated. After the experimental manipulations the rats were allowed to recover and were extubated; 24 to 48 hours later they were killed and prepared for 2,3,5triphenyltetrazolium chloride (TTC) staining. In addition, 5 rats were subjected to 2.5 or 5 minutes of elevation of ICP and were immediately allowed to recover from anesthesia. After 24 to 48 hours, they were again anesthetized and MCA occlusion was attempted; however, these rats' brains were swollen and fragile, and uncontrollable cortical hemorrhage occurred at the slightest touch. All died during or shortly after the surgical procedure, and no cerebral specimens were taken. Clearly, the effect of the previous transient ICP elevation prevailed after 24 to 48 hours, even in rats subjected to only 2.5 minutes of ICP elevation.
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(MCA).
Received for publication, March 4, 1991; accepted, final form, December 11, 1991. Dr. Jiang is a visiting scientist from the Department of Neurology, Norman Bethune University, Changchun, Jilin Province, People's Republic of China. Reprint requests: Dr. Lennart Persson, the Department of Neurosurgery, Uppsala University Hospital, S-751 85 Uppsala, Sweden. REFERENCES: (1-19) 1.
2.
3.
4.
5. 6.
Bederson JB, Pitts LH, Tsuji M, Nishimura MC, Davis RL, Barkowski: Rat middle cerebral artery occlusion: Evaluation of the model and development of a neurological examination. Stroke 17:472-476, 1986. Bolander HG, Persson L, Hillered L, d'Argy R, Pontén U, Olsson Y: Regional cerebral blood flow changes after middle cerebral occlusion in rats. Stroke 20:930-937, 1989. Bose B, Osterholm JL, Berry R: A reproducible experimental model of focal cerebral ischemia in the cat. Brain Res 31:385391, 1984. Brinkler T, Seifert V, Stolke D: Acute changes in the dynamics of the cerebrospinal fluid system during experimental subarachnoid hemorrhage. Neurosurgery 27:369-372, 1990. Grote E, Hassler W: The first critical minutes after subarachnoid hemorrhage. Neurosurgery 22:654-661, 1988. Hårdemark H-G, Almquist O, Johansson T, Påhlman S, Persson L: S-100 protein in cerebrospinal fluid after aneurysmal
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DISCUSSION Our findings show that sudden, brief elevation of the ICP, in itself consistent with survival and recovery of consciousness, increased the vulnerability of the brain to a subsequent focal ischemic insult. In other words, the combination of insults resulted in significantly larger infarcts than did MCA occlusion alone. Furthermore, the combination of insults resulted in an disproportionate enlargement of the affected hemisphere not explained by the increased infarct size alone. The phenomenon of increased vulnerability to repeated brain insults implies that the brain tolerates the first insult but that the effects of the first insult become manifest by a subsequent insult. We chose to elevate the ICP to a level above that of the blood pressure for 5 minutes, because the effect of this maneuver has proved to be consistent with metabolic recovery (8); the present study also showed that the rats survived and recovered from the insult. Brain swelling, however, was present 24 to 48 hours later, as demonstrated during the surgical attempt to occlude the MCA. The mechanism behind the increased vulnerability shown in the present experiment is unclear. We found that the enlargement of the infarct after the combined insults took place predominantly in the cortex, whereas a much smaller enlargement occurred in the striatum. The discrepancy may presumably be explained by differences in the vascular collateral supply from adjacent vascular territories in the cortex and the medial striatum, respectively. This observation indicates that the increased vulnerability was manifested in the border zones between the vascular territories. In studies on the effect of repeated global ischemia in gerbils, episodes of 5 minutes of global ischemia caused delayed brain edema with capillary compression and microcirculatory disturbances (12). We observed brain swelling in rats allowed to survive 24 to 48 hours after ICP elevation alone, presumably owing to the accumulation of edema. Our previous studies in this rat model showed that the cerebral blood flow is reduced and that brain edema is present in the border zones surrounding the infarct (2,19). It thus seems logical that the threshold for irreversible ischemic injury was passed in the border zones as a result of the combined effect of brain edema and microcirculatory disturbances caused by transient ICP elevation and the further reduction in flow from MCA occlusion. The combined insults also produced disproportionate swelling of the affected hemisphere. Because the degree of swelling was greater than expected from the infarct size, it must represent swelling of brain tissue surrounding the enlarged infarct. Another mechanism of tentative significance that
might contribute to aggravating the vulnerability of the combined insults could be a "traumatic" effect of suddenly subjecting the intracranial cavity to the fluid column of mock CSF when the ICP elevation was started. This maneuver has some similarity to the fluid percussion trauma model. Jenkins et al. (7) showed that a mild fluid percussion trauma consistent with recovery rendered the brain vulnerable to a subsequent mild global ischemic insult. During aneurysm rupture the intracranial cavity is also suddenly subjected to the arterial blood pressure, so ictus could theoretically exert such a "traumatic effect"; this might explain the different clinical response to ICP elevation due to other causes, for example, the plateau wave during which the cerebral perfusion pressure may reach a level close to zero without causing sudden, deep unconsciousness. The results of the present study are consistent with the hypothesis that sudden, transient elevation of the ICP could increase the vulnerability of the brain to a subsequent focal reduction in blood flow. This phenomenon could be of importance for the understanding of the pathophysiological events that may follow SAH and emphasize that the ictal effects, other than those related to the amount of subarachnoid blood, may influence the propensity for infarction to develop when the focal blood flow is compromised by vasospasm.
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size alone. The enlargement of the infarct in Group I rats was predominantly ascribable to enlargement of the cortical infarct. Less pronounced enlargement of the infarct occurred at the medial border of the striatum.
9. 10. 11.
12.
13.
14.
15.
16.
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19.
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8.
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7.
subarachnoid haemorrhage: Relation to functional outcome, late CT and SPECT changes, and signs of higher cortical dysfunction. Acta Neurochir (Wien) 99:135144, 1989. Jenkins LW, Marmarou W, Lewelt W, Becker DP: Increased vulnerability of the traumatized brain to early ischemia, in Baethmann A, Go GK, Unterberg A (eds): Mechanisms of Secondary Brain Damage (NATO Advanced Research Workshop). Italy, Plenum Publishing, 1986, pp 273-282. Ljunggren B, Schutz H, Siesjö BK: Changes in energy state and acid-base parameters of the rat brain during complete compression ischemia. Brain Res 73:277-289, 1974. Maurice-Williams RS: Subarachnoid Haemorrhage. Bristol, Wright, 1987. Nornes H, Magnaes B: Intracranial pressure in patients with ruptured saccular aneurysm. J Neurosurg 36:537-547, 1972. Nornes H: The role of intracranial pressure in the arrest of hemorrhage in patients with ruptured intracranial aneurysm. J Neurosurg 39:226-234, 1973. Nowak TS, Tomida S, Pluta R, Xu S, Kozuka M, Vass K, Wagner HG, Klatzo I: Cumulative effect of repeated ischemia on brain edema in the gerbil. Biochemical and physiological correlates of repeated ischemic insults. Adv Neurol 52:1-9, 1990. Osborne KA, Shigeno T, Balarsky AM, Ford I, McCulloch J, Teasdale GM, Graham DI: Quantitative assessment of early brain damage in a rat model of focal cerebral ischemia. J Neurol Neurosurg Psychiatry 50:402-410, 1987. Pazstor E, Vajda J: Plasticity of the brain in respect of functional restoration after subarachnoid haemorrhage. Acta Neurochir (Wien) 41:29-40, 1987. Persson L, Hårdemark H, Edner G, Ronne E, Mendel-Hartvig I, Påhlman S: S-100 protein in cerebrospinal fluid of patients with subarachnoid haemorrhage: A potential marker of brain damage. Acta Neurochir (Wien) 93:116-122, 1988. Persson L, Hårdemark H-G, Bolander HG, Hillered L, Olsson Y: Neurologic and neuropathologic outcome after middle cerebral artery occlusion in rats. Stroke 20:641-645, 1989. Steiner L, Löfgren J, Zwetnow N: Lethal mechanisms in repeated subarachnoid hemorrhage in dogs. Acta Neurol Scand 52:268- 276, 1975. Tamura A, Graham DI, McCulloch J, Teasdale GM: Focal cerebral ischemia in the rat: 1. Description of technique and early neuropathological consequences following middle cerebral artery occlusion. J Cereb Blood Flow Metab 1:53-60, 1981. Thoumas, K-Å, Kotwica Z, Bergström K, Bolander B, Hillered L, Olsson Y, Pontén U,
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Table 2. Design of Experiment
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Table 1. Comparison of Physiological and Chemical Parameters in Rats Subjected to 5 Minutes of ICP Elevation followed 2.5 Hours Later by MCA Occlusion and to MCA Occlusion Alone
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Table 3. Infarct Volume, Volume of Hemisphere Expansion, and the Relationship between Infarct Size and Hemisphere Expansiona
Neurosurgery 30; 887-890, 1992 ABSTRACT: The objective of this study was to mimic in a simple experiment the two major brain insults sustained by the patient with a subarachnoid hemorrhage, that is, the ictus and the subsequent delayed reduction of focal cerebral blood flow caused by vasospasm without the interference of subarachnoid blood, to test the hypothesis that ictal events not related to the presence of blood in the subarachnoid space per se may be important for the development of ischemic deficits and cerebral infarction when vasospasm develops. Groups of rats were subjected to a sudden transient elevation of the intracranial pressure to a level causing a brief period of complete global ischemia by infusion of mock cerebrospinal fluid into the cisterna magna (this manipulation was designed to allow survival of the animal and recovery of consciousness). Two and onehalf hours later, a focal ischemic insult was induced by occlusion of the middle cerebral artery. Rats subjected to middle cerebral artery occlusion alone and sham operation served as controls. The infarct size was used as the end point and was calculated on brain slices stained with 2,3,5-triphenyltetrazolium chloride. The study demonstrates that a brief sudden elevation in intracranial pressure, in itself consistent with survival and recovery, increased the vulnerability of the brain to a subsequent focal ischemic insult. Thus the combination of insults resulted in significantly (P < 0.05) larger infarcts than did middle cerebral artery occlusion alone. Further, this combination of insults resulted in a disproportionate enlargement of the affected hemisphere, which could not be explained by the increased infarct size alone. KEY WORDS: Cerebral blood flow; Cerebral ischemia; Subarachnoid hemorrhage INTRODUCTION Rupture of an intracranial arterial aneurysm causing subarachnoid hemorrhage (SAH) initiates a complex pathophysiological process, which in many patients ultimately leads to permanent brain damage resulting in morbidity or death. In the individual patient, the extent of damage is obviously determined by the accumulated effects of sustained insults to the brain during this process. The two major insults are presumably those directly related to ictus and to the
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Department of Neurosurgery, Uppsala University Hospital, Uppsala, Sweden
delayed arterial narrowing (vasospasm). Other insults include such related to intracerebral hematoma, acute hydrocephalus, or surgical trauma. All involve cerebral hypoxia/ischemia, and complications such as hypoxemia, hypotension, hyperthermia, hyperglycemia, and epileptic seizures can therefore aggravate the insults. The direct effects of rupture of an aneurysm have been subjected to both experimental and clinical repeated bleeding studies (4,5,6,10,11,15,17). Rupture is often followed by an instant rise in intracranial pressure (ICP) to the level of the arterial blood pressure, thereby transiently stopping the cerebral perfusion and causing an episode of global ischemia of variable severity. In patients who regain consciousness, the ICP usually returns to normal or slightly higher. Such patients are generally supposed to be out of danger of the ictal effects of the hemorrhage and are considered to be at low risk for ischemic complications. The second major insult, delayed vasospasm, has been blamed for development of delayed ischemic deficits and infarction. Clinical and experimental studies have shown that blood in the subarachnoid space is necessary for the development of vasospasm (for review see ref. 9). Severe vasospasm without delayed ischemic deficits or infarction is seen; on the other hand, delayed ischemic deficits and infarction sometimes appear without signs of vasospasm seen on angiograms (14). Thus mechanisms other than vasospasm alone are apparently involved in the pathogenesis of the delayed ischemic deficits and cerebral infarction that follow SAH. In this study, we explore the hypothesis that events directly related to ictus, such as the instant increase in ICP and subsequent transient global ischemia, albeit consistent with clinical recovery after ictus, render the brain vulnerable to subsequent insults, for example reduction in focal blood flow caused by vasospasm, for a considerable time (6,15). Experimental models of SAH have usually involved the introduction of blood into the cerebrospinal fluid (CSF) compartment by some means, and variations of this manipulation are then studied by various techniques. In patients the amount of subarachnoid blood appears to correlate not only with vasospasm but also to the severity of ictus; this fact may confuse studies on the possible influence of ictal events on the development of cerebral infarction. The objective of the present experiment was to mimic in a simple fashion the two major insults sustained by the SAH patient: the ictus and the subsequent reduction of focal blood flow (vasospasm), without interference from subarachnoid blood, to test a basic prerequisite for our hypothesis, namely, that a transient increase in ICP renders the brain more vulnerable to a subsequent decrease in focal blood flow. Groups of rats were subjected to a sudden transient rise in ICP to a level causing a brief period of global ischemia (this manipulation was designed to allow survival of the animal and recovery of consciousness). A focal ischemic insult was then induced by occluding of the middle cerebral artery
Redistribution of this article permitted only in accordance with the publisher’s copyright provisions.
Neurosurgery 1992-98 June 1992, Volume 30, Number 6 887 Transient Elevation of the Intracranial Pressure Increases the Infarct Size and Perifocal Edema after Subsequent Middle Cerebral Artery Occlusion in the Rat Experimental and Clinical Study
Elevation of the intracranial pressure The complete compression ischemia model described by Ljunggren et al. (8) was used with minor modifications. Briefly, the ICP was instantly elevated by infusion of mock CSF through a needle (Periplex, Braun, Hannover, Germany) placed in the cisterna magna with the aid of a stereotactic instrument (Carnegie Medicine). The needle was connected to two catheters, one for the introduction of mock CSF and one for ICP registration (Grass Model 79D; Goldstath physiological pressure transducer). The position of the needle in the CSF compartment was checked continuously by following the ICP pulsations before and after the rise in ICP. During ICP elevation no pulsation was observed. The ICP was raised by opening the catheter to a reservoir containing mock CSF hanging above the rat's head. In this way the intracranial cavity was suddenly subjected to the hydrostatic pressure of the fluid column in the catheter and reservoir, resulting in instant elevation of the ICP to a level above the systemic blood pressure. The rise in ICP caused a reflex increase in arterial blood pressure, which was countered by adding more halothane to the gas mixture. In this way, the ICP was elevated to about 10% above the systemic blood pressure. After 2.5 or 5 minutes the ICP elevation was stopped by closing the catheter, and the ICP returned to slightly above normal almost immediately. Middle cerebral artery occlusion MCA occlusion was produced by bipolar coagulation of the left MCA as described elsewhere (16,18) . Care was taken to coagulate the vessel along a line from a point proximal to the olfactory tract to the inferior cerebral vein (1). Design of the experiment The protocol is shown in Table 2. Sixteen rats were subjected to elevation of ICP for 5 minutes or to a sham procedure in which cisterna magna was punctured and the ICP only registered for 5 minutes. The rats were then maintained on controlled ventilation for 2.5 hours and then subjected to MCA
Evaluation of brain damage The anesthetized rats were swiftly decapitated, and the brains were removed and cut into three 2-mm coronal slices centered at the level of the bregma. The slices were stained with 1% TTC for 60 minutes at 37 to 40°C and immersed in 4% buffered formaldehyde (3) . They were used for mapping the area of the ipsilateral (infarct-containing) and contralateral hemispheres and the area of the infarct, with the aid of a camera lucida. The area measurements obtained with the aid of a computer-based digitizing system (ABC 80, Luxor AB, Motala, Sweden) were used to calculate the infarct volume as described elsewhere (13) and modified by us (J. Valtysson, M. Jiang, and L. Persson, unpublished observations). For statistical analysis, commercial software (StatView SE+Graphic, Brain Power Inc.) on a personal computer (Macintosh, Apple Computer Inc.) was used. Student's t test was used, and a probability level of P < 0.05 was considered to be significant. RESULTS The sham procedures did not cause any additional changes in the TTC-stained brains. The clinical signs observed 24 and 48 hours after elevation in ICP alone were those of moderate lethargy; the rats moving around slowly but in an almost normal fashion. Some rats had a "hunchback" posture. The animals appeared to react normally to sound, touch, and pain. Vision was not specifically tested, but appeared to be abnormal. Comparison of infarct size in the different groups (Table 3) showed that rats subjected to a 5-minute elevation of ICP followed by MCA occlusion 2.5 hours later (Group I) had larger infarcts than those subjected to MCA occlusion alone (Group II). The difference is statistically significant (P < 0.05; Students t test). Also, the expansion of the hemisphere (ipsilateral minus contralateral hemispheres) harboring the infarct was significantly larger in Group I. The proportion between the volume of ipsilateral hemisphere expansion and the infarct volume differed between Groups I and II, the ipsilateral hemisphere expansion in Group I being greater than could be explained by increased infarct
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MATERIALS AND METHODS We used 21 male Sprague-Dawley rats weighing 350 to 450 g; they were allowed water and food ad libitum. They were anesthetized in a closed box with 4% halothane and intubated. Artificial ventilation was maintained (Harvard rodent respirator, Millis, Boston, MA) with a gas mixture of halothane (0.52%) and N2O/O2 (3:1). An arterial catheter was inserted into the tail artery for continuous registration of arterial blood pressure (Grass Model 79D; Goldstath physiological pressure transducer, Quincy, Boston, MA). Frequent checks of the blood gases were made throughout the experiment and the body temperature was maintained constant at ∼37.5°C using a thermal pad (CMA 150, Carnegie Medicine AB, Stockholm, Sweden). Blood samples were taken for determination of glucose concentration (Table 1).
occlusion or to a sham operation in which the MCA was exposed but not coagulated. After the experimental manipulations the rats were allowed to recover and were extubated; 24 to 48 hours later they were killed and prepared for 2,3,5triphenyltetrazolium chloride (TTC) staining. In addition, 5 rats were subjected to 2.5 or 5 minutes of elevation of ICP and were immediately allowed to recover from anesthesia. After 24 to 48 hours, they were again anesthetized and MCA occlusion was attempted; however, these rats' brains were swollen and fragile, and uncontrollable cortical hemorrhage occurred at the slightest touch. All died during or shortly after the surgical procedure, and no cerebral specimens were taken. Clearly, the effect of the previous transient ICP elevation prevailed after 24 to 48 hours, even in rats subjected to only 2.5 minutes of ICP elevation.
Redistribution of this article permitted only in accordance with the publisher’s copyright provisions.
(MCA).
Received for publication, March 4, 1991; accepted, final form, December 11, 1991. Dr. Jiang is a visiting scientist from the Department of Neurology, Norman Bethune University, Changchun, Jilin Province, People's Republic of China. Reprint requests: Dr. Lennart Persson, the Department of Neurosurgery, Uppsala University Hospital, S-751 85 Uppsala, Sweden. REFERENCES: (1-19) 1.
2.
3.
4.
5. 6.
Bederson JB, Pitts LH, Tsuji M, Nishimura MC, Davis RL, Barkowski: Rat middle cerebral artery occlusion: Evaluation of the model and development of a neurological examination. Stroke 17:472-476, 1986. Bolander HG, Persson L, Hillered L, d'Argy R, Pontén U, Olsson Y: Regional cerebral blood flow changes after middle cerebral occlusion in rats. Stroke 20:930-937, 1989. Bose B, Osterholm JL, Berry R: A reproducible experimental model of focal cerebral ischemia in the cat. Brain Res 31:385391, 1984. Brinkler T, Seifert V, Stolke D: Acute changes in the dynamics of the cerebrospinal fluid system during experimental subarachnoid hemorrhage. Neurosurgery 27:369-372, 1990. Grote E, Hassler W: The first critical minutes after subarachnoid hemorrhage. Neurosurgery 22:654-661, 1988. Hårdemark H-G, Almquist O, Johansson T, Påhlman S, Persson L: S-100 protein in cerebrospinal fluid after aneurysmal
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DISCUSSION Our findings show that sudden, brief elevation of the ICP, in itself consistent with survival and recovery of consciousness, increased the vulnerability of the brain to a subsequent focal ischemic insult. In other words, the combination of insults resulted in significantly larger infarcts than did MCA occlusion alone. Furthermore, the combination of insults resulted in an disproportionate enlargement of the affected hemisphere not explained by the increased infarct size alone. The phenomenon of increased vulnerability to repeated brain insults implies that the brain tolerates the first insult but that the effects of the first insult become manifest by a subsequent insult. We chose to elevate the ICP to a level above that of the blood pressure for 5 minutes, because the effect of this maneuver has proved to be consistent with metabolic recovery (8); the present study also showed that the rats survived and recovered from the insult. Brain swelling, however, was present 24 to 48 hours later, as demonstrated during the surgical attempt to occlude the MCA. The mechanism behind the increased vulnerability shown in the present experiment is unclear. We found that the enlargement of the infarct after the combined insults took place predominantly in the cortex, whereas a much smaller enlargement occurred in the striatum. The discrepancy may presumably be explained by differences in the vascular collateral supply from adjacent vascular territories in the cortex and the medial striatum, respectively. This observation indicates that the increased vulnerability was manifested in the border zones between the vascular territories. In studies on the effect of repeated global ischemia in gerbils, episodes of 5 minutes of global ischemia caused delayed brain edema with capillary compression and microcirculatory disturbances (12). We observed brain swelling in rats allowed to survive 24 to 48 hours after ICP elevation alone, presumably owing to the accumulation of edema. Our previous studies in this rat model showed that the cerebral blood flow is reduced and that brain edema is present in the border zones surrounding the infarct (2,19). It thus seems logical that the threshold for irreversible ischemic injury was passed in the border zones as a result of the combined effect of brain edema and microcirculatory disturbances caused by transient ICP elevation and the further reduction in flow from MCA occlusion. The combined insults also produced disproportionate swelling of the affected hemisphere. Because the degree of swelling was greater than expected from the infarct size, it must represent swelling of brain tissue surrounding the enlarged infarct. Another mechanism of tentative significance that
might contribute to aggravating the vulnerability of the combined insults could be a "traumatic" effect of suddenly subjecting the intracranial cavity to the fluid column of mock CSF when the ICP elevation was started. This maneuver has some similarity to the fluid percussion trauma model. Jenkins et al. (7) showed that a mild fluid percussion trauma consistent with recovery rendered the brain vulnerable to a subsequent mild global ischemic insult. During aneurysm rupture the intracranial cavity is also suddenly subjected to the arterial blood pressure, so ictus could theoretically exert such a "traumatic effect"; this might explain the different clinical response to ICP elevation due to other causes, for example, the plateau wave during which the cerebral perfusion pressure may reach a level close to zero without causing sudden, deep unconsciousness. The results of the present study are consistent with the hypothesis that sudden, transient elevation of the ICP could increase the vulnerability of the brain to a subsequent focal reduction in blood flow. This phenomenon could be of importance for the understanding of the pathophysiological events that may follow SAH and emphasize that the ictal effects, other than those related to the amount of subarachnoid blood, may influence the propensity for infarction to develop when the focal blood flow is compromised by vasospasm.
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size alone. The enlargement of the infarct in Group I rats was predominantly ascribable to enlargement of the cortical infarct. Less pronounced enlargement of the infarct occurred at the medial border of the striatum.
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Table 2. Design of Experiment
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Table 1. Comparison of Physiological and Chemical Parameters in Rats Subjected to 5 Minutes of ICP Elevation followed 2.5 Hours Later by MCA Occlusion and to MCA Occlusion Alone
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Table 3. Infarct Volume, Volume of Hemisphere Expansion, and the Relationship between Infarct Size and Hemisphere Expansiona
