Hemodynamic and clinicopathologic verification of a stroke model in the dog

A novel embolic stroke model resembling lacunar infarction following proximal middle cerebral artery occlusion in beagle dogs

It is estimated that lacunar infarcts account for 25% of all ischemic strokes, but its exact etiology is still on debating. The existing controversies include whether the embolisms can indeed cause lacunar stroke in humans or animal models. We hypothesized that lacunar infarction can be induced by the proximal middle cerebral artery (MCA) segmental occlusion involving the orifices of lenticulostriate arteries in animal models, which have abundant distal cerebral collateral anastomosis. Our work here establishes a proximal MCA occlusion model using thrombi (autologous blood clots about 1.7 mm in diameter and 5 mm in length) in 8 beagle dogs, evaluates the progression of ischemic lesions at 30 min interval within 6 h after embolization using the diffusion weighted imaging (DWI), and discusses the potential mechanisms of lacunar infarction. Our results indicate that the left proximal MCAs can be successfully occluded in all dogs using interventional single-thrombus method. The small solitary or multiple ischemic lesions shown in DWI were observed in the deep brain area, with the mean detecting time of 1.21 ± 0.45 h using DWI and diameter of 6.62 ± 0.60mm in 6h-DWI after procedure. In conclusion, our method established an ischemic model which can recapitulate the radiologic and histologic changes in lacunar infarcts, suggesting that emboli can cause lacunar infarcts in animal model.

Focal brain ischemia in the rat: methods for reproducible neocortical infarction using tandem occlusion of the distal middle cerebral and ipsilateral common carotid arteries

This article describes a 3-year experience with focal neocortical ischemia in three rat strains. Multiple groups of adult Wistar (n = 50), Fisher 344 (n = 31), and spontaneously hypertensive (n = 72) rats were subjected to permanent occlusion of the distal middle cerebral (MCA) and ipsilateral common carotid arteries (CCA). Twenty-four hours later the animals were killed, and frozen brain sections were stained with hematoxylin and eosin to demarcate infarcted tissue. The infarct volume for each section was quantified with an image analyzer, and the total infarct volume was calculated with an iterative program that summed all interval volumes. Neocortical infarct volume was the largest and most reproducible in the spontaneously hypertensive rats (SHR). Statistical power analysis to project the numbers of animals necessary to detect a 25 or 50% change in infarct volume with alpha = 0.05 and beta = 0.2 revealed that only the SHR model was practical in terms of requisite animals: i.e., less than 10 animals per group. Tandem occlusion of the distal MCA and ipsilateral CCA in the SHR strain provides a surgically simple method for causing large neocortical infarcts with reproducible topography and volume. The interanimal variability in infarct volume that occurs even in the SHR strain dictates that randomized, concomitant controls are necessary in each study to ensure the accurate assessment of experimental manipulations or pharmacologic therapies.

Isovolemic hemodilution in experimental focal cerebral ischemia. Part 1: Effects on hemodynamics, hemorheology, and intracranial pressure

A total of 76 splenectomized dogs were entered in a study of the value and effects of isovolemic hemodilution. Of these, seven were not included in the analysis because of technical errors. Of the remaining 69 dogs, 35 were treated with hemodilution; 28 were subjected to a 6-hour period of temporary occlusion of the distal internal carotid artery and the proximal middle cerebral artery, and seven underwent a sham operation only, with arterial manipulation but no occlusion. The other 34 dogs were not subjected to hemodilution; 26 of these underwent temporary arterial occlusion and eight had a sham operation only. In each group the animals were about equally divided into 1) an acute protocol with regional cerebral blood flow measurements by a radioactive microsphere technique and sacrifice at the end of the acute experiment, and 2) a chronic protocol with survival for 1 week to permit daily neurological assessment and final histopathological examination but without blood flow measurements. Isovolemic hemodilution was performed about 1 hour after the arterial occlusion or sham operation and was accomplished by phlebotomy and infusions of low molecular weight dextran to bring the hematocrit to a level of 30% to 32%. This treatment resulted in a very significant reduction in viscosity and fibrinogen levels. The decrease in hematocrit lasted throughout the week in the animals in the chronic protocol. The decrease in viscosity correlated almost linearly with the decrease in hematocrit. There was a slight decrease in systemic arterial pressure with hemodilution but there were no significant changes in central venous pressure or in pulmonary arterial or wedge pressure. There was a slight decrease in cardiac index in both the hemodilution and control groups, which may have been due to the effects of barbiturate anesthesia. There was a slight increase in the measured blood volume in both groups, which was probably artifactual and related to the method of calculation. Intracranial pressure increased significantly with time in all animals subjected to arterial occlusion, but this increase was less severe in the hemodilution group. There was no significant change in intracranial pressure in sham-operated animals, whether hemodiluted or not. The results of cerebral blood flow measurements, assessment of neurological conditions, and measurement of infarct size are given in Part 2 of this report.

Quantitation of photochemically induced focal cerebral ischemia in the rat

This study was carried out with a recently developed model of focal cerebral ischemia in the rat based on the photochemical induction of thrombotic stroke using the dye Rose Bengal. We examined the change in the volume of the lesion and brain water content, in separate groups of rats, at different times (1, 4, 24, 72, and 168 h) after the induction of the ischemic lesion. The volume of ischemic damage increased rapidly between 1 and 24 h after the ischemic insult and decreased between 24 and 168 h. The lesion at 168 h was significantly larger than that following 1 h of ischemia and similar to that obtained at 4 h, suggesting that the maximum extent of tissue damage (without the involvement of significant edema) was reached within the first 4 h in this model. The enlargement of the lesion after 4 h correlated closely with changes in brain water content.

Effects of preexisting bypass graft on rCBF and SSEP's following acute stroke in dogs

Regional cerebral blood flow (rCBF) was measured with radiolabeled microspheres in a canine model of superficial temporal artery-middle cerebral artery (STA-MCA) bypass and acute ischemia. Ischemic zone flows in seven dogs with the bypass first closed and then open showed no significant contribution of bypass flow in the intact vascular system. Following acute proximal occlusion, rCBF was preserved by bypass flow. A significant flow decrease ensued when the bypass was then clipped, confirming the adequacy of the lesion and the protective effect of the bypass. Reopening the bypass after 15 minutes of ischemia restored 76% of the previous flow. This was a significant increase from the global ischemia values, and was not statistically different from preocclusive values. Preocclusion somatosensory evoked potentials (SSEP's) in these animals showed a consistent biphasic wave at 8 to 10 msec after stimulation. This wave, with some decrease in amplitude, was preserved by bypass flow following creation of the arterial lesion. Bypass clipping abolished these ipsilateral SSEP's. Variable return of SSEP's occurred following reopening of the graft, but the recordings never reached preischemic amplitudes. This experimental study shows that, in this model, a prophylactic bypass subjected to immediate demand (with no time for "maturation") can adequately augment cortical rCBF and is superior to delayed revascularization. The data lend theoretical support to placement of a prophylactic STA-MCA bypass prior to elective carotid artery sacrifice or in surgery where the risk of acute vascular injury is high.

Practicability and reliability of model of cerebral infarction in dog by microneurosurgical technique

The authors used somatosensory evoked potentials (SEPs) and the electron microscope to evaluate the practicability and reliability of a model of cerebral infarction produced by microneurosurgery in the dog. Complete cerebral hemisphere infarction was produced by occluding various vessels from the circle of Willis. After occlusion, there was a precipitous decrease in the amplitude of cerebral cortical components (85.65 +/- 20.85 and 91.88 +/- 24.59 microV before compared to 4.08 +/- 1.99 and 2.85 +/- 1.38 microV after occlusion, P less than .001). The majority of the neurons at the 6th hour after occlusion became degenerated and contained no recognizable organelles. This study shows that the occlusion of various vessels from the base of the brain by microneurosurgery could produce a practical, reliable model of infarction with a high rate of success. The size and location of infarction can be controlled, and it is suitable for intracranial microvascular research.

Hypervolemic hemodilution in experimental focal cerebral ischemia. Elevation of cardiac output, regional cortical blood flow, and ICP after intravascular volume expansion with low molecular weight dextran

Cerebrovascular and cardiac alterations evoked by intravascular volume expansion with low molecular weight dextran (LMD, molecular weight 40,000), an advocated adjunct in the clinical prevention or therapy of acute stroke and cerebral vasospasm, were studied in splenectomized dogs. Clipping of the right distal internal carotid artery and the proximal middle cerebral artery (MCA) in eight dogs decreased regional cortical blood flow (rCoBF) by 58% without changing cardiac output (CO), and caused 10% +/- 5% (SE) hemispheric infarction. Ten other dogs underwent similar cerebral arterial occlusion and were infused twice with LMD within 2 hours; each infusion equaled 20% of the respective dog's total blood volume. Both CO and rCoBF in the territory of the occluded MCA increased significantly by 119% +/- 13% and 42% +/- 6%, respectively. following the two LMD infusions. Although the mean arterial blood pressure was unaltered, the hematocrit decreased significantly and the intracranial pressure (ICP) increased significantly. The mean hemispheric infarction in these 10 treated dogs was 4% +/- 2%. Another nine dogs underwent arterial manipulation without clipping. Two hemodiluting LMD infusions, similar to those in the 10 dogs, significantly elevated CO and ICP but not rCoBF. These data suggest that hypervolemic hemodilution with LMD effectively elevates collateral perfusion to ischemic regions of brain distal to occluded MCA segments and concomitantly raises the CO and ICP.

Omental transposition or transplantation to the brain and superficial temporal artery--middle cerebral artery anastomosis in preventing experimental cerebral ischaemia

Transposition of lengthened omentum to the brain surface, transplantation of an omental graft, or superficial temporal artery--middle cerebral artery anastomosis were performed in dogs prior to transcranial occlusion of the ipsilateral middle cerebral artery at its origin, including the bifurcation of the internal carotid artery. Both omentum and by-pass were able to reduce the changes in cerebral blood flow, somatosensory evoked responses, cerebral water and electrolyte content, consequent to the ischaemic insult. In the experimental conditions adopted in this study, the effect of omental transposition in maintaining high levels of flow throughout the entire occluded hemisphere was more marked compared to that resulting from the other methods, while the onset of ischaemic cerebral oedema was affected approximately at the same degree by all procedures. The results point to the role of the transposed omentum in providing an effective collateral circulation to the ischaemic brain.

Qualitative measurement of cerebral infarction using ultraviolet fluorescence

A reliable method of macroscopically determining the volume of cerebral infarction using ultraviolet fluorescence was developed in an animal model. Cerebral infarction was induced in 40 dogs by occluding the distal internal carotid and middle cerebral arteries. No barbiturates were administered. Intravenous sodium fluorescein was given before the animal was killed. Following fixation, 1 cm coronal sections were evaluated with ultraviolet light of 366 nm wavelength. The area of induced fluorescence for each section was determined using a grid overlay. Microscopic examination revealed that the areas of ischemic cell necrosis corresponded to areas of maximal fluorescence. This is an easily reproducible method to determine the volume of cerebral infarction.

Failure of intravascular volume expansion without hemodilution to elevate cortical blood flow in region of experimental focal ischemia

Cerebrovascular and cardiac alterations evoked by intravascular volume expansion with whole blood, a popular adjunct in the clinical prevention or therapy of the focal ischemic deficits of cerebral vasospasm and acute stroke, were studied in splenectomized dogs. Clipping of the right distal internal carotid and proximal middle cerebral arteries in eight dogs reduced regional cortical blood flow (rCoBF) by 49% to 58% without altering cardiac output (CO), and produced about 10% hemispheric infarction. Eight dogs underwent similar cerebral arterial occlusion and eight dogs underwent arterial manipulation without clipping. Both latter groups received two autologous whole blood infusions within 2 hours, each equal to 20% of the respective dog's total blood volume. Despite significant CO elevations after the infusions, rCoBF in the middle cerebral arterial territory did not rise. These whole-blood infusions did not significantly alter mean arterial blood pressure, hematocrit, intracranial pressure, or, in dogs with clipped cerebral arteries, the relative size of infarction. These data suggest that nondilutional hypervolemia neither elevates collateral perfusion to ischemic regions of the brain nor reduces infarction. In addition, elevations in CO do not appear to augment blood flow in either ischemic or normal brain.

Effect of extracranial-intracranial bypass and pentobarbital on acute stroke in dogs

Ninety-three mongrel dogs underwent intracranial carotid and middle cerebral artery occlusions. They were then randomized into four groups: 1) the untreated control group (no surgical or medical therapy) showed significant neurological deficit, 16% mortality, and 17% mean hemisphere infarction; 2) in the bypass group (superficial temporal to middle cerebral artery (STA-MCA) anastomosis completed within 3 hours of occlusion), neurological deficit was diminished, mortality was 7%, and mean infarction 5.66%; 3) in the pentobarbital group (single dose of pentobarbital, 35 mg/kg administered intravenously 30 minutes after occlusion), neurological deficit was essentially the same as in the previous group, there was no mortality, and mean infarction was 5.52%; and 4) in the pentabarbital/bypass group (pentabarbital dose plus STA-MCA bypass), neurological deficit was slightly lower than in previous treatment groups, there was no mortality , and mean hemisphere infarction was 1.78%. Extracranial-intracranial bypass produced an immediate 31.6% increase in regional cortical blood flow. The combination of pentobarbital postocclusive therapy and early extracranial-intracranial bypass beneficial synergism.