Local cerebral blood flow autoregulation following "asymptomatic" cerebral venous occlusion in the rat

Evaluation of extent vs velocity of cortical venous filing in stroke outcome after endovascular thrombectomy

PURPOSE

Abnormal venous drainage may affect the prognosis of patients undergoing endovascular reperfusion therapy (ERT). Herein, time-resolved dynamic computed tomography arteriography (dCTA) was applied to evaluate the relationship between the velocity and extent of cortical venous filling (CVF), collateral status and outcomes.

METHODS

Thirty-five consecutive patients with acute anterior circulation occlusion who underwent ERT within 24 h of onset and successfully recanalized were enrolled. All patients underwent dCTA before ERT. Slow first or end of CVF was considered to occur when the time point of CVF appearance or disappearance on the affected side occurred after than that on the healthy side, whereas an equal CVF, a CVF reduced by ≤ 50%, or by > 50% on the affected side, were considered good, intermediate, and poor CVF extent, respectively.

RESULTS

Slow first CVF (29 patients, 82.8%), slow end of CVF (29, 85.7%), and intermediate extent of CVF (7, 20.0%) were not associated with collateral status or outcomes. Poor extent of CVF (6, 17.1%) was associated with poor collateral status, higher proportion of midline shift, larger final infarct volume, higher modified Rankin Scale (mRS) score at discharge, and higher proportion of in-hospital mortality. All patients with transtentorial herniation had poor extent of CVF, and those with poor CVF extent had an mRS score ≥ 3 at discharge.

CONCLUSION

Poor CVF extent, as assessed by dCTA, is a more accurate and specific marker than slow CVF to identify patients at high risk for poor outcomes after ERT.

Blood-brain Barrier Disruption May Contribute to White Matter Lesions in the Setting of Internal Jugular Venous Stenosis

BACKGROUND AND PURPOSE

Cloudy white matter lesions are associated imaging features of internal jugular venous stenosis (IJVS). However, the mechanism of the IJVS associated cloudy white matter lesions is still unclear. This study aims to evaluate blood-brain barrier integrity of the patients with IJVS.

MATERIALS AND METHODS

A total of 45 eligible patients with IJVS confirmed by computed tomography venography (CTV) and 45 healthy controls were enrolled into this study. The levels of serum MMP-9 and the markers of tight junctions, including occludin and ZO-1 obtained from IJVS patients and control group were tested by enzyme-linked immune-sorbent assay and compared.

RESULTS

Both the levels of serum MMP-9 (0.2ng/ml) and occludin (0.05ng/ml) in IJVS group were higher than in the control group (0.01ng/ml vs. 0 ng/ml, all p<0.001). While, the levels of serum ZO-1 showed no statistical significance between the two groups (0.55ng/ml vs 0.735ng/ml, P=0.34). The levels of serum MMP-9 between the subset with or without white matter lesions in IJVS group showed a significant difference (0.22 [0.06, 0.43] vs. 0.01 [0.01, 0.06], P =0.019).

CONCLUSION

BBB disruption may participate in the formation of IJVS-associated white matter lesions; the mechanism of BBB disruption may involve MMP-9 and occludin.

Early BBB breakdown and subacute inflammasome activation and pyroptosis as a result of cerebral venous thrombosis

Cerebral venous thrombosis (CVT) is a rare form of cerebral stroke that causes a variety of symptoms, ranging from mild headache to severe morbidity or death in the more severe forms. The use of anti-coagulant or thrombolytic agents is the classical treatment for CVT. However, the development of new therapies for the treatment of the condition has not been the focus. In this study, we aimed to analyze the pathophysiology of CVT and to identify the pathways associated with its pathology. Moreover, mechanisms that are potential drug targets were identified. Our data showed the intense activation of immune cells, particularly the microglia, along with the increase in macrophage activity and NLRP3 inflammasome activation that is indicated by NLRP3, IL-1β, and IL-18 gene and caspase-1 upregulation and cleavage as well as pyroptotic cell death. Leukocytes were observed in the brain parenchyma, indicating a role in CVT-induced inflammation. In addition, astrocytes were activated, and they induced glial scar leading to parenchymal contraction during the subacute stage and tissue loss. MMP9 was responsible primarily for the BBB breakdown after CVT and it is mainly produced by pericytes. MMP9 activation was observed before inflammatory changes, indicating that BBB breakdown is the initial driver of the pathology of CVT. These results show an inflammation driven pathophysiology of CVT that follows MMP9-mediated BBB breakdown, and identified several targets that can be targeted by pharmaceutical agents to improve the neuroinflammation that follows CVT, such as MMP9, NLRP3, and IL-1β. Some of these pharmaceutical agents are already in clinical practice or under clinical trials indicating a good potential for translating this work into patient care.

Multiple Factors Involved in the Pathogenesis of White Matter Lesions

White matter lesions (WMLs), also known as leukoaraiosis (LA) or white matter hyperintensities (WMHs), are characterized mainly by hyperintensities on T2-weighted or fluid-attenuated inversion recovery (FLAIR) images. With the aging of the population and the development of imaging technology, the morbidity and diagnostic rates of WMLs are increasing annually. WMLs are not a benign process. They clinically manifest as cognitive decline and the subsequent development of dementia. Although WMLs are important, their pathogenesis is still unclear. This review elaborates on the advances in the understanding of the pathogenesis of WMLs, focusing on anatomy, cerebral blood flow autoregulation, venous collagenosis, blood brain barrier disruption, and genetic factors. In particular, the attribution of WMLs to chronic ischemia secondary to venous collagenosis and cerebral blood flow autoregulation disruption seems reasonable. With the development of gene technology, the effect of genetic factors on the pathogenesis of WMLs is gaining gradual attention.

Photothrombosis combined with thrombin injection establishes a rat model of cerebral venous sinus thrombosis

OBJECTIVE

Cerebral venous sinus thrombosis (CVST) is a rare but life-threatening disease and an animal model for in-depth study of CVST is needed. This study aimed to develop a rat model suitable for studying clinically relevant aspects of CVST and investigating its dynamic pathophysiological changes during a 7-day period.

METHOD

A photothrombosis method was used to create a rat sinus-vein thrombosis model. A spot size-adjustable Diode Pumped Solid State laser (DPSS) combined with thrombin injection occluded the rostral and caudal superior sagittal sinus (SSS). The model was used to evaluate pathophysiological changes at different time points over 7 days. Evans Blue dye injection was used to detect alterations in blood-brain barrier (BBB) permeability. Brain water content was also measured. Moreover, we examined changes in brain infarct volume, neurological function, as well as histology after induction of CVST.

RESULT

CVST in rats significantly altered BBB permeability, consistent with the development of brain edema. It was accompanied by an increase in brain infarct volume and deficits in neurological function that began on day 1, peaked on day 2, and typically improved by day 7 due to the neuroprotective effects of angiogenesis and gliocyte proliferation.

CONCLUSION

In this study, we describe a rat model that produces clinically relevant pathophysiology and pathology that will facilitate evaluation of therapeutic regimens for CVST. Furthermore, our results indicate a period of optimal clinical intervention for patients with CVST, which may reduce the probability of dependency and death.

Generating and measuring photochemical changes inside the brain using optical fibers: exploring stroke

We report here on the development of a method for inducing a stroke in a specific location within a mouse brain through the use of an optical fiber. By capturing the emitted fluorescence signal generated using the same fiber it is possible to monitor photochemical changes within the brain in real-time, and directly measure the concentration of the stroke-inducing dye, Rose Bengal, at the infarct site. This technique reduces the requirement for post-operative histology to determine if a stroke has successfully been induced within the animal, and therefore opens up the opportunity to explore the recovery of the brain after the stroke event.

Potential involvement of the extracranial venous system in central nervous system disorders and aging

BACKGROUND

The role of the extracranial venous system in the pathology of central nervous system (CNS) disorders and aging is largely unknown. It is acknowledged that the development of the venous system is subject to many variations and that these variations do not necessarily represent pathological findings. The idea has been changing with regards to the extracranial venous system.

DISCUSSION

A range of extracranial venous abnormalities have recently been reported, which could be classified as structural/morphological, hemodynamic/functional and those determined only by the composite criteria and use of multimodal imaging. The presence of these abnormalities usually disrupts normal blood flow and is associated with the development of prominent collateral circulation. The etiology of these abnormalities may be related to embryologic developmental arrest, aging or other comorbidities. Several CNS disorders have been linked to the presence and severity of jugular venous reflux. Another composite criteria-based vascular condition named chronic cerebrospinal venous insufficiency (CCSVI) was recently introduced. CCSVI is characterized by abnormalities of the main extracranial cerebrospinal venous outflow routes that may interfere with normal venous outflow.

SUMMARY

Additional research is needed to better define the role of the extracranial venous system in relation to CNS disorders and aging. The use of endovascular treatment for the correction of these extracranial venous abnormalities should be discouraged, until potential benefit is demonstrated in properly-designed, blinded, randomized and controlled clinical trials.

Neuroprotective effect of ceftriaxone on the penumbra in a rat venous ischemia model

OBJECTIVE

Glutamate transporter-1 (GLT-1) maintains low concentrations of extracellular glutamate by removing glutamate from the extracellular space. It is controversial, however, whether upregulation of GLT-1 is neuroprotective under all ischemic/hypoxic conditions. Recently, a neuroprotective effect of preconditioning with a β-lactam antibiotic ceftriaxone (CTX) that increases expression of GLT-1 has been reported in animal models of focal ischemia. On the other hand, it is said that CTX does not play a neuroprotective role in an in vitro study. Thus, we examined the effect of CTX on ischemic injury in a rat model of two-vein occlusion (2VO). This model mimics venous ischemia during, e.g. tumor surgery, a clinical situation that is best suitable for pretreatment with CTX.

METHODS

CTX (100mg/kg, 200mg/kg per day) or vehicle (0.9% NaCl) was intraperitoneally injected into Wistar rats for 5days before venous ischemia (n=57). Then, animals were prepared for occlusion of two adjacent cortical veins (2VO) by photothrombosis with rose bengal that was followed by KCl-induced cortical spreading depression (CSD). Infarct volume was evaluated with hematoxylin and eosin (H&E) staining 2days after venous occlusion. [(3)H]MK-801, [(3)H]AMPA and [(3)H]Muscimol ligand binding were examined autoradiographically in additional two groups without 2VO (n=5/group). Animals were injected either with NaCl (vehicle) or CTX 200mg/kg for 5days in order to evaluate whether NMDA, AMPA and GABAA ligand binding densities were affected.

RESULTS

CTX pretreatment reduced infarct volume compared to vehicle pretreatment (p<0.05). The effect of CTX pretreatment was attenuated by administration of the GLT-1 inhibitor, dihydrokainate (DHK) 30min before 2VO. CTX had no effect on the number of spontaneous spreading depressions after 2VO. Analysis of quantitative receptor autoradiography showed no statistically significant difference between rats after administration with CTX compared to control rats.

CONCLUSIONS

Pretreatment with CTX has neuroprotective potential without effect on NMDA, AMPA and GABAA receptor density and spontaneous spreading depression. This effect can be abolished by GLT-1 inhibition, indicating that upregulation of GLT-1 is an important mechanism for neuroprotective action in penumbra-like conditions, e.g. if neurosurgeons plan to occlude cerebral veins during tumor surgery.

The effect of a gap-junction blocker, carbenoxolone, on ischemic brain injury and cortical spreading depression

Cortical spreading depression (CSD) has been shown to cause secondary cell loss in experimental models of brain injury and in patients, and blocking of CSD is a potential neuroprotective strategy. Here we tested the hypothesis that gap junctions affect CSD under physiological conditions as well as infarct development in a rat two-vein occlusion model suited to study pathophysiology of the penumbra (n = 71). We applied the gap junction blocker carbenoxolone (CBX) or saline intra-ventricularly. Interestingly, CBX temporarily increased systemic blood pressure and cortical blood flow (41% and 53%, 15 min after 250 μg CBX). We induced CSD with cortical microinjection of potassium chloride (KCl), counted how many spontaneous CSDs after CSD induction were elicited and measured the propagation velocity. After 250 μg CBX administration, significant 37.5 ± 6.5 additional CSDs were seen. CSD velocity increased significantly after 50 μg and 250 μg CBX. Occlusion of two adjacent cortical veins using Rose Bengal dye and fiberoptic illumination followed by 250 μg CBX or saline showed a significant more than doubling of infarct volumes 7 days after CBX. The current experiments provide evidence that CBX can accelerate the initiation and propagation of CSD suggesting opening of gap junctions is not required for CSD propagation. Blocking gap junctions worsens outcome from focal cerebral ischemia. Hence, measures intended to improve spatial buffering via astroglial gap junctions could have therapeutic potential in disease processes involving CSD.

Incidence of venous infarction after sacrificing middle-third superior sagittal sinus cortical bridging veins in a pediatric population

OBJECT

The interhemispheric transcallosal approach offers an excellent surgical corridor for the treatment of deep-seated midline lesions. The approach typically requires the sacrifice of one or more middle-third superior sagittal sinus (SSS) cortical bridging veins, which introduces the risk of venous infarction and associated neurological injury. The authors studied the incidence of venous infarcts following this operative approach in a pediatric population.

METHODS

The authors performed a retrospective review of surgical cases involving pediatric patients treated at the Children's Hospital Los Angeles between 1990 and 2007, in which an interhemispheric transcallosal operative procedure was performed and one or more middle-third SSS cortical bridging veins were occluded. Postoperative MR imaging studies done 1-3 days following the procedure were analyzed and compared with preoperative studies.

RESULTS

Sixty-three patients met the inclusion criteria. No patient developed MR imaging evidence of venous infarction.

CONCLUSIONS

The occlusion of one or more middle-third SSS cortical bridging veins related to the interhemispheric transcallosal approach resulted in no incidence of cerebral venous infarction in this pediatric population.

Pathogenesis of leukoaraiosis: role of jugular venous reflux

Leukoaraiosis (LA) is a major cause of vascular dementia and disability in the elderly. Age and hypertension are the most two important risk factors. Despite its clinical significance, the etiology is so far unclear. Chronic cerebral hypoperfusion associated with vasogenic edema, microbleeding or/and endothelial dysfunction found in LA favors venous ischemia, in stead of arterial ischemia, as its pathogenesis. The involved regions in LA, periventricular and subcortical regions, are the drainage territory of deep cerebral venous system and the watershed region between the superficial and deep cerebral venous system respectively. Adding the facts that periventricular venule collagenosis, and retinal and intraparenchymal venules dilatation are related to the severity of LA, cerebral venous hypertension caused by downstream venous outflow impairment might play a major role in the pathogenesis of LA. Internal jugular vein is the main venous outflow pathway for cerebral venous drainage. The frequency of jugular venous reflux (JVR) is increased with aging. Hypertension, which has a decreased venous distensibility, might further exacerbate the sustained or long-term repetitive retrograde-transmitted cerebral venous pressure and venous outflow insufficiency caused by JVR. Clinically, JVR caused by a dural AV fistula does lead to cerebral hypoperfusion, white matter abnormalities, vasogenic edema and cognitive impairment in several published reports. JVR is suggested to play a key role in the pathogenesis of LA through a sustained or long-term repetitive retrograde-transmitted cerebral venous pressure and venous outflow insufficiency, which might lead to chronic cerebral venous hypertensions, abnormal cerebral venules structural changes, decreased cerebral blood flow, endothelial dysfunction, and vasogenic edema in cerebral white matters.

Cerebral venous ischemia by dural arteriovenous fistulas

Intracranial dural arteriovenous fistulas (AVFs) are potentially at risk for hemorrhage, and their symptoms and prognosis are highly variable. We present 7 surgical cases with the initial symptoms of venous ischemia by dural AVF. The series comprises 3 male and 4 female, ranging in age from 37 to 76 years (mean age, 61.1 years). Initial symptoms were dizziness in 3 cases, headache in 2 cases, unconsciousness in 1 case, and hemiparesis in 1 case. The locations included the superior sagittal sinus in 3 cases and the transverse-sigmoid sinus in 4 cases. Computed tomography with contrast media and magnetic resonance imaging revealed abnormal vessels. In all cases, retrograde feeding into the cortical veins was observed. On angiography, multiple retrograde venous drainage into the cortical veins were observed in all cases. Single photon emission computed tomography (SPECT) demonstrated apparent hypoperfusion in all 7 cases and further decrease by diamox challenging test in 4 cases. The dural AVFs were removed, and the symptoms disappeared in all cases, although transient aphasia was observed in a single case postoperatively. Postoperative SPECT showed improvement of cerebral blood flow in 4 and no change in 2 of 6 follow-up cases. Cerebral ischemia was induced by venous hypertension, and the hypoperfused brain improved immediately after the operation. Cerebral venous ischemia is a reversible condition that can be improved by appropriate early-stage treatment.

Sequential and spatial profiles of apoptosis in ischemic penumbra after two-vein occlusion in rats

Object

The two-vein occlusion model is known to be useful for ischemic penumbra studies in vivo. It was applied here to examine sequential changes in the expression of Bax and Bcl-2 proteins and in apoptotic cells to assess the relationship between penumbra and apoptosis.

Methods

Two cortical veins were occluded photochemically by using rose bengal dye in 27 Wistar rats. The animals were killed with perfusion fixation at the following intervals: 4, 12, 24, 48, 96, and 168 hours after vein occlusion (four at each interval; three additional rats were sham-treated). Immunohistochemical analysis for the Bcl-2 family of proteins was performed along with the terminal deoxynucleotidyl transferase–mediated deoxyuridine triphosphate nick-end labeling (TUNEL) assay to examine the relationship to single-cell death.

Cells positive for antiapoptotic proteins began to appear in the TUNEL assay for animals killed 24 hours after vein occlusion, with a peak at 48 hours. These cells were localized in the core of infarction. Immunohistochemical staining for Bax protein showed an increased presence around ischemic lesions at 4 hours after vein occlusion, and the amounts continued to rise until 24 hours, when the localization was diffuse around the core of infarction. Negative findings on immunohistochemical studies for Bcl-2 protein were seen at the early phase after two-vein occlusion.

Conclusions

After vein occlusion, apoptosis appeared sequentially and widely in cortical lesions considered to be the penumbra. Therefore, control of apoptosis would be expected to offer a therapeutic window for treatment of venous infarction.

MitoKATP-Channel Opener Protects against Neuronal Death in Rat Venous Ischemia

OBJECTIVE

Mitochondrial adenosine triphosphate-dependent potassium (mitoKATP) channels are present in the brain, and several reports have shown their neuroprotective, preconditioning effect against an ischemic insult. The role of mitoKATP channels in the penumbra area has not been studied thoroughly. In a model of venous ischemia, widespread penumbra-like low flow areas are created, which are susceptible to cortical spreading depression. Thus, we studied effects of mitoKATP channels on infarct size in this model.

METHODS

Male Wistar rats were subjected to two-vein occlusion by photochemical thrombosis of two adjacent cortical veins combined with KCl-induced cortical spreading depression. The rats were assigned to four experimental groups pretreated intraventricularly 15 minutes before two-vein occlusion with 1) vehicle, 2) the mitoKATP channel opener diazoxide (2 mmol/L), 3) diazoxide (2 mmol/L) plus the selective mitoKATP channel blocker 5-hydroxydecanoate (5-HD; 100 mmol/L), or 4) 5-HD alone (100 mmol/L). Regional cerebral blood flow (laser Doppler scanning) and brain cell swelling (impedance) were monitored acutely. Infarct volume was assessed 7 days after ischemia.

RESULTS

Pretreatment with diazoxide significantly reduced the infarct volume from 6.2 +/- 0.7 mm3 to 3.8 +/- 0.4 mm3, whereas regional cerebral blood flow in the vicinity of the two veins was comparable in both groups 70 minutes after two-vein occlusion. Effects of diazoxide were abolished by 5-HD, whereas 5-HD alone even increased infarct volume.

CONCLUSION

These results suggest that the opening of mitoKATP channels plays a major role in brain protection under penumbra-like conditions, as shown in this venous occlusion model.

Cluster analysis: a useful tool for the analysis of cerebral laser-Doppler scanning data

Laser-Doppler (LD) fluxmetry (LDF) is a widely used method for the measurement of relative tissue perfusion. Assessing LD-flux at multiple locations using a scanning technique greatly reduces movement artefacts and makes repetitive measurements at the same location possible. However, measurements in brain are often confounded by superficial cortical vessels. Commonly applied strategies to circumvent this problem, such as defining a cut-off point to exclude the high flux data of vessels or calculating the median from multiple locations to estimate regional cerebral blood flow (rCBF) all have specific shortcomings. The aim of this study was to analyse LD-data by mathematically discriminating between parenchymal and vessel data based on the distribution of flux data. Data was obtained by scanning the cortex of 15 male Sprague-Dawley rats using a matrix of 6x10 equidistant (500 microm) points. Standard statistical analysis as well as cluster analysis using the complete linkage algorithm was performed. The LD-data showed a bimodal frequency distribution with low values representing parenchymal and high values representing vessel flux. Parenchyma and vessels were reliably discriminated by cluster analysis. This was shown by mapping the vessel clusters on the scan matrix with the location of the superficial cortical vessels using Chi-square testing (p<0.0001). The parenchymal data followed a Gaussian normal distribution (p<0.851), whereas the vessel data did not (p<0.0001). Thus, cluster analysis is useful to discriminate parenchymal from vessel flux, thereby significantly improving the accuracy of LD-scanning data.

Cerebral Venous Infarction: The Pathophysiological Concept

Cerebral venous occlusion represents an often underdiagnosed cause for acute or slowly progressive neurological deterioration. The underlying pathophysiological basis is not well understood, but is different from those of arterial occlusion reflecting therefore different anatomical and physiological features of the cerebral venous system. Extensive collateral circulation within the cerebral venous system allows for a significant degree of compensation in the early stages of venous occlusion. Elevated cerebral venous pressure due to cerebral venous occlusion can result in a spectrum of phenomena including a dilated venous and capillary bed, development of interstitial edema, increased cerebrospinal fluid production, decreased cerebrospinal fluid absorption and rupture of venous structures (hematoma). All of these pathophysiological changes may explain the clinical observation that cerebral venous occlusion, if promptly diagnosed and adequately managed, contains reversible alterations and need not always lead to venous infarction. The present review outlines this different pathophysiological behavior of venous compared to arterial occlusion in the cerebral vasculature; special reference is given to the effect of these changes on the therapeutic impact.

Cerebral venous steal: blood flow diversion with increased tissue pressure

PURPOSE

Flow in areas with increased tissue pressure is described by a Starling resistor and is determined by the inflow pressure (P(i)), the external pressure (P(e)), and the outflow or venous pressure (P(v)). Flow is in Zone 1 at P(e) > P(i) > P(v), Zone 2 at P(i) > P(e) > P(v), and Zone 3 at P(i) > P(v) > P(e). A focal tissue pressure increase after stroke or trauma may lead to a transition from Zone 1 or 2 in the center to Zone 3 in the periphery. We hypothesize that the coexistence of different zones may lead to steal-like blood flow diversion in the perifocal area.

CONCEPT

We used a lumped-parameter model of two parallel Starling resistors with a common inflow. The first resistor, with higher P(e), represented the area with increased tissue pressure. The second resistor, with P(e)' = 0, represented the surrounding area. We evaluated the effects of venous pressure on the flow distribution between the two Starling resistors.

RATIONALE

The model demonstrated blood flow diversion toward the second Starling resistor with low external pressure. High inflow resistance facilitates this "steal." Flow diversion is caused by effective outflow pressure differences for the Starling resistors (P(e) for the first and P(v) for the second). The venous pressure increase equilibrates the effective backpressure and decreases flow diversion. When the venous pressure equals the external tissue pressure, blood flow diversion (cerebral venous steal) is abolished. Although increased venous pressure causes global flow reduction, it may restore flow to more than 50% of baseline values in areas of increased tissue pressure.

DISCUSSION

Cerebral venous steal is a potential cause of secondary brain injury in areas of increased tissue pressure. It can be eliminated with increased venous pressure. Increased venous pressure may recruit the collapsed vascular network and correct perifocal perfusion maldistribution. This resembles how positive end expiratory pressure recruits collapsed airways and decreases the ventilation/perfusion mismatch.

Impairment of autoregulation following cortical venous occlusion in the rat

Recent experiments showed an upward shift of the lower limit of autoregulation (AR) following photochemical occlusion of cortical veins in the rat. The goal of the present study was to prove the hypothesis that occlusion of cortical veins will be associated with impairment of the upper limit of autoregulation as well. In n = 28 Wistar rats unilateral frontoparietal cranial windows were drilled for transdural assessment of regional cerebral blood flow (rCBF) by laser Doppler scanning. The animals were allotted to two groups: (1) Group A (n = 5), control group for determination of the upper limit of autoregulation with stepwise induced arterial hypertension by intravenous administration of the alpha adrenergic drug methoxamine under continuous monitoring of mean arterial blood pressure (MABP); (2) Group B (n = 23), in which two cortical veins were photochemically occluded with rose bengal dye and fiberoptic illumination upon baseline CBF measurement. This was followed by repeated rCBF measurements under AR testing. Loss of AR in control Group A with passive increase of rCBF occurred at MABP of 147.5 +/- 2.9 mmHg. In Group B venous occlusion was followed by an initial phase of reduced rCBF, and then by pressure passive increases, thereby indicating loss of AR. Statistically significant changes of rCBF when compared to baseline MABP occurred at MABPbaseline + 10% (112.7 +/- 6.6 mmHg). We conclude that AR is impaired upon cortical venous occlusion with the propensity for hyperperfusion injury at a lower level of MABP when compared with a control group. In the context with earlier findings this may lead to narrowing of the corridor for MABP management following intra-operative occlusion of large cortical veins.

Laser Doppler flowmetry mapping of cerebrocortical microflow: characteristics and limitations

The aim of this study was to quantitatively analyze the amount of methodological noise and the spatial and temporal variability of laser Doppler flowmetry (LDF) signals mapping cerebrocortical microflow. In an experimental setup with latex beads, the methodological LDF-signal variability was determined (coefficient of variation or CV(method)). The biological variability of the LDF signals was measured in animal experiments using 10 anesthetized rabbits. One stationary reference probe was used to assess temporal heterogeneity (CV(temp)) and a micromanipulator-driven scanning probe was used to assess spatial heterogeneity (CV(spat)) in a cortical area of 3.5 x 4.5 mm with 252 measurement points. CO(2) tests were used to modulate cerebrovascular resistance. CV(method) was found to be 4.94 +/- 1.7. The CV(temp) for the LDF-velocity signal was assessed to be 13.93 +/- 5.9 during normocapnia. Scanning of the brain surface with the scanning probe revealed a CV(spat) for LDF velocity of 65.0 +/- 16.2 during normocapnia. CO(2) modulation (hypocapnia --> normocapnia --> hypercapnia) of the cerebral resistance did not show a significant change in temporal heterogeneity (10.84 +/- 3.1 --> 13.93 +/- 5.9 --> 14.82 +/- 3.9), whereas spatial heterogeneity decreased significantly (81.31 +/- 12.0 --> 65.0 +/- 16.2 --> 54.04 +/- 21.8). Although the spatial and temporal variability of LDF signals evoked by cerebrocortical microflow is in the same range as with other methods and in other organs, LDF cerebrocortical mapping is restricted by the large temporal and spatial heterogeneity of the cerebrocortical vasculature. The definitions of sample volume, scanning step width, probe to brain surface distance, and average time per scanning point are critical concerning reliable LDF cerebrocortical mapping techniques.

Novel intraoperative cerebral blood flow monitoring by laser-Doppler scanner

Laser-Doppler (LD) flowmetry was used to measure tissue perfusion non-invasively and continuously during neurosurgical operations using an LD scanner. Scanning was usually completed in 20 seconds. Measurements were processed in software to provide a color-coded image of the tissue perfusion. Moreover, the measurement data, expressed in LD-units, could be used for statistical data analysis. No physical contact was necessary between the scanning device and the exposed brain tissue. The imager provided two-dimensional microvascular flow maps non-invasively and quantitatively during brain operations, and could show the CO2 reactivity in the vessels. LD scanning flowmetry is a promising intraoperative monitoring method for cerebral blood flow changes.

Cerebral blood flow and tissue oxygen saturation in immediate and progressive ischemia in rat brain

The aim of the present study was to investigate whether immediate ischemia is more harmful to the brain than progressive ischemia. To do so, we examined the correlation between the degree and the process of ischemia using hypobaric hypotension technique, which was used to reduce systemic blood pressure acutely or progressively below the lower threshold of CBF regulation, in rat brain. In Wistar rats (n = 21), global ischemia using bilateral carotid arteries occlusion coupled with hypobaric hypotension was induced by lowering mean arterial blood pressure (MABP) progressively to 55, 45 and 35 mmHg or immediately to 35 mm Hg. Local cerebral blood flow (ICBF) by laser Doppler (LD) flowmetry and tissue hemoglobin oxygen saturation (HbSO2) by a microspectrophotometric method were measured at 25 corresponding locations using a 'scanning' technique which employs a computer-controlled micromanipulator. Regional CBF (rCBF) and rHbSO2 were determined by calculation of the median value from the 25 ICBF and IHbSO2 data. In the 'progressive' group, rCBF and rHbSO2 decreased gradually and reached 12.2 +/- 15.8 LD-units and 44.9% +/- 13.4% at 35 mm Hg of MABP, respectively. In the 'immediate' group, both parameters dropped suddenly to 7.86 +/- 10.6 LD-units (p < 0.01 vs. CBF of the progressive group) and 22.5% +/- 15.5% (p < 0.001 vs. tissue HbSO2 of the progressive group) from the control at 35 mmHg. These data suggested that cerebral ischemia is better tolerated if it is induced gradually. CBF recorded by LD-scanning technique and HbSO2 value by microspectrophotometric method correlated well in the ischemic condition, indicating that HbSO2 can be preserved if CBF is decreased gradually.

A scanning technique to measure regional cerebral blood flow and oxyhemoglobin level

OBJECTIVE

The application of a laser scanning technique to measure regional cerebral blood flow (CBF) and tissue hemoglobin oxygenation (HbO2) using the rat closed cranial window preparation is described.

METHODS

Twenty-nine male Wistar rats were used to consecutively measure local CBF by laser Doppler flowmetry and tissue HbO2 by a microspectrophotometric method at multiple corresponding cortical locations. The scanning technique used a computer-controlled micromanipulator. Data from three experimental models are presented: the whisker stimulation model, the ischemia-reperfusion model, and the sinus-vein thrombosis model. Sequential changes in local CBF and HbO2 data before, during, and after stimulation, ischemia, and sinus thrombosis were examined. Data from predefined locations within the same region were correlated with the topographical location and then arranged in a three-dimensional image.

RESULTS

In the whisker stimulation model, we found a disproportionate increase in CBF (32 +/- 12%) as compared with that of HbO2 (9 +/- 4%) during stimulation. In the ischemia-reperfusion model, the three-dimensional image showed heterogeneous low CBF (depending on the area) and homogeneous HbO2 at a reduced level during ischemia and postischemic hyperperfusion. However, the range of oxygenation was normal after reperfusion. In the sinus-vein thrombosis model, drainage of the unsaturated blood via the collateral pathways was noted.

CONCLUSION

The laser scanning technique is useful for visualizing sequential changes in hemodynamic-metabolic interactions of cortical brain tissue. This technique can reveal phenomena not detected by traditional monitoring procedures.

Effect of age on cerebral venous circulation disturbances in the rat

OBJECT

Mild cerebral venous circulation disturbances (CVCDs) in aged patients are frequently known to cause unexpectedly severe postoperative complications in neurosurgical practice. The object of the present study was to determine whether there are age-related differences involved in vulnerability to CVCDs.

METHODS

Thirty-eight male Wistar rats were used. A single cortical vein with a 100-microm diameter was occluded photochemically by using rose bengal dye and fiberoptic illumination in young (Group Y, 19 animals aged 10-14 weeks) and aged (Group A, seven animals aged 80-100 weeks) rats. Five young and seven aged animals served as sham-operated controls. Regional cerebral blood flow (rCBF) was determined from local CBF, which was measured at 25 (5 x 5) identical locations, with the occluded vein located central to the scanning field, by using a laser Doppler scanning technique every 15 minutes for 90 minutes after venous occlusion. The cerebral venous flow pattern was examined using fluorescence angiography until 90 minutes after occlusion. Histological specimens were examined 24 hours after occlusion. In Group Y, rCBF did not change significantly after venous occlusion. However, in Group A, rCBF decreased rapidly beginning 15 minutes after occlusion. Significant intergroup differences were observed 30, 60, and 90 minutes after occlusion. Venous flow arrest, which resulted in venous infarct, was observed on angiography 90 minutes after occlusion in two (10.5%) of 19 young and six (85.7%) of seven aged rats. The venous thrombus in Group A rats was significantly larger than that in Group Y rats 90 minutes after occlusion. Venous infarction was seen in all aged rats (100%) and in six young rats (31.6%); the infarct size, expressed as a percentage of the size of the ipsilateral hemisphere, was significantly larger in aged rats than in young rats.

CONCLUSIONS

This study demonstrated an age-related increase in the rate and size of venous infarct following vein occlusion, suggesting that the greater vulnerability to CVCDs in the aged brain might be attributed to early and extensive hypoperfusion of circumscribed brain areas drained by the occluded vein. The larger thrombus formation in aged animals indicates that a shift in the thrombogenetic/thrombolytic equilibrium is responsible for the observed effect.

Effects of cortical spreading depression on cortical blood flow, impedance, DC potential, and infarct size in a rat venous infarct model

A cortical venous infarction model has been evaluated as to the degree of regional flow reduction and by studying effects of cortical spreading depression (CSD). Two adjacent cortical veins were occluded photochemically with rose bengal and fiberoptic illumination. Seven rats served to demonstrate effects on regional cortical blood flow using laser Doppler scanning. In 36 rats local CBF, DC potential, and brain tissue impedance were measured continuously for 75 min after vein occlusion. No, 3, or 10 CSD waves were induced by potassium chloride injection during the initial 75 min. Rats were compared for spontaneous CSDs; baseline local CBF, CBF, and impedance response to CSD; and infarct volume. Seventy-five minutes after vein occlusion regional cortical flow in a 3.5x7-mm window was reduced to 34.3+/-13.2%. At 45% of the 840 measured locations in 7 rats flow was <40% baseline and at 27.3% <30%, indicating a widespread penumbra territory. During the initial 75 min 2.1+/-1.1 spontaneous CSDs were observed. There was a positive correlation between the number of spontaneous CSDs seen acutely and infarction volume after 5 days. Moreover, brain injury was significantly increased in the group with 10 KCl-induced CSDs. A reduced 1CBF response and an overshooting tissue impedance change during CSD were predictors of ischemic damage. This study demonstrates a CSD-related growth of the venous infarct. Second, the data indicate that flow after two-vein occlusion resembles that seen under penumbra conditions, allowing for studies of damage mechanisms responsible for infarct growth.