Placement of a Catheter into the Transverse Sinus in Monitoring Intracranial Lesions: A Technical Note

High intracranial pressure (ICP) can be induced by stroke, brain trauma, and brain tumor, and lead to cerebral injury. Monitoring the blood flow of a damaged brain is important for detecting intracranial lesions. Blood sampling is a better way to monitor changes in brain oxygen and blood flow than computed tomography perfusion and magnetic resonance imaging. This article describes how to take blood samples from the transverse sinus in a high ICP rat model. Also, it compares the blood samples from the transverse sinus and femoral artery/vein through blood gas analysis and neuronal cell staining. The findings may be of significance to the monitoring of the oxygen and blood flow of intracranial lesions.

Intracranial dynamics biomarkers at traumatic cerebral vasospasm

Introduction

Patients who suffer severe traumatic brain injury (sTBI) and cerebral vasospasm (CVS) frequently have posttraumatic cerebral ischemia (PCI).

The research question

was to study changes in cerebral microcirculatory bed parameters in sTBI patients with CVS and with or without PCI.

Material and methods

A total of 136 severe TBI patients were recruited in the study. All patients underwent perfusion computed tomography, intracranial pressure monitoring, and transcranial Doppler. The levels of cerebrovascular resistance (CVR), cerebral arterial compliance (CAC), cerebrovascular time constant (CTC), and critical closing pressure (CCP) were measured using the neuromonitoring complex. Statistical analysis was performed using parametric and nonparametric methods and factor analysis. The patients were dichotomized into PCI-positive (n = 114) and PCI-negative (n = 22) groups. Data are presented as mean values (standard deviations).

Results

CVR was significantly increased, whereas CAC, CTC, and CCP were significantly decreased in sTBI patients with CVS and PCI development (p < 0.05). Factor analyses revealed that all studied microcirculatory bed parameters were significantly associated with the development of PCI (p < 0.05).

Discussion and conclusion

The changes in all studied microcirculatory bed parameters in TBI patients with CVS were significantly associated with PCI development, which enables us to regard them as the biomarkers of CVS and PCI development. The causes of the described microcirculatory bed parameters changes might include complex (cytotoxic and vasogenic) brain edema development, regional microvascular spasm, and dysfunction of pericytes. A further prospective study is warranted.

Dynamics of Intracranial Pressure and Cerebrovascular Reactivity During Intrahospital Transportation of Traumatic Brain Injury Patients in Coma

BACKGROUND

Intrahospital transportation (IHT) of patients with traumatic brain injury (TBI) is common and may have adverse consequences, incurring inherent risks. The data on the frequency and severity of clinical complications linked with IHT are contradictory, and there is no agreement on whether it is safe or potentially challenging for neurocritical care unit patients. Continuous intracranial pressure (ICP) monitoring is essential in neurointensive care. The role of ICP monitoring and management of cerebral autoregulation impairments in IHT of patients with severe TBI is underinvestigated. The purpose of this nonrandomized retrospective single-center study was to assess the dynamics of ICP and an improved pressure reactivity index (iPRx) as a measure of autoregulation during IHT.

METHODS

Seventy-seven men and fourteen women with severe TBI admitted in 2012-2022 with a mean age of 33.2 ± 5.2 years were studied. ICP and arterial pressure were invasively monitored, and cerebral perfusion pressure and iPRx were calculated from the measured parameters. All patients were subjected to dynamic helical computed tomography angiography using a 64-slice scanner Philips Ingenuity computed tomography scan 1-2 days after TBI. Statistical analysis of all results was done using a paired t-test, and p was preset at < 0.05. The logistic regression analysis was performed for cerebral ischemia development dependent on intracranial hypertension and cerebrovascular reactivity.

RESULTS

IHT led to an increase in ICP in all the patients, especially during vertical movement in an elevator (maximum 75.2 mm Hg). During the horizontal transportation on the floor, ICP remained increased (p < 0.05). The mean ICP during IHT was significantly higher (26.1 ± 13.5 mm Hg, p < 0.001) than that before the IHT (19.9 ± 5.3 mm Hg). The mean iPRx after and before IHT was 0.52 ± 0.04 and 0.23 ± 0.14, respectively (p < 0.001).

CONCLUSIONS

Both horizontal and vertical transportation causes a significant increase in ICP and iPRx in patients with severe TBI, potentially leading to the outcome worsening.

Arteriovenous cerebral blood flow correlation in moderate-to-severe traumatic brain injury: CT perfusion study

Introduction

The relationship between arterial and venous blood flow in moderate-to-severe traumatic brain injury (TBI) is poorly understood.

The research question

was to compare differences in perfusion computed tomography (PCT)-derived arterial and venous cerebral blood flow (CBF) in moderate-to-severe TBI as an indication of changes in cerebral venous outflow patterns referenced to arterial inflow.

Material and methods

Moderate-to-severe TBI patients (women 53; men 74) underwent PCT and were stratified into 3 groups: I (moderate TBI), II (diffuse severe TBI without surgery), and III (severe TBI after the surgery). Arterial and venous CBF were measured by PCT in both the internal carotid arteries (CBFica) and the confluence of upper sagittal, transverse, and straight sinuses (CBFcs).

Results

In group I, CBFica on the left and right sides were significantly correlated with each other (p < 0.0001) and with CBFcs (p = 0.048). In group II, CBFica on the left and right sides were also correlated (P < 0.0000001) but not with CBFcs. Intracranial pressure reactivity (PRx) and CBFcs were correlated (p = 0.00014). In group III, CBFica on the side of the removed hematoma was not significantly different from the opposite CBFica (P = 0.680) and was not correlated with CBFcs.

Discussion and conclusion

The increasing severity of TBI is accompanied by a rising uncoupling between the arterial and venous CBF in the supratentorial vessels suggesting a shifting of cerebral venous outflow.

Abstract WMP118: Sex-specific And Dose-dependent Effects Of Drag-reducing Polymers On Post-traumatic Ischemia In Rats After Traumatic Brain Injury Of Different Severity

Introduction: Previously, we showed that drag-reducing polymers (DRP) improve hemodynamics in rat models of brain injury (TBI). Here we examined the dose- and sex-dependent DRP effects on post-TBI ischemia.

Methods: In-vivo 2-photon microscopy over the rat parietal cortex was used to monitor the effect of DRP on microvascular perfusion and tissue oxygenation (NADH) and blood-brain barrier permeability. Lateral fluid-percussion TBI (1.5 ATA-moderate or 2.5 ATA-severe, 100 ms) was induced after baseline imaging and followed by 4 hours of monitoring. DRP injected at 1, 2, or 4 ppm. Data analysis was done by GraphPad Prism 7.

Results: Moderate TBI progressively decreased microvascular circulation and hypoxia in the pericontusion zone (p<0.05). The i.v. injection of DRP increased near-wall flow velocity and flow rate in arterioles, leading to an increase in the number of erythrocytes entering capillaries, enhancing capillary perfusion in a dose-dependent manner without distinguishable difference between males and females (p<0.01). The severe TBI resulted in intracranial pressure increase (31±3.2 mmHg, p<0.05), leading to microcirculation redistribution to non-nutritive microvascular shunt (MVS) flow and stagnation of capillary flow. Tissue hypoxia was more prominent, especially in male rats; the pericontusion zone was 25±5.2% larger than after moderate TBI (p<0.01). Both were reverted by DRP in a dose-related manner with better efficiency in females (p<0.01). After severe TBI, BBB degradation was faster and more prominent. DRP was more efficient in attenuating the progression of permeability increase in moderate TBI (p<0.05).

Conclusion: DRP at 4 ppm was most efficient, with a better effect on female rats. Supported by NIH/NINDS R01NS112808

Abstract WP53: The Assessment Of Brain Water Content At Posttraumatic Ischemia: Ct Perfusion Study

Background: The influence of cerebral edema and secondary insults on the clinical outcome of traumatic brain injury (TBI) is well known. The studies of the brain water homeostasis dynamics at TBI remain rare, which determines the relevance of our work. The purpose is to study the changes in brain water homeostasis after TBI of varying severity compared to the cerebral microcirculation parameters.

Materials: This non-randomized retrospective single-center study complies with the Helsinki Declaration. One hundred twenty-eight patients with posttraumatic ischemia (PCI) after moderate-to-severe TBI in the middle cerebral artery territory who presented between July 2015 and February 2022 to our hospital were included. PCI was determined using perfusion computed tomography (CT), and brain edema was determined using net water uptake (NWU) on baseline CT images. The patients were divided according to Marshall’s classification. Multivariate linear regression models were performed to analyze data.

Results: NWU in PCI zones was significantly higher than in non-ischemic zones (8.1% versus 4.2%; P <0.001). In the multivariable regression analysis, the mean transit time increase was significantly and independently associated with higher NWU ( R 2 = 0,089, P <0.01). In the PCI zone, cerebral blood flow (CBF), volume (CBV), and time to peak (TTP) were not significantly associated with NWU values ( P >0.05). No significant differences existed between the NWU values in PCI foci in different Marshall groups ( P =0.308).

Conclusion: The Marshall classification does not seem to be able to predict the progression of posttraumatic ischemia. The blood passage delay through the cerebral microvascular bed was significantly accompanied by brain tissue water uptake increase in the PCI focus.

Sex-Specific and Dose-Dependent Effects of Drag-Reducing Polymers on Microcirculation and Tissue Oxygenation in Rats After Traumatic Brain Injury

Traumatic brain injury (TBI) ultimately leads to a reduction in the cerebral metabolic rate for oxygen due to ischemia. Previously, we showed that 2 ppm i.v. of drag-reducing polymers (DRP) improve hemodynamic and oxygen delivery to tissue in a rat model of mild-to-moderate TBI. Here we evaluated sex-specific and dose-dependent effects of DRP on microvascular CBF (mvCBF) and tissue oxygenation in rats after moderate TBI. In vivo two-photon laser scanning microscopy over the rat parietal cortex was used to monitor the effects of DRP on microvascular perfusion, tissue oxygenation, and blood-brain barrier (BBB) permeability. Lateral fluid-percussion TBI (1.5 ATA, 100 ms) was induced after baseline imaging and followed by 4 h of monitoring. DRP was injected at 1, 2, or 4 ppm within 30 min after TBI. Differences between groups were determined using a two-way ANOVA analysis for multiple comparisons and post hoc testing using the Mann-Whitney U test. Moderate TBI progressively decreased mvCBF, leading to tissue hypoxia and BBB degradation in the pericontusion zone (p < 0.05). The i.v. injection of DRP increased near-wall flow velocity and flow rate in arterioles, leading to an increase in the number of erythrocytes entering capillaries, enhancing capillary perfusion and tissue oxygenation while protecting BBB in a dose-dependent manner without significant difference between males and females (p < 0.01). TBI resulted in an increase in intracranial pressure (20.1 ± 3.2 mmHg, p < 0.05), microcirculatory redistribution to non-nutritive microvascular shunt flow, and stagnation of capillary flow, all of which were dose-dependently mitigated by DRP. DRP at 4 ppm was most effective, with a non-significant trend to better outcomes in female rats.

Low Flow and Microvascular Shunts: A Final Common Pathway to Cerebrovascular Disease: A Working Hypothesis

Low flow and microvascular shunts (MVS) is the final common pathway in cerebrovascular disease. Low flow in brain capillaries (diam. 3-8 μm) decreases endothelial wall shear rate sensed by the glycocalyx regulating endothelial function: water permeability; nitric oxide synthesis via nitric oxide synthase; leucocyte adhesion to the endothelial wall and penetration into the tissue; activation of cytokines and chemokines initiating inflammation in tissue. Tissue edema combined with pericyte and astrocyte capillary constriction increases capillary resistance. Increased capillary resistance diverts flow through MVS (diam. 10-25 μm) that are non-nutritive, without gas exchange, waste or metabolite clearance and cerebral blood flow (CBF) regulation. MVS predominate in subcortical and periventricular white matter. The shift in flow from capillaries to MVS is a pathological, maladaptive process. Low perfusion in the injured tissue exacerbates brain edema. Low blood flow and MVS alone can lead to all of the processes involved in tissue injury including inflammation and microglial activation.

Drag-Reducing Polymers Improve Vascular Hemodynamics and Tissue Oxygen Supply in Mouse Model of Diabetes Mellitus

Diabetes mellitus (DM) is a chronic metabolic disease characterised by hyperglycaemia and glucose intolerance caused by impaired insulin action and/or defective insulin secretion. Long-term hyperglycaemia leads to various structural and functional microvascular changes within multiple tissues, including the brain, which involves blood-brain barrier alteration, inflammation and neuronal dysfunction. We have shown previously that drag-reducing polymers (DRP) improve microcirculation and tissue oxygen supply, thereby reducing neurologic impairment in different rat models of brain injury. We hypothesised that DRP could improve cerebral and skin microcirculation in the situation of progressive microangiopathies associated with diabetes using a mouse model of diabetes mellitus. Diabetes was induced in C57BL/6 J mice with five daily consecutive intraperitoneal injections of streptozotocin (50 mg/kg/day). Animals with plasma glucose concentrations greater than 250 mg/dL were considered diabetic and were used in the study following four months of diabetes. DRP (2 ppm) was injected biweekly during the last two weeks of the experiment. Cortical and skin (ear) microvascular cerebral blood flow (mCBF) and tissue oxygen supply (NADH) were measured by two-photon laser scanning microscopy (2PLSM). Cerebrovascular reactivity (CVR) was evaluated by measuring changes in arteriolar diameters and NADH (tissue oxygen supply) during the hypercapnia test. Transient hypercapnia was induced by a 60-second increase of CO₂ concentration in the inhalation mixture from 0% to 10%. Compared to non-diabetic animals, diabetic mice had a significant reduction in the density of functioning capillaries per mm³ (787 ± 52 vs. 449 ± 25), the linear velocity of blood flow (1.2 ± 0.31 vs. 0.54 ± 0.21 mm/sec), and the tissue oxygen supply (p < 0.05) in both brain and skin. DRP treatment was associated with a 50% increase in all three parameters (p < 0.05). According to the hypercapnia test, CVR was impaired in both diabetic groups but more preserved in DRP mice (p < 0.05). Our study in a diabetic mouse model has demonstrated the efficacy of hemorheological modulation of blood flow by DRP to achieve increased microcirculatory flows and tissue oxygen supply.

Haemorheologic Enhancement of Cerebral Perfusion Improves Oxygen Supply and Reduces Aβ Plaques Deposition in a Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is a consequence of complex interactions of age-related neurodegeneration and vascular-associated pathologies, affecting more than 44 million people worldwide. For the last decade, it has been suggested that chronic brain hypoperfusion and consequent hypoxia play a direct role in the pathogenesis of AD. However, current treatments of AD have not focused on restoring or improving microvascular perfusion. In a previous study, we showed that drag reducing polymers (DRP) enhance cerebral blood flow and tissue oxygenation. We hypothesised that haemorheologic enhancement of cerebral perfusion by DRP would be useful for treating Alzheimer's disease. We used double transgenic B6C3-Tg(APPswe, PSEN1dE9) 85Dbo/Mmjax AD mice. DRP or vehicle (saline) was i.v. injected every week starting at four months of age till 12 months of age (10 mice/group). In-vivo 2-photon laser scanning microscopy was used to evaluate amyloid plaques development, cerebral microcirculation, and tissue oxygen supply/metabolic status (NADH autofluorescence). The imaging sessions were repeated once a month till 12 months of age. Statistical analyses were done by independent Student's t-test or Kolmogorov-Smirnov tests where appropriate. Differences between groups and time were determined using a two-way repeated measures ANOVA analysis for multiple comparisons and post hoc testing using the Mann-Whitney U test. In the vehicle group, numerous plaques completely formed in the cortex by nine months of age. The development of plaques accumulation was accompanied by cerebral microcirculation disturbances, reduction in tissue oxygen supply and metabolic impairment (NADH increase). DRP mitigated microcirculation and tissue oxygen supply reduction - microvascular perfusion was 29.5 ± 5%, and tissue oxygen supply was 22 ± 4% higher than in the vehicle group (p < 0.05). In the DRP group, amyloid plaques deposition was substantially less than in the vehicle group (p < 0.05). Thus, rheological enhancement of blood flow by DRP is associated with reduced rate of beta amyloid plaques deposition in AD mice.

Cerebrovascular Reserve (CVR) and Stages of Hemodynamic Compromise

The concept of hemodynamic compromise (HC) is used to detect brain regions under ischemic stress by impaired ability to dilate in response to a vasodilatory challenge for cerebrovascular reserve (CVR). The vasodilatory challenges are either inhaled CO2 or a carbonic anhydrase inhibitor acetazolamide (AZ) with measurements of cerebral blood flow (CBF) before and during the challenge. The rationale for CVR is that the brain under ischemic stress is vasodilated and the increase in CBF is attenuated. However, regional oxygen extraction fraction (OEF) by positron emission tomography (PET) is the gold standard for measurement of HC. We showed a strong correlation between CVR and OEF and the OEF response (OEFR) before and after vasodilation in patients with acute ischemic stroke. These observations suggest that CVR measurements alone identify brain regions under ischemic stress without the need for expensive, time consuming and difficult PET OEF.

Cerebral Spreading Depression Transient Disruption of Cross-Frequency Coupling in the Rat Brain: Preliminary Observations

Normal brain function requires an integrated, simultaneous communication between brain regions in a coordinated manner. In our studies on cortical spreading depolarization (CSD) induced electrically in the rat brain while recording electrocorticography (ECoG) and delta wave activity, we found for the first time that CSD suppressed delta wave activity, which began even before the CSD was fully developed. We pursued this observation to determine whether repeated CSD suppressed delta wave activity in rats. CSD was produced by electrical stimulation of the neocortex while recording the development of CSD and changes in the coupling of low-frequency band cross coupling to four typical physiological neuronal activity frequency bands, i.e., 5-7 Hz, 8-12 Hz, 13-30 Hz, and 30-80 Hz. Band-pass filters were applied to achieve the corresponding physiological band signals. Besides the cross-frequency coupling (CFC) analysis, the distribution of delta wave density in time domain was analyzed. We calculated the delta wave density per 30 seconds but represent the density as frequency per minute. A Generalized Linear Models (GLM) was used to carry out the CFC analysis in Matlab. Because delta waves dominated the ECoG recorded, we modeled the higher-frequency amplitude envelope as a function of low-frequency phase using a spline basis. Besides the CFC analysis, we also characterized the distribution of the delta wave density in time domain. Four CFC, Theta, Alpha, Beta, and Gamma were at very small values after CSD, and after about 8 minutes, the CFC recovered to the pre-CSD level. CFC were seen to decrease before a CSD occurred at the higher-frequency bands and tended to decrease quickly. Whether the attenuated CFC by CSD has long-term consequences remains to be determined. Future studies will explore the impact of cortical CSD on CFC with deeper brain structures, including the thalamus and the caudate putamen.

Near-Infrared Spectroscopy (NIRS) of Muscle HbO2 and MbO2 Desaturation During Exercise

Continuous noninvasive monitoring of muscle oxygenation has important clinical applications for muscle disorders such as compartmentation syndrome, fibromyalgia, deep vein thrombosis, malignant hyperthermia, and the assessment of training in athletic performance. NIRS has precisely such potential and has been used to detect deep venous thrombosis, evaluate athletic performance, and assess limb reperfusion and revascularization. The aim of this study was to examine the relationship between muscle hemoglobin oxygen (HbO₂) and myoglobin (MbO₂) desaturation using NIRS combined with venous blood sampling and HbO₂ desaturation during forearm muscle exercise. Eleven normal subjects were studied, with informed consent and an IRB-approved protocol. A NIRS sensor (INVOS4100, Somanetics, Corp.) was applied on the volar aspect of the forearm. The subjects exercised their forearm by clenching and relaxing their fist while observing the oximeter and driving the reading to specified levels from 90% to 15% (minimum possible reading). Venous blood samples were withdrawn for measurement of blood gases and oxygen saturation (IL-Co-Oximeter). RSO₂ (%) vs VO₂ Sat showed a two-component HbO₂ desaturation suggesting representation of venous HbO₂ desaturation and perhaps myoglobin oxygen (MBO₂) desaturation. Subtraction of the linear venous HbO₂ curve from the two-component curve suggests MbO₂ desaturation at venous hemoglobin oxygen saturation of about 10-20%. Conclusions: The kinetics of desaturation during exercise revealed two components representing HbO₂ and MbO₂ deoxygenation. The data show that MbO₂ represents approximately 40% of the NIRS signal and the balance or 60% to HbO₂.

Improved Cerebral Perfusion Pressure and Microcirculation by Drag Reducing Polymer-Enforced Resuscitation Fluid After Traumatic Brain Injury and Hemorrhagic Shock

Hemorrhagic shock (HS) after traumatic brain injury (TBI) reduces cerebral perfusion pressure (CPP) and cerebral blood flow (CBF), increasing hypoxia and doubling mortality. Volume expansion with resuscitation fluids (RFs) for HS does not improve CBF and tissue oxygen, while hypervolemia exacerbates brain edema and elevates intracranial pressure (ICP). We tested whether drag-reducing polymers (DRPs), added to isotonic Hetastarch (HES), would improve CBF but prevent ICP increase. TBI was induced in rats by fluid percussion, followed by controlled hemorrhage to mean arterial pressure (MAP) = 40 mmHg. HES-DRP or HES was infused to MAP = 60 mmHg for 1 h, followed by blood reinfusion to MAP = 70 mmHg. Temperature, MAP, ICP, cortical Doppler flux, blood gases, and electrolytes were monitored. Microvascular CBF, tissue hypoxia, and neuronal necrosis were monitored by two-photon laser scanning microscopy 5 h after TBI/HS. TBI/HS reduced CPP and CBF, causing tissue hypoxia. HES-DRP (1.9 ± 0.8 mL) more than HES (4.5 ± 1.8 mL) improved CBF and tissue oxygenation (p < 0.05). In the HES group, ICP increased to 23 ± 4 mmHg (p < 0.05) but in HES-DRP to 12 ± 2 mmHg. The number of dead neurons, microthrombosis, and the contusion volume in HES-DRP were significantly less than in the HES group (p < 0.05). HES-DRP required a smaller volume, which reduced ICP and brain edema.

Addition of Drag-Reducing Polymers to Colloid Resuscitation Fluid Enhances Cerebral Microcirculation and Tissue Oxygenation After Traumatic Brain Injury Complicated by Hemorrhagic Shock

Hemorrhagic shock (HS) is a severe complication of traumatic brain injury (TBI) that doubles mortality due to severely compromised microvascular cerebral blood flow (mvCBF) and oxygen delivery reduction, as a result of hypotension. Volume expansion with resuscitation fluids (RF) for HS does not improve microvascular CBF (mvCBF); moreover, it aggravates brain edema. We showed that the addition of drag-reducing polymers (DRP) to crystalloid RF (lactated Ringer's) significantly improves mvCBF, oxygen supply, and neuronal survival in rats suffering TBI+HS. Here, we compared the effects of colloid RF (Hetastarch) with DRP (HES-DRP) and without (HES). Fluid percussion TBI (1.5 ATA, 50 ms) was induced in rats and followed by controlled HS to a mean arterial pressure (MAP) of 40 mmHg. HES or HES-DRP was infused to restore MAP to 60 mmHg for 1 h (prehospital period), followed by blood reinfusion to a MAP of 70 mmHg (hospital period). In vivo two-photon microscopy was used to monitor cerebral microvascular blood flow, tissue hypoxia (NADH), and neuronal necrosis (i.v. propidium iodide) for 5 h after TBI+HS, followed by postmortem DiI vascular painting. Temperature, MAP, blood gases, and electrolytes were monitored. Statistical analyses were done using GraphPad Prism by Student's t-test or Kolmogorov-Smirnov test, where appropriate. TBI+HS compromised mvCBF and tissue oxygen supply due to capillary microthrombosis. HES-DRP improved mvCBF and tissue oxygenation (p < 0.05) better than HES. The number of dead neurons in the HES-DRP was significantly less than in the HES group: 76.1 ± 8.9 vs. 178.5 ± 10.3 per 0.075 mm³ (P < 0.05). Postmortem visualization of painted vessels revealed vast microthrombosis in both hemispheres that were 33 ± 2% less in HES-DRP vs. HES (p < 0.05). Thus, resuscitation after TBI+HS using HES-DRP effectively restores mvCBF and reduces hypoxia, microthrombosis, and neuronal necrosis compared to HES. HES-DRP is more neuroprotective than lactated Ringer's with DRP and requires an infusion of a smaller volume, which reduces the development of hypervolemia-induced brain edema.

Abstract WMP74: Resuscitation Fluid With Drag Reducing Additive Reduces Microthrombosis and Oxidative Stress After Traumatic Brain Injury Complicated by Hemorrhagic Shock

Objective: Traumatic brain injury (TBI) is frequently accompanied by hemorrhagic shock (HS) significantly worsening morbidity and mortality. Existing colloid or crystalloid resuscitation fluids (RF) for volume expansion do not adequately mitigate impaired microvascular cerebral blood flow (mCBF) and causes post-reperfusion mitochondrial oxidative stress. We previously showed that resuscitation fluid with drag reducing polymers (DRP-RF) improves CBF by rheological modulation of hemodynamics. In this work, we have evaluated the efficiency of DRP-RF in the reduction of microthrombosis and post-reperfusion mitochondrial oxidative stress.

Methods: TBI was induced in rats by fluid percussion (1.5 ATA, 50 ms) and followed by controlled hemorrhage to a mean arterial pressure (MAP) =40 mmHg. DRP-RF or Lactated Ringers (LR-RF) was infused to MAP =60 mmHg for one hour (pre-hospital), followed by blood re-infusion to a MAP=70 mmHg (hospital). In vivo 2-photon laser scanning microscopy over the parietal cortex was used to monitor microvascular blood flow, tissue hypoxia (NADH) and level of superoxide in the cortex as a measure of mitochondrial oxidative stress (i.v. hydroethidine [HEt], 1 mg/kg) for 5 hours after TBI/HS, followed by DiI vascular painting during perfusion-fixation. Temperatures, MAP, blood gases and electrolytes were monitored.

Results: TBI/HS compromised CBF leading to capillary microthrombosis and tissue hypoxia. As in our previous work, DRP-RF better than LR-RF improved mCBF and tissue oxygenation (p<0.05). Reperfusion-induced oxidative stress, reflected by HEt fluorescence, was 32 ± 6% higher in LR-RF vs. DRP-RF (p < 0.05). Post-mortem whole-brain visualization of DiI painted vessels revealed multiple microthromboses in both hemispheres that were 29 ± 3% less in DRP-RF vs. LR-RF group (p < 0.05).

Conclusions: Resuscitation after TBI/HS using DRP-RF effectively restores mCBF, reduces hypoxia, microthrombosis formation and mitochondrial oxidative stress compared to conventional volume expansion with LR-RF. Supported by DOD DM160142.

Abstract WP171: Hemodynamic Compromise Identified by Oxygen Extraction Fraction Response (OEFR) to Acetazolamide in Stroke Patients With Large Vessel Occlusion

Hemodynamic compromise identified by cerebrovascular reserve (CVR) and oxygen extraction fraction (OEF) in stroke patients with large artery occlusion is an independent predictor of stroke risk ranging from 27 to 57%. However, comparison of both methods indicates that the sensitivity of CVR is substantially greater than OEF in detecting hemodynamic compromise which may be because CVR includes a vasodilator challenge with acetazolamide as opposed to OEF made in the resting state. We hypothesized that the response of OEF (OEFR) to an acetazolamide challenge would better correlate with CVR than OEF. We examined the correlation between CVR and OEFR to acetazolamide in stroke patients with large artery occlusion.

Methods: Stroke patients with large artery occlusion (internal carotid or middle cerebral artery) were studied by positron emission tomography (PET) using H2 15O2 (water) for cerebral blood flow (CBF) and 15O2 (gas) for cerebral metabolic rate for oxygen before and after acetazolamide. CVR was calculated as: CVR (%) = [(CBFa- CBFb)/CBFb] X 100; where: CBFb = CBF before acetazolamide, CBFa = CBF after acetazolamide. OEF response (OEFR) was similarly calculated as: OEFR (%) = [(OEFa-OEFb)/OEFb]X100; for the entire middle cerebral artery territory of each hemisphere.

Results: There was a highly significant (P=0.0001) negative linear correlation between CVR and OEFR indicating increasing ischemic stress (Figure). Hemispheres from three patients showed a positive OEFR.

Discussion: A positive OEFR in response to a cerebrovascular challenge definitively indicates hemodynamic compromise and eliminates the problem of deciding on the absolute threshold for OEF to signify hemodynamic compromise. A negative OEFR reflects sufficient cerebrovascular reserve relative to oxygen demand.

Induced Dynamic Intracranial Pressure and Cerebrovascular Reactivity Assessment of Cerebrovascular Autoregulation After Traumatic Brain Injury with High Intracranial Pressure in Rats

OBJECTIVE

In previous work we showed that high intracranial pressure (ICP) in the rat brain induces a transition from capillary (CAP) to pathological microvascular shunt (MVS) flow, resulting in brain hypoxia, edema, and blood-brain barrier (BBB) damage. This transition was correlated with a loss of cerebral blood flow (CBF) autoregulation undetected by static autoregulatory curves but identified by induced dynamic ICP (iPRx) and cerebrovascular (iCVRx) reactivity. We hypothesized that loss of CBF autoregulation as correlated with MVS flow would be identified by iPRx and iCVRx in traumatic brain injury (TBI) with elevated ICP.

METHODS

TBI was induced by lateral fluid percussion (LFP) using a gas-driven device in rats. Using in vivo two-photon laser scanning microscopy, cortical microcirculation, tissue oxygenation (NADH autofluoresence), and BBB permeability (fluorescein dye extravasation) were measured before and for 4 h after TBI. Laser Doppler cortical flux, rectal and brain temperature, ICP and mean arterial pressure (MAP), blood gases, and electrolytes were monitored. Every 30 min, a transient 10 mmHg rise in MAP was induced by i.v. bolus of dopamine. iPRx = ΔICP/ΔMAP and iCVRx = ΔCBF/ΔMAP.

RESULTS

We demonstrated that iPRx and iCVRx correctly identified more severe loss of CBF autoregulation correlated with a transition of blood flow to MVS after TBI with high ICP compared to TBI without an increase in ICP.

CONCLUSIONS

In TBI with high ICP, high-velocity MVS flow is responsible for the loss of CBF autoregulation identified by iPRx and iCVRx.

Increases in Microvascular Perfusion and Tissue Oxygenation via Vasodilatation After Anodal Transcranial Direct Current Stimulation in the Healthy and Traumatized Mouse Brain

Traumatic brain injury (TBI), causing neurological deficit in 70% of survivors, still lacks a clinically proven effective therapy. Transcranial direct current stimulation (tDCS) has emerged as a promising electroceutical therapeutic intervention possibly suitable for TBI; however, due to limited animal studies the mechanisms and optimal parameters are unknown. Using a mouse model of TBI we evaluated the acute effects of the anodal tDCS on cerebral blood flow (CBF) and tissue oxygenation, and assessed its efficacy in long-term neurologic recovery. TBI was induced by controlled cortical impact leading to cortical and hippocampal lesions with reduced CBF and developed hypoxia in peri-contusion area. Sham animals were subjected to craniotomy only. Repetitive anodal tDCS (0.1 mA/15 min) or sham stimulation was done over 4 weeks for four consecutive days with 3-day intervals, beginning 1 or 3 weeks after TBI. Laser speckle contrast imaging (LSCI) revealed that anodal tDCS causes an increase in regional cortical CBF in both traumatized and Sham animals. On microvascular level, using in-vivo two-photon microscopy (2PLSM), we have shown that anodal tDCS induces arteriolar dilatation leading to an increase in capillary flow velocity and tissue oxygenation in both traumatized and Sham animals. Repetitive anodal tDCS significantly improved motor and cognitive neurologic outcome. The group with stimulation starting 3 weeks after TBI showed better recovery compared with stimulation starting 1 week after TBI, suggesting that the late post-traumatic period is more optimal for anodal tDCS.

Resuscitation Fluid with Drag Reducing Polymer Enhances Cerebral Microcirculation and Tissue Oxygenation After Traumatic Brain Injury Complicated by Hemorrhagic Shock

Traumatic brain injury (TBI) is frequently accompanied by hemorrhagic shock (HS) which significantly worsens morbidity and mortality. Existing resuscitation fluids (RF) for volume expansion inadequately mitigate impaired microvascular cerebral blood flow (mvCBF) and hypoxia after TBI/HS. We hypothesized that nanomolar quantities of drag reducing polymers in resuscitation fluid (DRP-RF), would improve mvCBF by rheological modulation of hemodynamics.

METHODS

TBI was induced in rats by fluid percussion (1.5 atm, 50 ms) followed by controlled hemorrhage to a mean arterial pressure (MAP) = 40 mmHg. DRP-RF or lactated Ringer (LR-RF) was infused to MAP of 60 mmHg for 1 h (pre-hospital), followed by blood re-infusion to a MAP = 70 mmHg (hospital). Temperature, MAP, blood gases and electrolytes were monitored. In vivo 2-photon laser scanning microscopy was used to monitor microvascular blood flow, hypoxia (NADH) and necrosis (i.v. propidium iodide) for 5 h after TBI/HS followed by MRI for CBF and lesion volume.

RESULTS

TBI/HS compromised brain microvascular flow leading to capillary microthrombosis, tissue hypoxia and neuronal necrosis. DRP-RF compared to LR-RF reduced microthrombosis, restored collapsed capillary flow and improved mvCBF (82 ± 9.7% vs. 62 ± 9.7%, respectively, p < 0.05, n = 10). DRP-RF vs LR-RF decreased tissue hypoxia (77 ± 8.2% vs. 60 ± 10.5%, p < 0.05), and neuronal necrosis (21 ± 7.2% vs. 36 ± 7.3%, respectively, p < 0.05). MRI showed reduced lesion volumes with DRP-RF.

CONCLUSIONS

DRP-RF effectively restores mvCBF, reduces hypoxia and protects neurons compared to conventional volume expansion with LR-RF after TBI/HS.

Improvement of Impaired Cerebral Microcirculation Using Rheological Modulation by Drag-Reducing Polymers

Nanomolar intravascular concentrations of drag-reducing polymers (DRP) have been shown to improve hemodynamics and survival in animal models of ischemic myocardium and limb, but the effects of DRP on the cerebral microcirculation have not yet been studied. We recently demonstrated that DRP enhance microvascular flow in normal rat brain and hypothesized that it would restore impaired microvascular perfusion and improve outcomes after focal ischemia and traumatic brain injury (TBI). We studied the effects of DRP (high molecular weight polyethylene oxide, 4000 kDa, i.v. at 2 μg/mL of blood) on microcirculation of the rat brain: (1) after permanent middle cerebral artery occlusion (pMCAO); and (2) after TBI induced by fluid percussion. Using in vivo two-photon laser scanning microscopy (2PLSM) over the parietal cortex of anesthetized rats we showed that both pMCAO and TBI resulted in progressive decrease in microvascular circulation, leading to tissue hypoxia (NADH increase) and increased blood brain barrier (BBB) degradation. DRP, injected post insult, increased blood volume flow in arterioles and red blood cell (RBC) flow velocity in capillaries mitigating capillary stasis, tissue hypoxia and BBB degradation, which improved neuronal survival (Fluoro-Jade B, 24 h) and neurologic outcome (Rotarod, 1 week). Improved microvascular perfusion by DRP may be effective in the treatment of ischemic stroke and TBI.

Effect of Cerebrospinal Fluid Drainage on Brain Tissue Oxygenation in Traumatic Brain Injury

The effectiveness of cerebrospinal fluid (CSF) drainage in lowering high intracranial pressure (ICP) is well established in severe traumatic brain injury (TBI). Recently, however, the use of external ventricular drains (EVDs) and ICP monitors in TBI has come under question. The aim of this retrospective study was to investigate the effect of CSF drainage on brain tissue oxygenation (PbtO₂). Using a multi-modality monitoring system, we continuously monitored PbtO₂ and parenchymal ICP during CSF drainage events via a ventriculostomy in 40 patients with severe TBI. Measurements were time-locked continuous recordings on a Component Neuromonitoring System in a neuroscience intensive care unit. We further selected for therapeutic CSF drainage events initiated at ICP values above 25 mm Hg and analyzed the 4-min periods before and after drainage for the physiologic variables ICP, cerebral perfusion pressure (CPP), and PbtO₂. We retrospectively identified 204 CSF drainage events for ICP EVD-opening values greater than 25 mm Hg in 23 patients. During the 4 min of opened EVD, ICP decreased by 5.7 ± 0.6 mm Hg, CPP increased by 4.1 ± 1.2 mm Hg, and PbtO₂ increased by 1.15 ± 0.26 mm Hg. ICP, CPP, and PbtO₂ all improved with CSF drainage at ICP EVD-opening values above 25 mm Hg. Although the average PbtO₂ changes were small, a clinically significant change in PbtO₂ of 5 mm Hg or greater occurred in 12% of CSF drainage events, which was correlated with larger decreases in ICP, displaying a complex relationship between ICP and PbtO₂ that warrants further studies.

Rheological effects of drag-reducing polymers improve cerebral blood flow and oxygenation after traumatic brain injury in rats

Cerebral ischemia has been clearly demonstrated after traumatic brain injury (TBI); however, neuroprotective therapies have not focused on improvement of the cerebral microcirculation. Blood soluble drag-reducing polymers (DRP), prepared from high molecular weight polyethylene oxide, target impaired microvascular perfusion by altering the rheological properties of blood and, until our recent reports, has not been applied to the brain. We hypothesized that DRP improve cerebral microcirculation and oxygenation after TBI. DRP were studied in healthy and traumatized rat brains and compared to saline controls. Using in-vivo two-photon laser scanning microscopy over the parietal cortex, we showed that after TBI, nanomolar concentrations of intravascular DRP significantly enhanced microvascular perfusion and tissue oxygenation in peri-contusional areas, preserved blood-brain barrier integrity and protected neurons. The mechanisms of DRP effects were attributable to reduction of the near-vessel wall cell-free layer which increased near-wall blood flow velocity, microcirculatory volume flow, and number of erythrocytes entering capillaries, thereby reducing capillary stasis and tissue hypoxia as reflected by a reduction in NADH. Our results indicate that early reduction in CBF after TBI is mainly due to ischemia; however, metabolic depression of contused tissue could be also involved.

Abstract WMP48: Delayed Intravenous Administration of Drag Reducing Polymers Improves Brain Microcirculation and Neurologic Outcome After Permanent Middle Cerebral Artery Occlusion in Rats

Introduction: Tissue plasminogen activator is used in only 5% of stroke patients because therapeutic window is short (∼3 hr) due to risk of hemorrhage. Rheological modulation of blood flow by nanomolar concentrations of drag-reducing polymers (DRP) improved hemodynamics and survival in animal models of the ischemic myocardium and limb. We previously showed that DRP applied early at 30 min after permanent middle cerebral artery occlusion (pMCAO) restored microvascular perfusion and improved neurologic outcome. We hypothesized that DRP applied after 3 hr delay would be effective in improving recovery.

Methods: DRP or saline (control) were i.v. injected 3 hours after pMCAO in rats. Evaluation of the acute DRP effects (5 hours after pMCAO) on microvascular perfusion, hypoxia (NADH) and blood brain barrier (BBB) was done by in-vivo 2-photon laser scanning microscopy (2PLSM) and followed by brain perfusion for Fluoro-Jade staining for neurodegeneration. Cerebral infarction and perfusion were evaluated by MRI at 24 hours, 1 and 3 weeks after pMCAO. Motor function was evaluated by Rotarod test at 1, 2 and 3 weeks after pMCAO.

Results: DRP compared to saline, applied after 3 hours following pMCAO, improved impaired microvascular circulation in the penumbra of the parietal cortex (Δ=33 %), reducing hypoxia (Δ=27 %) and BBB damage (Δ=42 %) thereby protecting neurons from neurodegeneration (Fluoro-Jade, Δ=36 %) (n=4, p<0.05). After prolonged recovery, DRP solution compared to saline reduced infarct expansion (Δ=23 %) and increased cerebral blood flow (Δ=31 %) in the penumbra at 24 hours, 1 and 3 weeks after pMCAO as measured by MRI (n=6, p<0.05). Rotarod tests showed that DRP treated rats performed better than saline treated (Δ=35 %) at 1, 2 and 3 weeks after the pMCAO (n=6, p<0.05).

Conclusions: Rheological enhancement of cerebral microcirculation by DRP improved neurologic outcome after permanent MCAO without reperfusion even with delayed application after stroke onset. Potential DRP mechanisms involve improved collateral flow and anti-inflammatory effects of the increased shear stress with enhanced microcirculatory flow. DRP may be an effective therapy for ischemic stroke even without reperfusion and after delayed administration following the stroke onset.

Abstract WP276: Drag Reducing Polymers Based Resuscitation Fluid Improves Cerebral Microcirculation After Mild Traumatic Brain Injury and Hemorrhagic Shock

Introduction: Hemorrhagic shock (HS), causing arterial hypotension, often occurs after traumatic brain injury (TBI). Current resuscitation fluids do not ameliorate the impaired cerebral microvascular perfusion leading to hypoxia, neuronal death, increased mortality and poor neurological outcome. Nanomolar concentrations of intravascular blood soluble drag reducing polymers (DRP) were shown to increase tissue perfusion and oxygenation and decrease peripheral vascular resistance by rheological modulation of hemodynamics. We hypothesized that the resuscitation fluid with DRP would improve cerebral microcirculation, oxygenation and neuronal recovery after TBI combined with HS (TBI+HS).

Methods: Mild TBI was induced in rats by fluid percussion pulse (1.5 ATA, 50 ms duration) followed by induced by phlebotomy arterial hypotension (40 mmHg). Resuscitation fluid (lactated Ringers, LR) with DRP (DRP/LR) or without (LR) was infused to restore mean arterial pressure (MAP) to 60 mmHg for one hour (pre-hospital care), followed by re-infusion of blood to a MAP of 100 mmHg (hospital care). Using in vivo 2-photon laser scanning microscopy over the parietal cortex we monitored changes in microvascular blood flow, tissue oxygenation (NADH) and neuronal necrosis (i.v. propidium Iodide) for 5 hr after TBI+HS. Doppler cortical flow, rectal and cranial temperatures, arterial pressure, blood gases and electrolytes were monitored.

Results: TBI+HS compromised brain microvascular flow leading to tissue hypoxia followed by neuronal necrosis. Resuscitation with DRP/LR compared to LR better improved cerebral microvascular perfusion (82 ± 9.7% vs. 62 ± 9.7%, respectively from pre-TBI baseline, p<0.05, n=7), attenuated capillary microtrombi formation and re-recruited collapsed during HS capillaries. Improved microvascular perfusion increased cortical oxygenation reducing hypoxia (77 ± 8.2% vs. 60 ± 10.5%, by DRP-LR vs. LR, respectively from baseline, p<0.05) and decreased neuronal necrosis (21 ± 7.2% vs. 36 ± 7.3%, respectively as a percentage of total neurons, p<0.05).

Conclusions: DRP/LR resuscitation fluid is superior in the restoration of the cerebral microcirculation and neuroprotection following TBI + HS compared to volume expansion with LR.

Drag-Reducing Polymer Enhances Microvascular Perfusion in the Traumatized Brain with Intracranial Hypertension

Current treatments for traumatic brain injury (TBI) have not focused on improving microvascular perfusion. Drag-reducing polymers (DRP), linear, long-chain, blood-soluble, nontoxic macromolecules, may offer a new approach to improving cerebral perfusion by primary alteration of the fluid dynamic properties of blood. Nanomolar concentrations of DRP have been shown to improve hemodynamics in animal models of ischemic myocardium and ischemic limb, but have not yet been studied in the brain. We recently demonstrated that DRP improved microvascular perfusion and tissue oxygenation in a normal rat brain. We hypothesized that DRP could restore microvascular perfusion in hypertensive brain after TBI. Using in vivo two-photon laser scanning microscopy we examined the effect of DRP on microvascular blood flow and tissue oxygenation in hypertensive rat brains with and without TBI. DRP enhanced and restored capillary flow, decreased microvascular shunt flow, and, as a result, reduced tissue hypoxia in both nontraumatized and traumatized rat brains at high intracranial pressure. Our study suggests that DRP could constitute an effective treatment for improving microvascular flow in brain ischemia caused by high intracranial pressure after TBI.

Matrix-derived inflammatory mediator N-acetyl proline-glycine-proline is neurotoxic and upregulated in brain after ischemic stroke

Background

N-acetyl proline-glycine-proline (ac-PGP) is a matrix-derived chemokine produced through the proteolytic destruction of collagen by matrix metalloproteinases (MMPs). While upregulation and activation of MMPs and concomitant degradation of the extracellular matrix are known to be associated with neurological injury in ischemic stroke, the production of ac-PGP in stroke brain and its effects on neurons have not been investigated.

Findings

We examined the effects of ac-PGP on primary cortical neurons and found that it binds neuronal CXCR2 receptors, activates extracellular signal-regulated kinase 1/2 (ERK1/2), and induces apoptosis associated with caspase-3 cleavage in a dose-dependent manner. After transient ischemic stroke in rats, ac-PGP was significantly upregulated in infarcted brain tissue.

Conclusions

The production of ac-PGP in brain in ischemia/reperfusion injury and its propensity to induce apoptosis in neurons may link MMP-mediated destruction of the extracellular matrix and opening of the blood-brain barrier to progressive neurodegeneration associated with the initiation and propagation of inflammation. Ac-PGP may be a novel neurotoxic inflammatory mediator involved in sustained inflammation and neurodegeneration in stroke and other neurological disorders associated with activation of MMPs.

Increases in microvascular perfusion and tissue oxygenation via pulsed electromagnetic fields in the healthy rat brain

OBJECT

High-frequency pulsed electromagnetic field stimulation is an emerging noninvasive therapy being used clinically to facilitate bone and cutaneous wound healing. Although the mechanisms of action of pulsed electromagnetic fields (PEMF) are unknown, some studies suggest that its effects are mediated by increased nitric oxide (NO), a well-known vasodilator. The authors hypothesized that in the brain, PEMF increase NO, which induces vasodilation, enhances microvascular perfusion and tissue oxygenation, and may be a useful adjunct therapy in stroke and traumatic brain injury. To test this hypothesis, they studied the effect of PEMF on a healthy rat brain with and without NO synthase (NOS) inhibition.

METHODS

In vivo two-photon laser scanning microscopy (2PLSM) was used on the parietal cortex of rat brains to measure microvascular tone and red blood cell (RBC) flow velocity in microvessels with diameters ranging from 3 to 50 μm, which includes capillaries, arterioles, and venules. Tissue oxygenation (reduced nicotinamide adenine dinucleotide [NADH] fluorescence) was also measured before and for 3 hours after PEMF treatment using the FDA-cleared SofPulse device (Ivivi Health Sciences, LLC). To test NO involvement, the NOS inhibitor N(G)-nitro-l-arginine methyl ester (L-NAME) was intravenously injected (10 mg/kg). In a time control group, PEMF were not used. Doppler flux (0.8-mm probe diameter), brain and rectal temperatures, arterial blood pressure, blood gases, hematocrit, and electrolytes were monitored.

RESULTS

Pulsed electromagnetic field stimulation significantly dilated cerebral arterioles from a baseline average diameter of 26.4 ± 0.84 μm to 29.1 ± 0.91 μm (11 rats, p < 0.01). Increased blood volume flow through dilated arterioles enhanced capillary flow with an average increase in RBC flow velocity by 5.5% ± 1.3% (p < 0.01). Enhanced microvascular flow increased tissue oxygenation as reflected by a decrease in NADH autofluorescence to 94.7% ± 1.6% of baseline (p < 0.05). Nitric oxide synthase inhibition by L-NAME prevented PEMF-induced changes in arteriolar diameter, microvascular perfusion, and tissue oxygenation (7 rats). No changes in measured parameters were observed throughout the study in the untreated time controls (5 rats).

CONCLUSIONS

This is the first demonstration of the acute effects of PEMF on cerebral cortical microvascular perfusion and metabolism. Thirty minutes of PEMF treatment induced cerebral arteriolar dilation leading to an increase in microvascular blood flow and tissue oxygenation that persisted for at least 3 hours. The effects of PEMF were mediated by NO, as we have shown in NOS inhibition experiments. These results suggest that PEMF may be an effective treatment for patients after traumatic or ischemic brain injury. Studies on the effect of PEMF on the injured brain are in progress.

Abstract W P197: Pulsed Electromagnetic Field Attenuates High Intracranial Pressure Induced Microvascular Shunting in Rats

Introduction: We previously reported that high intracranial pressure (ICP) in rats caused a transition from capillary (CAP) to non-nutritive microvascular shunt (MVS) flow associated with tissue hypoxia and increased blood brain barrier (BBB) permeability. We also showed that pulsed electromagnetic field (PEMF) increases blood flow velocity and tissue oxygenation in the normal rat brain. We hypothesized that PEMF attenuates the detrimental effects of non-nutritive MVS flow induced by high ICP.

Methods: Using in vivo 2-photon laser scanning microscopy (2PLSM) over the rat parietal cortex, we studied the effects of PEMF on microvascular blood flow velocity, tissue oxygenation (NADH) and BBB permeability (dye extravasation) before and during 4 hours of elevated ICP. Doppler cortical flow, rectal and cranial temperatures, intracranial and arterial pressures, blood gases and electrolytes were monitored.

After baseline imaging at normal ICP (10 mmHg), rats were subjected to intracranial hypertension (30 mmHg) by raising an artificial cerebrospinal fluid reservoir connected to a catheter in the cisterna magna. After control recording at high ICP of 30 mmHg, PEMF was applied for 30 min and imaging was continuously performed for up to 4 hours after the treatment. In control animals PEMF was not applied.

Results: PEMF treatment reduced tissue hypoxia as reflected by a decrease in NADH by 14.6±3.7% (n=7 rats per group, mean ± SEM, p<0.05). BBB permeability was also reduced as reflected by reduction of dye extravasation by 17.2±5.4% (p<0.05). This effect was consistent with dilation of arterioles (+4.5±3.2%) and an increase in capillary blood flow velocity (+4.7±3.2%). PEMF did not completely mitigated the gradual increase in MVS flow at high ICP but, as reflected by MVS/capillary ratio, the transition to non-nutritive flow over 4 hours was less steep in the PEMF treated rats compared to the untreated (2.3±1.1 and 3.8±2.1% change per hour, respectively, p<0.05).

Conclusions: PEMF reduces tissue hypoxia and BBB degradation by modulating cerebral blood flow topography at intracranial hypertension in a rat brain. PEMF could be an effective treatment for intracranial hypertension after severe cerebral insults.

Abstract W P93: Drag-Reducing Polymer Improves Microcirculation and Outcome after Permanent Middle Cerebral Artery Occlusion in Rats

Introduction: Current treatments for ischemia after stroke have not focused directly on the physiological effects of restoring or improving cerebral microvascular perfusion. Nanomolar concentrations of drag-reducing polymers (DRP) have been shown to improve hemodynamics and survival in animal models of the ischemic myocardium and peripheral circulation. We recently demonstrated that DRP improved microvascular perfusion in normal and traumatized rat brain. We hypothesized that DRP restores microvascular perfusion after focal ischemia and improves neurologic recovery in the rat.

Methods: The suture permanent middle cerebral artery occlusion (MCAO) model in the rat was used. DRP was injected i.v. 90 minutes after MCAO. Controls were injected with an equal volume of saline. Using in vivo 2-photon laser scanning microscopy over the parietal cortex, we studied the acute effects of DRP on microvascular blood flow velocity, tissue oxygenation (NADH) and blood brain barrier (BBB) permeability for 5 hr after MCAO. Doppler cortical flow, rectal and cranial temperatures, arterial pressure, blood gases and electrolytes were monitored. Cerebral infarction was evaluated by triphenyltetrazolium chloride (TTC) staining 24 hr after MCAO and motor function by Rotarod at one week.

Results: MCAO resulted in a progressive decrease in microvascular flow in the penumbra of the parietal cortex with hypoxia and increased BBB permeability during 5 hr monitored. DRP partially restored microvascular flow compared to control (21±6.7%, Mean ± SEM, p<0.05, n=4) and reduced the progression of ischemia and BBB permeability by 14±4.6 and 18±6.5%, respectively (p<0.05). Infarction volume was reduced by 24±8.1% in DRP treated rats (n=2, p<0.05). The Rotarod tests showed that one week after MCAO, DRP treated rats performed better than saline treated rats with times of 75.6±16.0% and 47.3±16.0%, respectively, as percent of normal rats.

Conclusions: DRP restores cerebral microvascular flow after MCAO reducing tissue hypoxia and BBB damage. The improvement in flow is reflected by a reduction in infarct size 24 hours after MCAO and by improved motor neurological recovery at one week after MCAO. DRP can be a new effective therapy for ischemic stroke targeting microvascular perfusion.

Transient middle cerebral artery occlusion with complete reperfusion in spontaneously hypertensive rats

Middle cerebral artery occlusion (MCAO) by the intraluminal suture method is widely used to model ischemic stroke in rats. Current methods include transection or ligation of the external carotid or common carotid artery and thus result in partial restoration of perfusion after transient MCAO. Since incomplete reperfusion may influence recovery and thus confound studies of the impact of neuroprotective compounds and therapies on outcomes after stroke, we have devised a novel method to induce transient MCAO with complete reperfusion. Advantages of the method include: MCAO is achieved through insertion of an intraluminal suture into the internal carotid artery through the common carotid artery.At the end of the occlusion period, the suture is withdrawn and the incision in the common carotid artery is closed with cyanoacrylate tissue adhesive and complete reperfusion is established.No residual subcutaneous sutures remain during recovery.Vasculature is restored to the preoperative state.

Increased cerebral oxygen metabolism and ischemic stress in subjects with metabolic syndrome-associated risk factors: preliminary observations

Hypertension, diabetes, obesity, and dyslipidemia are risk factors that characterize metabolic syndrome (MetS), which increases the risk for stroke by 40%. In a preliminary study, our aim was to evaluate cerebrovascular reactivity and oxygen metabolism in subjects free of vascular disease but with one or more of these risk factors. Volunteers (n=15) 59±15 (mean±SD)years of age clear of cerebrovascular disease by magnetic resonance angiography but with one or more risk factors were studied by quantitative positron emission tomography for measure ment of cerebral blood flow, oxygen consumption, oxygen extraction fraction (OEF), and acetazolamide cerebrovascular reactivity. Eight of ten subjects with MetS risk factors had OEF >50%. None of the five without risk factors had OEF >50%. The presence of MetS risk factors was highly correlated with OEF >50% by Fisher's exact test (p<0.007). The increase in OEF was significantly (P<0.001) correlated with cerebral metabolic rate for oxygen. Increased OEF was not associated with compromised acetazolamide cerebrovascular reactivity. Subjects with one or more MetS risk factors are characterized by increased cerebral oxygen consumption and ischemic stress, which may be related to increased risk of cerebrovascular disease and stroke.

Quantitative temporal profiles of penumbra and infarction during permanent middle cerebral artery occlusion in rats

The basic premise of neuroprotection in acute stroke is the presence of salvageable tissue, but the spatiotemporal volume profiles of the penumbra and infarction remain poorly defined in preclinical animal models of acute stroke used to evaluate therapies for clinical application. Our aim was to define these profiles using magnetic resonance imaging (MRI) quantitative cerebral blood flow (CBF) and apparent diffusion coefficient (ADC) for dual-parameter voxel analysis in the rat suture permanent middle cerebral artery occlusion (pMCAO) model. Eleven male Sprague Dawley rats were subjected to pMCAO with MRI measurements of quantitative CBF and ADC at baseline, over the first 4 h (n=9) and at 7, 14, and 21 days (n=4). Voxel analysis of CBF and ADC was used to characterize brain tissue ischemic transitions. Penumbra, core, and hyperemic infarction volumes were significantly elevated (P<0.05) and unchanged over the first 4 h of pMCAO while the total lesion volume progressively rose. At 7, 14, and 21 days, tissue compartment transitions reflected infarction, tissue cavitation, and selective ischemic neuronal necrosis. Anatomical distribution of penumbra and core revealed marked heterogeneity with penumbra scattered within core and penumbra persisting even after 4 h of permanent MCAO.

Basic physiology of hyperbaric oxygen in brain

Oxygen is the proverbial 'double-edged sword' in that it is a necessity for life in moderation and toxic and detrimental to life in excess. This too is the dilemma in hyperbaric oxygen (HBO) treatment in cerebral ischemic-anoxic insults such as stroke, head injury, near drowning, asphyxia, cardiac arrest, etc., i.e. the brain at risk, where regions of ischemia are beside regions of marked hyperemia. The natural heterogeneity of normal brain tissue oxygenation compounds the problem with different microvascular brain regions living at various levels of oxygenation from 0 to arterial PO(2) as an added complication. The application of HBO, whether normobaric or hyperbaric, will result in brain tissue oxygenation ranging from normoxic to highly hyperoxic with the latter possibly exacerbating the injury sustained. On this basis, the application of multiple therapeutic interventions may be considered, for example, HBO in combination with free radical scavengers or inhibitors of free radical generating enzymes. Despite these difficulties in moderating oxygen delivery to treat cerebral ischemic-anoxic insults, overwhelming preclinical evidence indicates that HBO administered during or within 2 hours post-insult effectively attenuates the severity of brain damage sustained. The primary disconnection between pre-clinical and clinical efficacy of HBO then appears to be the time of application. Clinically, HBO therapy is applied at the earliest 6 hours post-insult but usually between 12 hours or longer post-insult. Pre-hospital application of HBO may be required for clear-cut demonstration of clinical efficacy.

Abstract TP262: Pulsed Electromagnetic Field (PEMF) Increases Microvascular Flow And Tissue Oxygenation In the Normal Rat Brain

Introduction: Pulsed Electromagnetic Field (PEMF) treatment has been shown to improve wound healing through increased nitric oxide levels. Thus, we hypothesized that PEMF improves microvascular (MV) flow and tissue oxygenation in the brain.

Methods: Using in-vivo 2-photon laser scanning microscopy (2PLSM) over the parietal cortex of the normal rat brain, we measured MV red blood cell (RBC) flow velocity, diameters (range 3 to 15 μm which includes arterioles and venules), and tissue oxygenation (NADH fluorescence) before, during 30 minutes PEMF treatment and for three hours thereafter (three sessions with 30 min intervals). Doppler flux (0.9 mm probe diameter), arterial blood pressure, intracranial pressure, and arterial blood gases were concurrently monitored.

Results: Microvascular flow velocities and diameters increased after PEMF treatment. Average MV diameters (300 MV measured in each of six rats) increased from 9.1±1.8 μm before to 9.4±2.1 μm during PEMF treatment (n=6, p<0.05). Blood flow velocities also increased by 4.4±1.3 and 2.3±1.1 % during and after PEMF treatment respectively in comparison to baseline (p<0.05). PEMF treatment decreased NADH autofluorescence indicating better tissue oxygenation and increased blood supply (96.1±2.4 and 98.2±1.3 % during and after PEMF treatment, respectively, compared to the baseline, p<0.05). Laser Doppler flux averaged over a brain volume of 1 mm3 was unchanged before and during PEMF treatment.

Conclusions: Thirty minutes of PEMF treatment induced MV dilation, increased RBC velocity and tissue oxygenation that persisted for 3 hours. Within the 3-hour period, however, MV diameters and RBC velocities gradually returned to baseline. Whether the effects observed are nitric oxide induced remains to be determined.

Abstract 42: Cerebrovascular Reactivity (CVRx) and Intracranial Pressure Reactivity (PRx) Assessment of Impaired Cerebrovascular Autoregulation in Intracranial Hypertension

Introduction: We previously showed that the decrease in critical cerebral perfusion pressure (CPP) to 30 mmHg obtained by cerebral blood flow (CBF) autoregulation curve with increasing intracranial pressure (ICP), compared to 60 mmHg when CPP is reduced by decreasing arterial pressure, was due to pathological microvascular shunting at high ICP. We concluded that determination of the critical CPP by the CBF autoregulation curve is not applicable to brains at high ICP. We hypothesized that dynamic ICP (PRx) and cerebrovascular (CVRx) reactivity would better detect impaired autoregulation.

Methods: In vivo 2-photon laser scanning microscopy (2PLSM) over the rat parietal cortex was used to measure microvascular (MV) flow velocity, NADH fluorescence (hypoxia) and blood brain barrier (BBB) integrity (fluorescein dye extravasation). Doppler flow, temperatures, ICP, arterial pressure and blood gases were monitored. CPP was reduced stepwise from 70 to 50 and 30 mmHg by increasing ICP. At each CPP, a transient 10 mmHg rise in mean arterial pressure (MAP) was induced by i.v. dopamine bolus. PRx is a ratio of the ICP change in response to MAP increase (PRx=ΔICP/ΔMAP). CVRx is a ratio of the change in CBF with MAP change (CVRx=ΔCBF/ΔMAP).

Results: CBF autoregulation curves indicated a critical CPP of 30 mmHg at high ICP. However, our 2PLSM data show that reduction of CPP to 50 mmHg by increasing ICP caused a transition from capillary to microvascular shunt flow associated with brain edema, hypoxia and BBB opening. At a normal CPP (70 mmHg) blood pressure challenge caused no change in ICP (PRx=-0.03±0.07, n=5), i.e., intact pressure reactivity. When CPP was decreased to 50 and 30 mmHg by ICP elevation, PRx increased to 0.09±0.16 and 0.26±0.14, respectively (n=7, p<0.05). Similarly at a normal CPP MAP challenge showed a CVRx of -0.02±0.05, reflecting intact cerebral autoregulation. When CPP was decreased to 50 and 30 mmHg by ICP, CVRx increased to 0.11±0.13 and 0.26±0.14, respectively, reflecting impaired autoregulation (p<0.05).

Conclusions: As determined by PRx and CVRx at high ICP the critical CPP is 50 mmHg where MV shunting, brain edema, hypoxia and BBB leakage begin to occur which is higher than the 30 mmHg determined by static autoregulation.

Effect of cerebral perfusion pressure on cerebral cortical microvascular shunting at high intracranial pressure in rats

BACKGROUND AND PURPOSE

Recently, we showed that decreasing cerebral perfusion pressure (CPP) from 70 mm Hg to 50 mm Hg and 30 mm Hg by increasing intracranial pressure (ICP) with a fluid reservoir induces a transition from capillary (CAP) to microvascular shunt (MVS) flow in the uninjured rat brain. This transition was associated with tissue hypoxia, increased blood-brain barrier (BBB) permeability, and brain edema. Our aim was to determine whether an increase in CPP would attenuate the transition to MVS flow at high ICP.

METHODS

Rats were subjected to progressive, step-wise increases in ICP of up to 60 mm Hg by an artificial cerebrospinal fluid reservoir connected to the cisterna magna. CPP was maintained at 50, 60, 70, or 80 mm Hg by intravenous dopamine infusion. Microvascular red blood cell flow velocity, BBB integrity (fluorescein dye extravasation), and tissue oxygenation (nicotinamide adenine dinucleotide) were measured by in vivo 2-photon laser scanning microscopy. Doppler cortical flux, rectal and cranial temperatures, ICP, arterial blood pressure, and gases were monitored.

RESULTS

The CAP/MVS ratio increased (P<0.05) at higher ICP as CPP was increased from 50 to 80 mm Hg. At an ICP of 30 mm Hg and CPP of 50 mm Hg, the CAP/MVS ratio was 0.6±0.1. At CPP of 60, 70, and 80 mm Hg, the ratio increased to 0.9±0.1, 1.4±0.1, and 1.9±0.1, respectively (mean±SEM; P<0.05). BBB opening and increase of reduced form of nicotinamide adenine dinucleotide occurred at higher ICP as CPP was increased.

CONCLUSIONS

Increasing CPP at high ICP attenuates the transition from CAP to MVS flow, development of tissue hypoxia, and increased BBB permeability.

Outcome prediction within twelve hours after severe traumatic brain injury by quantitative cerebral blood flow

We measured quantitative cortical mantle cerebral blood flow (CBF) by stable xenon computed tomography (CT) within the first 12 h after severe traumatic brain injury (TBI) to determine whether neurologic outcome can be predicted by CBF stratification early after injury. Stable xenon CT was used for quantitative measurement of CBF (mL/100 g/min) in 22 cortical mantle regions stratified as follows: low (0-8), intermediate (9-30), normal (31-70), and hyperemic (>70) in 120 patients suffering severe (Glasgow Coma Scale [GCS] score ≤8) TBI. For each of these CBF strata, percentages of total cortical mantle volume were calculated. Outcomes were assessed by Glasgow Outcome Scale (GOS) score at discharge (DC), and 1, 3, and 6 months after discharge. Quantitative cortical mantle CBF differentiated GOS 1 and GOS 2 (dead or vegetative state) from GOS 3-5 (severely disabled to good recovery; p<0.001). Receiver operating characteristic (ROC) curve analysis for percent total normal plus hyperemic flow volume (TNHV) predicting GOS 3-5 outcome at 6 months for CBF measured <6 and <12 h after injury showed ROC area under the curve (AUC) cut-scores of 0.92 and 0.77, respectively. In multivariate analysis, percent TNHV is an independent predictor of GOS 3-5, with an odds ratio of 1.460 per 10 percentage point increase, as is initial GCS score (OR=1.090). The binary version of the Marshall CT score was an independent predictor of 6-month outcome, whereas age was not. These results suggest that quantitative cerebral cortical CBF measured within the first 6 and 12 h after TBI predicts 6-month outcome, which may be useful in guiding patient care and identifying patients for randomized clinical trials. A larger multicenter randomized clinical trial is indicated.

CT Density Changes with Rapid Onset Acute, Severe, Focal Cerebral Ischemia in Monkeys

Computerized tomography (CT) is the most often used imaging modality in the evaluation of acute clinical stroke. However, the rapidity with which CT density changes occur after acute, severe, focal ischemia cannot be determined clinically. Even if the time of symptom onset is known, clinical stroke severity is highly variable. We studied the time course of CT density change after severe, rapid onset, acute, focal ischemia as documented by stable xenon CT cerebral blood flow (CBF) in monkeys. Eight monkeys (Macaca mulatta) were subjected to transorbital occlusion of the left posterior cerebral, anterior, middle, and internal carotid arteries to induce focal ischemia. CT density Hounsfield units (HU), CBF by stable xenon CT, arterial blood pressure, and blood gases were measured before occlusion, immediately after occlusion, at 30 min, and hourly for up to 6 h. Occlusion of the cerebral arteries decreased CBF to 8 ± 5 ml/100 g/ min within 15 min postocclusion. At 6 h, CBF was unchanged at 9 ± 4 ml/100 g/ min. CT density within the ischemic core fell from 42 to 38 HU immediately after occlusion (P < 0.05), rose transiently, then fell at 2 h (P < 0.01) and plateaued at 36 ± 5 HU for a total decrease of 4-5 HU between 4 and 6 h poststroke. Changes in CT density lag severe focal ischemia by 2 h. Thus, when CT hypodensity is seen in acute stroke, it is likely 2 h old. It also provides an explanation for the phenomenon of clinical CT mismatch with clinical deficits and normal CT.

Failure of cerebral hemodynamic selection in general or of specific positron emission tomography methodology?: Carotid Occlusion Surgery Study (COSS)

BACKGROUND AND PURPOSE

The Carotid Occlusion Surgery Study (COSS) was an improvement over the Extracranial-Intracranial Bypass Study, which did not utilize physiological selection. To assess possible reasons for early closure of the COSS trial, we reviewed COSS methods used to identify high-risk patients and compared results with separate quantitative data.

METHODS

Increased oxygen extraction fraction (OEF) by positron emission tomography is a gold standard for ischemia, but the specific thresholds and equivalency of the semiquantitative OEF ratio utilized in COSS and quantitative OEF are at issue.

RESULTS

The semiquantitative hemispheric OEF ratio used in COSS did not identify the same group of patients as did quantitative OEF using a threshold of 50%.

CONCLUSIONS

The failure of COSS is likely caused by a failure of the semiquantitative, hemispheric OEF ratio method rather than by the selection for bypass based on hemodynamic compromise.

High intracranial pressure effects on cerebral cortical microvascular flow in rats

To manage patients with high intracranial pressure (ICP), clinicians need to know the critical cerebral perfusion pressure (CPP) required to maintain cerebral blood flow (CBF). Historically, the critical CPP obtained by decreasing mean arterial pressure (MAP) to lower CPP was 60 mm Hg, which fell to 30 mm Hg when CPP was reduced by increasing ICP. We examined whether this decrease in critical CPP was due to a pathological shift from capillary (CAP) to high-velocity microvessel flow or thoroughfare channel (TFC) shunt flow. Cortical microvessel red blood cell velocity and NADH fluorescence were measured by in vivo two-photon laser scanning microscopy in rats at CPP of 70, 50, and 30 mm Hg by increasing ICP or decreasing MAP. Water content was measured by wet/dry weight, and cortical perfusion by laser Doppler flux. Reduction of CPP by raising ICP increased TFC shunt flow from 30.4±2.3% to 51.2±5.2% (mean±SEM, p<0.001), NADH increased by 20.3±6.8% and 58.1±8.2% (p<0.01), and brain water content from 72.9±0.47% to 77.8±2.42% (p<0.01). Decreasing CPP by MAP decreased TFC shunt flow with a smaller rise in NADH and no edema. Doppler flux decreased less with increasing ICP than decreasing MAP. The decrease seen in the critical CPP with increased ICP is likely due to a redistribution of microvascular flow from capillary to microvascular shunt flow or TFC shunt flow, resulting in a pathologically elevated CBF associated with tissue hypoxia and brain edema, characteristic of non-nutritive shunt flow.

PET OEF Reactivity for Hemodynamic Compromise in Occlusive Vascular Disease

BACKGROUND AND PURPOSE

Hemodynamic compromise in symptomatic patients with occlusive vascular disease (OVD) identified by cerebrovascular reserve (CVR) and oxygen extraction fraction (OEF) is an independent predictor of high stroke risk. However, up to 60% of patients compromised by CVR have normal OEF indicating a high rate of discordance. CVR is measured with an acetazolamide challenge, and OEF reactivity (OEFR) to acetazolamide, ie, a hemodynamic challenge, may reveal hemodynamic compromise and less discordance with measurements of CVR.

METHODS

Nine symptomatic patients with OVD were studied by positron emission tomography before and 15 minutes after 15 mg/kg intravenous acetazolamide in the middle cerebral artery territories of each hemisphere.

RESULTS

A close correlation between hemispheric CVR and OEFR was observed. Two hemispheres from two different patients showed an increase in OEF to acetazolamide challenge despite a normal baseline OEF. The two hemispheres showing an increase in OEF in response to acetazolamide were also associated with the lowest CVR and severest white matter hyperintensities.

CONCLUSIONS

These observations suggest that positive OEFR may distinguish hemispheres in hemodynamic compromise despite normal OEF and show less discordance with CVR. However, these preliminary observations require confirmation in a larger study.

Dynamics of cerebral venous and intracranial pressures

Traumatic brain injury and stroke are both characterized by an ischemic core surrounded by a penumbra of low to hyperemic flows. The underperfused ischemic core is the focus of edema development, but the source of the edema fluid is not known. We hypothesized that flow of edema fluid into the tissue is derived from cerebral venous circulation pressure, which always exceeds intracranial pressure (ICP). As a first step toward testing this hypothesis, the aim of the current study was to determine whether cerebral venous pressure in the normal brain is always equal to or higher than ICP. In studies on 2 pigs, cerebral cortical venous, intracranial (subarachnoid), sagittal sinus, and central venous pressures were monitored with manipulation of ICP by raising and lowering a reservoir above and below the external auditory meatus zero point. The results show that cerebral venous pressure is always higher than or equal to ICP at pressures of up to 60 mmHg. On the basis of these observations, we hypothesize that increased cerebral venous pressure initiated after traumatic brain injury and stroke drives edema fluid into the tissue, which thereby increases ICP and a further increase in cerebral venous pressure in a vicious cycle of brain edema.

Differentiating hemodynamic compromise by the OEF response to acetazolamide in occlusive vascular disease

Identification of increased stroke risk in a population of symptomatic patients with occlusive vascular disease (OVD) is presently accomplished by measurement of oxygen extraction fraction (OEF) or cerebrovascular reserve (CVR). However, many regions identified by compromised CVR are not identified by OEF. Our aim was to determine whether the response of OEF to acetazolamide, namely, oxygen extraction fraction response (OEFR) would identify those hemispheres in hemodynamic compromise with normal OEF. Nine patients symptomatic with transient ischemic attacks and strokes, and with occlusive vascular disease were studied. Anatomical MRI scans and T2-weighted images were used to identify and grade subcortical white matter infarcts. PET cerebral blood flow (CBF) and OEF were measured after acetazolamide. The relationship between CVR and oxygen extraction fraction response (OEFR) showed that positive OEFR occurred after acetazolamide despite normal baseline OEF values. The two hemispheres with positive OEFR were also associated with severe (> 3 cm) subcortical white matter infarcts. We found that the OEFR was highly correlated with CVR and identified hemispheres that were hemodynamically compromised despite normal baseline OEF.

Identifying regions of compromised hemodynamics in symptomatic carotid occlusion by cerebrovascular reactivity and oxygen extraction fraction

OBJECTIVES

Oxygen extraction fraction (OEF) and cerebrovascular reserve (CVR) are both proven predictors of stroke risk in symptomatic patients with carotid occlusion. Accordingly, hemispheric comparisons of CVR and OEF are significantly correlated. However, there was also substantial disagreement: hemispheres identified as compromised by CVR were normal by OEF. Our aim was to determine whether regional comparisons could resolve the CVR-OEF discordance. We also studied the relationship between white matter (WM) infarction and hemodynamic compromise.

METHODS

Quantitative CVR and OEF were measured in 12 symptomatic patients with internal carotid artery occlusion. CVR and OEF comparisons were made in the anterior watershed (AWS), middle cerebral artery (MCA) and WM territories using various thresholds for hemodynamic compromise. Associations with WM infarction were also recorded.

RESULTS

Comparison of CVR and OEF for the AWS and MCA showed high sensitivity (100%) with specificities of 83 and 40%, respectively. There was also agreement (k=Cohen's Kappa) for the AWS (k=0.83) and MCA (k=0.39) territories. CVR-OEF discordance was reduced with regional analysis. Hemodynamic compromise was more often found in patients with WM infarction.

DISCUSSION

Regional comparison of CVR and OEF reduced the discordance compared with hemispheric analysis, especially for the AWS territory. Despite the persistence of some regions with compromised CVR and normal OEF, CVR is able to identify all regions with elevated OEF making it a useful screening technology. Future studies are needed to understand whether those remaining regions with compromised CVR are also at increased stroke risk despite normal OEF.

Hyperbaric nitrogen and pentobarbital on synaptosomal membrane lipids and free fatty acids

Nitrogen at high pressures and anesthetics increase lipid monolayer surface pressure and in turn modulates monolayer associated lipolytic enzyme activity that could alter membrane lipids. We tested the hypothesis that nitrogen at pressures of 5 and 10 megapascals (MPa) and pentobarbital induce alterations in synaptosomal membrane phospholipid and free fatty acid (FFA). Rat cortical synaptosomes in Krebs-Henseleit buffer were placed in steel chambers and incubated for four hours at 37 degrees C: at 5 or 10 MPa of O2/balance N2; at one 0.1 MPa on room air, and with 10 mg pentobarbital. Free fatty acids (FFA) were quantified by thin-layer and gas chromatography, and neutral and acidic lipids by high-pressure thin layer chromatography and protein by Biorad colorimetric assay. Statistical analyses were by ANOVA and posthoc analysis by Neuman-Keuls and Kruskal-Wallis tests at p < 0.05. Sphyngomyelin, phosphatidylcholine, phosphatidylethanolamine, cerebroside and cholesterol were unchanged by 5 and 10 MPa nitrogen and pentobarbital. Free fatty acids (16:00, 18:00, 18:01, 20:00, 22:0, 22:01 and 24:01) at 10 MPa were reduced compared to 5 MPa (p < 0.05) but unaffected by pentobarbital. The decrease in synaptosomal membrane FFA at 10 MPa suggests attenuated hydrolysis of membrane phospholipids without detectable alterations in membrane phospholipid composition.

Hyperthermia and hypermetabolism in focal cerebral ischemia

The reliable and reproducible creation of an animal model of focal cerebral ischemia is not easily accomplished. Using a transortibal approach, we showed that occlusion of the posterior cerebral artery (PCA), middle cerebral artery (MCA), and the contralateral anterior cerebral artery (ACA) created a large cortical and subcortical stroke in the non-human primate (NHP). Subsequently, we created the same stroke endovascularly in the NHP. Using the endovascular stroke model in the NHP, we measured brain temperature with thermocouples and cerebral blood flow (CBF) by stable xenon CT in one NHP, and CMRO2 and CBF by positron emission tomography (PET) in another NHP. Two female non-human primates (M. mulatta) weighing 7.0 and 8.0 kg, respectively, were studied under fentanyl-diazepam anesthesia with continuous monitoring of arterial blood pressure, rectal temperature, and end-tidal CO2 with intermittent blood gas measurements. Using an endovascular approach, the PCA (P2), MCA (M1), and the ICA at the bifurcation and contralateral ACA produced a large hemispheric stroke. In the right ischemic hemisphere, temperatures increased by 2 degrees C-3 degrees C. PET measurement of CBF and CMRO2 showed that CMRO2 increased in the region of the ischemic stroke. We found that both hyperthermia and hypermetabolism occur in acute stroke.

Identification of hemodynamic compromise by cerebrovascular reserve and oxygen extraction fraction in occlusive vascular disease

Cerebrovascular reserve (CVR) and oxygen extraction fraction (OEF) are used to identify hemodynamic compromise in symptomatic patients with carotid occlusive vascular disease, but evidence suggests that they are not equivalent. The authors studied the relationship between CVR and OEF to evaluate their equivalence and stages of hemodynamic compromise. Symptomatic patients (N = 12) with carotid occlusion were studied by stable xenon-computed tomography CBF after intravenous acetazolamide administration for CVR, followed within 24 hours by positron emission tomography (PET) for OEF. Middle cerebral artery territories were analyzed by hemisphere and level. Hemispheric subcortical white matter infarctions were graded with magnetic resonance imaging. Both hemispheric and level analysis of CVR and OEF showed a significant (P = 0.001), negative linear relationship [CVR (%) = -1.5 (OEF) + 83.4, (r = -0.57, P = 0.001, n = 24]. However, 37.5% of the hemispheres showed compromised CVR but normal OEF and were associated (P = 0.019) with subcortical white matter infarction. CMRO2 was elevated in stage II hemodynamic compromise (CVR < 10%, OEF > 50%). CVR and OEF showed a significant negative linear relationship in stage II hemodynamic compromise but revealed hemispheres in hemodynamic compromise by CVR but normal OEF that were associated with subcortical white matter infarction.