Regional dependence of cerebral reperfusion after circulatory arrest in rats

Association of hyperosmolar therapy with cerebral oxygen extraction after cardiac arrest

BACKGROUND

Elevated jugular bulb venous oxygen saturation (SjvO2) after cardiac arrest may be due to diffusion-limited oxygen extraction secondary to perivascular edema. Treatment with hyperosmolar solution (HTS) may decrease this edema and thus the barrier to oxygen diffusion. Alternatively, SjvO2 may rise when cerebral metabolic rate declines due to irreversible cellular injury, which would not be affected by HTS. Electroencephalography (EEG) may differentiate between these etiologies of elevated SjvO2. We hypothesized SjvO2 would be lower after treatment with HTS and EEG could identify treatment responders.

METHODS

We conducted a retrospective observational cohort study including comatose survivors of cardiac arrest who had at least one elevated SjvO2 (>75%) and were EEG-monitored. We quantified the change in consecutive SjvO2 values within a sample pair using a multivariable mixed-effects regression, treating HTS as a fixed effect, adjusting for mean arterial pressure, partial pressure of arterial oxygen, and partial pressure of carbon dioxide. We classified pretreatment EEG patterns as benign or indicative of potential metabolic failure and tested for an interaction of EEG pattern with HTS.

RESULTS

Our primary adjusted analysis showed an independent association of HTS treatment with change in SjvO2 (β -2.2; 95% confidence interval [CI], -4.0 to -0.3%). In our interaction model, the effect of treatment differed by EEG pattern (β for interaction term -10.9%, 95% CI -17.9 to -3.9%). HTS was associated with a significant change in SjvO2 among those with benign pre-treatment EEG patterns (-12.4%, 95% CI -18.4 to -6.4%) but was not associated with a change in SjvO2 in those with ominous pre-treatment EEG patterns (-1.6%, 95% CI -3.6 to 0.4%).

CONCLUSIONS

HTS was independently associated with decreased SjvO2 in patients resuscitated from cardiac arrest, and this effect was limited to patients with benign pretreatment EEG patterns. Our results suggest diffusion-limited oxygen extraction secondary to modifiable perivascular edema as the etiology of elevated SjvO2, and EEG pattern may be useful to identify treatment responders.

Fingerprint of Circulating Immunocytes as Biomarkers for the Prognosis of Brain Inflammation and Neuronal Injury after Cardiac Arrest

Cardiac arrest is one of the most dangerous health problems in the world. Outcome prognosis is largely based on cerebral performance categories determined by neurological evaluations. Few systemic tests are currently available to predict survival to hospital discharge. Here, we present the results from the preclinical studies of cardiac arrest and resuscitation (CAR) in mice to identify signatures of circulating immune cells as blood-derived biomarkers to predict outcomes after CAR. Two flow cytometry panels for circulating blood lymphocytes and myeloid-derived cells, respectively, were designed to correlate with neuroinflammation and neuronal and dendritic losses in the selectively vulnerable regions of bilateral hippocampi. We found that CD4+CD25+ regulatory T cells, CD11b+CD11c- and CD11b+Ly6C+Ly6G+ myeloid-derived cells, and cells positive for the costimulatory molecules CD80 and CD86 in the blood were correlated with activation of microglia and astrocytosis, and CD4+CD25+ T cells are additionally correlated with neuronal and dendritic losses. A fingerprint pattern of blood T cells and monocytes is devised as a diagnostic tool to predict CAR outcomes. Blood tests aimed at identifying these immunocyte patterns in cardiac arrest patients will guide future clinical trials to establish better prognostication tools to avoid unnecessary early withdrawal from life-sustaining treatment.

Effects of Sodium Nitroprusside Administered Via a Subdural Intracranial Catheter on the Microcirculation, Oxygenation, and Electrocortical Activity of the Cerebral Cortex in a Pig Cardiac Arrest Model

Background

Postischemic cerebral hypoperfusion has been indicated as an important contributing factor to secondary cerebral injury after cardiac arrest. We evaluated the effects of sodium nitroprusside administered via a subdural intracranial catheter on the microcirculation, oxygenation, and electrocortical activity of the cerebral cortex in the early postresuscitation period using a pig model of cardiac arrest.

Methods and Results

Twenty‐nine pigs were resuscitated with closed cardiopulmonary resuscitation after 14 minutes of untreated ventricular fibrillation. Thirty minutes after restoration of spontaneous circulation, 24 pigs randomly received either 4 mg of sodium nitroprusside (IT‐SNP group) or saline placebo (IT‐saline group) via subdural intracranial catheters and were observed for 5 hours. The same dose of sodium nitroprusside was administered intravenously in another 5 pigs. Compared with the IT‐saline group, the IT‐SNP group had larger areas under the curve for tissue oxygen tension and percent changes of arteriole diameter and number of perfused microvessels from baseline (all P<0.05) monitored on the cerebral cortex during the 5‐hour period, without severe hemodynamic instability. This group also showed faster recovery of electrocortical activity measured using amplitude‐integrated electroencephalography. Repeated‐measures analysis of variance revealed significant group–time interactions for these parameters. Intravenously administered sodium nitroprusside caused profound hypotension but did not appear to increase the cerebral parameters.

Conclusions

Sodium nitroprusside administered via a subdural intracranial catheter increased post–restoration of spontaneous circulation cerebral cortical microcirculation and oxygenation and hastened electrocortical activity recovery in a pig model of cardiac arrest. Further studies are required to determine its impact on the long‐term neurologic outcomes.

Increased cerebral endothelium-dependent vasodilation in rats in the postcardiac arrest period

Cardiovascular lability is common after cardiac arrest. We investigated whether altered endothelial function is present in cerebral and mesenteric arteries 2 and 4 h after resuscitation. Male Sprague-Dawley rats were anesthetized, intubated, ventilated, and intravascularly catheterized whereupon rats were randomized into four groups. Following 7 min of asphyxial cardiac arrest and subsequent resuscitation, cardiac arrest and sham rats were observed for either 2 or 4 h. Neuron-specific enolase levels were measured in blood samples. Middle cerebral artery segments and small mesenteric arteries were isolated and examined in microvascular myographs. qPCR and immunofluorescence analysis were performed on cerebral arteries. In cerebral arteries, bradykinin-induced vasodilation was inhibited in the presence of either calcium-activated K⁺ channel blockers (UCL1684 and senicapoc) or the nitric oxide (NO) synthase inhibitor, N^ω-nitro-L-arginine methyl ester hydrochloride (l-NAME), whereas the combination abolished bradykinin-induced vasodilation across groups. Neuron-specific enolase levels were significantly increased in cardiac arrest rats. Cerebral vasodilation was comparable between the 2-h groups, but markedly enhanced in response to bradykinin, NS309 (an opener of small and intermediate calcium-activated K⁺ channels), and sodium nitroprusside 4 h after cardiac arrest. Endothelial NO synthase and guanylyl cyclase subunit α-1 mRNA expression was unaltered after 2 h, but significantly decreased 4 h after resuscitation. In mesenteric arteries, the endothelium-dependent vasodilation was comparable between corresponding groups at both 2 and 4 h. Our findings show enhanced cerebral endothelium-dependent vasodilation 4 h after cardiac arrest mediated by potentiated endothelial-derived hyperpolarization and NO pathways. Altered cerebral endothelium-dependent vasodilation may contribute to disturbed cerebral perfusion after cardiac arrest.NEW & NOTEWORTHY This is the first study, to our knowledge, to demonstrate enhanced endothelium-dependent vasodilation in middle cerebral arteries in a cardiac arrest rat model. The increased endothelium-dependent vasodilation was a result of potentiated endothelium-derived hyperpolarization and endothelial nitric oxide pathways. Immunofluorescence microscopy confirmed the presence of relevant receptors and eNOS in cerebral arteries, whereas qPCR showed altered expression of genes related to guanylyl cyclase and eNOS. Altered endothelium-dependent vasoregulation may contribute to disturbed cerebral blood flow in the postcardiac arrest period.

Brain Hypoxia Is Associated With Neuroglial Injury in Humans Post-Cardiac Arrest

Supplemental Digital Content is available in the text.

Secondary brain hypoxia portends significant mortality in ischemic brain diseases; yet, our understanding of hypoxic ischemic brain injury (HIBI) pathophysiology in humans remains rudimentary.

Effect of Epinephrine Administered during Cardiopulmonary Resuscitation on Cerebral Oxygenation after Restoration of Spontaneous Circulation in a Swine Model with a Clinically Relevant Duration of Untreated Cardiac Arrest

Severe neurological impairment was more prevalent in cardiac arrest survivors who were administered epinephrine than in those administered placebo in a randomized clinical trial; short-term reduction of brain tissue O2 tension (PbtO2) after epinephrine administration in swine following a short duration of untreated cardiac arrest has also been reported. We investigated the effects of epinephrine administered during cardiopulmonary resuscitation (CPR) on cerebral oxygenation after restoration of spontaneous circulation (ROSC) in a swine model with a clinically relevant duration of untreated cardiac arrest. After 7 min of ventricular fibrillation, 24 pigs randomly received either epinephrine or saline placebo during CPR. Parietal cortex measurements during 60-min post-resuscitation period showed that the area under the curve (AUC) for PbtO2 was smaller in the epinephrine group than in the placebo group during the initial 10-min period and subsequent 50-min period (both p < 0.05). The AUC for number of perfused cerebral capillaries was smaller in the epinephrine group during the initial 10-min period (p = 0.005), but not during the subsequent 50-min period. In conclusion, epinephrine administered during CPR reduced PbtO2 for longer than 10 min following ROSC in a swine model with a clinically relevant duration of untreated cardiac arrest.

Epinephrine's effects on cerebrovascular and systemic hemodynamics during cardiopulmonary resuscitation

BACKGROUND

Despite controversies, epinephrine remains a mainstay of cardiopulmonary resuscitation (CPR). Recent animal studies have suggested that epinephrine may decrease cerebral blood flow (CBF) and cerebral oxygenation, possibly potentiating neurological injury during CPR. We investigated the cerebrovascular effects of intravenous epinephrine in a swine model of pediatric in-hospital cardiac arrest. The primary objectives of this study were to determine if (1) epinephrine doses have a significant acute effect on CBF and cerebral tissue oxygenation during CPR and (2) if the effect of each subsequent dose of epinephrine differs significantly from that of the first.

METHODS

One-month-old piglets (n = 20) underwent asphyxia for 7 min, ventricular fibrillation, and CPR for 10-20 min. Epinephrine (20 mcg/kg) was administered at 2, 6, 10, 14, and 18 min of CPR. Invasive (laser Doppler, brain tissue oxygen tension [PbtO₂]) and noninvasive (diffuse correlation spectroscopy and diffuse optical spectroscopy) measurements of CBF and cerebral tissue oxygenation were simultaneously recorded. Effects of subsequent epinephrine doses were compared to the first.

RESULTS

With the first epinephrine dose during CPR, CBF and cerebral tissue oxygenation increased by > 10%, as measured by each of the invasive and noninvasive measures (p < 0.001). The effects of epinephrine on CBF and cerebral tissue oxygenation decreased with subsequent doses. By the fifth dose of epinephrine, there were no demonstrable increases in CBF of cerebral tissue oxygenation. Invasive and noninvasive CBF measurements were highly correlated during asphyxia (slope effect 1.3, p < 0.001) and CPR (slope effect 0.20, p < 0.001).

CONCLUSIONS

This model suggests that epinephrine increases CBF and cerebral tissue oxygenation, but that effects wane following the third dose. Noninvasive measurements of neurological health parameters hold promise for developing and directing resuscitation strategies.

Multi-parametric functional ultrasound imaging of cerebral hemodynamics in a cardiopulmonary resuscitation model

Patient mortality at one year reaches 90% after out-of-hospital cardiac arrest and resuscitation. Temperature management is one of the main strategies proposed to improve patient outcome after resuscitation and preclinical studies have shown neuroprotective effects when hypothermia is achieved rapidly, although the underlying mechanisms have not yet been elucidated. State-of-the-art brain imaging technologies can bring new insights into the early cerebral events taking place post cardiac arrest and resuscitation. In this paper, we characterized cerebral hemodynamics in a post-cardiac arrest rabbit model using functional ultrasound imaging. Ultrasound datasets were processed to map the dynamic changes in cerebral blood flow and cerebral vascular resistivity with a 10 second repetition rate while animals underwent cardiac arrest and a cardiopulmonary resuscitation. We report that a severe transient hyperemia takes place in the brain within the first twenty minutes post resuscitation, emphasizing the need for fast post-cardiac arrest care. Furthermore, we observed that this early hyperemic event is not spatially homogeneous and that maximal cerebral hyperemia happens in the hippocampus. Finally, we show that rapid cooling induced by total liquid ventilation reduces early cerebral hyperemia, which could explain the improved neurological outcome reported in preclinical studies.

Invasion of Peripheral Immune Cells into Brain Parenchyma after Cardiac Arrest and Resuscitation

Although a direct link has long been suspected between systemic immune responses and neuronal injuries after stroke, it is unclear which immune cells play an important role. A question remains as to whether the blood brain barrier (BBB) is transiently disrupted after circulatory arrest to allow peripheral immune cells to enter brain parenchyma. Here, we developed a clinically relevant cardiac arrest and resuscitation model in mice to investigate the BBB integrity using noninvasive magnetic resonance imaging. Changes in immune signals in the brain and periphery were assayed by immunohistochemistry and flow cytometry. Quantitative variance maps from T1-weighted difference images before and after blood-pool contrast clearance revealed BBB disruptions immediately after resuscitation and one day after reperfusion. Time profiles of hippocampal CA1 neuronal injuries correlated with the morphological changes of microglia activation. Cytotoxic T cells, CD11b⁺CD11c⁺ dendritic cells, and CD11b⁺CD45^+hi monocytes and macrophages were significantly increased in the brain three days after cardiac arrest and resuscitation, suggesting direct infiltration of these cells following the BBB disruption. Importantly, these immune cell changes were coupled with a parallel increase in the same subset of immune cell populations in the bone marrow and blood. We conclude that neurovascular breakdown during the initial reperfusion phase contributes to the systemic immune cell invasion and subsequent neuropathogenesis affecting the long-term outcome after cardiac arrest and resuscitation.

Comparison of quantitative T2 and ADC mapping in the assessment of 3-nitropropionic acid-induced neurotoxicity in rats

To assess the relative performance of MRI T₂ relaxation and ADC mapping as potential biomarkers of neurotoxicity, a model of 3-nitropropionic acid (NP)-induced neurodegeneration in rats was employed. Male Sprague-Dawley rats received NP (N = 20, 16-20 mg/kg, ip or sc) or saline (N = 6, 2 ml/kg, ip) daily for 3 days. MRI was performed using a 7 T system employing quantitative T₂ and ADC mapping based on spin echo pulse sequence. All maps were skull stripped and co-registered and the changes were quantified using baseline subtraction and anatomical segmentation. Following the in vivo portion of the study, rat brains were histologically examined. Four NP-treated rats were considered responders based on their MRI and histology data. T₂ values always increased in the presence of toxicity, while ADC changes were bidirectional, decreasing in some lesion areas and increasing in others. In contrast to T₂ in some cases, ADC did not change. The effect sizes of T₂ and ADC signals suggestive of neurotoxicity were 2.64 and 1.66, respectively, and the variability of averaged T₂ values among anatomical regions was consistently lower than that for ADC. The histopathology data confirmed the presence of neurotoxicity, however, a more detailed assessment of the correlation of MRI with histology is needed. T₂ mapping provides more sensitive and specific information than ADC about changes in the rat brain thought to be associated with neurotoxicity due to a higher signal-to-noise ratio, better resolution, and unidirectional changes, and presents a better opportunity for biomarker development.

Impact of age on cardiovascular function, inflammation, and oxidative stress in experimental asphyxial cardiac arrest

BACKGROUND

Advanced age is an independent predictor of poor outcome after cardiac arrest (CA). From experimental studies of regional ischemia-reperfusion injury, advanced age is associated with larger infarct size, reduced organ function, and augmented oxidative stress. The objective of this study was to investigate the effect of age on cardiovascular function, oxidative stress, inflammation, and endothelial activation after CA representing global ischemia-reperfusion.

METHODS

Aged (26 months) and young (5 months) rats were subjected to 8 min of asphyxia induced CA, resuscitated and observed for 360 min. Left ventricular pressure-derived cardiac function was measured at baseline and 360 min after CA. Blood samples obtained at baseline, 120 min, and 360 min after CA were analyzed for IL-1β, IL-6, IL-10, TNF-α, elastase, sE-selectin, sL-selectin, sI-CAM1, hemeoxygenase-1 (HO-1) and protein carbonyl. Tissue samples of brain, heart, kidney, and lung were analyzed for HO-1.

RESULTS

Cardiac function, evaluated by dP/dt_max and dP/dt_min , was decreased after CA in both young and aged rats, with no group differences. Mean arterial pressure increased after CA in young, but not old rats. Aged rats showed significantly higher plasma levels of elastase and sE-selectin after CA, and there was a significant different development over time between groups for IL-6 and IL-10. Young rats showed higher levels of HO-1 in plasma and renal tissue after CA.

CONCLUSION

In a rat model of asphyxial CA, advanced age is associated with an attenuated hyperdynamic blood pressure response and increased endothelial activation.

Alterations in Cerebral Blood Flow after Resuscitation from Cardiac Arrest

Greater than 50% of patients successfully resuscitated from cardiac arrest have evidence of neurological disability. Numerous studies in children and adults, as well as in animal models have demonstrated that cerebral blood flow (CBF) is impaired after cardiac arrest. Stages of cerebral perfusion post-resuscitation include early hyperemia, followed by hypoperfusion, and finally either resolution of normal blood flow or protracted hyperemia. At the level of the microcirculation the blood flow is heterogeneous, with areas of no flow, low flow, and increased flow. CBF directed therapies in animal models of cardiac arrest improved neurological outcome, and therefore, the alterations in CBF after cardiac arrest likely contribute to the development of hypoxic ischemic encephalopathy. Current intensive care after cardiac arrest is centered upon maintaining systemic oxygenation, normal blood pressure values for age, maintaining general homeostasis, and avoiding hyperthermia. Assessment of CBF and oxygenation is not routinely performed after cardiac arrest. Currently available and underutilized techniques to assess cerebral perfusion include transcranial doppler, near-infrared spectroscopy, and arterial spin labeling magnetic resonance imaging. Limited clinical studies established the role of CBF and oxygenation monitoring in prognostication after cardiac arrest and few studies suggest that guiding critical care post-resuscitation to mean arterial pressures above the minimal autoregulatory range might improve outcome. Important knowledge gaps thus remain in cerebral monitoring and CBF and oxygen goal-directed therapies post-resuscitation from cardiac arrest.

Effects of levosimendan on hemodynamics, local cerebral blood flow, neuronal injury, and neuroinflammation after asphyctic cardiac arrest in rats

OBJECTIVES

Despite advances in cardiac arrest treatment, high mortality and morbidity rates after successful cardiopulmonary resuscitation are still a major clinical relevant problem. The post cardiac arrest syndrome subsumes myocardial dysfunction, impaired microcirculation, systemic inflammatory response, and neurological impairment. The calcium-sensitizer levosimendan was able to improve myocardial function and initial resuscitation success after experimental cardiac arrest/cardiopulmonary resuscitation. We hypothesized that levosimendan exerts beneficial effects on cerebral blood flow, neuronal injury, neurological outcome, and inflammation 24 hours after experimental cardiac arrest/cardiopulmonary resuscitation.

DESIGN

Laboratory animal study.

SETTING

University animal research laboratory.

SUBJECTS

Sixty-one male Sprague-Dawley rats.

INTERVENTIONS

Animals underwent asphyxial cardiac arrest/cardiopulmonary resuscitation, randomized to groups with levosimendan treatment (bolus 12 µg/kg and infusion for 3 hr [0.3 µg/min/kg]) or vehicle (saline 0.9% bolus and infusion for 3 hr [equivalent fluid volume]). Cardiac index, local cerebral blood flow, and hemodynamic variables were measured for 180 minutes after cardiac arrest/cardiopulmonary resuscitation. Behavioral and neurological evaluations were conducted 24 hours after cardiac arrest/cardiopulmonary resuscitation. Furthermore, neuronal injury, expressed as Fluoro-Jade B-positive cells in the hippocampal formation, cortical and hippocampal inflammatory cytokine gene expression, and blood plasma interleukin-6 values were assessed.

MEASUREMENTS AND MAIN RESULTS

Treatment with levosimendan reduced neuronal injury and improved neurological outcome after 24 hours of reperfusion and resulted in elevated cardiac index and local cerebral blood flow compared with vehicle after cardiac arrest/cardiopulmonary resuscitation. Mean arterial blood pressure was reduced during the early reperfusion period in the levosimendan group. Cortical and hippocampal inflammatory cytokine gene expression and blood plasma interleukin-6 levels were not influenced.

CONCLUSIONS

Levosimendan increased cerebral blood flow after experimental cardiac arrest/cardiopulmonary resuscitation. This effect coincided with reduced neuronal injury and improved neurologic outcome. Findings seem to be independent of inflammatory effects because no effects by levosimendan on cerebral or systemic inflammation could be detected. In summary, levosimendan is a promising agent to improve neurological outcome after cardiac arrest/cardiopulmonary resuscitation.

The role of Levosimendan in cardiopulmonary resuscitation

Although initial resuscitation from cardiac arrest (CA) has increased over the past years, long term survival rates remain dismal. Epinephrine is the vasopressor of choice in the treatment of CA. However, its efficacy has been questioned, as it has no apparent benefits for long-term survival or favorable neurologic outcome. Levosimendan is an inodilator with cardioprotective and neuroprotective effects. Several studies suggest that it is associated with increased rates of return of spontaneous circulation as well as improved post-resuscitation myocardial function and neurological outcome. The purpose of this article is to review the properties of Levosimendan during cardiopulmonary resuscitation (CPR) and also to summarize existing evidence regarding the use of Levosimendan in the treatment of CA.

Global and regional differences in cerebral blood flow after asphyxial versus ventricular fibrillation cardiac arrest in rats using ASL-MRI

Both ventricular fibrillation cardiac arrest (VFCA) and asphyxial cardiac arrest (ACA) are frequent causes of CA. However, only isolated reports compared cerebral blood flow (CBF) reperfusion patterns after different types of CA, and even fewer reports used methods that allow serial and regional assessment of CBF. We hypothesized that the reperfusion patterns of CBF will differ between individual types of experimental CA. In a prospective block-randomized study, fentanyl-anesthetized adult rats were subjected to 8min VFCA or ACA. Rats were then resuscitated with epinephrine, bicarbonate, manual chest compressions and mechanical ventilation. After the return of spontaneous circulation, CBF was then serially assessed via arterial spin-labeling magnetic resonance imaging (ASL-MRI) in cortex, thalamus, hippocampus and amygdala/piriform complex over 1h resuscitation time (RT). Both ACA and VFCA produced significant temporal and regional differences in CBF. All regions in both models showed significant changes over time (p<0.01), with early hyperperfusion and delayed hypoperfusion. ACA resulted in early hyperperfusion in cortex and thalamus (both p<0.05 vs. amygdala/piriform complex). In contrast, VFCA induced early hyperperfusion only in cortex (p<0.05 vs. other regions). Hyperperfusion was prolonged after ACA, peaking at 7min RT (RT7; 199% vs. BL, Baseline, in cortex and 201% in thalamus, p<0.05), then returning close to BL at ∼RT15. In contrast, VFCA model induced mild hyperemia, peaking at RT7 (141% vs. BL in cortex). Both ACA and VFCA showed delayed hypoperfusion (ACA, ∼30% below BL in hippocampus and amygdala/piriform complex, p<0.05; VFCA, 34-41% below BL in hippocampus and amygdala/piriform complex, p<0.05). In conclusion, both ACA and VFCA in adult rats produced significant regional and temporal differences in CBF. In ACA, hyperperfusion was most pronounced in cortex and thalamus. In VFCA, the changes were more modest, with hyperperfusion seen only in cortex. Both insults resulted in delayed hypoperfusion in all regions. Both early hyperperfusion and delayed hypoperfusion may be important therapeutic targets. This study was approved by the University of Pittsburgh IACUC 1008816-1.

Isoflurane does not cause neuroapoptosis but reduces astroglial processes in young adult mice

BACKGROUND

Isoflurane, a volatile anesthetic widely used clinically, has been implicated to be both neuroprotective and neurotoxic. The claim about isoflurane causing neural apoptosis remains controversial. In this study, we investigated the effects of isoflurane exposures on apoptotic and anti-apoptotic signals, cell proliferation and neurogenesis, and astroglial processes in young adult mouse brains.

METHODS

Sixty 6-week-old mice were randomly assigned to four anesthetic concentration groups (0 as control and 0.6%, 1.3%, and 2%) with four recovery times (2 h and 1, 6, and 14 d) after 2-h isoflurane exposure. Immunohistochemistry measurements of activated caspase-3 and Bcl-xl for apoptotic and anti-apoptotic signals, respectively, glial fibrillary acidic protein (GFAP) and vimentin for reactive astrocytosis, doublecortin (Dcx) for neurogenesis, and BrdU for cell proliferation were performed.

RESULTS

Contrary to the previous conclusion derived from studies with neonatal rodents, we found no evidence of isoflurane-induced apoptosis in the adult mouse brain. Neurogenesis in the subgranule zone of the dentate gyrus was not affected by isoflurane. However, there is a tendency of reduced cell proliferation after 2% isoflurane exposure. VIM and GFAP staining showed that isoflurane exposure caused a delayed reduction of astroglial processes in the hippocampus and dentate gyrus.

CONCLUSION

Two-hour exposure to isoflurane did not cause neuroapoptosis in adult brains. The delayed reduction in astroglial processes after isoflurane exposure may explain why some volatile anesthetics can confer neuroprotection after experimental stroke because reduced glial scarring facilitates better long-term neuronal recoveries.

Model of cardiac arrest in rats by transcutaneous electrical epicardium stimulation

OBJECTIVE

To establish a new model of cardiac arrest (CA) in rats by transcutaneous electrical epicardium stimulation.

METHODS

Two acupuncture needles connected to the anode and cathode of a stimulator were transcutaneously inserted into the epicardium as electrodes. The stimulating current was steered to the epicardium and the stimulation was maintained for 3 min to induce CA. Cardiopulmonary resuscitation (CPR) was performed at 6 min after a period of nonintervention.

RESULTS

CA was successfully induced in a total of 20 rats. The success rate of induction was 12/20 at the current intensity of 1 mA; and reached 20/20 when the current intensity was increased to 2 mA. After the electrical stimulation, the femoral blood pressure quickly dropped below 25 mmHg and the arterial pulse waveform disappeared. The average time from the electrical stimulation to CA induction was 5.10 (+/-2.81) s. When the electrical stimulation stopped, 18/20 rats had ventricular fibrillation and 2/20 rats had pulseless electrical activity. CPR was performed for averagely 207.4 (+/-148.8) s. The restoration of spontaneous circulation (ROSC) was 20/20. The death rate within 4h after ROSC was 5/20, and the 72-h survival rate was 10/20. There were only two cases of complications, a minor muscle contraction and a minor lung lobe injury.

CONCLUSION

The model of CA in rats induced by transcutaneous electrical epicardium stimulation is a stable model that requires low-intensity current and has fewer complications. This model may provide another option for experimental research of CA induced by malignant arrhythmia (especially VF).

Therapeutic benefits of human mesenchymal stem cells derived from bone marrow after global cerebral ischemia

Although intravenous delivery of mesenchymal stem cells (MSCs) prepared from adult bone marrow reduces infarction size and ameliorates functional deficits in rat middle cerebral artery occlusion models, there are few reports of MSC treatment in global cerebral ischemia. We utilized a global cerebral ischemia model induced by arresting the heart with a combination of hypovolemia and intracardiac injections of a cold potassium chloride solution in order to study the potential therapeutic benefits of human mesenchymal stem cells (hMSCs) on global cerebral ischemia. hMSCs were intravenously injected into the rats 3 h after resuscitation from cardiac arrest. The effects on structural and functional outcome of hMSC were assessed at 5 h and 1, 3, and 7 days using magnetic resonance spectroscopy (MRS), histology, and cognitive functional analysis. Intravenous delivery of hMSCs reduced the Lac/Cr ratios, nuclear DNA fragmentation, neuronal loss, and elicited functional improvement compared with the control sham group. Enzyme-linked immunosorbent assay (ELISA) of the hippocampus revealed an increase in BDNF in hMSC-treated group. These data suggest that intravenous delivery of hMSC may have a therapeutic effect in global cerebral ischemia.

Faster recovery of cerebral perfusion in SOD1-overexpressed rats after cardiac arrest and resuscitation

BACKGROUND AND PURPOSE

Protracted hypoperfusion is one of the hallmarks of secondary cerebral derangement after cardiac arrest and resuscitation (CAR), and reactive oxygen species have been implicated in reperfusion abnormalities.

METHODS

Using transgenic (Tg) rats overexpressing copper zinc superoxide dismutase (SOD1), we investigated the role of this intrinsic antioxidant in the restoration of cerebral blood flow (CBF) after CAR. Nine Tg and 11 wild-type (WT) rats were subjected to a nominal 15-minute cardiac arrest, and CBF was measured using the noninvasive arterial spin labeling MRI method before and during cardiac arrest, and 0 to 2 hours and 1 to 5 days after resuscitation.

RESULTS

The SOD1-Tg rats showed rapid normalization of CBF 1 day after the insult, whereas CBF in WT animals remained abnormal for at least 5 days, showing a progressive increase in CBF from hypo- to hyperperfusion on postresuscitation days 1 to 5. The long-term outcome, as measured by survival time, change in body weight, and mapping of apparent diffusion coefficient (ADC) for ion/water homeostasis, was significantly better in the SOD1-Tg rats.

CONCLUSIONS

Our results support the notion that reactive oxygen species are at least partially responsible for microvascular reperfusion disorders.

Edaravone, a free radical scavenger, mitigates both gray and white matter damages after global cerebral ischemia in rats

Recent studies have shown that similar to cerebral gray matter (mainly composed of neuronal perikarya), white matter (composed of axons and glias) is vulnerable to ischemia. Edaravone, a free radical scavenger, has neuroprotective effects against focal cerebral ischemia even in humans. In this study, we investigated the time course and the severity of both gray and white matter damage following global cerebral ischemia by cardiac arrest, and examined whether edaravone protected the gray and the white matter. Male Sprague-Dawley rats were used. Global cerebral ischemia was induced by 5 min of cardiac arrest and resuscitation (CAR). Edaravone, 3 mg/kg, was administered intravenously either immediately or 60 min after CAR. The morphological damage was assessed by cresyl violet staining. The microtubule-associated protein 2 (a maker of neuronal perikarya and dendrites), the beta amyloid precursor protein (the accumulation of which is a maker of axonal damage), and the ionized calcium binding adaptor molecule 1 (a marker of microglia) were stained for immunohistochemical analysis. Significant neuronal perikaryal damage and marked microglial activation were observed in the hippocampal CA1 region with little axonal damage one week after CAR. Two weeks after CAR, the perikaryal damage and microglial activation were unchanged, but obvious axonal damage occurred. Administration of edaravone 60 min after CAR significantly mitigated the perikaryal damage, the axonal damage, and the microglial activation. Our results show that axonal damage develops slower than perikaryal damage and that edaravone can protect both gray and white matter after CAR in rats.

Epinephrine reduces cerebral perfusion during cardiopulmonary resuscitation

OBJECTIVE

Epinephrine has been the primary drug for cardiopulmonary resuscitation (CPR) for more than a century. The therapeutic rationale was to restore threshold levels of myocardial and cerebral blood flows by its alpha1 (alpha1) and alpha2 (alpha2)-adrenergic agonist vasopressor actions. On the basis of coincidental observations on changes in microvascular flow in the cerebral cortex, we hypothesized that epinephrine selectively decreases microvascular flow.

DESIGN

Randomized prospective animal study.

SETTING

University-affiliated research laboratory.

SUBJECTS

Domestic pigs.

INTERVENTIONS

Four groups of five male domestic pigs weighing 40 +/- 3 kg were investigated. After induction of anesthesia, endotracheal intubation was followed by mechanical ventilation. A frontoparietal bilateral craniotomy was created. Ventricular fibrillation was induced and untreated for 3 minutes before the start of precordial compression, mechanical ventilation, and attempted defibrillation. Animals were randomized to receive central venous injections during CPR of 1) placebo, 2) epinephrine, 3) epinephrine in which both alpha1- and beta (beta)-adrenergic effects were blocked by previous administration of prazosin and propranolol, and 4) epinephrine in which both alpha2- and beta-adrenergic effects were blocked by previous administration of yohimbine and propranolol.

MEASUREMENTS AND MAIN RESULTS

Cerebral cortical microcirculatory blood flow (MBF) was measured with orthogonal polarization spectral imaging. Cerebral cortical carbon dioxide and oxygen tensions (Pbco2 and Pbo2) were concurrently measured using miniature tissue optical sensors. Each animal was resuscitated. No differences in the number of electrical shocks for defibrillation or in the duration of CPR preceding return of spontaneous circulation were observed. Yet when epinephrine induced increases in arterial pressure, it significantly decreased Pbo2 tension and increased Pbco2 tension. Epinephrine therefore significantly decreased MBF and increased indicators of cerebral ischemia. Reduced MBF and magnified brain tissue ischemia during and after cardiopulmonary resuscitation were traced to the alpha1-adrenergic agonist action of epinephrine. When the alpha2 effects of epinephrine were blocked, reduced MBF and tissue ischemia persisted. No differences in cardiac output, end tidal Pco2, arterial Po2 and Pco2, and brain temperature were observed before inducing cardiac arrest and following return of spontaneous circulation.

CONCLUSIONS

In this model, epinephrine through its alpha1-agonist action had adverse effects on cerebral microvascular blood flow such as to increase the severity of cerebral ischemia during CPR.

Magnetic resonance imaging assessment of regional cerebral blood flow after asphyxial cardiac arrest in immature rats

Cerebral blood flow (CBF) alterations after asphyxial cardiac arrest (CA) are not defined in developmental animal models or humans. We characterized regional and temporal changes in CBF from 5 to 150 mins after asphyxial CA of increasing duration (8.5, 9, 12 min) in postnatal day (PND) 17 rats using the noninvasive method of arterial spin-labeled magnetic resonance imaging (ASL-MRI). We also assessed blood-brain barrier (BBB) permeability, and evaluated the relationship between CBF and mean arterial pressure after resuscitation. After all durations of asphyxia CBF alterations were region dependent. After 8.5- and 9-min asphyxia, intense subcortical hyperemia at 5 min was followed by return of CBF to baseline values by 10 mins. After 12-min asphyxia, hyperemia was absent and hypoperfusion reached a nadir of 38% to 65% of baselines with the lowest values in the cortex. BBB was impermeable to gadoteridol 150 mins after CA. CBF in the 12-min CA group was blood pressure passive at 60 min assessed via infusion of epinephrine. ASL-MRI assessment of CBF after asphyxial CA in PND 17 rats reveals marked duration and region-specific reperfusion patterns and identifies possible new therapeutic targets.

Modulation of inflammatory responses after global ischemia by transplanted umbilical cord matrix stem cells

Rat umbilical cord matrix (RUCM) cells are stem-cell-like cells and have been shown to reduce neuronal loss in the selectively vulnerable brain regions after cardiac arrest (CA). Here, we investigate whether this protection is mediated by the RUCM cells' modulation of the postischemia inflammation responses, which have long been implicated as a secondary mechanism of injury following ischemia. Brain sections were examined immunohistochemically for glial fibrillary acidic protein (GFAP), vimentin, and nestin as markers for astroglia and reactive astrogliosis, Ricinus Communis Agglutinin-1 (RCA-1) as a marker for microglia, and Ki67 as a marker for cell proliferation. Rats were randomly assigned to six experimental groups: (1) 8-minute CA without treatment, (2) 8-minute CA pre-treated with culture medium injection, (3) 8-minute CA pre-treated with RUCM cells, (4) sham-operated CA, (5) medium injection without CA, and (6) RUCM cell transplantation without CA. Groups 1-3 have significantly higher Ki67(+) cell counts and higher GFAP(+) immunoreactivity in the hippocampal Cornu Ammonis layer 1 (CA1) region compared to groups 4-6, irrespective of treatment. Groups 1 and 2 have highly elevated GFAP(+), vimentin(+), and nestin(+) immunoreactivity, indicating reactive astrogliosis. Strikingly, RUCM cell treatment nearly completely inhibited the appearance of vimentin(+) and greatly reduced nestin(+) reactive astrocytes. RUCM cell treatment also greatly reduced RCA-1 staining, which is found to strongly correlate with the neuronal loss in the CA1 region. Our study indicates that treatment with stem-cell-like RUCM cells modulates the inflammatory response to global ischemia and renders neuronal protection by preventing permanent damage to the selectively vulnerable astrocytes in the CA1 region. Disclosure of potential conflicts of interest is found at the end of this article.

Cerebral cortical microvascular flow during and following cardiopulmonary resuscitation after short duration of cardiac arrest

AIM

To examine changes in cerebral cortical macro- and microcirculation and their relationship to the severity of brain ischaemia during and following resuscitation from a short duration of cardiac arrest.

METHODS

Bilateral cranial windows were created in eight domestic pigs weighing 41+/-1 kg, exposing the frontoparietal cortex for orthogonal polarization spectral imaging together with estimation of cortical-tissue partial pressure of carbon dioxide, a quantitator of the severity of cerebral ischaemia. After 3 min of untreated ventricular fibrillation, cardiopulmonary resuscitation was begun and continued for 4 min before defibrillation. Aortic pressure, end-tidal and cortical-tissue partial pressure of carbon dioxide, and cortical microcirculatory blood flow in vessels of less and more than 20 microm in diameter were continuously measured.

RESULTS

Cerebral microcirculatory blood flow progressively decreased over the 3-min interval that followed onset of ventricular fibrillation. Chest compression restored cortical microvascular flow to approximately 40% of the pre-arrest value. Following return of spontaneous circulation, microvascular flow velocity was restored to baseline values over 3 min. Reversal of cerebral ischaemia with normalisation of cerebral cortical-tissue partial pressure of carbon dioxide occurred over 7 min after resuscitation. Cortical microcirculatory blood flow in microvessels less than 20 microm was highly correlated with flow in vessels more than 20 microm together with mean aortic pressure and end-tidal partial pressure of carbon dioxide.

CONCLUSION

Cerebral cortical microcirculatory flow ceased only 3 min after onset of cardiac arrest. Flow was promptly restored to 40% of its pre-arrest value after start of chest compression. After resuscitation, both macro- and microcirculatory flows were fully restored over 3 min, but cerebral ischaemia reversed more slowly.

Exsanguination cardiac arrest in rats treated by 60min, but not 75min, emergency preservation and delayed resuscitation is associated with intact outcome

Emergency preservation and resuscitation (EPR) is a new approach for resuscitation of exsanguination cardiac arrest (CA) victims to buy time for surgical hemostasis. EPR uses a cold aortic flush to induce deep hypothermic preservation, followed by resuscitation with cardiopulmonary bypass (CPB). We previously reported that 20 min of EPR was feasible with intact outcome. In this report, we tested the limits for EPR in rats. Adult male isoflurane-anesthetized rats were subjected to rapid hemorrhage (12.5 ml over 5 min), followed by esmolol/KCl-induced CA and 1 min of no-flow. EPR was then induced by perfusion with 270 ml of ice-cold Plasma-Lyte to decrease body temperature to 15 degrees C. After 60 min (n=7) or 75 min (n=7) of EPR, resuscitation was attempted with CPB over 60 min, blood transfusion, correction of acid-base balance and electrolyte disturbances, and mechanical ventilation for 2h. Survival, overall performance category (OPC: 1=normal, 5=death), neurological deficit score (NDS), and histological damage score (HDS) were assessed in survivors on day 3. While all rats after 60 min EPR survived, only two out of seven rats after 75 min EPR survived (p<0.05). All rats after 60 min EPR achieved OPC 1 and normal NDS by day 3. Survivors after 75 min EPR achieved best OPC 3 (p<0.05 vs. 60 min EPR). HDS of either brain or individual viscera was not statistically different after 60 versus 75 min EPR, except for kidneys (0+/-0 vs. 1.9+/-1.3, respectively; p<0.05), with a strong trend toward greater injury in all extracerebral organs in the 75-min EPR group (p<0.06). Histological findings were dominated by cardiac lesions observed in both groups and acute renal tubular and liver necrosis in the 75-min EPR group. In conclusion, we have shown that 60 min of EPR after exsanguination CA is associated with survival and favorable neurological outcome, while 75 min of EPR results in significant mortality and neurological damage in survivors. Surprisingly, extracerebral lesions predominated at 75-min EPR group. This model should serve as a screening model both for testing new pharmacological adjuncts to improve survival after exsanguination CA, and for elucidating the underlying mechanisms of ischemia/reperfusion injury.

Simultaneous observation of superficial cortical and intracerebral microvessels in vivo during reperfusion after transient forebrain ischemia in rats using synchrotron radiation

Using a newly developed angiography system that combines monochromatic synchrotron radiation (MSR) as an X-ray source with a high-definition camera or video system, we observed superficial cortical and intracerebral microvessels simultaneously in vivo during reperfusion after transient forebrain ischemia. Transient brain ischemia was induced by 10-min four-vessel occlusion in rats under general anesthesia. Angiographic images were then sequentially obtained at 3 frames/s. The detector features a 7-microm equivalent pixel size projected onto the input area and a 7 mmx7 mm input field. Changes in the cerebral microvessels were observed before and 1, 5, 10, 15, 20 and 30 min after transient cerebral ischemia using the MSR angiography system. The calibers of the internal carotid artery (ICA), middle cerebral artery (MCA), and striate artery (SA) significantly increased 1 min after reperfusion, while the pial arteriole (PA) caliber significantly decreased (76% of base line). The MCA, PA and SA were significantly dilated 5 and 10 min after reperfusion. Although the caliber of the ICA significantly decreased after 30 min reperfusion compared with the basal value, the calibers of the other three vessels remained larger than the basal values throughout the experiment. Early venous filling was observed at 5 and 10 min after reperfusion. The MSR angiography system is useful for investigating morphological changes in both cortical and central branches of cerebral vessels in rats during reperfusion after cerebral ischemia.

Prolonged deep hypothermic circulatory arrest in rats can be achieved without cognitive deficits

Cardiopulmonary bypass (CPB) and deep hypothermic circulatory arrest (DHCA) enable surgical repair of cardiovascular defects. However, neurological complications can result after both CPB and DHCA. We sought to investigate if 75 min of CPB or DHCA caused motor, cognitive or histological deficits in rats. Three groups were studied: DHCA, CPB, and sham. Rats in the DHCA group were subjected to 75 min DHCA at 15 degrees C, with a total CPB duration of 75 min. Rats in the CPB group were subjected to 75 min of normothermic CPB. Shams received the same anesthesia, cannulations and infusions. Motor function was assessed using beam testing on days 3-13. Cognitive performance was evaluated using Morris water maze tasks on days 7-13. Overall Performance Category (OPC) and Neurologic Deficit Score (NDS) were assessed daily. Histological Damage Score (HDS) was assessed in survivors on day 14. Sustained deficits on beam testing were seen only in the CPB group. Rats in the CPB and DHCA groups exhibited similar cognitive performance vs. sham. There were no differences in OPC or NDS between groups. Neuronal degeneration was present only in small foci in rats after DHCA (n=4/7). However, HDS was not different in individual brain regions or viscera between DHCA or CPB vs. sham. Surprisingly, CPB, but not DHCA was associated with motor deficits vs. sham, and no cognitive deficits were seen in either group vs. sham. Future studies with longer DHCA duration will be necessary to provide targets to assess novel preservation strategies.

Different mechanisms account for extracellular-signal regulated kinase activation in distinct brain regions following global ischemia and reperfusion

Oxidative stress after cerebral ischemia and reperfusion activates extracellular signal-regulated kinases (ERK) in brain. However, the mechanism of this activation has not been elucidated. We have previously reported that in an in vitro model of oxidative stress in immature cortical neuronal cultures, the inhibition of ERK phosphatase activity contributes to ERK1/2 activation and subsequent neuronal toxicity. This study examined whether ERK activation was associated with altered activity of ERK phosphatases in a rat cardiac arrest model. Rats in experimental groups were subjected to asphyxial cardiac arrest for 8 min and then resuscitated for 30 min. Significant ERK activation was detected in both cortex and hippocampus following ischemia/reperfusion by immunoblotting. ERK phosphatase activity was reversibly inhibited in cerebral cortex but not affected in hippocampus following ischemia/reperfusion. MEK1/2 was activated in both cerebral cortex and hippocampus following ischemia/reperfusion. Using a specific inhibitor of protein phosphatase 2A (PP2A), okadaic acid (OA), we have identified PP2A to be the major ERK phosphatase that is responsible for regulating ERK activation in ischemic brain tissues. Orthovanadate inhibited ERK phosphatase activity in brain tissues, suggesting that tyrosine phosphatases and dual specificity phosphatases may also contribute to the ERK phosphatase activity in brain tissues. Together, these data implicate ERK phosphatase in the regulation of ERK activation in distinct brain regions following global ischemia.

Potential treatment of cerebral global ischemia with Oct-4+ umbilical cord matrix cells

Potential therapeutic effects of Oct-4-positive rat umbilical cord matrix (RUCM) cells in treating cerebral global ischemia were evaluated using a reproducible model of cardiac arrest (CA) and resuscitation in rats. Animals were randomly assigned to four groups: A, sham-operated; B, 8-minute CA without pretreatment; C, 8-minute CA pretreated with defined media; and D, 8-minute CA pretreated with Oct-4(+) RUCM cells. Pretreatment was done 3 days before CA by 2.5-microl microinjection of defined media or approximately 10(4) Oct-4(+) RUCM cells in left thalamic nucleus, hippocampus, corpus callosum, and cortex. Damage was assessed histologically 7 days after CA and was quantified by the percentage of injured neurons in hippocampal CA1 regions. Little damage (approximately 3%-4%) was found in the sham group, whereas 50%-68% CA1 pyramidal neurons were injured in groups B and C. Pretreatment with Oct-4(+) RUCM cells significantly (p < .001) reduced neuronal loss to 25%-32%. Although the transplanted cells were found to have survived in the brain with significant migration, few were found directly in CA1. Therefore, transdifferentiation and fusion with host cells cannot be the predominant mechanisms for the observed protection. The Oct-4(+) RUCM cells might repair nonfocal tissue damage by an extracellular signaling mechanism. Treating cerebral global ischemia with umbilical cord matrix cells seems promising and worthy of further investigation.

Perfusion imaging using arterial spin labeling

Arterial spin labeling is a magnetic resonance method for the measurement of cerebral blood flow. In its simplest form, the perfusion contrast in the images gathered by this technique comes from the subtraction of two successively acquired images: one with, and one without, proximal labeling of arterial water spins after a small delay time. Over the last decade, the method has moved from the experimental laboratory to the clinical environment. Furthermore, numerous improvements, ranging from new pulse sequence implementations to extensive theoretical studies, have broadened its reach and extended its potential applications. In this review, the multiple facets of this powerful yet difficult technique are discussed. Different implementations are compared, the theoretical background is summarized, and potential applications of various implementations in research as well as in the daily clinical routine are proposed. Finally, a summary of the new developments and emerging techniques in this field is provided.

Contribution of the heme oxygenase pathway to the maintenance of the hypothalamic blood flow during diminished nitric oxide synthesis

The cerebrovascular effects of the heme oxygenase-carbon monoxide pathway were studied in the rat hypothalamus. Intraperitoneal administration of the heme oxygenase inhibitor zinc deuteroporphyrin 2,4-bis glycol (ZnDPBG, 45 micro mol/kg) had no significant effect on the resting cerebral blood flow, but increased hypothalamic nitric oxide synthase activity by 67% without changing the CSF cyclic GMP concentration. After pharmacologic inhibition of nitric oxide synthase, the diminished cerebral blood flow was further reduced by 22% after administration of ZnDPBG, and the effect showed direct correlation with the baseline perfusion level. Therefore, endogenous carbon monoxide may significantly contribute to the cerebral vasoregulation under resting conditions and in pathophysiologic states associated with diminished nitric oxide synthesis.

Deferoxamine improves early postresuscitation reperfusion after prolonged cardiac arrest in rats

The no-reflow phenomenon and delayed hypoperfusion after transient cardiac arrest (CA) impede postischemic recovery. Activation of lipid peroxidation (LPO) after ischemia and reperfusion is considered one of the mechanisms responsible for such abnormalities. The present study investigates the influence of iron-dependent LPO inhibitor deferoxamine (DFO) on the cerebral perfusion after prolonged CA and resuscitation. Fourteen male Sprague-Dawley rats were subjected to 17 minutes of CA, induced by esmolol (an ultrashort-acting beta-blocker) and apnea, followed by resuscitation by retrograde intraaortic infusion of oxygenated donor blood mixed with a resuscitation cocktail inside a vertical-bore 9.4-T magnetic resonance imaging (MRI) magnet. Animals were randomized double-blindly into two groups to receive DFO or saline, respectively. Cerebral perfusion was measured by MRI continuously using the arterial spin-labeling method before, during, and after CA. All animals were successfully resuscitated in 1.36 +/- 0.04 minutes with well-controlled arrest time (17.99 +/- 0.03 minutes) in both groups. Deferoxamine significantly increased cerebral perfusion in hippocampus, thalamus, hypothalamus, and amygdala, but not in cortex, during the first 20 minutes of reperfusion. In the DFO-treated group, the neurologic deficit score was significantly better (400 +/- 30 vs. 250 +/- 47, out of 500 as the best, P < 0.05) and weight loss was significantly less (33 +/- 6 vs. 71 +/- 19 g, P < 0.05) 5 d after arrest. The finding supports the notion that early reperfusion immediately after resuscitation is important for long-term outcome and that LPO may be involved in microvascular disorders during the reperfusion, particularly in the brain after prolonged cardiac arrest and resuscitation.

Dependence of early cerebral reperfusion and long-term outcome on resuscitation efficiency after cardiac arrest in rats

BACKGROUND AND PURPOSE

While it is well known that longer duration of cardiac arrest (CA) is often associated with poorer long-term outcome, the influence of resuscitation efficacy on postischemia recovery is less clear. The objective of the present study is to investigate whether an inadequate and prolonged resuscitation after a shorter CA can lead to worse long-term outcomes than an effective resuscitation after a longer CA, provided that the total time from the onset of CA to the return of spontaneous circulation is comparable.

METHODS

Thirty-eight rats were randomized into 2 groups with nominal 9 minutes (group 1) and 15 minutes (group 2) of normothermic asphyxial CA. Each group was further divided into 2 subgroups on the basis of the duration of resuscitation efforts (labeled as S and L for short and long, respectively). Thus, the asphyxia and nominal resuscitation times were 8 and 1 minute, respectively, for group 1S, 5 and 4 minutes for group 1L, 14 and 1 minute for group 2S, and 11 and 4 minutes for group 2L. Cerebral perfusion was measured continuously at the dorsal hippocampus level before, during, and after the CA, with the use of the arterial spin labeling MRI technique. The survival time, histological damage, and neurological deficit were evaluated 5 days after resuscitation.

RESULTS

Groups 1S and 1L had nearly the same duration of CA (9.02 +/- 0.17 minutes, n=6 versus 8.58 +/- 0.80 minutes, n=6). The same is true for groups 2S and 2L (15.51 +/- 0.59 minutes, n=11 versus 15.65 +/- 1.25 minutes, n=15). Despite longer asphyxia, shorter and more effective resuscitation was associated with significantly improved long-term outcomes and higher cerebral perfusion at the early stage of reperfusion.

CONCLUSIONS

Effective resuscitation increased early reperfusion and improved survival after CA. The clinical implication is that inadequate and prolonged resuscitation may have detrimental effects on the recovery of CA patients.

Late reversal of cerebral perfusion and water diffusion after transient focal ischemia in rats

Region-specific cerebral blood flow (CBF) and the apparent diffusion coefficient (ADC) of tissue water in the rat brain were quantified by high-field magnetic resonance imaging at 9.4 T in the rat suture occlusion model. Cerebral blood flow and ADC were compared during the short- (4.5 hours) and long-term (up to 6 days) reperfusion after 80 minutes of transient middle cerebral artery occlusion, and correlated with the histology analysis. On occlusion, average CBF fell from approximately 100 to less than 50 mL x 100 g(-1) x min(-1) in the cortex, and to less than 20 mL x 100 g(-1) x min(-1) in the caudate putamen (CP). Corresponding ADC values decreased from (6.98 +/- 0.82) x 10(-4) to (5.49 +/- 0.54) x 10(-4) mm2/s in the cortex, and from (7.16 +/- 0.58) x 10(-4) to (4.86 +/- 0.62) x 10(-4) mm2/s in the CP. On average, CBF recovered to approximately 50% of baseline in the first 24 hours of reperfusion. After 2 to 4 days, a strong hyperperfusion in the ipsilateral cortex and CP, up to approximately 300 mL x 100 g(-1) x min(-1), was observed. The ADC ratio in the ipsilateral and contralateral CP was also inverted in the late reperfusion period. Histology revealed more severe tissue damage at the late stage of reperfusion than at 4.5 hours. Significant reversal of CBF and ADC during the late reperfusion period may reflect the impairment of autoregulation in the ischemic regions. Vascular factors may play an important role in the infarct development after 80-minute focal ischemia.

ADC characterization of region-specific response to cerebral perfusion deficit in rats by MRI at 9.4 T

Region-specific cerebral blood flow (CBF) and apparent diffusion coefficient (ADC) of water in the rat brain were quantified in vivo by high-field MRI (9.4 T) for 6-7 h after middle cerebral artery occlusion (MCAO). Upon occlusion, average CBF fell from about 1.5-2 ml/g/min to below 0.5 ml/g/min in cortical areas and the amygdala, and below 0.2 ml/g/min in the caudate putamen. CBF in some of the homologous contralateral areas also decreased by 20-30%. Average ADC decreased from about 8 center dot 10(-4) to 5 center dot 10(-4) mm(2)/s in the caudate putamen and parietal cortex. Corresponding changes in ADC were lower in the frontal cortex and negligible in the piriform cortex, suggesting that the perfusion threshold for ADC decrease may be different for different brain regions in the same animal. The area of decreased ADC correlated well with the infarction area revealed by 2,3,5-triphenyltetrazolium chloride (TTC) staining of brain slices in vitro. A better understanding of the mechanisms linking ADC and CBF changes to ischemic cell disorders may prove useful in characterizing the degree of tissue damage, and in developing and evaluating treatment strategies.