The role of cerebral blood flow for the recovery of the brain after prolonged ischemia

Hypothermia After Cardiac Arrest in Large Animals (HACA-LA): Study protocol of a randomized controlled experimental trial

Background

Induced hypothermia post-cardiac arrest is neuroprotective in animal experiments, but few high-quality studies have been performed in larger animals with human-like brains. The neuroprotective effect of postischemic hypothermia has recently been questioned in human trials. Our aim is to investigate whether hypothermia post-cardiac arrest confers a benefit compared to normothermia in large adult animals. Our hypothesis is that induced hypothermia post cardiac arrest is neuroprotective and that the effect diminishes when delayed two hours.

Methods

Adult female pigs were anesthetized, mechanically ventilated and kept at baseline parameters including normothermia (38 °C). All animals were subjected to ten minutes of cardiac arrest (no-flow) by induced ventricular fibrillation, followed by four minutes of cardiopulmonary resuscitation with mechanical compressions, prior to the first countershock. Animals with sustained return of spontaneous circulation (systolic blood pressure >60 mmHg for ten minutes) within fifteen minutes from start of life support were included and randomized to three groups; immediate or delayed (2 h) intravenous cooling, both targeting 33 °C, or intravenously controlled normothermia (38 °C). Temperature control was applied for thirty hours including cooling time, temperature at target and controlled rewarming (0.5 °C/h). Animals were extubated and kept alive for seven days. The primary outcome measure is histological brain injury on day seven. Secondary outcomes include neurological and neurocognitive recovery, and the trajectory of biomarkers of brain injury.

Conclusion

High-quality animal experiments in clinically relevant large animal models are necessary to close the gap of knowledge regarding neuroprotective effects of induced hypothermia after cardiac arrest.Trial registration:Preclinicaltrials.eu (PCTE0000272), published 2021-11-03.

Emergent Management of Hypoxic-Ischemic Brain Injury

OBJECTIVE

This article outlines interventions used to improve outcomes for patients with hypoxic-ischemic brain injury after cardiac arrest.

LATEST DEVELOPMENTS

Emergent management of patients after cardiac arrest requires prevention and treatment of primary and secondary brain injury. Primary brain injury is minimized by excellent initial resuscitative efforts. Secondary brain injury prevention requires the detection and correction of many pathophysiologic processes that may develop in the hours to days after the initial arrest. Key physiologic parameters important to secondary brain injury prevention include optimization of mean arterial pressure, cerebral perfusion, oxygenation and ventilation, intracranial pressure, temperature, and cortical hyperexcitability. This article outlines recent data regarding the treatment and prevention of secondary brain injury. Different patients likely benefit from different treatment strategies, so an individualized approach to treatment and prevention of secondary brain injury is advisable. Clinicians must use multimodal sources of data to prognosticate outcomes after cardiac arrest while recognizing that all prognostic tools have shortcomings.

ESSENTIAL POINTS

Neurologists should be involved in the postarrest care of patients with hypoxic-ischemic brain injury to improve their outcomes. Postarrest care requires nuanced and patient-centered approaches to the prevention and treatment of primary and secondary brain injury and neuroprognostication.

LncRNA CEBPA-AS1 alleviates cerebral ischemia-reperfusion injury by sponging miR-340-5p regulating APPL1/LKB1/AMPK pathway

Long non-coding RNAs (lncRNAs) regulate neurological damage in cerebral ischemia-reperfusion injury (CIRI). This study aimed to investigate the biological roles of lncRNA CEBPA-AS1 in CIRI. Middle cerebral artery occlusion and ischemia-reperfusion injury (MCAO/IR) rat model and oxygen-glucose deprivation and reoxygenation (OGD/R) cell lines were generated; the expression of CEBPA-AS1 was evaluated by qRT-PCR. The effects of CEBPA-AS1 on cell apoptosis and nerve damage were examined. The downstream microRNA (miRNA) and mRNA of CEBPA-AS1 were predicted and verified. We found that overexpression of CEBPA-AS1 could attenuate MCAO/IR-induced nerve damage and neuronal apoptosis in the rat model. Knockdown of CEBPA-AS1 aggravated cell apoptosis and enhanced the production of LDH and MDA in the OGD/R cells. Upon examining the molecular mechanisms, we found that CEBPA-AS1 stimulated APPL1 expression by combining with miR-340-5p, thereby regulating the APPL1/LKB1/AMPK pathway. In the rescue experiments, CEBPA-AS1 overexpression was found to attenuate OGD/R-induced cell apoptosis and MCAO/IR induced nerve damage, while miR-340-5p reversed these effects of CEBPA-AS1. In conclusion, CEBPA-AS1 could decrease CIRI by sponging miR-340-5, regulating the APPL1/LKB1/AMPK pathway.

A method to evaluate dynamic cerebral pressure-flow relationships in the conscious rat

The classic dogma of cerebral autoregulation is that cerebral blood flow is steadily maintained across a wide range of perfusion pressures. This has been challenged by recent studies suggesting little to no "autoregulatory plateau" in the relationship between cerebral blood flow and blood pressure (BP). Therefore, the mechanisms underlying the cerebral pressure-flow relationship still require further understanding. Here, we present a novel approach to examine dynamic cerebral autoregulation in conscious Wistar rats (n = 16) instrumented to measure BP and internal carotid blood flow (iCBF), as an indicator of cerebral blood flow. Transient reductions in BP were induced by occluding the vena cava via inflation of a chronically implanted intravascular silicone balloon. Falls in BP were paralleled by progressive decreases in iCBF, with no evidence of a steady-state plateau. No significant changes in internal carotid vascular resistance (iCVR) were observed. In contrast, intravenous infusions of the vasoactive drug sodium nitroprusside (SNP) produced a similar fall in BP but increases in iCBF and decreases in iCVR were observed. These data suggest a considerable confounding influence of vasodilatory drugs such as SNP on cerebrovascular tone in the rat, making them unsuitable to investigate cerebral autoregulation. We demonstrate that our technique of transient vena cava occlusion produced reliable and repeatable depressor responses, highlighting the potential for our approach to permit assessment of the dynamic cerebral pressure-flow relationship over time in conscious rats.NEW & NOTEWORTHY We present a novel technique to overcome the use of vasoactive agents when studying cerebrovascular dynamics in the conscious rat. Our method of vena cava occlusion to reduce BP was associated with decreased iCBF and no change in iCVR. In contrast, comparable BP falls with intravenous SNP increased iCBF and reduced iCVR. Thus, the dynamic cerebral pressure-flow relationship shows a narrower, less level autoregulatory plateau than conventionally thought. We confirm our method allows repeatable assessment of cerebrovascular dynamics in conscious rats.

Therapeutic hypothermia promotes cerebral blood flow recovery and brain homeostasis after resuscitation from cardiac arrest in a rat model

Laboratory and clinical studies have demonstrated that therapeutic hypothermia (TH), when applied as soon as possible after resuscitation from cardiac arrest (CA), results in better neurological outcome. This study tested the hypothesis that TH would promote cerebral blood flow (CBF) restoration and its maintenance after return of spontaneous circulation (ROSC) from CA. Twelve Wistar rats resuscitated from 7-min asphyxial CA were randomized into two groups: hypothermia group (7 H, n = 6), treated with mild TH (33-34℃) immediately after ROSC and normothermia group (7 N, n = 6,37.0 ± 0.5℃). Multiple parameters including mean arterial pressure, CBF, electroencephalogram (EEG) were recorded. The neurological outcomes were evaluated using electrophysiological (information quantity, IQ, of EEG) methods and a comprehensive behavior examination (neurological deficit score, NDS). TH consistently promoted better CBF restoration approaching the baseline levels in the 7 H group as compared with the 7 N group. CBF during the first 5-30 min post ROSC of the two groups was 7 H:90.5% ± 3.4% versus 7 N:76.7% ± 3.5% (P < 0.01). Subjects in the 7 H group showed significantly better IQ scores after ROSC and better NDS scores at 4 and 24 h. Early application of TH facilitates restoration of CBF back to baseline levels after CA, which in turn results in the restoration of brain electrical activity and improved neurological outcome.

Blockade of Acid-Sensing Ion Channels Attenuates Recurrent Hypoglycemia-Induced Potentiation of Ischemic Brain Damage in Treated Diabetic Rats

Diabetes is a chronic metabolic disease and cerebral ischemia is a serious complication of diabetes. Anti-diabetic therapy mitigates this complication but increases the risk of exposure to recurrent hypoglycemia (RH). We showed previously that RH exposure increases ischemic brain damage in insulin-treated diabetic (ITD) rats. The present study evaluated the hypothesis that increased intra-ischemic acidosis in RH-exposed ITD rats leads to pronounced post-ischemic hypoperfusion via activation of acid-sensing (proton-gated) ion channels (ASICs). Streptozotocin-diabetic rats treated with insulin were considered ITD rats. ITD rats were exposed to RH for 5 days and were randomized into Psalmotoxin1 (PcTx1, ASIC1a inhibitor), APETx2 (ASIC3 inhibitor), or vehicle groups. Transient global cerebral ischemia was induced overnight after RH. Cerebral blood flow was measured using laser Doppler flowmetry. Ischemic brain injury in hippocampus was evaluated using histopathology. Post-ischemic hypoperfusion in RH-exposed rats was of greater extent than that in control rats. Inhibition of ASICs prevented RH-induced increase in the extent of post-ischemic hypoperfusion and ischemic brain injury. Since ASIC activation-induced store-operated calcium entry (SOCE) plays a role in vascular tone, next we tested if acidosis activates SOCE via activating ASICs in vascular smooth muscle cells (VSMCs). We observed that SOCE in VSMCs at lower pH is ASIC3 dependent. The results show the role of ASIC in post-ischemic hypoperfusion and increased ischemic damage in RH-exposed ITD rats. Understanding the pathways mediating exacerbated ischemic brain injury in RH-exposed ITD rats may help lower diabetic aggravation of ischemic brain damage.

Clinical pathophysiology of hypoxic ischemic brain injury after cardiac arrest: a "two-hit" model

Hypoxic ischemic brain injury (HIBI) after cardiac arrest (CA) is a leading cause of mortality and long-term neurologic disability in survivors. The pathophysiology of HIBI encompasses a heterogeneous cascade that culminates in secondary brain injury and neuronal cell death. This begins with primary injury to the brain caused by the immediate cessation of cerebral blood flow following CA. Thereafter, the secondary injury of HIBI takes place in the hours and days following the initial CA and reperfusion. Among factors that may be implicated in this secondary injury include reperfusion injury, microcirculatory dysfunction, impaired cerebral autoregulation, hypoxemia, hyperoxia, hyperthermia, fluctuations in arterial carbon dioxide, and concomitant anemia.Clarifying the underlying pathophysiology of HIBI is imperative and has been the focus of considerable research to identify therapeutic targets. Most notably, targeted temperature management has been studied rigorously in preventing secondary injury after HIBI and is associated with improved outcome compared with hyperthermia. Recent advances point to important roles of anemia, carbon dioxide perturbations, hypoxemia, hyperoxia, and cerebral edema as contributing to secondary injury after HIBI and adverse outcomes. Furthermore, breakthroughs in the individualization of perfusion targets for patients with HIBI using cerebral autoregulation monitoring represent an attractive area of future work with therapeutic implications.We provide an in-depth review of the pathophysiology of HIBI to critically evaluate current approaches for the early treatment of HIBI secondary to CA. Potential therapeutic targets and future research directions are summarized.

Early MEK1/2 inhibition after global cerebral ischemia in rats reduces brain damage and improves outcome by preventing delayed vasoconstrictor receptor upregulation

Background

Global cerebral ischemia following cardiac arrest is associated with increased cerebral vasoconstriction and decreased cerebral blood flow, contributing to delayed neuronal cell death and neurological detriments in affected patients. We hypothesize that upregulation of contractile ET_B and 5-HT_1B receptors, previously demonstrated in cerebral arteries after experimental global ischemia, are a key mechanism behind insufficient perfusion of the post-ischemic brain, proposing blockade of this receptor upregulation as a novel target for prevention of cerebral hypoperfusion and delayed neuronal cell death after global cerebral ischemia. The aim was to characterize the time-course of receptor upregulation and associated neuronal damage after global ischemia and investigate whether treatment with the MEK1/2 inhibitor U0126 can prevent cerebrovascular receptor upregulation and thereby improve functional outcome after global cerebral ischemia. Incomplete global cerebral ischemia was induced in Wistar rats and the time-course of enhanced contractile responses and the effect of U0126 in cerebral arteries were studied by wire myography and the neuronal cell death by TUNEL. The expression of ET_B and 5-HT_1B receptors was determined by immunofluorescence.

Results

Enhanced vasoconstriction peaked in fore- and midbrain arteries 3 days after ischemia. Neuronal cell death appeared initially in the hippocampus 3 days after ischemia and gradually increased until 7 days post-ischemia. Treatment with U0126 normalised cerebrovascular ET_B and 5-HT_1B receptor expression and contractile function, reduced hippocampal cell death and improved survival rate compared to vehicle treated animals.

Conclusions

Excessive cerebrovascular expression of contractile ET_B and 5-HT_1B receptors is a delayed response to global cerebral ischemia peaking 3 days after the insult, which likely contributes to the development of delayed neuronal damage. The enhanced cerebrovascular contractility can be prevented by treatment with the MEK1/2 inhibitor U0126, diminishes neuronal damage and improves survival rate, suggesting MEK1/2 inhibition as a novel strategy for early treatment of neurological consequences following global cerebral ischemia.

The significance of protein S-100B testing in cardiac arrest patients

Cardiac arrest often represents the first expression of an underlying cardiac disease. Despite advances in neurocritical care, the neurological assessment of cardiac arrest patients relies on clinical, instrumental and biochemical parameters. The clinical significance of S-100 calcium binding protein B (S-100B) has substantially increased throughout several areas of clinical neuroscience, but reliable evidences attest it can be used as a reliable and early predictor of poor physiological and cognitive neurological outcomes after cardiac arrest.

The role of systemic hemodynamic disturbances in prematurity-related brain injury

Premature infants who experience cerebrovascular injury frequently have acute and long-term neurologic complications. In this article, we explore the relationship between systemic hemodynamic insults and brain injury in this patient population and the mechanisms that might be at play.

Cerebrovascular injury in premature infants: current understanding and challenges for future prevention

Cerebrovascular insults are a leading cause of brain injury in premature infants, contributing to the high prevalence of motor, cognitive, and behavioral deficits. Understanding the complex pathways linking circulatory immaturity to brain injury in premature infants remains incomplete. These mechanisms are significantly different from those causing injury in the mature brain. The gaps in knowledge of normal and disturbed cerebral vasoregulation need to be addressed. This article reviews current understanding of cerebral perfusion, in the sick premature infant in particular, and discusses challenges that lie ahead.

The prognostic value of early transcranial Doppler ultrasound following cardiopulmonary resuscitation

The aim of the presented study was to estimate the prognostic value of transcranial Doppler sonography (TCD) for the prediction of clinical outcome of patients after cardiopulmonary resuscitation (CPR) on the basis of the measured flow velocity changes in the basal cerebral arteries. Thirty-nine patients (27 men, 12 women) aged 66 +/- 15 y (+/-SD) who had undergone CPR were involved. Serial TCD examinations of the intracranial arteries were performed 1.5, 4, 8, 16, 24 and 72 h after CPR. Plasma neuron specific enolase (NSE), ventilation parameters (pH, paO(2), paCO(2)) and hemodynamic parameters were registered. Seventeen patients (group 1) survived with moderate or without neurologic deficits. Twenty-two patients (group 2) either died (n = 21) within 9 +/- 14 days or remained in vegetative state (n = 1). NSE levels ranged from 9 to 29 microg/L in group 1 and from 22 to 1242 microg/L in group 2 (p < 0.05). Four and 72 h after CPR, peak systolic flow velocities in the middle cerebral artery (MCA) were significantly higher in group 1 than in group 2 (p < 0.05). Twenty-four h after CPR, peak systolic and diastolic flow velocities in the ACA and PCA were also significantly higher in group 1 than in group 2 (p < 0.05). At this time, patients of group 2 showed significantly higher resistance index-values (RI = (sys-dia)/sys) in the anterior cerebral artery (ACA) and the posterior cerebral artery (PCA) (p < 0.05). A high correlation between peak systolic blood flow velocity in the MCA and systemic systolic blood pressure was observed in group 2 early 4 to 16 h after CPR (r = +0.52 to + 0.81, p < 0.05), while there was no such correlation in group 1. Using serial TCD examinations, patients with severely disabling or fatal outcome could be identified within the first 24 h. Besides established clinical and laboratory parameters, postanoxic myoclonus and NSE, serial TCD examinations following CPR may be helpful to predict the clinical outcome, but further studies with a larger number of patients are necessary to approve this hypothesis.

Cognitive impairment associated with intraoperative and postoperative hypoperfusion without neurologic deficits in a patient undergoing carotid endarterectomy

BACKGROUND

Neuropsychological testing detects cognitive impairment in 20% to 30% of patients after carotid endarterectomy (CEA).

CASE DESCRIPTION

A 51-year-old man with asymptomatic right cervical internal carotid artery (ICA) stenosis underwent a CEA. Intraoperative transcranial regional cerebral oxygen saturation monitoring revealed ischemia in the right cerebral hemisphere during ICA clamping and transient hyperemia subsequent to ICA declamping. The patient recovered without the appearance of new neurologic deficits. Brain single-photon emission computed tomography performed immediately after CEA showed a decrease in cerebral blood flow in the right cerebral hemisphere. Diffusion-weighted magnetic resonance imaging showed no new abnormal findings. Positron emission tomography performed 2 months after surgery revealed decreased cerebral metabolic rate of oxygen in the right cerebral hemisphere, and neuropsychological testing demonstrated a decline in performance IQ relative to preoperative levels.

CONCLUSIONS

Intraoperative ischemia and postischemic delayed hypoperfusion in CEA can impair cognition even in the absence of development of postoperative neurologic deficit.

Cerebral resuscitation: state of the art, experimental approaches and clinical perspectives

Neuronal injury following global cerebral ischemia continues to bea central problem of patients in the postresuscitation phase following cardiocirculatory arrest. In addition to measures focusing on rapid restoration of spontaneous circulation, the most effective treatment after cardiac arrest, as shown by large randomized trials,is the use of therapeutic mild hypothermia. Current guidelines of the International Liaison Committee on Resuscitation (ILCOR)are recommending the use of therapeutic mild hypothermia for all unconscious patients after cardiac arrest. At present there is no specific neuroprotective treatment available. Promising animal experimental data concerning the use of thrombolytic agents during cardiopulmonary resuscitation have led to a large European multicenter trial (TROICA trial) that will provide its data in 2006.

Time course of circulatory and metabolic recovery of cat brain after cardiac arrest assessed by perfusion- and diffusion-weighted imaging and MR-spectroscopy

Brain recovery after cardiac arrest (CA) was assessed in cats using arterial spin tagging perfusion-weighted imaging (PWI), diffusion-weighted imaging (DWI), and 1H-spectroscopy (1H-MRS). Cerebral reperfusion and metabolic recovery was monitored in the cortex and in basal ganglia for 6 h after cardiopulmonary resuscitation (CPR). Furthermore, the effects of an hypertonic/hyperoncotic solution (7.5% NaCl/6% hydroxyl ethyl starch, HES) and a tissue-type plasminogen activator (TPA), applied during CPR, were assessed on brain recovery. CA and CPR were carried out in the MR scanner by remote control. CA for 15-20 min was induced by electrical fibrillation of the heart, followed by CPR using a pneumatic vest. PWI after successful CPR revealed initial cerebral hyperperfusion followed by delayed hypoperfusion. Initial cerebral recirculation was improved after osmotic treatment. Osmotic and thrombolytic therapy were ineffective in ameliorating delayed hypoperfusion. Calculation of the apparent diffusion coefficient (ADC) from DWI demonstrated complete recovery of ion and water homeostasis in all animals. 1H-MRS measurements of lactate suggested an extended preservation of post-ischaemic anaerobic metabolism after TPA treatment. The combination of noninvasive MR techniques is a powerful tool for the evaluation of therapeutical strategies on circulatory and metabolic cerebral recovery after experimental cerebral ischaemia.

The effect of mild hypothermia and induced hypertension on long term survival rate and neurological outcome after asphyxial cardiac arrest in rats

STUDY OBJECTIVE

we studied the long-term effect of a combined treatment with resuscitative mild hypothermia and induced hypertension on survival rate and neurological outcome after asphyxial cardiac arrest (CA) in rats.

METHODS

36 male Wistar rats, were randomised into three groups: Group I (n=10): anaesthetised with halothane and N(2)O/O(2) (70/30%) had vessel cannulation but no asphyxial CA; mechanical ventilation was continued to 1 h. Group II (n=13): under the same anaesthetic conditions and vessel cannulation, was subjected to asphyxial CA of 8 min, reversed by brief external heart massage and followed by mechanical ventilation to 1 h post restoration of spontaneous circulation (ROSC). Group III (n=13): received the same insult and resuscitation as described in group II, but in contrast to the previous group, a combination treatment of hypothermia (34 degrees C) and induced hypertension was started immediately after ROSC and maintained for 60 min ROSC. Survival rate and neurological deficit (ND) scores were determined before arrest, at 2 and 24 h, and each 24-h up to 4 weeks after ROSC.

RESULTS

Baseline variables were the same in the three groups. Comparison of the asphyxial CA groups (groups II and III), showed an increased, although not statistically significant, survival rate at 72 h after ROSC in group III, and it became highly significant at 4 weeks after ROSC. The ND scores were the same in both asphyxial CA groups (groups II and III).

CONCLUSIONS

Resuscitative mild hypothermia and induced hypertension after asphyxial CA in rats is associated with a better survival rate. This beneficial effect persisted for 4 weeks after ROSC.

Autoregulation of cerebral blood flow in patients resuscitated from cardiac arrest

BACKGROUND AND PURPOSE

Under normal circumstances, autoregulation maintains cerebral blood flow (CBF) constant within a wide range of mean arterial pressure (MAP). It remains unknown whether patients resuscitated from cardiac arrest have preserved CBF autoregulation. In this study, CBF autoregulation was investigated within the first 24 hours after resuscitation from cardiac arrest.

METHODS

Eighteen patients and 6 healthy volunteers had relative changes in CBF determined by transcranial Doppler mean flow velocity (V(mean)) in the middle cerebral artery during a stepwise rise in MAP by use of norepinephrine infusion. V(mean) was plotted against MAP, and a lower limit of autoregulation was identified by double regression analysis based on the least-squares method.

RESULTS

In patients, V(mean) increased from a median of 33 (range 19 to 73) to 37 (22 to 100) cm/s (P:<0.001) during a norepinephrine-induced rise in MAP from 78 (46 to 118) to 106 (60 to 149) mm Hg. Eight of 18 patients had impaired CBF autoregulation, and in 5 of the 10 patients with preserved CBF autoregulation, the lower limit of autoregulation could be identified. The lower limit of CBF autoregulation was 76 mm Hg (41 to 105 mm Hg) in the volunteers and 114 mm Hg (80 to 120 mm Hg) in the 5 patients with preserved autoregulation (P:<0.01).

CONCLUSIONS

We conclude that in a majority of patients in the acute phase after cardiac arrest, cerebral autoregulation is either absent or right-shifted. These results indicate that MAP should be kept at a higher level than commonly accepted to secure cerebral perfusion. We recommend, however, that further randomized clinical trials are performed to determine whether sympathomimetic drugs improve neurological outcome.

Hypotensive hemorrhagic necrosis in basal ganglia and brainstem

Hypotensive hemorrhagic necrosis of the basal ganglia and brainstem has only occasionally been described. Three such cases are reported. Cardiac arrest had occurred in all cases, and it took at least 1 hour to restore adequate circulation. The patients remained comatose for 2 days to 2 weeks until death. Persistent hypotension causing ischemia in the distribution of deep perforating arteries is considered to have been the key underlying mechanism. Hemorrhage is thought to have been caused by extravasation of red blood cells through damaged blood vessels.

Cerebrovascular reactivity in comatose patients resuscitated from a cardiac arrest

BACKGROUND AND PURPOSE

Cerebral blood flow after cardiac arrest is reduced during the delayed hypoperfusion phase, while cerebral metabolic rate of oxygen returns to baseline values. Hypocapnia can induce cerebral ischemia in neurosurgical patients who already have reduced cerebral blood flow. The purpose of the present study was to determine whether comatose patients resuscitated from a cardiac arrest have a normal cerebrovascular reactivity to changes in PaCO2 and whether hypocapnia causes cerebral ischemia.

METHODS

We measured mean flow velocity (MFV) and pulsatility index (PI) in the middle cerebral artery, jugular bulb oxygen saturation (SjbO2), and arterial-jugular lactate difference (AJLD) during normo-, hypo-, and hyperventilation in 10 comatose patients resuscitated from a cardiac arrest. The first measurements were made within 6 hours after cardiac arrest and repeated 6, 12, and 24 hours later.

RESULTS

During hypoventilation we observed a significant decrease in PI and an increase in MFV and SjbO2. During hyperventilation PI and MFV did not change, but SjbO2 showed a significant decrease. This was accompanied by an increase in AJLD, suggesting cerebral ischemia. In four patients the SjbO2 decreased below the ischemic threshold of 55%.

CONCLUSIONS

The cerebrovascular reactivity to changes in arterial carbon dioxide tension is preserved in comatose patients resuscitated from a cardiac arrest. Hyperventilation may induce cerebral ischemia in the postresuscitation period.

The cerebral 'no-reflow' phenomenon after cardiac arrest in rats--influence of low-flow reperfusion

OBJECTIVE

Experimental data indicate that early microcirculatory reperfusion is disturbed after cardiac arrest. We investigated the influence of prolonged cardiac arrest and basic life support (BLS) procedures on the quality of cerebral microcirculatory reperfusion.

MATERIALS AND METHODS

In mechanically ventilated male Wistar rats anesthetized with N2O and halothane, cardiac arrest was induced by electrical fibrillation. Ten animals (group I) were subjected to 17 min of cardiac arrest (no-flow). Nine additional animals (group II) underwent only 12 min of cardiac arrest (no-flow), which was followed by a 5-min phase of BLS (i.e. mechanical ventilation and external cardiac compressions). In both groups, advanced resuscitation procedures including mechanical ventilation, external cardiac massage, 0.2 mg kg-1 epinephrine, 0.5 mmol kg-1 NaHCO3, and defibrillation were started 17 min after induction of cardiac arrest. The perfusion of the cerebral microcirculation was visualized by injection of 0.3 g kg-1 15% fluorescein isothiocyanate (FITC)-albumin 5 min after restoration of spontaneous circulation (ROSC), and the animals were decapitated 2 min later. The left hemispheres were fixed in 4% formalin, and coronal sections of 200 microns thickness at three different standard levels of the rat brain were investigated using fluorescence microscopy. Areas without capillary filling (cerebral 'no-reflow') were identified and calculated.

RESULTS

ROSC could be achieved in five of 10 animals (50%) of group I, and in six of nine animals (67%) of group II (P = n.s.). The severity of cerebral 'no-reflow' was higher in group II compared with group I (6.9 +/- 7.6 vs. 0.7 +/- 0.7% of total sectional areas; P < or = 0.05). Two sham-operated animals showed homogeneous reperfusion.

CONCLUSIONS

Wistar rats did not develop a marked cerebral 'no-reflow' phenomenon after circulatory arrest. A relevant degree of cerebral 'no-reflow' occurred, however, in animals subjected to a phase of BLS before circulatory stabilization. Therefore, low-flow states following prolonged cardiocirculatory arrest may aggravate early cerebral microcirculatory reperfusion disorders.

ZTTA, a postproline cleaving enzyme inhibitor, improves cerebral ischemia-induced deficits in a three-panel runway task in rats

We investigated the effect of N-benzyloxycarbonyl-thioprolyl-thioprolinal-dimethylaceta l (ZTTA), a novel postproline cleaving enzyme (prolyl endopeptidase, PPCE) inhibitor, on the in vitro activity of rat brain PPCE and memory impairment induced by cerebral ischemia. ZTTA noncompetitively inhibited rat brain PPCE (ki = 2.9 microM). Cerebral ischemia for 5 min increased the number of errors in a working memory task with a three-panel runway paradigm. ZTTA at 6 mg/kg, administered immediately after blood flow reperfusion, significantly reduced the increase in working memory errors expected to occur 24 h after 5 min of ischemia. The antiamnesic action of ZTTA may be ascribable to a neuroprotective effect on the central nervous system due to some neuropeptides that are substrates of PPCE in the brain.

Improved cerebral resuscitation from cardiac arrest in dogs with mild hypothermia plus blood flow promotion

BACKGROUND AND PURPOSE

In past studies, cerebral outcome after normothermic cardiac arrest of 10 or 12.5 minutes in dogs was improved but not normalized by resuscitative (postarrest) treatment with either mild hypothermia or hypertension plus hemodilution. We hypothesized that a multifaceted combination treatment would achieve complete cerebral recovery.

METHODS

With our established dog outcome model, normothermic ventricular fibrillation of 11 minutes (without blood flow) was followed by controlled reperfusion (with brief normothermic cardiopulmonary bypass simulating low flow and low PaO2 of external cardiopulmonary resuscitation) and defibrillation at < 2 minutes. Controlled ventilation was provided to 20 hours and intensive care to 96 hours. Control group 1 (n = 8) was kept normothermic (37.5 degrees C), normotensive, and hypocapnic throughout. Experimental group 2 (n = 8) received mild resuscitative hypothermia (34 degrees C) from about 10 minutes to 12 hours (by external and peritoneal cooling) plus cerebral blood flow promotion with induced moderate hypertension, mild hemodilution, and normocapnia.

RESULTS

All 16 dogs in the protocol survived. At 96 hours, all 8 dogs in control group 1 achieved overall performance categories 3 (severe disability) or 4 (coma). In group 2, 6 of 8 dogs achieved overall performance category 1 (normal); 1 dog achieved category 2 (moderate disability), and 1 dog achieved category 3 (P < .001). Final neurological deficit scores (0% [normal] to 100% [brain death]) at 96 hours were 38 +/- 10% (22% to 45%) in group 1 versus 8 +/- 9% (0% to 27%) in group 2 (P < .001). Total brain histopathologic damage scores were 138 +/- 22 (110 to 176) in group 1 versus 43 +/- 9 (32 to 56) in group 2 (P < .001). Regional scores showed similar group differences.

CONCLUSIONS

After normothermic cardiac arrest of 11 minutes in dogs, resuscitative mild hypothermia plus cerebral blood flow promotion can achieve functional recovery with the least histological brain damage yet observed with the same model and comparable insults.

Experimental growth retardation produced by transient period of uteroplacental ischemia in pregnant Sprague-Dawley rats

OBJECTIVE

Introduction of experimental growth retardation, which was based on the hypothesis of uteroplacental postischemic hypoperfusion, was attempted by a transient period of uteroplacental ischemia in dated-pregnant Sprague-Dawley rats.

STUDY DESIGN

On day 17 of gestation right uterine horn circulation was occluded for 5 to 60 minutes in 35 dams. The fetuses were delivered by cesarean section and studied on day 21 of gestation. For each experiment the fetuses in the right horn served as the ischemia group and those in the left horn were used as the control group.

RESULTS

Statistical analysis by Wilcoxon signed-rank test demonstrated a significant decrease in the fetal weights and in the liver-to-body weight ratios, in contrast to an increase in the brain-to-body weight ratios in the 60-minute ischemia group, compared with those in the control group. This ischemia resulted in a 14% incidence of fetal deaths.

CONCLUSION

Ischemia of a single uterine horn circulation in pregnant rat for 60 minutes should readily serve as a suitable model for asymmetric intrauterine growth retardation.

Mild intraischemic hypothermia reduces postischemic hyperperfusion, delayed postischemic hypoperfusion, blood-brain barrier disruption, brain edema, and neuronal damage volume after temporary focal cerebral ischemia in rats

Mild to moderate hypothermia (30-33 degrees C) reduces brain injury after brief (< 2-h) periods of focal ischemia, but its effectiveness in prolonged temporary ischemia is not fully understood. Thirty-two Sprague-Dawley rats anesthetized with 1.5% isoflurane underwent 3 h of middle cerebral artery occlusion under hypothermic (33 degrees C) or normothermic (37 degrees C) conditions followed by 3 or 21 h of reperfusion under normothermic conditions (n = 8/group). Laser-Doppler estimates of cortical blood flow showed that intraischemic hypothermia reduced both postischemic hyperperfusion (p < or = 0.01) and postischemic delayed hypoperfusion (p < or = 0.01). Hypothermia reduced the extent of blood-brain barrier (BBB) disruption as estimated from the extravasation of Evans blue dye at 6 h after the onset of ischemia (p < or = 0.01). Hypothermia also reduced the volume of both brain edema (p < or = 0.01) and neuronal damage (p < or = 0.01) as estimated from Nissl-stained slides at both 6 and 24 h after the onset of ischemia. These results demonstrate that mild intraischemic hypothermia reduces tissue injury after prolonged temporary ischemia, possibly by attenuating postischemic blood flow disturbances and by reducing vasogenic edema resulting from BBB disruption.

Ischemia-mediated neuronal injury

Resuscitation of the brain after a period of global ischemia is limited by two classes of post-ischemic pathologies: hemodynamic disturbances which prevent the adequate re-oxygenation of the ischemic brain, and metabolic disturbances which may lead to delayed neuronal death in so-called selectively vulnerable brain regions. The hemodynamic disturbances can be classified into the no-reflow phenomenon and the post-ischemic hypoperfusion syndrome. The no-reflow phenomenon results from a combination of increased blood viscosity and perivascular edema; the severity increases with the duration of ischemia, and the treatment is by combining arterial hypertension with dehydration and anticoagulation. The post-ischemic hypoperfusion syndrome is independent of the duration of ischemia, it develops after a delay and is due to an impairment of the metabolic/hemodynamic coupling mechanisms; there is no specific treatment at the present. The most important metabolic disturbance leading to delayed neuronal death is prolonged inhibition of protein synthesis. The injury is manifested already after 5 min ischemia but it progresses little if ischemia is prolonged to 1 h. Inhibition occurs at the translation level due to selective inhibition of polypeptide chain initiation. After brief periods of ischemia, the disturbance can be reversed by various anesthetics and hypothermia but there is no treatment if ischemia is prolonged. Exitotoxity, free radical-mediated reactions, disturbances of polyamine metabolism, acidosis and selective disturbances of gene expression may also be involved but are probably of lesser importance.

Brain pHi, cerebral blood flow, and NADH fluorescence during severe incomplete global ischemia in rabbits

BACKGROUND AND PURPOSE

The aim of this experiment was to study the serial changes in brain intracellular pH, cerebral blood flow, and the oxidation/reduction level of intramitochondrial nicotinamide adenine dinucleotide fluorescence across the cortical surface during severe incomplete global ischemia.

METHODS

Reduced nicotinamide adenine dinucleotide fluorescence and brain intracellular pH using the pH-sensitive indicator umbelliferone were measured with in vivo panoramic fluorescence imaging of the cortical surface. Cerebral blood flow was measured with the clearance of both umbelliferone and xenon-133. Fifteen minutes of severe incomplete global ischemia was produced by temporary occlusion of the innominate, left carotid, and subclavian arteries in five fasted New Zealand White rabbits.

RESULTS

Baseline brain intracellular pH was homogeneous over the exposed cortex, measuring 7.00 +/- 0.02, while cerebral blood flow was 48.0 +/- 2.6 ml/100 g/min. During 15 minutes of ischemia, cerebral blood flow measured 6.3 +/- 1.8 ml/100 g/min and brain pH declined to 6.61 +/- 0.02 (p < 0.005); in addition, there were acidotic foci with pH measuring 6.40 +/- 0.10. During reperfusion, there was an initial normalization of brain intracellular pH without an alkaline shift followed by a recurrent cortical acidosis of pH 6.88 +/- 0.06. There was a heterogeneous pattern of fluorescence that increased significantly following 60 minutes of reperfusion, coinciding with a postischemic hypoperfusion. The hypoperfusion was a uniform reduction in cerebral blood flow over the brain's surface, with reductions of 42.5% and 44.2% at 30 and 45 minutes, respectively.

CONCLUSIONS

During incomplete global ischemia there is a heterogeneous pattern of brain intracellular pH and reduced nicotinamide adenine dinucleotide changes that do not correlate with changes in cortical blood flow. The acidotic foci that were approximately 0.2 pH units more acidotic than the surrounding cortex may be the result of continued glucose delivery under anaerobic conditions. The degree of reduced nicotinamide adenine dinucleotide fluorescence suggests that the cortex is most vulnerable to metabolic failure after 60 minutes of reperfusion following severe incomplete global ischemia. The heterogeneous pattern of brain intracellular pH and reduced nicotinamide adenine dinucleotide changes suggest that there may be a selective vulnerability of cortical tissue to an ischemic challenge.

Cerebral resuscitation after cardiac arrest: research initiatives and future directions

At present, fewer than 10% of cardiopulmonary resuscitation (CPR) attempts prehospital or in hospitals outside special care units result in survival without brain damage. Minimizing response times and optimizing CPR performance would improve results. A breakthrough, however, can be expected to occur only when cerebral resuscitation research has achieved consistent conscious survival after normothermic cardiac arrest (no flow) times of not only five minutes but up to ten minutes. Most cerebral neurons and cardiac myocytes tolerate normothermic ischemic anoxia of up to 20 minutes. Particularly vulnerable neurons die, in part, because of the complex secondary post-reflow derangements in vital organs (the postresuscitation syndrome) which can be mitigated. Brain-orientation of CPR led to the cardiopulmonary-cerebral resuscitation (CPCR) system of basic, advanced, and prolonged life support. In large animal models with cardiac arrest of 10 to 15 minutes, external CPR, life support of at least three days, and outcome evaluation, the numbers of conscious survivors (although not with normal brain histology) have been increased with more effective reperfusion by open-chest CPR or emergency cardiopulmonary bypass, an early hypertensive bout, early post-arrest calcium entry blocker therapy, or mild cerebral hypothermia (34 C) immediately following cardiac arrest. More than ten drug treatments evaluated have not reproducibly mitigated brain damage in such animal models. Controlled clinical trials of novel CPCR treatments reveal feasibility and side effects but, in the absence of a breakthrough effect, may not discriminate between a treatment's ability to mitigate brain damage in selected cases and the absence of any treatment effect. More intensified, coordinated, multicenter cerebral resuscitation research is justified.

NMR-spectroscopic investigation of cerebral reanimation after prolonged ischemia

The severity of brain injury following interruption of blood flow depends on a number of ischemic and post-ischemic variables. The most important ischemic variables are the duration of ischemia, the amount of residual blood flow, the type and depth of anesthesia, brain glucose content and temperature. Among the post-ischemic factors the no-reflow phenomenon, edema and a variety of biochemical disturbances are of particular importance. Due to the complex interaction of these factors irreversible brain injury usually occurs after less than 10 min cerebrocirculatory arrest in normothermia. However, the safe ischemia time of the brain can be substantially extended when appropriate therapeutic measures are used to alleviate post-ischemic injury. NMR-spectroscopy is particularly suited for the analysis of this process. Recording of 31P, 1H and 19F spectra allow the continuous non-invasive assessment of such basic parameters as brain energy state, tissue pH, the content of lactate and blood flow (using Freon-23 as an inert tracer). In addition, information is obtained about changes in the content of phosphomonoesters and -diesters, glutamate, glutamine, aspartate and N-acetyl aspartate. These measurements can be combined with in vivo electrophysiological and post-mortem biochemical investigations for the further refinement of functional/metabolic monitoring. We have used this approach to study the potentials of post-ischemic resuscitation after one hour complete ischemia of the normothermic cat brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship of cerebral blood flow disturbances with brain oedema formation

Brain oedema is an important factor which compromises maintenance of the cerebral blood flow. Conversely, primary blood flow disturbances are leading to brain oedema. The mechanisms underlying blood flow impairment by brain oedema are associated with an increased regional tissue pressure in proportion to the degree of water accumulation in the parenchyma. The release of vasoactive mediator compounds might be considered in addition. Primary disturbances of the cerebral blood flow, such as focal or global cerebral ischaemia are leading to an increased cerebral water content. A decrease of the cerebral blood flow to ca. 40% of normal or below has been found to result in the development of brain oedema. This flow threshold is in the neighbourhood of the ischaemic flow level causing irreversible tissue damage. Whereas in focal ischaemia oedema formation is a function of the severity of the flow decrease, it is a pathophysiological hallmark of early postischaemic recirculation in global cerebral ischaemia. Nevertheless, during complete interruption of cerebral blood flow translocation of interstitial fluid into the intracellular compartment occurs as manifestation of ischaemic cell swelling. Cell swelling under these conditions may, however, not necessarily indicate cell damage, but more likely a compensatory response attributable to the uptake of excitotoxic transmitters such as glutamate, and of K(+)-ions which are excessively released at the onset of ischaemia into the extracellular space. Purpose of the swelling process, thus, is clearance of extracellular fluid from this material to re-establish homeostasis.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain-oriented intensive care after resuscitation from cardiac arrest

The 'chain-of-survival' concept has gained general acceptance in the care of cardiac arrest victims. Most standards and guidelines for cardiopulmonary resuscitation, however, focus on the initial links in the chain. We consider appropriate in-hospital care for the survivors a logical extension of the chain of survival. In recent years extensive research activity has probed the pathophysiology and pharmacology of postischemic reperfusion. The present review discusses the current understanding of mechanisms for cerebral damage following global ischemia. Promising pharmacological principles for protection or resuscitation from cerebral ischemia are reviewed. None of them are considered ready for clinical application. Clinical guidelines are proposed, based on the reviewed data and previously published clinical observations. Cornerstones of the proposed brain-oriented intensive care protocol are: (1) hemodynamic monitoring and meticulous treatment of circulatory disturbances, (2) controlled ventilation providing normoventilation and normoxia to all comatose patients, (3) avoiding hyperglycemia and hyperthermia in comatose patients, (4) adequate analgesia and sedation, tempered by the understanding that oversedation impedes neurological evaluation without promoting recovery. An accurate prognosis can usually be made 48-72 h after resuscitation. This permits reevaluation and assignment to an appropriate level of continued hospital care.

Multifocal cerebral blood flow by Xe-CT and global cerebral metabolism after prolonged cardiac arrest in dogs. Reperfusion with open-chest CPR or cardiopulmonary bypass

Using the stable xenon-enhanced computed tomography (Xe-CT) method in dogs, we studied local, regional and global cerebral blood flow (LCBF, rCBF and gCBF) in two sham experiments and nine cardiac arrest experiments. Within the same experiments without arrest, gCBF and rCBF values were reproducible and stable. LCBF values varied over time. In group I (n = 4), ventricular fibrillation cardiac arrest (no blood flow) of 10 min was reversed by open-chest cardiopulmonary resuscitation (CPR). In group II (n = 5), ventricular fibrillation cardiac arrest of 12.5 min was reversed by brief closed-chest cardiopulmonary bypass. This was followed by controlled ventilation, normotension, normoxia, normocarbia and normothermia to 4 h (n = 7) or 20 h (n = 2) postarrest. The postarrest CBF patterns were similar in both groups. Open-chest CPR during ventricular fibrillation generated near-baseline gCBF and lower LCBF ranges. During postarrest spontaneous circulation, transient diffuse hyperemia was without low-flow regions, longer in brain stem and basal ganglia than in neocortex. During delayed hypoperfusion at 1-4 h postarrest (n = 9), mean gCBF was 44-60% baseline, rCBF in primarily gray matter regions was 15-49 ml/100 cm3 per min and LCBF voxels with trickle-flow and low-flow values, in percent of CT cut area, were increased over baseline. Global CMRO2 (n = 3 of group II) recovered to near baseline values between 1 and 4 h postarrest, while gCBF and O2 delivery were about 50% baseline (mismatching of O2 uptake and O2 delivery).

Recovery of intracellular pH in cortical brain slices following anoxia studied by nuclear magnetic resonance spectroscopy: role of lactate removal, extracellular sodium and sodium/hydrogen exchange

[31P]- and [1H]nuclear magnetic resonances recorded in an interleaved fashion were used in order to quantify high-energy phosphates, intracellular pH and lactate in cortical brain slices of the guinea-pig superfused in a CO2/HCO3(-)-buffered medium during and after anoxic insults. The volume-averaged intracellular pH and energy status of the preparation following anoxia were determined. In the presence of external Na+, intracellular pH normalized in 3 min and was significantly more alkaline from 10 to 12 min of recovery, but lactate remained elevated for 12 min of reoxygenation following anoxia. The amount of lactate removed was only 40% of the quantity of acid extruded showing operation of H+ neutralizing transmembrane mechanisms other than transport of lactic acid. Amiloride (1 or 2 mM) did not prevent the recovery of intracellular pH, but it blocked the "overshoot" of the alkalinization at 10-12 min of recovery. In a medium containing 70 mM K+, 60 mM Na+ and 0.1 mM Ca2+, the recovery of pH, but not lactate washout, was significantly delayed. Removal of external Na+ caused severe energetic failure, decreases both in oxygen uptake and in N-acetyl aspartate concentration, indicating loss of viable tissue. In Na(+)-free superfusion, lactic acidosis caused a more severe drop in intracellular pH than in the presence of Na+. Complexing of extracellular Ca2+ in the Na(+)-free medium inhibited the acidification by 0.38 pH units during anoxia which is as much as the acidification caused by lactate accumulation in the absence of Na+. In Na(+)-free medium intracellular pH recovered, however, from an anoxic level to a normoxic value in 6 min. Metabolic damage of the slice preparation induced by anoxia in the absence of Na+ was as profound in the presence as in the absence of Ca2+ showing that accumulation of Ca2+ is not the only reason for the damage. It is concluded that recovery of intracellular pH from lactic-acidosis can occur independently of energetic recovery and involves acid extrusion mechanism(s) that is(are) dependent on external Na+ and sensitive to high K+.

Dynamic heterogeneity of cerebral hypoperfusion after prolonged cardiac arrest in dogs measured by the stable xenon/CT technique: a preliminary study

After prolonged cardiac arrest and reperfusion, global cerebral blood flow (gCBF) is decreased to about 50% normal for many hours. Measurement of gCBF does not reveal regional variation of flow or permit testing of hypotheses involving multifocal no-flow or low-flow areas. We employed the noninvasive stable Xenon-enhanced Computerized Tomography (Xe/CT) local CBF (LCBF) method for use in dogs before and after ventricular fibrillation (VF) cardiac arrest of 10 min. This was followed by external cardiopulmonary resuscitation (CPR) and control of cardiovascular pulmonary variables to 7 h postarrest. In a sham (no arrest) experiment, the three CT levels studied showed normal regional heterogeneity of LCBF values, all between 10 and 75 ml/100 cm3 per min for white matter and 20 and 130 ml/100 cm3 per min for gray matter. In four preliminary CPR experiments, the expected global hyperemia at 15 min after arrest, was followed by hypoperfusion with gCBF reduced to about 50% control and increased heterogeneity of LCBF. Trickle flow areas (LCBF less than 10 ml/100 cm3 per min) not present prearrest, were interspersed among regions of low, normal, or even high flow. Regions of 125-500 mm3 with trickle flow or higher flows, in different areas at different times, involving deep and superficial structures migrated and persisted to 6 h, with gCBF remaining low. These preliminary results suggest: no initial no-reflow foci (less than 10 ml/100 cm3 per min) larger than 125 mm3 persisting through the initial global hyperemic phase; delayed multifocal hypoperfusion more severe than suggested by gCBF measurements; and trickle flow areas caused by dynamic factors.

Global cerebral ischemia in piglets under conditions of mild and deep hypothermia

BACKGROUND AND PURPOSE

To investigate the effects of hypothermia on the rate of change and degree of recovery of brain adenosine triphosphate and phosphocreatine concentrations and intracellular pH, we have developed a model that allows phosphorus nuclear magnetic resonance spectroscopy of the intact piglet brain during circulatory arrest.

METHODS

Three groups of piglets were studied. Three control animals underwent cardiopulmonary bypass at normothermia for 1 hour; five group 1 animals underwent bypass at a brain temperature of 15 degrees C, followed by a period of circulatory arrest such that adenosine triphosphate was absent for 21 minutes, followed by 1 hour of reperfusion; and five group 2 animals underwent bypass at a brain temperature of 37 degrees C, followed by a period of circulatory arrest such that adenosine triphosphate was absent for 21 minutes, followed by reperfusion for 1 hour.

RESULTS

Control animals showed no significant metabolic effects of bypass. Group 1 animals showed a slower decay of the adenosine triphosphate and phosphocreatine concentrations than group 2 animals, consistent with a lower metabolic rate, and had a higher pH at the onset of ischemia. Recovery of the adenosine triphosphate concentration was significantly better in group 1 animals (95%) than in group 2 animals (30%) (p less than 0.02), and recovery of the phosphocreatine concentration was also better in group 1 animals (93%) than in group 2 animals (32%) (p less than 0.02). Intracellular pH recovered in group 1 animals, but not in group 2 animals. Regional biochemical assays of metabolites performed in the group 2 piglets and in five pilot piglets exposed to deep hypothermia generally confirmed the spectroscopic findings but demonstrated considerable regional variation, specially in the group 2 piglets' brains.

CONCLUSIONS

We conclude that hypothermia exerts a protective effect on the piglet brain during global ischemia even after the adenosine triphosphate pool has been completely depleted.

A multi-arterial clamping method with arterial hypotension does not bring about complete brain ischemia in dogs

The completeness of brain ischemia with a multi-arterial clamping method in dogs was examined using EEG, evoked potentials (EPs) and vessel staining with Evans blue. EEG was monitored by bipolar parietal lead. EPs stimulating electrodes were inserted into the first thoracic (T1) epidural space and recording electrodes into the C2 epidural space, brain stem and cerebral cortex. EPs were measured at 30 s intervals with 50 measurements each time using 3.0 mA current of 100 microseconds duration. In dogs in which brain ischemia was brought about by ventricular fibrillation (VF group, n = 5) EEG disappeared within 40 s in all dogs and the amplitudes of EPs at the C2 spinal cord, brain stem and cerebral cortex after 10 min ischemia were 57%, 0% and 0%, respectively. In the dogs in which a multi-arterial clamping method (clamping internal thoracic arteries, brachiocephalic trunk and left subclavian artery while lowering systolic arterial pressure (AP) below 50 Torr) was used (AC group, n = 5) EEG was still recognizable at 5 min in 2 dogs and the amplitudes of EPs at the C2, brain stem and cerebral cortex at 10 min ischemia were 103%, 53% and 0%, respectively. Stainings with Evans blue were observed in all soft tissue at and below thoracic level, entire intervertebral venous plexus, venous sinuses of cranial dura mater and spinal cord below the lower part of cervical region. Bright red fluorescence by Evans blue was observed microscopically in the vessels of the spinal cord, brain stem and cerebrum (1 dog only). In conclusion a multi-arterial clamping method with arterial hypotension brings about only incomplete brain ischemia.

Cerebral polyamine metabolism in reversible hypoglycemia of rat: relationship to energy metabolites and calcium

Thirty minutes of insulin-induced reversible hypoglycemic coma (defined in terms of cessation of EEG activity) was produced in anesthetized rats. At the end of the hypoglycemic coma or after recovery for 3, 24, or 72 h induced by glucose infusion, the animals were reanesthetized and their brains frozen in situ. Two control groups were used: untreated controls without prior manipulations, and insulin controls, which received injections of insulin followed by glucose infusion to maintain blood glucose within the physiological range. The brains of these latter animals were frozen 3, 24, or 72 h after glucose infusion. Tissue samples from the cortex, striatum, hippocampus, and thalamus were taken to measure ornithine decarboxylase (ODC) activity, and putrescine and spermidine levels, as well as phosphocreatine (PCr), ATP, glucose, and lactate content. In addition, 20-microns thick coronal sections taken from the striatum and dorsal hippocampus were used for histological evaluation of cell damage and also stained for calcium. Insulin in the absence of hypoglycemia produced a significant increase in ODC activity and putrescine level but had no effect on the profiles of energy metabolites or spermidine. During hypoglycemic coma, brain PCr, ATP, glucose, and lactate levels were sharply reduced, as expected. Energy metabolites normalized after 3 h of recovery. In the striatum, significant secondary decreases in PCr and ATP contents and rises in glucose and lactate levels were observed after 24 h of recovery. ODC activity, and putrescine and spermidine levels were unchanged during hypoglycemic coma. After 3 h of recovery, ODC activity increased markedly throughout the brain, except in the striatum. After 24 h of recovery, ODC activity decreased and approached control values 2 days later. Putrescine levels increased significantly throughout the brain after reversible hypoglycemic coma, the highest values observed after 24 h of recovery (p less than or equal to 0.001, compared with controls). After 72 h of recovery, putrescine levels decreased, but still significantly exceeded control values. Reversible hypoglycemic coma did not produce significant changes in regional spermidine levels except in the striatum, where an approximately 30% increase was observed after 3 and 72 h of recovery (p less than or equal to 0.01 and p less than or equal to 0.05, respectively). Twenty-four hours after hypoglycemic coma, intense calcium staining was apparent in layer III of the cerebral cortex, the lateral striatum, and the crest of the dentate gyrus. After 72 h of recovery, the intense calcium staining included also cortical layer II, the septal nuclei, the subiculum, and the hippocampal CA1-subfield.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of calcium antagonists on EEG, evoked potentials and neurologic recovery after complete global brain ischemia for 15 minutes in dogs

The effects of three calcium antagonists on the recovery from neurologic damages after complete global brain ischemia were examined by evaluating the change of a electroencephalogram (EEG), evoked potentials (EP) and a neurologic recovery score (NRS) in dogs. Fifteen minutes global brain ischemia was achieved by occluding the ascending aorta and the caval veins. Nicardipine (NC), flunarizine (FL) and diltiazem (DL) were administered with continuous infusions for three days after the ischemia. The EEG-EP scores (0 : no response - 6 : normal) 3 hr after the ischemia were 1.4 +/- 0.4 (mean +/- SE) in the control, 2.2 +/- 0.3 in the NC, 2.2 +/- 0.4 in the FL and 2.1 +/- 0.2 in the DL. There were no significant differences between the 4 groups. The survival rates on the 7th day after the ischemia were 67% (6/9) in the control, 78% (7/9) in the NC, 56% (5/9) in the FL and 89% (8/9) in the DL. No significant differences were presented between the 4 groups. The NRSs (0 : death - 100 : normal) on the 7th day were 40.3 +/- 7.3 in the control, 59.0 +/- 8.5 in the NC, 63.2 +/- 9.7 in the FL and 55.7 +/- 3.3 in the DL. Each treated group showed a tendency to have a higher NRS than that in the untreated control group. The NRS in all dogs treated by the Ca(++) antagonists on the 7th day was 58.7 +/- 4.1, which was significantly higher than that in the control group ( P < 0.05). We conclude that the continuous administration of calcium antagonists for three days after the global brain ischemia would be beneficial for the neurologic recovery.