Return of ATP/PCr and EEG after 75 min of global brain ischemia

The beneficial effect of mild therapeutic hypothermia depends on the time of complete circulatory standstill in patients with cardiac arrest

AIM

Mild therapeutic hypothermia has shown to improve long-time survival as well as favorable functional outcome after cardiac arrest. Animal models suggest that ischemic durations beyond 8 min results in progressively worse neurologic deficits. Based on these considerations, it would be obvious that cardiac arrest survivors would benefit most from mild therapeutic hypothermia if they have reached a complete circulatory standstill of more than 8 min.

METHODS

In this retrospective cohort study we included cardiac arrest survivors of 18 years of age or older suffering a witnessed out-of-hospital cardiac arrest, which remain comatose after restoration of spontaneous circulation. Data were collected from 1992 to 2010. We investigated the interaction of 'no-flow' time on the association between post arrest mild therapeutic hypothermia and good neurological outcome. 'No-flow' time was categorized into time quartiles (0, 1-2, 3-8, >8 min).

RESULTS

One thousand-two-hundred patients were analyzed. Hypothermia was induced in 598 patients. In spite of showing a statistically significant improvement in favorable neurologic outcome in all patients treated with mild therapeutic hypothermia (odds ratio [OR]: 1.49; 95% confidence interval [CI]: 1.14-1.93) this effect varies with 'no-flow' time. The effect is significant in patients with 'no-flow' times of more than 2 min (OR: 2.72; CI: 1.35-5.48) with the maximum benefit in those with 'no-flow' times beyond 8 min (OR: 6.15; CI: 2.23-16.99).

CONCLUSION

The beneficial effect of mild therapeutic hypothermia increases with cumulative time of complete circulatory standstill in patients with witnessed out-of-hospital cardiac arrest.

Combination pharmacotherapy improves neurological outcome after asphyxial cardiac arrest

AIM

To study the effects of the combination of adrenaline (epinephrine) and vasopressin compared to adrenaline alone on initial resuscitation success, 24h survival, and neurological outcome in a swine model of asphyxial cardiac arrest (CA).

METHODS

This prospective randomized experimental study was conducted at a laboratory research department. Twenty female Landrace/Large-White pigs, 12-15 weeks of age, were investigated. Asphyxial CA was induced by clamping of the endotracheal tube. After 4min of untreated CA, resuscitation was initiated by unclamping the endotracheal tube, mechanical ventilation, chest compressions and adrenaline (Group A) or a combination of adrenaline with vasopressin (Group A+V) administered intravenously. In case of restoration of spontaneous circulation (ROSC), the animals were monitored for 30min and then observed for 24h.

RESULTS

Hemodynamic variables were measured at baseline during CPR and in the post-resuscitation period. Statistically significant difference was observed in groups A and A+V regarding coronary perfusion pressure (CPP) during the first minute of CPR. In both groups, ROSC and survival rates were comparable (p=NS). Neurological deficit score (NDS) was significantly higher in the combination group 24h following CA (p<0.001). Brain histological damage score (HDS) was also better in the combination group (p<0.001). Total HDS and NDS showed a statistical significant correlation (p<0.001).

CONCLUSIONS

In this porcine model of asphyxial CA, adrenaline alone as well as the combined administration of adrenaline and vasopressin resulted in similar ROSC and survival rates, but the combination of adrenaline and vasopressin resulted in improved neurological and cerebral histopathological outcomes.

Reperfusion normalizes motor activation patterns in large-vessel disease

OBJECTIVE

Hemodynamic impairment in one hemisphere has been shown to trigger ipsilateral motor activation in the opposite hemisphere on functional imaging. We hypothesized that reversing the hypoperfusion would normalize the motor activation pattern.

METHODS

We studied four patients with high-grade stenosis and impaired vasomotor reactivity (VMR) but no stroke. Functional magnetic resonance imaging motor activation pattern before and after VMR normalization was compared with seven healthy control subjects scanned at an interval of 3 months using voxel-wise statistical parametric maps and region of interest analysis. Subjects performed a repetitive hand closure task in synchrony with 1Hz metronome tone. We used repeated-measures analysis of variance to compute the interaction between group (patients/control subjects) and time by obtaining the average blood oxygen level dependent signal of three motor regions of interest in each hemisphere.

RESULTS

Two patients normalized their VMR after spontaneous resolution of dissection, and two after revascularization procedures. Both voxel-wise statistical maps and region of interest analysis showed that VMR normalization was associated in each case with a reduction in the atypical activation in the hemisphere opposite to the previously hypoperfused hemisphere (p < 0.001).

INTERPRETATION

In the presence of a physiological stressor such as hypoperfusion, the brain is capable of dynamic functional reorganization to the opposite hemisphere that is reversible when normal blood flow is restored. These findings are important to our understanding of the clinical consequences of hemodynamic failure and the role of the ipsilateral hemisphere in maintaining normal neurological function.

Chronic ischemia and neurocognition

Cognitive impairment from a major stroke as a consequence of carotid disease is an acknowledged clinical outcome; however, cognitive impairment without major stroke is open to discussion. The three recognized mechanisms for cognitive dysfunction from internal carotid artery are microembolization, white-matter disease, and hypoperfusion. The last has been most difficult to characterize physiologically. In this article, the authors review evidence supporting the existence of chronic ischemia in the brain and its direct impact on cognitive functions. By incorporating the pathophysiology of chronic ischemia into the algorithm of the management of carotid artery disease, we may be able to extend the goals of carotid artery revascularization beyond merely preventing stroke to include preventing or reversing cognitive decline.

Overexpression of GRK2 in Alzheimer disease and in a chronic hypoperfusion rat model is an early marker of brain mitochondrial lesions

Heterotrimeric guanine nucleotide-binding (G) protein-coupled receptor kinases (GRKs) are cytosolic proteins that are known to contribute to the adaptation of the heptahelical G protein-coupled receptors (GPCRs) and to regulate downstream signals through these receptors. GPCRs mediate the action of messengers that are key modulators of cardiac and vascular cell function, such as growth and differentiation. GRKs are members of a multigene family, which are classified into three subfamilies and are found in cardiac, vascular and cerebral tissues. Increasing evidence strongly supports the hypothesis that vascular damage is an early contributor to the development of Alzheimer disease (AD) and/or other pathology that can mimic human AD. Based on this hypothesis, and since kinases of this family are known to regulate numerous receptor functions both in the brain, myocardium and elsewhere, we explored cellular and subcellular localization by immunoreactivity of G protein-coupled receptor kinase 2 (GRK2), also known as beta-adrenergic receptor kinase-1(betaARK1), in the early pathogenesis of AD and in ischemia reperfusion injury models of brain hypoperfusion. In the present study, we used the two-vessel carotid artery occlusion model, namely the 2-VO system that results in chronic brain hypoperfusion (CBH) and mimics mild cognitive impairment (MCI) and vascular changes in AD pathology. Our findings demonstrate the early overexpression of GRK2 member kinase in the cerebrovasculature, especially endothelial cells (EC) following CBH, as well as in select cells from human AD tissue. We found a significant increase in GRK2 immunoreactivity in the EC of AD patients and after CBH, which preceded any amyloid deposition. Since GRK2 activity is associated with certain compensatory changes in brain cellular compartments and in ischemic cardiac tissue, our findings suggest that chronic hypoperfusion initiates oxidative stress in these conditions and appears to be the main initiating injury stimulus for disruption of brain and cerebrovascular homeostasis and metabolism.

Open-chest CPR improves survival and neurologic outcome following cardiac arrest

STUDY OBJECTIVE

To determine if 15 min of open-chest cardiac massage (OC-CPR) versus closed-chest compressions (CC-CPR) improves 72-h survival and neurologic outcome (behavioral and histologic) after 5 min of untreated cardiac arrest.

METHODS

Mongrel dogs were anesthetized and instrumented. Cardiac arrest was induced by KCl injection and after a 5-min period of non-intervention, dogs were randomized to receive either CC-CPR (N = 7) or OC-CPR (N = 5) performed for 15 min. The dogs were then resuscitated and physiologic data was recorded. Surviving dogs were scored at 72 h using canine neurodeficit score of Safar et al. (NDS; 0 = behaviorally normal, 500 = brain death). Dogs that could not be resuscitated or died before 72 h were assigned a score of 500. Brain histology was performed on all survivors.

RESULTS

All OC-CPR dogs were successfully resuscitated and were behaviorally normal at 72 h (NDS = 0). Histology in OC-CPR dogs showed little to no injury. Only three out of the seven CC-CPR dogs survived to 72 h. Of the survivors, one dog exhibited minor ataxia (NDS = 15), and two had incapacitating deficits (both NDS = 180). Two dogs died within 24 h after extubation, and one could not be resuscitated and the other could not be weaned from the ventilator (each NDS = 500). Histology of the CC-CPR survivors revealed moderate to severe lesions. NDS between groups was statistically significant (p < 0.0079).

CONCLUSION

In our canine model of cardiac arrest, OC-CPR significantly improved 72-h survival and neurologic outcome when compared to CC-CPR.

Inhibition of vascular nitric oxide after rat chronic brain hypoperfusion: spatial memory and immunocytochemical changes

An aging rat model of chronic brain hypoperfusion (CBH) that mimics human mild cognitive impairment (MCI) was used to examine the role of nitric oxide synthase (NOS) isoforms on spatial memory function. Rats with CBH underwent bilateral common carotid artery occlusion (2-vessel occlusion (2-VO)) for either 26 or 8 weeks and were compared with nonoccluded sham controls (S-VO). The neuronal and endothelial (nNOS/eNOS) constitutive inhibitor nitro-L-arginine methyl ester (L-NAME) 20 mg/kg was administered after 26 weeks for 3 days to 2-VO and S-VO groups and spatial memory was assessed with a modified Morris watermaze test. Only 2-VO rats worsened their spatial memory ability after L-NAME. Electron microscopic immunocytochemical examination using an antibody against eNOS showed 2-VO rats had significant loss or absence of eNOS-containing positive gold particles in hippocampal endothelium and these changes were associated with endothelial cell compression, mitochondrial damage and heavy amyloid deposition in hippocampal capillaries and perivascular region. In the 8-week study, three groups of 2-VO rats were administered an acute dose of 7-NI, aminoguanidine or L-NIO, the relatively selective inhibitors of nNOS, inducible NOS and eNOS. Only rats administered the eNOS inhibitor L-NIO worsened markedly their watermaze performance (P = 0.009) when compared with S-VO nonoccluded controls. We conclude from these findings that vascular nitric oxide derived from eNOS may play a critical role in spatial memory function during CBH possibly by keeping cerebral perfusion optimal through its regulation of microvessel tone and cerebral blood flow and that disruption of this mechanism can result in spatial memory impairment. These findings may identify therapeutic targets for preventing MCI and treating Alzheimer's disease.

Brain water diffusion in normal and creatine-supplemented rats during transient global ischemia

Brain water diffusion in response to transient global ischemia (12 min), reperfusion (60 min), and cardiac arrest was monitored by localized proton magnetic resonance spectroscopy. The trace of the apparent diffusion coefficient tensor (ADC(Av)) was determined at high temporal resolution (10 sec) to assess the putative neuroprotective potential of oral creatine (Cr) in rats that received 2.2 g Cr-monohydrate per kg body weight per day for 10 days (n = 8) relative to controls (n = 9). Cr-fed rats revealed a statistically significant increase of the cerebral concentration ratio of Cr to choline-containing compounds (20%). The decrease of the ADC(Av) value during acute ischemia showed a three-phasic behavior in line with energy depletion, cytotoxic edema, and brain cooling. In Cr-fed rats, slightly less severe and mildly delayed diffusion changes during ischemia and similar beneficial trends during early reperfusion did not reach statistical significance. Magn Reson Med 42:798-802, 1999.

O2-sensing mechanisms in excitable cells: role of plasma membrane K+ channels

Although carotid chemosensitive glomus cells have been the most extensively studied from the vantage point of how cells sense the lack of O2, it is clear that all tissues sense O2 deprivation. In addition, all mammalian cells can trigger a cascade of events that, depending on the severity and duration of hypoxia-induced stress, can lead to permanent injury and death or to adaptation and survival. Crucial in this cascade, we believe, how the cascade is initiated, how O2 lack is detected by cells, and how these initial steps can activate further processes. In this chapter, we focus on the initial steps of O2 sensing in tissues most commonly studied, i.e. carotid glomus cells, central neurons, smooth muscle cells, and neuro-epithelial bodies of the airways. Recently it has become clear that plasma membranes of various tissues can sense the lack of O2, not only indirectly via alterations in the intracellular milieu (such as pH, Ca, ATP, etc), but also directly through an unknown mechanism that involves plasma-membrane K channels and possibly other membrane proteins. This latter mechanism is suspected to be totally independent of cytosolic changes because excised patches from plasma membranes were used in these experiments from carotid cells and neurons. There are a number of questions in this exciting area of research that pertain to the role of this plasma-membrane O2-sensing mechanism in the overall cell response, identification of all the important steps in O2 sensing, differences between O2-tolerant and O2-susceptible cells, and differences between acute and chronic cell responses to lack of O2.

pH-associated Brain Injury in Cerebral Ischemia and Circulatory Arrest

Neuronal injury remains a major limitation in therapies directed toward cardiopulmonary resuscitation and cerebral ischemia. We summarize clinical and experimental information regarding pH-modulated mechanisms of cerebral ischemic injury and the status of antiacidosis therapies relative to the brain. A large body of evidence in animals and humans indicates that cerebral pH can modulate, and perhaps mediate, ischemic brain pathology and influence functional outcome. The importance of low pH and brain bicarbonate levels during reperfusion as a secondary injury remains an open question of therapeutic importance. Under specific conditions, acidosis may be neuroprotective, but this is an area of current controversy. Effective antiacidosis therapy must address the possibility of synergism and competition among multiple injury mechanisms.

Ischaemia-induced long-term hyperexcitability in rat neocortex

The long-term structural and functional consequences of transient forebrain ischaemia were studied with morphological, immunohistochemical and in vitro electrophysiological techniques in the primary somatosensory cortex of Wistar rats. After survival times of 10-17 months postischaemia, neocortical slices obtained from ischaemic animals were characterized by a pronounced neuronal hyperexcitability in comparison with untreated age-matched controls. Extra- and intracellular recordings in supragranular layers revealed all-or-none long-latency recurrent responses to orthodromic synaptic stimulation of the afferent pathway. These responses were characterized by durations up to 1.7 s, by multiple components and by repetitive synaptic burst discharges. The reversible blockade of this late activity by DL-amino-phosphonovaleric acid (APV) suggested that this activity was mediated by N-methyl-D-aspartate (NMDA) receptors. The peak conductance of inhibitory postsynaptic potentials was significantly smaller in neurons recorded in neocortical slices obtained from ischaemic animals than those from the controls. However, the average number of parvalbumin (PV)-labelled neurons per mm3, indicative of a subpopulation of GABAergic interneurons, and the average number and length of dendritic processes arising from PV-containing cells was not significantly different between ischaemic and control cortex. The prominent dysfunction of the inhibitory system in ischaemic animals occurred without obvious structural alterations in PV-labelled cells, indicating that this subpopulation of GABAergic interneurons is not principally affected by ischaemia. Our data suggest a long-term down-regulation of inhibitory function and a concurrent NMDA receptor-mediated hyperexcitability in ischaemic neocortex. These alterations may result from structural and/or functional properties of inhibitory non-PV-positive neurons or permanent functional modifications on the subcellular molecular level, i.e. alterations in the phosphorylation status of GABA and/or NMDA receptors. The net result of these long-term changes is an imbalance between the excitatory and inhibitory systems in the ischaemic cortex with the subsequent expression and manifestation of intracortical hyperexcitability.

Brain blood flow restoration 'rescues' chronically damaged rat CA1 neurons

Middle aged rats (13 months) were subjected to chronic cerebrovascular insufficiency (CVI) for 9 weeks using a 3-vessel occlusion technique. This CVI injury targets CA1 neuron damage selectively. Three groups of rats had their cerebral blood flow restored after 1, 2 or 3 weeks following CVI by removal of their carotid artery occluders. Another rat group did not undergo deocclusion for the 9 week observation period. Rats were tested for memory acquisition and retention 6 and 9 weeks after CVI using a modified water maze test. At the end of the 9 weeks, cerebral blood flow was measured in the fronto-parietal cortex and rats were killed by fixation-perfusion. Hippocampal morphometry was done to assess the % of damaged CA1 neurons and the density of GFAP-positive hyperplasia and hypertrophy. Results show that restoration of cerebral blood flow 1 and 2 weeks after CVI but not after 3 weeks of CVI, reversed a significant increase in reactive astrocytosis and prevented memory impairment in these deoccluded rats when compared to the non-deoccluded group. It appears from these results that 'neuronal rescue' of CA1 neurons is possible when cerebral blood flow is restored in rats subjected to chronic CVI during a 2 week (but not 3 week) 'window of opportunity'. This chronic brain ischemia model may be useful in screening potential therapy in patients with dementia where spatial memory impairment and hippocampal damage may be manifested.

Simultaneous 31P NMR spectroscopy and laser Doppler flowmetry of rat brain during global ischemia and reperfusion

The relationship between blood flow and metabolism was studied in halothane-anaesthetized, normothermic rats submitted to 30 min global ischemia by four-vessel occlusion. Phosphocreatine (PCr), ATP, intracellular pH and intracellular magnesium (pMg) were measured by 31P NMR spectroscopy, and blood flow by laser Doppler flowmetry. Prior to ischemia the PCr/ATP ratio of fully relaxed spectra was 2.4 +/- 0.3, intracellular pH was 7.26 +/- 0.15 and pMg was 3.26 +/- 0.13. Vascular occlusion led to complete cessation of blood flow in four out of eight rats, and to incomplete ischaemia (< 10% of control) in the other four animals. During vascular occlusion EEG flattened and energy metabolism broke down in all but one animal with a residual blood flow of 8% of control. pH declined to 6.70 +/- 0.08. The speed of electrophysiological and metabolic recovery after 30 min ischemia varied considerably from animal to animal. Variability depended mainly on the recirculation delay (i.e., the interval from vascular release to normalization of blood flow) but was independent of residual blood flow during ischemia, pre-ischemic glucose, ischemic or post-ischemic acidosis, or the degree of post-ischemic hypoperfusion. After 3 h recirculation PCr and intracellular pH returned to normal but pMg was slightly increased, and ATP was reduced by up to 50% in all animals except the rat with incomplete breakdown of energy metabolism during ischemia. The dissociation between PCr and ATP is attributed to a loss of total adenylate, the severity of which depends on the quality of post-ischemic recirculation.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlation between electroencephalogram isoelectric time and hippocampal norepinephrine levels, measured by microdialysis, during ischemia in rats

It is suggested that norepinephrine (NE) plays a role during transient forebrain ischemia. NE may have a protective action against neuronal cell death in the hippocampus, or it may be one of the causes of injurious ischemic effects. We used the microdialysis technique to study extracellular NE levels in the rat hippocampus before, during, and after 30 min of transient incomplete forebrain ischemia (induced by four-vessel occlusion) to describe the time course of NE in this condition. There was a maximal increase (fivefold) in extracellular NE after 10 min of reflow only when the electroencephalogram was isoelectric. NE levels returned to baseline 40 min after release of the carotid clamps and remained constant for the next 80 min. Thus there appears to be a transient NE overflow in the hippocampus during ischemia, closely related to the complete loss of brain electrical activity.

Chronic cerebrovascular insufficiency induces dementia-like deficits in aged rats

Young and aged rats were subjected to cerebrovascular insufficiency (CVI) for 3 and 9 weeks. At the end of each time period, local cerebral blood flow (lCBF), spatial memory function, 31P- and 1H-NMR spectroscopy and imaging of the brains were evaluated in vivo. Morphometric counts of CA1 hippocampal neuron damage and staining for glial fibrillary acidic protein (GFAP) were done post-mortem. Results show that after 3 weeks of CVI, cortical and hippocampal lCBF was significantly reduced in young and aged animals respectively. In addition, young and aged rats at 3 weeks following CVI showed spatial memory deficits in the Morris water maze and elevation of 31P-phosphomonoester as measured by non-invasive NMR spectroscopy. At the same time period, in vivo 1H-microimaging (MRI) of brains showed areas of high signal intensity (suggesting local edema) localized asymmetrically to the right hippocampal region in young and aged CVI rats. Morphometry of the hippocampal CA1 sector at post-mortem confirmed the in vivo MRI changes and demonstrated that a significant percentage of the CA1 pyramidal cells were damaged after CVI. Nine weeks after CVI, hippocampal CBF reductions, spatial memory impairment, spectroscopic-microimaging changes and CA1 sector cell damage continued to be observed in the aged animals but were resolved in the young rat brains. In addition, GFAP immunoreaction progressively increased in the hippocampus of aged rats subjected to CVI for 9 weeks. It is concluded that cognitive, metabolic and morphologic damage was significantly more severe and longer lasting in aged than young rat brain after chronic CVI. The deficits observed in this rat model appear to mimic the early pathology reported in Alzheimer's disease and suggest that the present model could provide fundamental clues relative to the etiology and possible management of this dementia.

The no-reflow phenomenon is a post-mortem artifact

Post-ischemic reperfusion impairment, ("no-reflow phenomenon"), was studied in rats subjected to 8-30 minutes of global brain ischemia. During ischemia, rapid and complete loss of cerebral blood flow, EEG and 31P-high energy phosphates (ATP/PCr) was observed. Brain intravascular perfusion defects were examined by injecting carbon black intravenously in a group of rats with stable cardiopulmonary function and in another group subjected to rapid thoracotomy and intraarterial infusion of the carbon marker. Results indicate that global brain ischemic or non-ischemic control rats given intraarterial carbon black after thoracotomy had varying degrees of vessel filling defects in brain resulting in "pale tissue areas" suggestive of impaired perfusion (no-reflow). All rats given carbon black intravenously whether global brain ischemic or not, showed normal cerebrovascular filling of the carbon black and absence of "pale tissue areas". In addition, post-ischemic cerebral reperfusion following 8-30 minutes global brain ischemia can reverse neuroelectric, energy metabolite and cerebral blood flow loss in rats whose cardiopulmonary function is not compromised. These findings indicate that the "no-reflow phenomenon" is an agonal or post-mortem artifact observed in the presence of cardiopulmonary failure.

Partial or global rat brain ischemia: the SCOT model

A model for inducing partial (PBI) or global brain ischemia (GBI) in awake or anesthetized rats was obtained by ligating one subclavian and both carotid arteries (for PBI) or both subclavian-carotid arteries (for GBI). Rats were intubated and ventilated mechanically then subjected to a midline ventral incision from larynx to xiphoid process. The thorax was entered to expose the aortic arch and either one or both subclavians were ligated to eliminate each vertebral artery supply to brain. After chest closure the common carotid arteries were exposed and immediately ligated or else catheter snares were installed to induce ischemia at a later date. PBI was induced in 3 groups of rats for 7, 30 and 60 days while GBI was given for 5, 10, 30 and 75 minutes in 4 other groups. EEG became flat within 15 seconds after GBI and cortical cerebral blood flow (CBF) was reduced to "zero." EEG was unaffected after PBI but cortical CBF was reduced from a mean 118 ml/100 g tissue/min to 77 ml after 7 days. Morphological damage of CA1 hippocampal neurons after GBI or PBI was found reproducible and time dependent on ischemic duration. Acute cell damage rose from 5-95% in CA1 as GBI duration increased from 5-75 minutes. Similarly, chronic cell damage of CA1 increased as ischemic duration continued from 7-60 days in rats subjected to PBI. The advantages of the present model provide the option of inducing partial or global brain ischemia and of introducing postischemic reperfusion in awake or anesthetized preparations without the use of drugs, blood pressure manipulation or direct contact with brain tissue.(ABSTRACT TRUNCATED AT 250 WORDS)