Mild hypothermia preserves cerebral cortex microcirculation after resuscitation in a rat model of cardiac arrest

COMBINATION OF HYPEROXYGENATION AND TARGETED TEMPERATURE MANAGEMENT IMPROVES FUNCTIONAL OUTCOMES OF POST CARDIAC ARREST SYNDROME IRRESPECTIVE OF CAUSES OF ARREST IN RATS

ABSTRACT

Background: The high mortality rates of patients who are resuscitated from cardiac arrest (CA) are attributed to post cardiac arrest syndrome (PCAS). This study evaluated the effect of hyperoxygenation and targeted temperature management (TTM) on PCAS in rats with different causes of CA. Methods and Results: One hundred sixty-eight Sprague-Dawley rats were equally divided into asphyxial and dysrhythmic groups. Animals were further randomized into four subgroups immediately after resuscitation: normoxia-normothermia (NO-NT), ventilated with 21% oxygen under normothermia; hyperoxia-normothermia (HO-NT), ventilated with 100% oxygen for 3 hours under normothermia; normoxia-hypothermia (NO-HT), ventilated with 21% oxygen for 3 hours under hypothermia; and hyperoxia-hypothermia (HO-HT), ventilated with 100% oxygen for 3 hours under hypothermia. Post resuscitation cardiac dysfunction, neurological recovery, and pathological analysis were assessed. For asphyxial CA, HO-NT and HO-HT (68.8% and 75.0%) had significantly higher survival than NO-NT and NO-HT (31.3% and 31.3%). For dysrhythmic CA, NO-HT and HO-HT (81.3% and 87.5%) had significantly higher survival than NO-NT and HO-NT (44.0% and 50.0%). When all of the rats were considered, the survival rate was much higher in HO-HT (81.3%). Compared with NO-NT (57.7% ± 14.9% and 40.3% ± 7.8%), the collagen volume fraction and the proportion of fluoro-jade B-positive area in HO-HT (14.0% ± 5.7% and 28.0% ± 13.3%) were significantly reduced. Conclusion: The beneficial effects of hyperoxygenation and TTM are dependent on the cause of arrest: hyperoxygenation benefits asphyxial, whereas TTM benefits dysrhythmic CA. The combination of hyperoxygenation and TTM could effectively improve the functional outcome of PCAS regardless of the cause of CA.

Optimal inhaled oxygen and carbon dioxide concentrations for post-cardiac arrest cerebral reoxygenation and neurological recovery

Prolonged cerebral hypoperfusion after the return of spontaneous circulation (ROSC) from cardiac arrest (CA) may lead to poor neurological recovery. In a 7-min asphyxia-induced CA rat model, four combinations of inhaled oxygen (iO2) and carbon dioxide (iCO2) were administered for 150 min post-ROSC and compared in a randomized animal trial. At the end of administration, the partial pressure of brain tissue oxygenation (PbtO2) monitored in the hippocampal CA1 region returned to the baseline for the 88% iO2 [ΔPbtO2, median: -0.39 (interquartile range: 5.6) mmHg] and 50% iO2 [ΔpbtO2, -2.25 (10.9) mmHg] groups; in contrast, PbtO2 increased substantially in the 88% iO2+12% iCO2 [ΔpbtO2, 35.05 (16.0) mmHg] and 50% iO2+12% iCO2 [ΔpbtO2, 42.03 (31.7) mmHg] groups. Pairwise comparisons (post hoc Dunn's test) indicated the significant role of 12% iCO2 in augmenting PbtO2 during the intervention and improving neurological recovery at 24 h post-ROSC. Facilitating brain reoxygenation may improve post-CA neurological outcomes.

A Commentary on the Effect of Targeted Temperature Management in Patients Resuscitated from Cardiac Arrest

The members of the International Liaison Committee on Resuscitation (ILCOR) Advanced Life Support Task Force have written a comprehensive summary of trials of the effectiveness of induced hypothermia (IH) or targeted temperature management (TTM) in comatose patients after cardiac arrest (CA). However, in-depth analysis of these studies is incomplete, especially since there was no significant difference in primary outcome between hypothermia versus normothermia in the recently reported TTM2 trial. We critically appraise trials of IH/TTM versus normothermia to characterize reasons for the lack of treatment effect, based on a previously published framework for what to consider when the primary outcome fails. We found a strong biologic rationale and external clinical evidence that IH treatment is beneficial. Recent TTM trials mainly included unselected patients with a high rate of bystander cardiopulmonary resuscitation. The treatment was not applied as intended, which led to a large delay in achievement of target temperature. While receiving intensive care, sedative drugs were likely used that might have led to increased neurologic damage as were antiplatelet drugs that could be associated with increased acute stent thrombosis in hypothermic patients. It is reasonable to still use or evaluate IH treatment in patients who are comatose after CA as there are multiple plausible reasons why IH compared to normothermia did not significantly improve neurologic outcome in the TTM trials.

Recent developments and controversies in therapeutic hypothermia after cardiopulmonary resuscitation

Therapeutic hypothermia was recommended as the only neuroprotective treatment in comatose patients after return of spontaneous circulation (ROSC). With new evidence suggesting a similar neuroprotective effect of 36 °C and 33 °C, the term "therapeutic hypothermia" was substituted by "targeted temperature management" in 2011, which in turn was replaced by the term "temperature control" in 2022 because of new evidence of the similar effects of target normothermia and 33 °C. However, there is no clear consensus on the efficacy of therapeutic hypothermia. In this article, we provide an overview of the recent evidence from basic and clinical research related to therapeutic hypothermia and re-evaluate its application as a post-ROSC neuroprotective intervention in clinical settings.

Inhaled Carbon Dioxide Improves Neurological Outcomes by Downregulating Hippocampal Autophagy and Apoptosis in an Asphyxia‐Induced Cardiac Arrest and Resuscitation Rat Model

Background

Protracted cerebral hypoperfusion following cardiac arrest (CA) may cause poor neurological recovery. We hypothesized that inhaled carbon dioxide (CO₂) could augment cerebral blood flow (CBF) and improve post‐CA neurological outcomes.

Methods and Results

After 6‐minute asphyxia‐induced CA and resuscitation, Wistar rats were randomly allocated to 4 groups (n=25/group) and administered with different inhaled CO₂ concentrations, including control (0% CO₂), 4% CO₂, 8% CO₂, and 12% CO₂. Invasive monitoring was maintained for 120 minutes, and neurological outcomes were evaluated with neurological function score at 24 hours post‐CA. After the 120‐minute experiment, CBF was 242.3% (median; interquartile range, 221.1%–267.4%) of baseline in the 12% CO₂ group while CBF fell to 45.8% (interquartile range, 41.2%–58.1%) of baseline in the control group (P<0.001). CBF increased along with increasing inhaled CO₂ concentrations with significant linear trends (P<0.001). At 24 hours post‐CA, compared with the control group (neurological function score, 9 [interquartile range, 8–9]), neurological recovery was significantly better in the 12% CO₂ group (neurological function score, 10 [interquartile range, 9.8–10]) (P<0.001) while no survival difference was observed. Brain tissue malondialdehyde (P=0.02) and serum neuron‐specific enolase (P=0.002) and S100β levels (P=0.002) were significantly lower in the 12% CO₂ group. TUNEL (terminal deoxynucleotidyl transferase–mediated biotin–deoxyuridine triphosphate nick‐end labeling)‐positive cell densities in hippocampal CA1 (P<0.001) and CA3 (P<0.001) regions were also significantly reduced in the 12% CO₂ group. Western blotting showed that beclin‐1 (P=0.02), p62 (P=0.02), and LAMP2 (lysosome‐associated membrane protein 2) (P=0.01) expression levels, and the LC3B‐II:LC3B‐I ratio (P=0.02) were significantly lower in the 12% CO₂ group.

Conclusions

Administering inhaled CO₂ augmented post‐CA CBF, mitigated oxidative brain injuries, ameliorated neuronal injury, and downregulated apoptosis and autophagy, thereby improving neurological outcomes.

The Effects of Temperature Management on Brain Microcirculation, Oxygenation and Metabolism

Purpose: Target temperature management (TTM) is often used in patients after cardiac arrest, but the effects of cooling on cerebral microcirculation, oxygenation and metabolism are poorly understood. We studied the time course of these variables in a healthy swine model.Methods: Fifteen invasively monitored, mechanically ventilated pigs were allocated to sham procedure (normothermia, NT; n = 5), cooling (hypothermia, HT, n = 5) or cooling with controlled oxygenation (HT-Oxy, n = 5). Cooling was induced by cold intravenous saline infusion, ice packs and nasal cooling to achieve a body temperature of 33–35 °C. After 6 h, animals were rewarmed to baseline temperature (within 5 h). The cerebral microvascular network was evaluated (at baseline and 2, 7 and 12 h thereafter) using sidestream dark-field (SDF) video-microscopy. Cerebral blood flow (laser Doppler MNP100XP, Oxyflow, Oxford Optronix, Oxford, UK), oxygenation (PbtO₂, Licox catheter, Integra Lifesciences, USA) and lactate/pyruvate ratio (LPR) using brain microdialysis (CMA, Stockholm, Sweden) were measured hourly. Results: In HT animals, cerebral functional capillary density (FCD) and proportion of small-perfused vessels (PSPV) significantly decreased over time during the cooling phase; concomitantly, PbtO₂ increased and LPR decreased. After rewarming, all microcirculatory variables returned to normal values, except LPR, which increased during the rewarming phase in the two groups subjected to HT when compared to the group maintained at normothermia. Conclusions: In healthy animals, TTM can be associated with alterations in cerebral microcirculation during cooling and altered metabolism at rewarming.

Effects of NLRP3 inflammasome blockade on postresuscitation cerebral function in a rat model of cardiopulmonary resuscitation

Cardiac arrest (CA) remains a major public health issue. Inflammatory responses with overproduction of interleukin-1β regulated by NLRP3 inflammasome activation play a crucial role in cerebral ischemia/reperfusion injury. We investigated the effects of the selective NLRP3-inflammasome inhibitor MCC950 on post-resuscitation cerebral function and neurologic outcome in a rat model of cardiac arrest. Thirty-six male rats were randomized into the MCC950 group, the control group, or the sham group (N = 12 of each group). Each group was divided into a 6 h non-survival subgroup (N = 6) and a 24 h survival subgroup (N = 6). Ventricular fibrillation (VF) was electrically induced and untreated for 6 min, followed by 8 min of precordial compressions and mechanical ventilation. Resuscitation was attempted with a 4J defibrillation. Either MCC950 (10 mg/kg) or vehicle was injected intraperitoneally immediately after the return of spontaneous circulation (ROSC). Rats in the sham group underwent the same surgical procedures without VF and CPR. Brain edema, cerebral microcirculation, plasma interleukin Iβ (IL-1β), and neuron-specific enolase (NSE) concentration were measured at 6 h post-ROSC of non-survival subgroups, while 24 h survival rate, neurological deficits were measured at 24 h post-ROSC of survival subgroups. Post-resuscitation brain edema was significantly reduced in animals treated with MCC950 (p < 0.05). Cerebral perfused vessel density (PVD) and microcirculatory flow index (MFI) values were significantly higher in the MCC950 group compared with the control group (p < 0.05). The plasma concentrations of IL-1β and NSE were significantly decreased in animals treated with MCC950 compared with the control group (p < 0.05). 24 h-survival rate and neurological deficits score (NDS) was also significantly improved in the MCC950 group compared with the control group (p < 0.05). NLRP3 inflammasome blockade with MCC950 at ROSC reduces the circulatory level of IL-1β, preserves cerebral microcirculation, mitigates cerebral edema, improves the 24 h-survival rate, and neurological deficits.

Quantitative magnetic resonance imaging assessment of brain injury after successful cardiopulmonary resuscitation in a rat model of asphyxia cardiac arrest

The aim of this study was to use dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and diffusion-weighted magnetic resonance imaging (DWI) to measure changes in blood-brain barrier (BBB) permeability and cerebral edema over time in a rat model of asphyxial cardiac arrest (ACA). ACA was established by endotracheal tube clamping. Male rats were randomized into a sham group (n = 5) and three ACA groups (n = 18). After return of spontaneous circulation (ROSC), the rats were randomized to perform DWI and DCE-MRI exam in the 6 h, 24 h and 72 h timepoint (ROSC + 6 h, ROSC + 24 h, and ROSC + 72 h). Results shows that fifteen of 18 animals achieved successful resuscitation in the ACA groups. The average apparent diffusion coefficient(ADC) value of the whole brain in ROSC + 6 h was markedly lower than those of the sham, ROSC + 24 h, and ROSC + 72 h. The aquaporin-4(AQP4) score in ROSC + 6 h was significantly higher than those in the other groups, which were negatively correlated with the ADC values. The ratio of whole brain to masseter muscle of volume transfer constant (rK^trans), tissue interstitium-to-plasma rate constant(rK_ep), and fractional extra-cellular space volume(rV_e) in ROSC + 6 h were all significantly higher than those in the sham, ROSC + 24 h, and ROSC + 72 h. The transforming growth factor β1(TGF-β1) and vascular endothelial growth factor A(VEGF-a) scores in ROSC + 6 h were significantly higher than those in the other groups, which were all positively correlated with rK^trans and rK_ep. In conclusions, brain injury is a frequent complication after CA and resuscitation. DWI and DCE-MRI can quantitatively evaluate brain injury in term of cerebral edema and BBB permeability after successful CPR.

Development and Evaluation of a Novel Mouse Model of Asphyxial Cardiac Arrest Revealed Severely Impaired Lymphopoiesis After Resuscitation

Background Animal disease models represent the cornerstone in basic cardiac arrest (CA) research. However, current experimental models of CA and resuscitation in mice are limited. In this study, we aimed to develop a mouse model of asphyxial CA followed by cardiopulmonary resuscitation (CPR), and to characterize the immune response after asphyxial CA/CPR. Methods and Results CA was induced in mice by switching from an O2/N2 mixture to 100% N2 gas for mechanical ventilation under anesthesia. Real-time measurements of blood pressure, brain tissue oxygen, cerebral blood flow, and ECG confirmed asphyxia and ensuing CA. After a defined CA period, mice were resuscitated with intravenous epinephrine administration and chest compression. We subjected young adult and aged mice to this model, and found that after CA/CPR, mice from both groups exhibited significant neurologic deficits compared with sham mice. Analysis of post-CA brain confirmed neuroinflammation. Detailed characterization of the post-CA immune response in the peripheral organs of both young adult and aged mice revealed that at the subacute phase following asphyxial CA/CPR, the immune system was markedly suppressed as manifested by drastic atrophy of the spleen and thymus, and profound lymphopenia. Finally, our data showed that post-CA systemic lymphopenia was accompanied with impaired T and B lymphopoiesis in the thymus and bone marrow, respectively. Conclusions In this study, we established a novel validated asphyxial CA model in mice. Using this new model, we further demonstrated that asphyxial CA/CPR markedly affects both the nervous and immune systems, and notably impairs lymphopoiesis of T and B cells.

Overnight Caloric Restriction Prior to Cardiac Arrest and Resuscitation Leads to Improved Survival and Neurological Outcome in a Rodent Model

While interest toward caloric restriction (CR) in various models of brain injury has increased in recent decades, studies have predominantly focused on the benefits of chronic or intermittent CR. The effects of ultra-short, including overnight, CR on acute ischemic brain injury are not well studied. Here, we show that overnight caloric restriction (75% over 14 h) prior to asphyxial cardiac arrest and resuscitation (CA) improves survival and neurological recovery as measured by, behavioral testing on neurological deficit scores, faster recovery of quantitative electroencephalography (EEG) burst suppression ratio, and complete prevention of neurodegeneration in multiple regions of the brain. We also show that overnight CR normalizes stress-induced hyperglycemia, while significantly decreasing insulin and glucagon production and increasing corticosterone and ketone body production. The benefits seen with ultra-short CR appear independent of Sirtuin 1 (SIRT-1) and brain-derived neurotrophic factor (BDNF) expression, which have been strongly linked to neuroprotective benefits seen in chronic CR. Mechanisms underlying neuroprotective effects remain to be defined, and may reveal targets for providing protection pre-CA or therapeutic interventions post-CA. These findings are also of high importance to basic sciences research as we demonstrate that minor, often-overlooked alterations to pre-experimental dietary procedures can significantly affect results, and by extension, research homogeneity and reproducibility, especially in acute ischemic brain injury models.

Synergistic Effects of Moderate Therapeutic Hypothermia and Levosimendan on Cardiac Function and Survival After Asphyxia-Induced Cardiac Arrest in Rats

Background

This study investigated whether levosimendan, an inotropic calcium sensitizer, when combined with moderate therapeutic hypothermia, may exert synergistic benefits on post–cardiac arrest myocardial dysfunction and improve outcomes.

Methods and Results

After 9.5‐minute asphyxia‐induced cardiac arrest and resuscitation, 48 rats were randomized equally into 4 groups following return of spontaneous circulation (ROSC), including normothermia, hypothermia, normothermia–levosimendan, and hypothermia–levosimendan groups. For the normothermia group, the target temperature was 37°C while for the hypothermia group, the target temperature was 32°C, both of which were to be maintained for 4 hours after ROSC. Levosimendan was administered after ROSC with a loading dose of 10 μg/kg and then infused at 0.1 μg/kg per min for 4 hours. In the hypothermia–levosimendan group, left ventricular systolic function and cardiac output increased significantly, whereas the heart rate and systemic vascular resistance decreased significantly compared with the normothermia group. Also, the concentrations of interleukin 1β at 4 hours post‐ROSC and the production of NO between 1 hour and 4 hours post‐ROSC were reduced significantly in the hypothermia–levosimendan group compared with the normothermia group. The 72‐hour post‐ROSC survival and neurological recovery were also significantly better in the hypothermia–levosimendan group compared with the normothermia group (survival, 100% versus 50%, χ² test, P=0.006).

Conclusions

Compared with normothermia, only combined moderate therapeutic hypothermia and levosimendan treatment could consistently improve post–cardiac arrest myocardial dysfunction and decrease the release of pro‐inflammatory molecules, thereby improving survival and neurological outcomes. These findings suggest synergistic benefits between moderate therapeutic hypothermia and levosimendan.

Conjunctival microcirculation is associated with cerebral cortex microcirculation in post-resuscitation mild hypothermia: A rat model

OBJECTIVE

This study aimed to compare the changes in sublingual and conjunctival microcirculation occurring with cerebral cortex microcirculation changes during mild hypothermia in a rat model of cardiac arrest.

METHODS

Twenty-four rats were randomized into mild hypothermia (M) or normothermia (C) groups. Ventricular fibrillation was electrically induced and left untreated for 8 minutes, followed by 8 minutes of cardiopulmonary resuscitation. The core temperature in group M reduced to 33 ± 0.5°C at 13 minutes after restoration of spontaneous circulation and was maintained for 8 hours. In group C, the core temperature was maintained at 37 ± 0.2°C. The hemodynamics and microcirculation in the sublingual region, bulbar conjunctiva, and cerebral cortex were measured at baseline and 1, 2, 3, 4, 6, and 8 hours after restoration of spontaneous circulation.

RESULTS

The M group showed significantly worse sublingual microcirculation at 6 hours post-resuscitation. However, microcirculation in the conjunctiva and cerebral cortex at 3 hours post-resuscitation were better in the M group. In the M group, microcirculation in the cerebral cortex was significantly correlated with that in the conjunctiva but not the sublingual microcirculation.

CONCLUSIONS

Changes in conjunctival microcirculation are closely related to cerebral cortex microcirculation during mild hypothermia, indicating that cerebral cortex microcirculation could be monitored by measuring conjunctival microcirculation.

Therapeutic Hypothermia Improves Hind Limb Motor Outcome and Attenuates Oxidative Stress and Neuronal Damage in the Lumbar Spinal Cord Following Cardiac Arrest

Hypothermia enhances outcomes of patients after resuscitation after cardiac arrest (CA). However, the underlying mechanism is not fully understood. In this study, we investigated effects of hypothermic therapy on neuronal damage/death, microglial activation, and changes of endogenous antioxidants in the anterior horn in the lumbar spinal cord in a rat model of asphyxial CA (ACA). A total of 77 adult male Sprague–Dawley rats were randomized into five groups: normal, sham ACA plus (+) normothermia, ACA + normothermia, sham ACA + hypothermia, and ACA + hypothermia. ACA was induced for 5 min by injecting vecuronium bromide. Therapeutic hypothermia was applied after return of spontaneous circulation (ROSC) via rapid cooling with isopropyl alcohol wipes, which was maintained at 33 ± 0.5 °C for 4 h. Normothermia groups were maintained at 37 ± 0.2 °C for 4 h. Neuronal protection, microgliosis, oxidative stress, and changes of endogenous antioxidants were evaluated at 12 h, 1 day, and 2 days after ROSC following ACA. ACA resulted in neuronal damage from 12 h after ROSC and evoked obvious degeneration/loss of spinal neurons in the ventral horn at 1 day after ACA, showing motor deficit of the hind limb. In addition, ACA resulted in a gradual increase in microgliosis with time after ACA. Therapeutic hypothermia significantly reduced neuronal loss and attenuated hind limb dysfunction, showing that hypothermia significantly attenuated microgliosis. Furthermore, hypothermia significantly suppressed ACA-induced increases of superoxide anion production and 8-hydroxyguanine expression, and significantly increased superoxide dismutase 1 (SOD1), SOD2, catalase, and glutathione peroxidase. Taken together, hypothermic therapy was found to have a substantial impact on changes in ACA-induced microglia activation, oxidative stress factors, and antioxidant enzymes in the ventral horn of the lumbar spinal cord, which closely correlate with neuronal protection and neurological performance after ACA.

The Effect of Therapeutic Mild Hypothermia on Brain Microvascular Endothelial Cells During Ischemia-Reperfusion Injury

BACKGROUND

To determine the cerebral protective effects of mild hypothermia (MH) on cerebral microcirculation.

METHODS

We established ischemia-reperfusion (I/R) injury and MH treatment models with rat brain microvascular endothelial cells (RBMECs) in vitro and examined the apoptotic changes. The cultured RBMECs were randomly divided into the control group, I/R group, and MH group, which was further divided into two subgroups: intra-ischemia hypothermia (IIH) and post-ischemia hypothermia (PIH). Cell morphological changes were assessed using fluorescence microscopy. Apoptotic rates were obtained by flow cytometry. Expressions of caspase-3, Bax, and Bcl-2 were analyzed by Western blot.

RESULTS

I/R injury in vitro induced apoptosis of RBMECs. The apoptotic rates in the control group, I/R group, and MH group were 0.13, 19.04, and 13.13%, respectively (P < 0.01). Compared with the I/R group, the MH group showed a significant decrease in the number of apoptotic cells, mainly in stage I apoptotic cells (P < 0.0083). The caspase-3 and Bax expressions were significantly enhanced (P < 0.05) in RBMECs after I/R injury, while substantial decreases in Bcl-2 expression were noted (P < 0.05). Following MH intervention, the increase in caspase-3 and Bax expression was suppressed (P < 0.05), while Bcl-2 expression significantly increased. The apoptotic rates or protein expressions between the two subgroups were not different significantly (P > 0.05).

CONCLUSIONS

These results indicate that MH could inhibit RBMEC apoptosis by preventing pro-apoptotic cells and early apoptotic cells from progressing to intermediate and advanced stages. This may be due to the effect of MH on I/R-induced apoptotic gene expression changes.

Ultrasound improves the outcomes of cardiopulmonary resuscitation in rats by stimulating the cholinergic anti‑inflammatory pathway

The present study investigated the effects of the ultrasound (US), a noninvasive technique, on ischemia-reperfusion injury (IRI) following cardiopulmonary resuscitation (CPR). The animals used in the present study were randomized into five groups (n=8 per group) as follows: i) The CPR group, where the rats underwent 6 min of untreated ventricular fibrillation (VF) followed by CPR and defibrillation; ii) the US group, in which the treatment was identical to the CPR group with the exception that rats were exposed to US treatment 24 h prior to CPR; iii) the MLA group, in which the treatment was identical to the US group with the exception that the α7 nicotinic acetylcholine receptor (α7nAChR) antagonist MLA (4 mg/kg) was administered 30 min prior to US and VF respectively; iv) the GTS group, in which the treatment was identical to the CPR group with the exception that the α7nAChR agonist GTS-21 (4 mg/kg) was injected 30 min prior to VF; and v) the SHAM group, in which the rats were exposed to surgical preparation without CPR and US application. At 1 day prior to CPR, the US treatment was administered to the left kidney by US pulses (contrast general mode with 9 MHz) with a bursting mechanical index of 0.72 for 2 min. Following treatment of the left kidney, the right kidney was exposed to identical US treatment for an additional 2 min. The results demonstrated that US preconditioning decreased the number of defibrillations required and shortened the duration of CPR. US also suppressed tumor necrosis factor-α and interleukin-6 levels following resuscitation (P<0.05), and a significantly longer overall survival time was observed in the US-treated animals (P<0.01). In addition, US attenuated neuronal injury and promoted the expression of α7nAChR in hippocampal neurons (P<0.05). However, the protective effects of US were abolished by MLA and imitated by GTS-21. The results of the present study demonstrated that prior exposure to US may improve animal outcomes following CPR, and the protective effects of US may be dependent on the cholinergic anti-inflammatory pathway (CAP) via α7nAChR.

CPCGI confers neuroprotection by enhancing blood circulation and neurological function in cerebral ischemia/reperfusion rats

The current study used a rat middle cerebral artery occlusion (MCAO) model with the aim to explore the effects of compound porcine cerebroside and ganglioside injection (CPCGI) on brain ischemia/reperfusion injury in rats. Improvement in the infarct‑side microcirculation and the overall recovery of neurological function were detected by triphenyltetrazolium chloride staining, laser speckle blood flow monitoring, latex perfusion, immunofluorescence and immunoblotting. The results revealed that administration of CPCGI for 7 consecutive days following ischemic stroke contributed to the recovery of neurological function and the reduction of cerebral infarct volume in rats. Blood flow monitoring results demonstrated that the administration of CPCGI effectively promoted cerebral blood flow following stroke, and contributed to the protection of the ischemic side blood vessels. In addition, CPCGI treatment increased the numbers of new blood vessels in the peripheral ischemic region, and upregulated the expression levels of vascular endothelial growth factor, angiopoietin 1 and its receptor TEK receptor tyrosine kinase, fibroblast growth factor and Wnt signaling pathway‑associated proteins. Taken together, the present results indicated that CPCGI improved the blood circulation and neurological function following cerebral ischemia/reperfusion in rats.

Mild hypothermia reduces endoplasmic reticulum stress-induced apoptosis and improves neuronal functions after severe traumatic brain injury

BACKGROUND

Mild hypothermia is wildly used in clinical treatment of traumatic brain injury (TBI). However, the effect of mild hypothermia on endoplasmic reticulum (ER) stress-induced apoptosis after severe TBI is still unknown.

METHODS

In the present study, we used BALB/c mice to investigate the efficacy of posttraumatic mild hypothermia in reducing ER stress. Severe TBI was induced by controlled cortical impact injury. Mild hypothermia treatment was performed immediately after surgery and maintained for 4 hr. The animals were euthanized at 1 and 7 days after severe TBI. The expression levels of ER stress marker proteins were evaluated using Western blot and immunofluorescence. Cell apoptosis rate was analyzed by TUNEL staining. Neuronal functions of the mice were assessed using rotarod test and Morris water maze.

RESULTS

Our results revealed that mild hypothermia significantly attenuated ER stress marker proteins, including p-eIF2α/eIF2α, ATF4, CHOP and IRE-1α, and reduced apoptosis rate in the pericontusion region at 1 and 7 days after severe TBI. Interestingly, mild hypothermia also prevented the translocation of CHOP into nucleus. In addition, posttraumatic mild hypothermia significantly improved neuronal functions after severe TBI.

CONCLUSIONS

Our findings illustrated that mild hypothermia could reduce ER stress-induced apoptosis and improve neuronal functions after severe traumatic brain injury.

Effect of mild hypothermia on cerebral microcirculation in a murine cardiopulmonary resuscitation model

BACKGROUND

We hypothesized that mild hypothermia may improve brain microcirculation by reducing cerebral microvascular endothelial cells apoptosis, and this effect may be maximized by moving up the initiation of mild hypothermia from after return of spontaneous circulation (ROSC) to the start of cardiopulmonary resuscitation (CPR).

METHODS

A total of 35 rats were randomized into the intra-arrest hypothermia group (IAH), post-resuscitation hypothermia group (PRH), normothermia group (NT), or the sham control group. A craniotomy exposed the parietal cortex for visualization of microcirculation. Ventricular fibrillation was electrically induced and untreated for 8 minutes, followed by 8 minutes of precordial compression and mechanical ventilation. Hypothermia (33 ± 0.5°C) in the IAH and PRH group was induced and maintained for 6 hours at the beginning of CPR or after ROSC, respectively. At baseline, 1, 3, and 6 hours, hemodynamic parameters were measured and the pial microcirculations were visualized with a sidestream dark field imaging video microscope. Microvascular flow index and perfused microvessel density (PMD) were calculated. Rats were euthanized, and brain tissues were removed at 3 and 6 hours separately. Expression of Bax, Bcl-2, and Caspase 3 in brain microvascular endothelial cells was examined by Western blot.

RESULTS

Microvascular flow index and PMD were significantly reduced after cardiac arrest and resuscitation (all P < 0.05), and the former was largely preserved by hypothermia regardless when the hypothermia treatment was induced (P < 0.05). Bax and Caspase 3 increased and Bcl-2 decreased significantly after resuscitation, and hypothermia treatment reversed the trend partly (all P < 0.05). A moderate correlation was observed between MFI and those proteins (Bcl-2/BAX: 3 hours: r = 0.730, P = 0.002; 6 hours: r = 0.743, P = 0.002).

CONCLUSION

Mild hypothermia improves cerebral microcirculatory blood supply, partly by inhibiting endothelial cell apoptosis. Mild hypothermia induced simultaneously with CPR has shown no additional benefit in microcirculation or endothelial cell apoptosis.

Selective beta-blocker esmolol improves cerebral cortex microcirculation in a swine ventricular fibrillation model

OBJECTIVE

This study aimed to identify whether esmolol attenuates cerebral cortex microcirculation blood flow due to epinephrine in prolonged ventricular fibrillation (VF) and cardiopulmonary resuscitation (CPR), and may improve neurological prognosis.

METHODS

Male pigs were randomized into the esmolol+epinephrine group (group EE), the epinephrine group (group EP), and the normal saline group (group NS) (n = 8 each group). Untreated VF for 8 minutes was induced in pigs. After CPR for 2 minutes, group EE received esmolol (500 µg/kg)+epinephrine (20 µg/kg), group EP received epinephrine 20 µg/kg, and group NS received 5 mL normal saline. Then, a 120 J electric shock was delivered. If the return of spontaneous circulation (ROSC) failed, epinephrine (20 µg/kg) was repeated in group EP and EE, followed by another 2 minutes of CPR, a 150 J electric shock was delivered every 2 minutes until ROSC. Cerebral microcirculation images were obtained at 0.5, 6, 12, and 24 hours by cranial windows after ROSC. Cerebral performance category scores and neurological deficit scores (NDS) were calculated. The frontal cortices were harvested after the animals were euthanized.

RESULTS

The NDS, the perfused vessel density, and the microcirculatory flow index of group EE were better than other two groups. The morphology of endothelial cells in the group EE remained intact; however, it was destroyed in the group EP.

CONCLUSIONS

Administration of esmolol with epinephrine may alleviate the impairment of cerebral microcirculation blood flow caused by the administration of epinephrine in prolonged VF and thereby improves neurological outcomes in a swine model.

Microvascular perfusion in cardiac arrest: a review of microcirculatory imaging studies

Cardiac arrest represents a leading cause of mortality and morbidity in developed countries. Extracorporeal cardiopulmonary resuscitation (ECPR) increases the chances for a beneficial outcome in victims of refractory cardiac arrest. However, ECPR and post-cardiac arrest care are affected by high mortality rates due to multi-organ failure syndrome, which is closely related to microcirculatory disorders. Therefore, microcirculation represents a key target for therapeutic interventions in post-cardiac arrest patients. However, the evaluation of tissue microcirculatory perfusion is still demanding to perform. Novel videomicroscopic technologies (Orthogonal polarization spectral, Sidestream dark field and Incident dark field imaging) might offer a promising way to perform bedside microcirculatory assessment and therapy monitoring. This review aims to summarise the recent body of knowledge on videomicroscopic imaging in a cardiac arrest setting and to discuss the impact of extracorporeal reperfusion and other therapeutic modalities on microcirculation.

Endovascular Cooling Method for Hypothermia in Injured Swine

We evaluated an endovascular cooling method to modulate core temperature in trauma swine models with and without fluid support. Anesthetized swine (N = 80) were uninjured (SHAM) or injured through a bone fracture plus soft tissue injury or an uncontrolled hemorrhage and then subdivided to target body temperatures of 38°C (normothermia) or 33°C (hypothermia) by using a Thermogard endovascular cooling device (Zoll Medical). Temperature regulation began simultaneously at onset of injury (T0). Body temperatures were recorded from a rectal probe (Rec Temp) and from a central pulmonary artery catheter (PA Temp). At T15, swine received 500 mL IV Hextend over 30 minutes or no treatment (NONE) with continued monitoring until 3 hours from injury. Hypothermia was attained in 105 ± 39 minutes, at a cooling rate of -0.061°C ± 0.007°C/min for NONE injury groups. Postinjury Hextend administration resulted in faster cooling (-0.080°C ± 0.006°C/min); target temperature was reached in 83 ± 11 minutes (p < 0.05). During active cooling, body temperature measured by the PA Temp was significantly cooler than the Rec Temp due to the probe's closer proximity to the blood-cooling catheter balloons (p < 0.05). This difference was smaller in SHAM and fluid-supported injury groups (1.1°C ± 0.4°C) versus injured NONE groups (2.1°C ± 0.3°C). Target temperatures were correctly maintained thereafter in all groups. In normothermia groups, there was a small initial transient overshoot to maintain 38°C. Despite the noticeable difference between PA Temp and Rec Temp until target temperature was attained, this endovascular method can safely induce moderate hypothermia in anesthetized swine. However, likely due to their compromised hemodynamic state, cooling in hypovolemic and/or injured patients will be different from those without injury or those that also received fluids.