Hyperoxic Reperfusion Research Articles

Controlling Reperfusion Injury With Controlled Reperfusion: Historical Perspectives and New Paradigms.

Cardiac reperfusion injury is a well-established outcome following treatment of acute myocardial infarction and other types of ischemic heart conditions. Numerous cardioprotection protocols and therapies have been pursued with success in pre-clinical models. Unfortunately, there has been lack of successful large-scale clinical translation, perhaps in part due to the multiple pathways that reperfusion can contribute to cell death. The search continues for new cardioprotection protocols based on what has been learned from past results. One class of cardioprotection protocols that remain under active investigation is that of controlled reperfusion. This class consists of those approaches that modify, in a controlled manner, the content of the reperfusate or the mechanical properties of the reperfusate (e.g., pressure and flow). This review article first provides a basic overview of the primary pathways to cell death that have the potential to be addressed by various forms of controlled reperfusion, including no-reflow phenomenon, ion imbalances (particularly calcium overload), and oxidative stress. Descriptions of various controlled reperfusion approaches are described, along with summaries of both mechanistic and outcome-oriented studies at the pre-clinical and clinical phases. This review will constrain itself to approaches that modify endogenously-occurring blood components. These approaches include ischemic postconditioning, gentle reperfusion, controlled hypoxic reperfusion, controlled hyperoxic reperfusion, controlled acidotic reperfusion, and controlled ionic reperfusion. This review concludes with a discussion of the limitations of past approaches and how they point to potential directions of investigation for the future.

Effects of hyperoxia and cardiovascular risk factors on myocardial ischaemia-reperfusion injury: a randomized, sham-controlled parallel study.

What is the central question of this study? The beneficial effects of supplemental oxygen in patients with acute myocardial infarction are still uncertain: what are the effects of ischaemia-reperfusion injury during hyperoxia and normoxia in mature rats with and without cardiovascular risk factors? What is the main finding and its importance? Despite elevated baseline oxidative stress in rodents with cardiovascular risk factors, hyperoxic reperfusion limited myocardial necrosis and anti/pro-oxidant imbalance in spontaneously hypertensive and Zucker rats. In contrast, this effect was exacerbated in healthy Wistar rats. These results suggest that oxygen supplementation may not be harmful in patients with acute myocardial injury. Recent studies on O2 supplementation in acute coronary syndrome patients are equivocal. We tested the hypothesis that oxidative stress is increased in rodents with cardiovascular risk factors and enhances ischaemia-reperfusion injury in the presence of hyperoxia. A total of 43 Wistar rats (WR), 30 spontaneously hypertensive rats (SHR) and 33 obese Zucker rats (ZR) were randomized in a sham procedure (one-third) or underwent a left anterior descending ligation of the coronary artery for 60min (two-thirds). This was followed by 3h of reperfusion while animals were randomized either in a hyperoxic (HR) or a normoxic reperfusion (NR) group. Myocardial infarction size and oxidative stress biomarkers (myeloperoxidase (MPO), malondialdehyde and total free thiols) were assessed in blood samples. Baseline troponin T was higher in SHR and ZR than in WR (both P<0.001). Baseline total MPO was elevated in ZR in comparison to SHR and WR (both P<0.001). SHR had lower thiol concentration compared to WR and ZR (P<0.000001). HR was associated with a lower troponin T rise in SHR and ZR than in NR (both P<0.001), while the reverse occurred in WR (P<0.001). In SHR, HR limited total MPO increase as compared to NR (P=0.0056) and the opposite effect was observed with total MPO in WR (P=0.013). NR was associated with a drastic reduction of total thiols as compared to HR both in SHR and in ZR (both P<0.001). Despite a heightened baseline oxidative stress level, HR limited myocardial necrosis and anti/pro-oxidant imbalance in SHR and ZR whereas this effect was exacerbated in healthy WR.

Hyperoxic reperfusion after a ST-elevation myocardial infarction n mature Wistar rats does not increase oxidative stress

Ischemia-reperfusion injury (IRI) is a paradoxical tissue response following reoxygenation of an ischemic organ. The predominant role of oxidative stress (OS) in IRI is well established. In humans, hyperpoxia exacerbates myocardial infarction (MI) size in the setting of STEMI (AVOID study. Circulation 2015). This is not seen in experimental studies in young and healthy animals. Effects of hyperoxia on OS during myocardial reperfusion (MR) in STEMI are unknown in mature rodents. To test the hypothesis that hyperoxic myocardial reperfusion (HMR) in mature Wistar rats increases IRI in comparison to normoxic reperfusion (NMR). Twenty-nine mature male Wistar rats (35–40vweeks old) underwent myocardial ischemia by LAD ligation for 60 minutes. Animals were randomised either in the HMR (receiving 100% oxygen, n = 13) or the NMR (ambient air, n = 16) groups. MR lasted for 3 hours after LAD reopening. The SHAM group underwent surgery without LAD ligation ( n = 7) and was ventilated with ambient air for 4 hours after surgery. Blood samples were collected before ischemia and after reperfusion. Troponin T was measured as a surrogate of MI size. Plasma superoxide dismutase (SOD) and total thiols (TT) were measured as antioxidant biomarkers. Plasma malondialdehyde (MDA) and 3-chlorotyrosine (3-ClT) (myeloperoxidase surrogate) were measured as oxidant biomarkers. Pre-ischemia troponin, plasma SOD, TT, MDA and 3-ClT were similar in the 3 groups (HMR, NMR and SHAM). There was a difference in the post-reperfusion troponin measurement between SHAM and HMR, and SHAM and NMR, P = 0.01 and 0.03 respectively. Post-reperfusion troponin levels did not differ between HMR and NMR ( P -value = 0.178). Post-reperfusion OS biomarkers did also not differ between HMR and NMR. HMR after STEMI in mature Wistar rats increased neither infarct size nor oxidative stress. Aging only may thus not explain the deleterious effect of HMR in humans.

Normoxic re-oxygenation ameliorates end-organ injury after cardiopulmonary bypass

BackgroundIn a rabbit model of cardiopulmonary bypass (CPB) and cardioplegic arrest, we previously showed that hyperoxic myocardial reperfusion was associated with increased left ventricular (LV) systolic dysfunction and myocardial injury compared with normoxic reperfusion. The aim of this study was to evaluate in our experimental model the impact of post-CPB reperfusion conditions on other organs potentially vulnerable to ischemic injury such as the brain and kidney.MethodsAfter 60 min of CPB, aortic cross-clamp, and cold cardioplegic arrest, rabbits were reperfused under hyperoxic or normoxic conditions for 120 min. Left ventricular systolic contractility (LV + dP/dt) and diastolic relaxation (LV –dP/dt) were continuously recorded, and end-organ injury was assessed by measuring circulating biomarkers specific for kidney (cystatin C and creatinine) and brain injury [S100B and neuron specific enolase (NSE)]. At completion of the protocol, kidney and brain tissues were harvested for measuring oxidant stress (OS), inflammation and apoptosis.ResultsFollowing aortic cross-clamp removal, rabbits exposed to normoxic reperfusion demonstrated preserved LV systolic and diastolic function compared with hyperoxic reperfusion (LV + dP/dt: 70 ± 14% of pre-CPB vs. 36 ± 21%, p = 0.018; LV -dP/dt: 72 ± 36% of pre-CPB vs. 33 ± 20%, p = 0.023). Similarly, CPB increased plasma creatinine, S100B and NSE that were significantly attenuated by normoxic reperfusion compared with hyperoxic reperfusion (creatinine: 4.0 ± 0.5 vs. 7.1 ± 0.8 mg/dL, p = 0.004; S100B: 4.0 ± 0.8 vs. 6.7 ± 1.0 ng/mL, p = 0.047; NSE: 57.7 ± 6.8 vs. 101.3 ± 16.1 pg/mL, p = 0.040). Furthermore, both kidney and brain tissues showed increased mRNA expression and activation of pathways for OS, inflammation, and apoptosis, that were reduced under normoxic compared with hyperoxic conditions.ConclusionsNormoxic reperfusion ameliorates cardiac, renal and neural injury compared with hyperoxic reperfusion in an in vivo animal model of CPB and cardioplegic arrest. This protective effect of normoxic reperfusion may be due to a reduction in signaling pathways for OS, inflammation, and apoptosis.

Effect of hyperoxic reperfusion on final infarct size after ST elevation myocardial infarction (STEMI) in old Wistar rats

Elderly people above 65 years old account for more than 80% of patients with ischemic heart disease [1] . Most of animal models of myocardial ischemia-reperfusion injury (IRI) involve young animals, with the assumption that findings are applicable to older animals and thus applicable to humans at highest risk, the elderly. Current studies failed to analyse the effect of hyperoxia during myocardial infarction (MI) reperfusion in old rodent model. Assess the final myocardial infarct size after normoxic and hyperoxic MI reperfusion in old Wistar rats. STEMI was induced in old male Wistar rats (35–40 weeks old) by ligation of the left anterior descending (LAD) artery and maintained for 60 minutes. Animals were randomised either in the hyperoxic reperfusion (HR) group (receiving 100% oxygen) or the normoxic reperfusion (NR) group (21% of oxygen) for a 3-hour reperfusion. At the end of reperfusion, Evans Blue dye solution was injected to delineate the ischemic area from the non-ischemic area. The heart was cut into transverse slices and immerged in TTC solution. Myocardial infarct size was assessed in two ways; first troponin T concentration was measured after reperfusion, secondly ischemic zone and area at risk of the myocardium slices were measured by planimetry. A total of 8 rats underwent HR vs 11 NR. No difference was observed in the final myocardial infarct size between the two groups in both methods of myocardial infarct size assessment. These very preliminary results corroborate the observations made in young animals’ studies [2] , [3] , however they should be taken cautiously since they are based on a very small cohort. There is a need to understand the effect of hyperoxic MI reperfusion as animal studies contradict the findings in human studies [4] .

Differential Effects of Normoxic and Hyperoxic Reperfusion on Global Myocardial Ischemia-Reperfusion Injury

The objectives were to investigate if after hypoxia or ischemia, normoxic reperfusion is associated with less oxidant stress (OS), inflammation, and myocardial injury than hyperoxic reperfusion. In this study, cardiomyocytes (H9c2 cells) were cultured in hypoxia, followed by reoxygenation in normoxia or hyperoxia. Cardiomyocyte OS, inflammation, and apoptosis were measured. In parallel experiments, rabbits were cannulated for cardiopulmonary bypass (CPB). Following cardioplegic arrest and aortic cross-clamp removal, hearts were reperfused under normoxic or hyperoxic conditions. Left ventricular developed pressure and contractility (LV +dP/dt) were recorded, and blood samples and heart tissues were collected for measurement of OS, inflammation, and cardiac injury. Results showed that H9c2 cells exposed to hyperoxic reoxygenation showed significant increases in OS, inflammation, and apoptosis compared to normoxic reoxygenation. Following CPB and 2-hour hyperoxic reperfusion, LV +dP/dt and left ventricular developed pressure were significantly decreased compared with pre-CPB values (to 36 ± 21%, P = 0.002; and 53 ± 20%, P = 0.02, respectively), associated with significant increases in all plasma and tissue biomarkers for OS, inflammation, and myocardial injury. In contrast, LV +dP/dt was relatively well preserved under normoxic reperfusion conditions (to 70 ± 14% after 2-hour reperfusion), and was associated with an attenuated myocardial OS, inflammatory, apoptotic, and injury response compared to the hyperoxia group (eg, cTn-I: 5.9 ± 1.5 vs 20.2 ± 7.6 ng/mL, respectively, P < 0.0001). Overall, in both in vitro and in vivo experiments, normoxic reperfusion/reoxygenation was associated with less robust OS, inflammation, apoptosis, and myocardial injury compared with hyperoxic reperfusion/reoxygenation. These results suggest that hyperoxia should be avoided to minimize myocardial OS, inflammation, and ventricular dysfunction after CPB.

Reanimación neonatal en prematuros de 27 a 30 semanas de gestación, con determinación de requerimientos de oxígeno, porcentaje de saturación y su relación con la morbilidad neonatal

IntroductionDue to the risk of premature infants suffering from hyperoxic reperfusion injury, it is reasonable to control the oxygen supply without exposing them to excessive levels. ObjectiveTo determine the oxygen requirements and saturation levels, at 5 and 10minutes during neonatal resuscitation, and their association with neonatal morbidity in premature neonates between 27 and 30 weeks of gestational age. Material and methodsAn observational and analytical study was conducted. The inclusion criteria were, neonates between 27 and 30 weeks of gestational age, and the exclusion criteria were, major congenital defects, and death before 36 weeks of gestational age. They were divided into two groups: Group 1, those with gestational age of 27-28 weeks, and Group 2, those with 29-30 weeks. An analysis was performed on the prenatal and neonatal variables, oxygen requirements, oxygen saturation, and neonatal morbidity. ResultsThere were 39 patients in Group 1, and 31 in Group 2. The fraction inspired average of oxygen for Group 1 at 5minutes was 77.56% and for Group 2 it was 64.9%, P=.045. Group 1 required a higher concentration of oxygen to reach saturations >80%. An increased risk of intraventricular haemorrhage was observed in Group 1 (OR 3.21, 95% CI; 1.07-9.60). As regards the morbidity of both groups, there was no relationship with oxygen saturation during the neonatal resuscitation. ConclusionNeonatal morbidity is multifactorial. In this study no relationship was found between neonatal morbidity and oxygen saturation during resuscitation.

Intraoperative cerebral oxygenation, oxidative injury, and delirium following cardiac surgery

BackgroundDelirium affects 20–30% of patients after cardiac surgery and is associated with increased mortality and persistent cognitive decline. Hyperoxic reperfusion of ischemic tissues increases oxidative injury, but oxygen administration remains high during cardiac surgery. We tested the hypothesis that intraoperative hyperoxic cerebral reperfusion is associated with increased postoperative delirium and that oxidative injury mediates this association. MethodsWe prospectively measured cerebral oxygenation with bilateral oximetry monitors in 310 cardiac surgery patients, quantified intraoperative hyperoxic cerebral reperfusion by measuring the magnitude of cerebral oxygenation above baseline after any ischemic event, and assessed patients for delirium twice daily in the ICU following surgery using the confusion assessment method for ICU (CAM-ICU). We examined the association between hyperoxic cerebral reperfusion and postoperative delirium, adjusted for the extent of cerebral hypoxia, the extent of cerebral hyperoxia prior to any ischemia, and additional potential confounders and risk factors for delirium. To assess oxidative injury mediation, we examined the association between hyperoxic cerebral reperfusion and delirium after further adjusting for plasma levels of F2-isoprostanes and isofurans at baseline and ICU admission, the association between hyperoxic cerebral reperfusion and these markers of oxidative injury, and the association between these markers and delirium. ResultsNinety of the 310 patients developed delirium following surgery. Every 10%·hour of intraoperative hyperoxic cerebral reperfusion was independently associated with a 65% increase in the odds of delirium (OR, 1.65 [95% CI, 1.12–2.44]; P=0.01). Hyperoxia prior to ischemia was also independently associated with delirium (1.10 [1.01–1.19]; P=0.02), but hypoxia was not (1.12 [0.97–1.29]; P=0.11). Increased hyperoxic cerebral reperfusion was associated with increased concentrations of F2-isoprostanes and isofurans at ICU admission, increased concentrations of these markers were associated with increased delirium, and the association between hyperoxic cerebral reperfusion and delirium was weaker after adjusting for these markers of oxidative injury. ConclusionsIntraoperative hyperoxic cerebral reperfusion was associated with increased postoperative delirium, and increased oxidative injury following hyperoxic cerebral reperfusion may partially mediate this association. Further research is needed to assess the potential deleterious role of cerebral hyper-oxygenation during surgery.

Reducing the duration of 100% oxygen ventilation in the early reperfusion period after cardiopulmonary resuscitation decreases striatal brain damage

Purpose Previous data indicate that 100% O 2 ventilation during early reperfusion after cardiac arrest (CA) and cardiopulmonary resuscitation (CPR) increases neuronal death. However, current guidelines encourage the use of 100% O 2 during resuscitation and for an undefined period thereafter. We retrospectively analyzed data from a porcine CA model and hypothesized that prolonged hyperoxic reperfusion would be associated with increased neurohistopathological damage and impaired neurological recovery. Methods Fifteen male pigs underwent 8 min of CA and 5 min of CPR. After resuscitation animals were ventilated with either 100% oxygen for 60 min (hyperoxia; n = 8) or 10 min (normoxia; n = 7). Physiological variables were obtained at baseline and 10, 60 and 240 min after resuscitation. Daily functional performance was assessed using an established neurocognitive test in parallel to a neurological deficit score (NDS). On day 5, brains of the re-anaesthetized pigs were harvested for neurohistopathological analyses. Results At baseline there were no differences in hemodynamics and neurological status between groups. Post-arrest only PaO 2, as a result of the different inspired oxygen fractions, was significantly higher in the hyperoxia group. There was a numerical trend towards improved clinical recovery in both the NDS and the neurocognitive testing for animals exposed to 10 min of 100% oxygen. However, hyperoxic animals showed a significantly greater degree of necrotic neurons and perivascular inflammation in the striatum in comparison to normoxic animals. Conclusion In this retrospective analysis prolonged hyperoxia after CA aggravated necrotic brain damage and perivascular inflammation in the striatum of pigs.

Hyperoxic Reperfusion after Global Cerebral Ischemia Promotes Inflammation and Long-Term Hippocampal Neuronal Death

In this study we tested the hypothesis that long-term neuropathological outcome is worsened by hyperoxic compared to normoxic reperfusion in a rat global cerebral ischemia model. Adult male rats were anesthetized and subjected to bilateral carotid arterial occlusion plus bleeding hypotension for 10 min. The rats were randomized to one of four protocols: ischemia/normoxia (21% oxygen for 1 h), ischemia/hyperoxia (100% oxygen for 1 h), sham/normoxia, and sham/hyperoxia. Hippocampal CA1 neuronal survival and activation of microglia and astrocytes were measured in the hippocampi of the animals at 7 and 30 days post-ischemia. Morris water maze testing of memory was performed on days 23-30. Compared to normoxic reperfusion, hyperoxic ventilation resulted in a significant decrease in normal-appearing neurons at 7 and 30 days, and increased activation of microglia and astrocytes at 7, but not at 30, days of reperfusion. Behavioral deficits were also observed following hyperoxic, but not normoxic, reperfusion. We conclude that early post-ischemic hyperoxic reperfusion is followed by greater hippocampal neuronal death and cellular inflammatory reactions compared to normoxic reperfusion. The results of these long-term outcome studies, taken together with previously published results from short-term experiments performed with large animals, support the hypothesis that neurological outcome can be improved by avoiding hyperoxic resuscitation after global cerebral ischemia such as that which accompanies cardiac arrest.

Effect of arterial oxygen tension during reperfusion on myocardial recovery in patients undergoing valvular heart surgery

BackgroundValvular heart surgery (VHS) utilizing cardiopulmonary bypass (CPB) is inevitably associated with ischemic-reperfusion injury, which is known to depend on oxygen tension during reperfusion. The aim of this study was to evaluate the effect of arterial oxygen tension during reperfusion on myocardial recovery in patients undergoing VHS.MethodsFifty-six patients undergoing isolated VHS were randomly exposed to an oxygen fraction of 0.7 (hyperoxic group, n = 28) or 0.5 (normoxic group, n = 28) during reperfusion. All patients received an oxygen fraction of 0.7 during CPB. In the normoxic group, the oxygen fraction was lowered to 0.5 from the last warm cardioplegia administration to 1 minute after aortic unclamping, and was then raised back to 0.7. Hemodynamic data were measured after induction of anesthesia, weaning from CPB, and sternum closure. The frequency of cardiotonic medications used during and after weaning from CPB, and the short-term outcomes during the hospital stay were also assessed.ResultsThe frequency of vasopressin and milrinone use during weaning from CPB, but not norepinephrine, was significantly less in the normoxic group. The post-operative cardiac enzyme levels and short-term outcomes were not different between the groups.ConclusionsNormoxic reperfusion from the last cardioplegia administration to 1 minute after aortic unclamping in patients undergoing VHS resulted in significantly less frequent use of vasopressin and inotropics during weaning from CPB than hyperoxic reperfusion, although it did not affect the post-operative myocardial enzyme release or short-term prognosis.

Hyperoxic Reperfusion After Global Ischemia Decreases Hippocampal Energy Metabolism

Previous reports indicate that compared with normoxia, 100% ventilatory O(2) during early reperfusion after global cerebral ischemia decreases hippocampal pyruvate dehydrogenase activity and increases neuronal death. However, current standards of care after cardiac arrest encourage the use of 100% O(2) during resuscitation and for an undefined period thereafter. Using a clinically relevant canine cardiac arrest model, in this study we tested the hypothesis that hyperoxic reperfusion decreases hippocampal glucose metabolism and glutamate synthesis. After 10 minutes of cardiac arrest, animals were resuscitated and ventilated for 1 hour with 100% O(2) (hyperoxic) or 21% to 30% O(2) (normoxic). At 30 minutes reperfusion, [1-(13)C]glucose was infused, and at 2 hours, brains were rapidly removed and frozen. Extracted metabolites were analyzed by (13)C nuclear magnetic resonance spectroscopy. Compared with nonischemic controls, the hippocampi from hyperoxic animals had elevated levels of unmetabolized (13)C-glucose and decreased incorporation of (13)C into all isotope isomers of glutamate. These findings indicate impaired neuronal metabolism via the pyruvate dehydrogenase pathway for carbon entry into the tricarboxylic acid cycle and impaired glucose metabolism via the astrocytic pyruvate carboxylase pathway. No differences were observed in the cortex, indicating that the hippocampus is more vulnerable to metabolic changes induced by hyperoxic reperfusion. These results represent the first direct evidence that hyperoxia after cardiac arrest impairs hippocampal oxidative energy metabolism in the brain and challenge the rationale for using excessively high resuscitative ventilatory O(2).

Normoxic Compared to Hyperoxic Reperfusion Improves Neurochemical and Histologic Outcome in Models of Global Cerebral Ischemia and Reperfusion Using Different Animal Species

Departments of 1Anesthesiology 2Cell Biology, Neurobiology and Anatomy, Loyola University Medical Center, Maywood, IL Abstracts published in the Journal of Neurosurgical Anesthesiology have been reviewed by the organizations or JNA Affiliate Societies at whose meetings the abstracts have been accepted for presentation. These abstracts have not undergone review by the Editorial Board of the Journal of Neurosurgical Anesthesiology. 34th Annual Meeting of the Society of Neurosurgical Anesthesia and Critical Care, Chicago, Illinois, October 13th, 2006

Resuscitation of severe but brief haemorrhagic shock with PFC in rabbits restores skeletal muscle oxygen delivery and does not alter skeletal muscle metabolism

Studies have demonstrated that perfluorocarbon (PFC) emulsions associated with hyperoxia improved whole body oxygen delivery during resuscitation of acute haemorrhagic shock (HS). Nevertheless the microcirculatory effects of PFC and the potential deleterious effects of hyperoxic reperfusion are still of concern. We investigated (i) the ability of a newly formulated, small sized and highly stable PFC emulsion to increase skeletal muscle oxygen delivery and (ii) the effect of hyperoxic reperfusion on skeletal muscle metabolism after a brief period of ischaemia using an original, microdialysis-based method that allowed simultaneous measurement tissue oxygen pressure (PtiO2) and interstitial lactate and pyruvate. These measurements were carried out in anaesthetised and ventilated (FiO2 = 1) rabbits subjected to acute HS (50% of blood volume withdrawal) and either resuscitated with a PFC emulsion diluted with a 5% albumin solution (16.2 g PFC per kg body weight) (n = 10) or with a modified fluid gelatin solution (Gelofusine) (n = 10). We found no difference between the two groups for the haemodynamic and haematological variables (except for the venous oxygen partial pressure). However, a significant difference was observed in the slope of the regression linear relationship exhibited between the mean arterial pressure (MAP) and the PtiO2, PFC group showing a much steeper slope than Gelofusine group. In addition, PtiO2 values increased linearly with decreasing haematocrit (Hct) values in PFC-resuscitated animals and decreased linearly with decreasing Hct values in Gelofusine-resuscitated animals. There were no differences between the two groups concerning the blood and interstitial lactate/pyruvate ratios suggesting no deleterious effect of hyperoxic resuscitation in skeletal muscle. In conclusion these results suggest that resuscitation of severe, but brief, HS with PFC increased skeletal muscle oxygen delivery without measurable deleterious effects.

Postischemic hyperoxia reduces hippocampal pyruvate dehydrogenase activity

The pyruvate dehydrogenase complex (PDHC) is a mitochondrial matrix enzyme that catalyzes the oxidative decarboxylation of pyruvate and represents the sole bridge between anaerobic and aerobic cerebral energy metabolism. Previous studies demonstrating loss of PDHC enzyme activity and immunoreactivity during reperfusion after cerebral ischemia suggest that oxidative modifications are involved. This study tested the hypothesis that hyperoxic reperfusion exacerbates loss of PDHC enzyme activity, possibly due to tyrosine nitration or S-nitrosation. We used a clinically relevant canine ventricular fibrillation cardiac arrest model in which, after resuscitation and ventilation on either 100% O 2 (hyperoxic) or 21–30% O 2 (normoxic), animals were sacrificed at 2 h reperfusion and the brains removed for enzyme activity and immunoreactivity measurements. Animals resuscitated under hyperoxic conditions exhibited decreased PDHC activity and elevated 3-nitrotyrosine immunoreactivity in the hippocampus but not the cortex, compared to nonischemic controls. These measures were unchanged in normoxic animals. In vitro exposure of purified PDHC to peroxynitrite resulted in a dose-dependent loss of activity and increased nitrotyrosine immunoreactivity. These results support the hypothesis that oxidative stress contributes to loss of hippocampal PDHC activity during cerebral ischemia and reperfusion and suggest that PDHC is a target of peroxynitrite.

Postischemic Reperfusion Injury Can Be Attenuated by Oxygen Tension Control

Oxygen-derived free radicals cause cytotoxic damage during reperfusion after a period of ischemia and the production of these free radicals may be proportionate to oxygen tension (PO2). The present study tested the hypothesis that oxidative damage may be limited by maintaining a more physiologic PO2 following ischemia. An experimental study in Wistar rats were mounted on a Langendorff apparatus was conducted to estimate baseline aortic flow (AF), coronary flow (CF), cardiac output (CO), systolic pressure (SP), heart rate (HR), and the rate-pressure product (RPP: HRxSP). The hearts were divided into 3 groups (n=7, hearts/group): group 1, hypoxic (PO2=300+/-50 mmHg) reperfusion; group 2, middleoxic (PO2=500+/-50 mmHg) reperfusion; and group 3, hyperoxic (PO2=700+/-50 mmHg) reperfusion. Following 30 min of warm ischemia, hearts in all groups were reperfused at each oxygen pressure. The recovery of cardiac function of each heart was measured at the end of reperfusion. Concentrations of lactate (LAC), lactate dehydrogenase (LDH), and creatine kinase (CK) in the coronary perfusate during reperfusion were measured. The recovery rate of CO, SP, and RPP in group 2 were all significantly better than in the other 2 groups. CK leakage in group 2 was significantly lower than in group 3. A clinical study was also conducted during elective coronary artery bypass grafts in 16 consecutive patients who underwent either hyperoxic (n=8, PO2=450-550 mmHg) or more physiologic (n=8, PO2=200-250 mmHg) cardiopulmonary bypass after aortic unclamping. The clinical study assessed CK-MB, LDH, LAC, and malondialdehyde (MDA) in patient blood prior to starting the surgical procedure and at 30 min and 3, 9, and 21 h after unclamping. Cardiac index (CI), central venous pressure, pulmonary capillary wedge pressure, systolic arterial pressure, and the dose of cathecholamines were also measured. Although no significant differences were present in the dose of cathecholamines, the CI in the more physiologic oxygen tension group was significantly higher than in the hyperoxic group at 3 and 6 h after unclamping. The levels of MDA in the more physiologic PO2 group was significantly lower at 30 min after aortic unclamping than in the hyperoxic group. The present results suggest that in the experimental as well as in the clinical study, high PO2 leads to myocardial reperfusion damage; however, maintaining a more physiologic PO2 during reperfusion following ischemia may attenuate reperfusion injury.

Hyperoxic reperfusion exacerbates postischemic renal dysfunction

Background. Hyperoxic reperfusion from global ischemia worsens functional outcome because of oxygen radical-mediated injury. This study tested the hypothesis that hyperoxic reperfusion would exacerbate postischemic renal dysfunction. Methods. Twenty-nine healthy, uninephrectomized, male mongrel rabbits (Oryctolagus cuniculus) in 3 groups were subjected to 30 minutes of complete normothermic renal ischemia followed by reperfusion under hyperoxic or normoxic conditions. The groups were: hyperoxically reperfused (n = 8), normoxically reperfused (n = 8), hyperoxic sham (no ischemia, n = 5), and allopurinol-pretreated (50 mg/kg, intravenously), hyperoxically reperfused animals (n = 8). Plasma concentrations of creatinine, urea nitrogen and electrolytes were measured at 0, 24, 48, and 72 hours after ischemia and served as functional outcome markers. Histopathologic analysis of kidneys for injury was performed by an expert who was blinded to the procedures. Results. Plasma creatinine in hyperoxically reperfused rabbits was significantly elevated above normoxic (P =.02) and sham (P =.003) animals by 48 hours and remained elevated to 72 hours. Plasma urea nitrogen in hyperoxically reperfused rabbits was significantly elevated above the normoxic group (P =.01), the sham group (P =.02), and the allopurinol group (P =.04) by 72 hours. These coincided with a significantly elevated histopathologic injury score in hyperoxically reperfused rabbits compared with sham (P =.019), normoxic (P =.035), and allopurinol-pretreated hyperoxically reperfused animals (P =.037). Conclusions. Hyperoxic reperfusion exacerbates renal dysfunction after 30 minutes of complete normothermic ischemia. This dysfunction may be mediated by oxygen radical-related injury. (Surgery 2000;128:815-21.)

Hyperoxic reperfusion is required to reduce infarct size after intravenous therapy with perfluorochemical (Fluosol-DA 20%) or its detergent component (poloxamer 188) in a poorly collateralized animal model: Absence of a role of polymorphonuclear leukocytes

Objectives. The aim of this study was to assess whether hyperoxic reperfusion contributes to the efficacy of Fluosol 20% or poloxamer 188 for infarct size reduction and whether suppression of polymorphonuclear leukocyte function is responsible for cardioprotection.Background. The perfluorochemical Fluosol and its detergent component poloxamer 188 limit myocardial reperfusion-induced injury; however, the underlying mechanism(s) are uncertain.Methods. A series of in vivo and ex vivo studies were performed in a 30-min temporary coronary occlusion rabbit model. Before reperfusion, rabbits received a 25-ml/kg infusion of 1) Fluosol; 2) poloxamer 188 (equivalent % w/v to Fluosol, 675 mg/kg body weight); or 3) 5% dextrose (control). In protocol A, animals were subjected to either normoxic or hyperoxic reperfusion; in protocols B and C, hyperoxic reperfusion was studied. In protocol B, myocardial blood flow was assessed. In protocol C, polymorphonuclear leukocyte function and myocardial myeloperoxidase were determined.Results. In rabbits subjected to normoxic reperfusion, infarct size (normalized to risk region weight) was not significantly different among groups. In rabbits subjected to hyperoxic reperfusion, infarcts were significantly reduced with both poloxamer 188 and Fluosol treatment compared with control animals (p = 0.05 and p = 0.0004, respectively). Blood flow at 3 h of reperfusion within the ischemic endocardium was greater in the Fluosol and poloxamer 188 groups than in the control group (p = 0.001 and p = 0.08, respectively). Myeloperoxidase activity was not affected by treatment, nor was there suppression of polymorphonuclear leukocyte function.Conclusions. Fluosol and poloxamer 188 reduce infarct size in rabbits subjected to hyperoxic reperfusion. Suppression of polymorphonuclear leukocyte function was not demonstrated, suggesting a greater role for increased arterial oxygen delivery in salvaging ischemic myocardium.

Postischemic hyperoxia enhances vulnerability in the rabbit spinal cord ischemic model

This study evaluated whether or not reperfusion of the rabbit ischemic spinal cord under conditions of varying blood oxygen tension combined with low blood viscosity can alter the neurological outcome after 15 min of infrarenal aortic occlusion. In group A (n = 20), hyperoxic reperfusion was performed during the initial 30 min of recirculation (pO2 = 460 ± 72 mmHg). In group B (n = 20), no attempt was made to manipulate the physiological arterial pO2 tension. In group C (n = 20), graded postischemic reoxygenation was applied during 15 min of recirculation beginning with 48 ± 12 mmHg as the initial arterial pO2. Neurological analysis revealed a high incidence of paraplegic animals after hyperoxic reperfusion as opposed to relatively undamaged animals after normoxic or graded postischemic reoxygenation. The possible role of different pathobiochemical events, specifically the high molecular oxygen availability and oxygen free-radical overproduction, is discussed below with attention to the interneuronal destructive process, detected during the early reoxygenation phase by means of the Nauta method permitting the visualization of the early signs of somatic and dendritic argyrophilia.

Hyperoxemic reperfusion does not increase myocardial infarct size

We tested the hypothesis that arterial hyperoxia during myocardial reperfusion increases reperfusion injury and infarct size. The anterolateral marginal coronary artery of 35 anesthetized rabbits was occluded for 45 min, then reperfused for 3 h with either normoxic [arterial PO2 (PaO2) = 96.7 +/- 22.9 mmHg)] or hyperoxic (PaO2 = 554.8 +/- 61.7 mmHg) blood. In the hyperoxic group only, PaO2 was adjusted 10 s before the onset of reperfusion by raising inspired oxygen concentration to 100%. The area of infarction (AI) was defined by triphenyltetrazolium staining, and the area at risk (AR) by fluorescent microspheres. These areas were measured by planimetry. Heart rates and blood pressures did not differ between the two groups during occlusion or reperfusion. Infarct size (AI/AR) was 49.1 +/- 16.5% in the normoxic group (n = 17) and 40.8 +/- 16.1% in the hyperoxic group (n = 18). From these data, 90% confidence limits establish that the maximal true increase in AI/AR caused by hyperoxia would be 0%-1%. Hyperoxic reperfusion of ischemic myocardium compared with normoxic reperfusion does not significantly increase myocardial infarct size.