Neurological injury during cardiopulmonary bypass in the rat

Suppression of Neuroinflammation Attenuates Persistent Cognitive and Neurogenic Deficits in a Rat Model of Cardiopulmonary Bypass

Post-operative cognitive dysfunction (POCD) can be a serious surgical complication, and patients undergoing cardiac procedures are at particular risk for POCD. This study examined the effect of blocking neuroinflammation on behavioral and neurogenic deficits produced in a rat model of cardiopulmonary bypass (CPB). Minocycline, a drug with established anti-inflammatory activity, or saline was administered daily for 30 days post-CPB. Treatment with minocycline reduced the number of activated microglia/macrophages observed in the dentate gyrus of the hippocampus at 6 months post-CPB, consistent with an anti-inflammatory action in this CPB model. Behavioral testing was conducted at 6 months post-CPB utilizing a win-shift task on an 8-arm radial maze. Minocycline-treated animals performed significantly better than saline-treated animals on this task after CPB. In addition, the CPB-induced reduction in adult neurogenesis was attenuated in the minocycline-treated animals. Together, these findings indicate that suppressing neuroinflammation during the early post-surgical phase can limit long-term deficits in both behavioral and neurogenic outcomes after CPB.

Establishment and evaluation of a rat model of extracorporeal membrane oxygenation (ECMO) thrombosis using a 3D-printed mock-oxygenator

Background

Extracorporeal membrane oxygenation (ECMO) research using large animals requires a significant amount of resources, slowing down the development of new means of ECMO anticoagulation. Therefore, this study developed and evaluated a new rat ECMO model using a 3D-printed mock-oxygenator.

Methods

The circuit consisted of tubing, a 3D-printed mock-oxygenator, and a roller pump. The mock-oxygenator was designed to simulate the geometry and blood flow patterns of the fiber bundle in full-scale oxygenators but with a low (2.5 mL) priming volume. Rats were placed on arteriovenous ECMO at a 1.9 mL/min flow rate at two different heparin doses (n = 3 each): low (15 IU/kg/h for eight hours) versus high (50 IU/kg/h for one hour followed by 25 IU/kg/h for seven hours). The experiment continued for eight hours or until the mock-oxygenator failed. The mock-oxygenator was considered to have failed when its blood flow resistance reached three times its baseline resistance.

Results

During ECMO, rats maintained near-normal mean arterial pressure and arterial blood gases with minimal hemodilution. The mock-oxygenator thrombus weight was significantly different (p < 0.05) between the low (0.02 ± 0.006 g) and high (0.003 ± 0.001 g) heparin delivery groups, and blood flow resistance was also larger in the low anticoagulation group.

Conclusions

This model is a simple, inexpensive system for investigating new anticoagulation agents for ECMO and provides low and high levels of anticoagulation that can serve as control groups for future studies.

History of cardiopulmonary bypass (CPB)

The development of cardiopulmonary bypass (CPB), thereby permitting open-heart surgery, is one of the most important advances in medicine in the 20th century. Many currently practicing cardiac anesthesiologists, cardiac surgeons, and perfusionists are unaware of how recently it came into use (60 years) and how much the practice of CPB has changed during its short existence. In this paper, the development of CPB and the many changes and progress that has taken place over this brief period of time, making it a remarkably safe endeavor, are reviewed. The many as yet unresolved questions are also identified, which sets the stage for the other papers in this issue of this journal.

A Brief History of Cardiopulmonary Bypass

The development and application of cardiopulmonary bypass (CPB) to permit open heart surgery is considered among the most important clinical advances in medicine during the last half of the 20th century. The birth of CPB for cardiac surgery is attributed to its first successful clinical use by John Gibbon Jr, 51 years ago but its practical clinical use really began in the spring and summer of 1955 when 2 groups led by John Kirklin at the Mayo Clinic and C Walton Lillehei at the University of Minnesota, initiated the routine use of CPB for open heart surgery. However, considerable developments were necessary and preceded the clinical accomplishment of CPB, and much has followed to make it the remarkably safe and effective procedure that it has become today. Many currently practicing cardiac anesthesiologists, cardiac surgeons, and perfusionists are unaware of how brief its history is and how much the practice of CPB has changed during its short existence. The aim of this article is to review this fascinating history and the lessons that can be learned from this review, and to indicate the opportunities that still exist for advancement.

Establishment of a novel rat model without blood priming during normothermic cardiopulmonary bypass

OBJECTIVE

An effective animal model was needed for research on the pathophysiology of cardiopulmonary bypass (CPB). Rat models were considered suitable for research into CPB, recently. The aim of the article is to establish a simple and safe CPB model without blood priming in rats, containing the advantages of controlling temperature precisely, being similar to the clinical process and laying the foundation for the further study of a deep hypothermic circulatory arrest (DHCA) model.

MATERIALS AND METHODS

Ten Sprague-Dawley rats, divided into a CPB group (n=7) and a sham group (n=3), received sevoflurane inhalation anesthesia and were maintained in an anesthesia state by intubation. The entire CPB circuit consisted of a reservoir, a membrane oxygenator, a roller pump, a heat exchanger and a heat cooler, all of which were connected via silicon tubes. The volume of the priming solution, composed of 6% HES130/0.4 and 125 IU heparin, was less than 12 ml. In the CPB group, a 22G catheter was placed in the left femoral artery for monitoring arterial blood pressure, a 20G catheter was placed in a tail artery for arterial inflow and a homemade, multiorificed catheter was inserted into a right jugular vein for venous drainage. After 90 minutes, the CPB process was terminated when vital signs were stable. In the sham group, the same surgical process was conducted except for the venous drainage. Post-oxygenator blood gas and hemodynamic parameters were measured at each time point before CPB, during CPB and after CPB.

RESULTS

All CPB processes were successfully achieved. Blood gas analysis and hemodynamic parameters of each time point were in accordance with normal ranges. The vital signs of all rats were stable.

CONCLUSION

The establishment of CPB without blood priming in rats can be achieved successfully. The rat model could be used to study short-term or long-term organ injury mechanisms caused by CPB. Furthermore, on the basis of the precise control of temperature and the depth of anesthesia, the DHCA model in rats could be developed further to study pathophysiological changes of neurological and other organ functions in the future.

Disruption of PF4/H multimolecular complex formation with a minimally anticoagulant heparin (ODSH)

Recent studies have shown that ultra-large complexes (ULCs) of platelet factor 4 (PF4) and heparin (H) play an essential role in the pathogenesis of heparin-induced thrombocytopenia (HIT), an immune-mediated disorder caused by PF4/H antibodies. Because antigenic PF4/H ULCs assemble through non-specific electrostatic interactions, we reasoned that disruption of charge-based interactions can modulate the immune response to antigen. We tested a minimally anticoagulant compound (2-O, 3-O desulfated heparin, ODSH) with preserved charge to disrupt PF4/H complex formation and immunogenicity. We show that ODSH disrupts complexes when added to pre-formed PF4/H ULCs and prevents ULC formation when incubated simultaneously with PF4 and UFH. In other studies, we show that excess ODSH reduces HIT antibody (Ab) binding in immunoassays and that PF4/ODSH complexes do not cross-react with HIT Abs. When ODSH and unfractionated heparin (UFH) are mixed at equimolar concentrations, we show that there is a negligible effect on amount of protamine required for heparin neutralisation and reduced immunogenicity of PF4/UFH in the presence of ODSH. Taken together, these studies suggest that ODSH can be used concurrently with UFH to disrupt PF4/H charge interactions and provides a novel strategy to reduce antibody mediated complications in HIT.

Animal models of cardiopulmonary bypass: development, applications, and impact

Neurologic and neurocognitive complications after cardiac surgery have been reported repeatedly. To better understand its etiology and design protective strategies, small animal models have been developed. This study describes the development of a survival rat cardiopulmonary bypass (CPB) model, along with the introduction of an appropriately sized oxygenator. This model led the way for even more complicated models with CPB, facilitating full cardiac arrest with anterograde cardioplegia administration, air embolization, and deep hypothermic circulatory arrest. In addition, the results of several of those rat CPB studies are summarized and their preclinical relevance is pointed out.

The impact of cardiopulmonary bypass on systemic interleukin-6 release, cerebral nuclear factor-kappa B expression, and neurocognitive outcome in rats

BACKGROUND

Neurocognitive deficits after cardiac surgery with cardiopulmonary bypass (CPB) continue to affect patients' quality of life, and an inflammatory reaction may be one of the contributors. We designed this experiment to study perioperative systemic interleukin-6 (IL-6) concentrations, cerebral expression of nuclear factor-kappa B (NF-kappaB), and neurocognitive outcome after CPB in young rats. The impact of oxygenator size on these outcomes was also assessed.

METHODS

Rats were randomly assigned to 1 of 4 groups: control (n = 7, nonanesthetized), sham-operated rats (n = 10, anesthetized, cannulated, and not connected to CPB), and 2 CPB groups, anesthetized, cannulated, and subjected to 90 min of CPB, using either a small-volume rat oxygenator (CPB/rat oxygenator, n = 10) or a neonate oxygenator (CPB/neonate oxygenator, n = 10). Systemic IL-6 was determined before, at the end of, and 2 h after CPB or at equivalent times. Hippocampal NF-kappaB expression was assessed on postoperative day 21 using immunohistochemistry. Neurocognitive performance was assessed with the modified hole-board test at baseline and for 21 postoperative days.

RESULTS

Both CPB groups had increased systemic IL-6 levels compared with sham, with the neonate oxygenator causing a substantially larger increase at 2 h after CPB compared with the rat oxygenator group (CPB/rat oxygenator: 220 pg/mL [16-415]; CPB/neonate oxygenator: 1400 pg/mL [592-5812]) (P < 0.05). Hippocampal NF-kappaB was increased in experimental groups compared with controls (10 +/- 4). CPB resulted in more NF-kappaB-positive neurons (271 +/- 57 CPB/neonate oxygenator and 269 +/- 72 CPB/rat oxygenator) compared with sham operation (173 +/- 24). Neurocognitive and behavioral performances were unaltered and comparable among all groups.

CONCLUSIONS

Pronounced systemic inflammatory responses to experimental CPB associated with increased hippocampal expression of NF-kappaB were not accompanied by neurocognitive impairment. This suggests that other factors beyond CPB and inflammatory responses might contribute to adverse neurocognitive outcomes after cardiac surgery.

Continuously infusing hyperpolarized 129Xe into flowing aqueous solutions using hydrophobic gas exchange membranes

Hyperpolarized (HP) (129)Xe yields high signal intensities in nuclear magnetic resonance (NMR) and, through its large chemical shift range of approximately 300 ppm, provides detailed information about the local chemical environment. To exploit these properties in aqueous solutions and living tissues requires the development of methods for efficiently dissolving HP (129)Xe over an extended time period. To this end, we have used commercially available gas exchange modules to continuously infuse concentrated HP (129)Xe into flowing liquids, including rat whole blood, for periods as long as one hour and have demonstrated the feasibility of dissolved-phase MR imaging with submillimeter resolution within minutes. These modules, which exchange gases using hydrophobic microporous polymer membranes, are compatible with a variety of liquids and are suitable for infusing HP (129)Xe into the bloodstream in vivo. Additionally, we have developed a detailed mathematical model of the infused HP (129)Xe signal dynamics that should be useful in designing improved infusion systems that yield even higher dissolved HP (129)Xe signal intensities.

Effect of profound hypothermia on genomics of hippocampus following complete cerebral ischemia in rats

OBJECTIVE

To determine differential gene expression of hippocampus in rats following complete cerebral ischemia with treatment of profound hypothermia compared to normothermia.

METHODS

Six rats got 5 minutes of complete cerebral ischemia with circulatory arrest and randomly divided into two groups: normothermia ischemia group (37 +/- 0.3 degrees C, n = 3) and profound hypothermia ischemia group (18 +/- 0.5 degrees C, n = 3). Affymetrix U34A rat arrays were applied to detect the difference of gene expression profile in hippocampus between the two groups.

RESULTS

Expression profiles of a total of 75 transcripts in the profound hypothermia ischemia group were statistically different from those of the normothermia ischemia group, and 33 of them were significantly up-regulated and other 42 were significantly down-regulated (p < 0.07).

CONCLUSIONS

Compared with normothermia, profound hypothermia had a significant effect on the gene expression profiles following complete cerebral ischemia, which may be involved in the mechanisms of cerebral protection by profound hypothermia.

Inflammatory lung injury after cardiopulmonary bypass is attenuated by adenosine A(2A) receptor activation

OBJECTIVE

Cardiopulmonary bypass has been shown to exert an inflammatory response within the lung, often resulting in postoperative pulmonary dysfunction. Several studies have shown that adenosine A(2A) receptor activation attenuates lung ischemia-reperfusion injury; however, the effect of adenosine A(2A) receptor activation on cardiopulmonary bypass-induced lung injury has not been studied. We hypothesized that specific adenosine A(2A) receptor activation by ATL313 would attenuate inflammatory lung injury after cardiopulmonary bypass.

METHODS

Adult male Sprague-Dawley rats were randomly divided into 3 groups: 1) SHAM group (underwent cannulation + heparinization only); 2) CONTROL group (underwent 90 minutes of normothermic cardiopulmonary bypass with normal whole-blood priming solution; and 3) ATL group (underwent 90 minutes of normothermic cardiopulmonary bypass with ATL313 added to the normal priming solution).

RESULTS

There was significantly less pulmonary edema and lung injury in the ATL group compared with the CONTROL group. The ATL group had significant reductions in bronchoalveolar lavage interleukin-1, interleukin-6, interferon-gamma, and myeloperoxidase levels compared with the CONTROL group. Similarly, lung tissue interleukin-6, tumor necrosis factor-alpha, and interferon-gamma were significantly decreased in the ATL group compared with the CONTROL group. There was no significant difference between the SHAM and ATL groups in the amount of pulmonary edema, lung injury, or levels of proinflammatory cytokines.

CONCLUSION

The addition of a potent adenosine A(2A) receptor agonist to the normal priming solution before the initiation of cardiopulmonary bypass significantly protects the lung from the inflammatory effects of cardiopulmonary bypass and reduces the amount of lung injury. Adenosine A(2A) receptor agonists could represent a new therapeutic strategy for reducing the potentially devastating consequences of the inflammatory response associated with cardiopulmonary bypass.

A novel survival model of cardioplegic arrest and cardiopulmonary bypass in rats: a methodology paper

Background

Given the growing population of cardiac surgery patients with impaired preoperative cardiac function and rapidly expanding surgical techniques, continued efforts to improve myocardial protection strategies are warranted. Prior research is mostly limited to either large animal models or ex vivo preparations. We developed a new in vivo survival model that combines administration of antegrade cardioplegia with endoaortic crossclamping during cardiopulmonary bypass (CPB) in the rat.

Methods

Sprague-Dawley rats were cannulated for CPB (n = 10). With ultrasound guidance, a 3.5 mm balloon angioplasty catheter was positioned via the right common carotid artery with its tip proximal to the aortic valve. To initiate cardioplegic arrest, the balloon was inflated and cardioplegia solution injected. After 30 min of cardioplegic arrest, the balloon was deflated, ventilation resumed, and rats were weaned from CPB and recovered. To rule out any evidence of cerebral ischemia due to right carotid artery ligation, animals were neurologically tested on postoperative day 14, and their brains histologically assessed.

Results

Thirty minutes of cardioplegic arrest was successfully established in all animals. Functional assessment revealed no neurologic deficits, and histology demonstrated no gross neuronal damage.

Conclusion

This novel small animal CPB model with cardioplegic arrest allows for both the study of myocardial ischemia-reperfusion injury as well as new cardioprotective strategies. Major advantages of this model include its overall feasibility and cost effectiveness. In future experiments long-term echocardiographic outcomes as well as enzymatic, genetic, and histologic characterization of myocardial injury can be assessed. In the field of myocardial protection, rodent models will be an important avenue of research.

A rat model of cardiopulmonary bypass with cardioplegic arrest and hemodynamic assessment by conductance catheter technique

BACKGROUND

Cardiopulmonary bypass (CPB) is known to induce systemic inflammation and cardiac dysfunction associated with a significant morbidity. Aim of the study was to develop an in vivo model of rat CPB with hypothermic cardiac arrest and the use of cardioplegia.

MATERIAL AND METHODS

The CPB circuit consisted of a venous reservoir, membrane oxygenator, heat exchanger, and roller pump. CPB was instituted in adult male Wistar rats (400-500 g) for 60 min at a flow rate of 120 ml x kg(-1) x min(-1), including 15 min cooling to 32 degrees C, 30 min cardiac arrest with the use of cold crystalloid cardioplegia after aortic cross clamping, and 15 min of reperfusion and rewarming to 37 degrees C. Arterial blood pressure (MAP) and heart rate (HR) were monitored, arterial blood samples were analyzed. Left ventricular (LV) function parameters were assessed by intraventricular conductance catheter. Important technical aspects are: ventilation is required during partial bypass; anticoagulation should be performed immediately prior to CPB to reduce blood loss; active suction on venous drainage allows higher pump flows; and the small priming volume of the extracorporeal circuit (8 ml) avoids the need for donor blood.

RESULTS

MAP remained stable prior to and during CPB.MAP and HR were significantly decreased 60 min after weaning from bypass. Hct was significantly lowered after hemodilution, but remained stable during CPB and 60 min after weaning from bypass. BE and pH remained stable throughout the experiment.Without inotropic support diastolic and systolic LV function parameters were impaired after 30 min of cardioplegic arrest followed by 15 min of reperfusion. Myocardial TNF-alpha mRNA levels were slightly increased (1.28-fold, p = 0.71), and IL-6 mRNA was significantly increased in the cardioplegia group (90.3-fold, p = 0.001). Both IL-6 and TNF-alpha plasma levels were significantly elevated in the cardioplegia group (TNF-alpha: 4.6-fold increase,p < 0.05; IL-6: 426.8-fold increase, p < 0.001).

CONCLUSIONS

We have developed a rat CPB with mild hypothermic cardioplegic arrest. This rodent model is suitable to study clinically relevant problems related to CPB,myocardial protection and systemic inflammation.

Effects of cardiopulmonary bypass on neurocognitive performance and cytokine release in old and diabetic rats

BACKGROUND

Age and diabetes mellitus have been identified as independent risk factors for cognitive decline after cardiac surgery with cardiopulmonary bypass (CPB). We tested the effects of CPB on cognitive function in aged and diabetic rats utilizing the Morris water maze (MWM).

METHODS

Aged rats (26 months) were randomized into a sham group (cannulation but no CPB, n = 11) and a 90 min CPB group (n = 11). In addition, young rats (n = 14) were made diabetic with streptozotocin 9 weeks before experimentation and randomized to a sham or 90 min CPB group. Cytokine release [interleukin (IL-6)] and short-term MWM performance (days 8-14 after operation) were assessed in all animals. Long-term MWM performance (8 weeks after operation) was assessed in aged rats only.

RESULTS

There were no differences between the aged groups in short-term (P = 0.58) or long-term MWM performances (P = 0.69). The diabetic animals also showed no differences between the sham and CPB groups in MWM performance (P = 0.64). IL-6 assays showed an increased inflammatory response after CPB in the diabetic animals, but not in the elderly groups.

CONCLUSIONS

Ninety minutes of normothermic CPB had no deleterious effect on neurocognitive outcome in elderly or chronically diabetic animals, suggesting that CPB in itself is not a sufficient stressor of the rat central nervous system.

Emergency preservation and delayed resuscitation allows normal recovery after exsanguination cardiac arrest in rats: A feasibility trial*

OBJECTIVE

Emergency preservation and resuscitation (EPR) comprise a novel approach for resuscitation of exsanguination cardiac arrest victims. EPR uses a cold aortic flush to induce deep hypothermic preservation, followed by resuscitation with cardiopulmonary bypass. Development of a rat EPR model would enable study of the molecular mechanisms of neuronal injury and the screening of novel agents for emergency preservation.

DESIGN

A prospective, randomized study.

SETTING

University research facility.

SUBJECTS

Adult male Sprague-Dawley rats.

INTERVENTIONS

Isoflurane-anesthetized rats were subjected to lethal hemorrhage (12.5 mL for 5 mins), followed by KCl-induced cardiac arrest and 1 min of no flow. Three groups (n=6) were studied: hypothermic EPR (H-EPR; 0 degrees C flush; target temperature, 15 degrees C); normothermic EPR (N-EPR; 38 degrees C flush); and controls. After 20 mins of H-EPR or N-EPR, resuscitation was initiated with cardiopulmonary bypass for 60 mins and mechanical ventilation. Controls were subjected to complete experimental preparation and anesthesia without cardiac arrest, followed by 60 mins of cardiopulmonary bypass and mechanical ventilation. Surviving rats were extubated 2 hrs later. Survival, Overall Performance Category (1, normal; 5, death), Neurologic Deficit Score, Histologic Damage Score, and biochemistry were assessed in survivors on day 7.

MEASUREMENTS AND MAIN RESULTS

All rats in H-EPR and control groups survived, whereas none of the rats in the N-EPR group had restoration of spontaneous circulation. All rats in the H-EPR and control groups achieved Overall Performance Category 1, normal Neurologic Damage Score, and normal or near normal Histologic Damage Score and biochemical markers of organ injury.

CONCLUSIONS

We have established an EPR model in rats showing no neurologic injury, despite an exsanguination cardiac arrest, followed by 20 mins of EPR using miniaturized cardiopulmonary bypass. Establishment of this model should facilitate application of molecular tools to study the effects of hypothermic preservation and reperfusion and to screen novel pharmacologic adjuncts.

Changes in Cerebral Vascular Reactivity Occur Early During Cardiopulmonary Bypass in the Rat

BACKGROUND

Cardiopulmonary bypass (CPB) is known to cause cerebrovascular dysfunction. The etiology of these complications is complex, but disruption of normal cerebral endothelial function as a consequence of inflammatory or hypoperfusion phenomena have been implicated. The aim of this study was to investigate the effect of CPB time on cerebrovascular reactivity and to investigate the correlation of these findings with measured inflammatory markers.

METHODS

Cardiopulmonary bypass was carried out for 30 or 60 minutes on two groups of rats. Sham groups underwent the same surgical procedure without CPB. The middle cerebral artery was harvested and prepared for assessment of induced endothelial and vascular smooth muscle cell responses. Systemic inflammation was evaluated by measuring tumor necrosis factor-alpha and immunohistochemical staining for intercellular adhesion molecule-1.

RESULTS

Acetylcholine caused a dose-dependent vasodilation in the control groups that was absent in animals undergoing CPB (21.3% +/- 1.3% increase in diameter at 30 minutes in the sham group compared with 5.4% +/- 1.1% in the corresponding CPB group, p < 0.001). Significantly, this was apparent after only 30 minutes of CPB. Cardiopulmonary bypass did not alter the response to sodium nitroprusside (45.3% +/- 8.6% after 30 minutes in the sham group compared with 57.8% +/- 8.0% in the corresponding CPB group, p < 0.2). Furthermore, the contractile response to serotonin remained intact in all groups (32.9 +/- 4.6 and 27.6 +/- 2.6 at 30 and 60 minutes, respectively, in the sham groups compared with 23.1 +/- 1.6 and 28.0 +/- 4.4 in the corresponding CPB groups, p < 0.2). Cardiopulmonary bypass also led to an early and marked increase in tumor necrosis factor-alpha and overexpression of intercellular adhesion molecule-1.

CONCLUSIONS

Cerebrovascular impairment appears early after the onset of CPB. The specific loss of acetylcholine-induced vasodilation suggests endothelial cell dysfunction rather than impaired vascular smooth muscle response to nitric oxide. This loss of endothelium-dependent regulatory factors after CPB may enhance vasoconstriction, impair cerebrovascular function, and contribute to neurologic injury after CPB.

Cardiopulmonary bypass and long-term neurocognitive dysfunction in the rat

Neurologic and neurocognitive complications after cardiac surgery with cardiopulmonary bypass (CPB) have been reported repeatedly. To better understand its etiology and design protective strategies, an appropriate animal model may prove useful. Although impaired short-term neurocognitive function has been recently demonstrated after CPB in rats, the demonstration of persistent long-term neurocognitive changes would be more relevant from a clinical perspective. We hypothesized that CPB results in long-term impairment of neurocognitive performance in rats. Male rats were exposed to either 60 min of normothermic non-pulsatile CPB, using a roller-pump and a neonatal membrane oxygenator, or to cannulation only (sham animals). Long-term neurocognitive function was assessed at 4 to 7 weeks after CPB (Can test), and again after 12 weeks (Morris water maze) in both operated groups and in a non-operated control group, followed by histologic evaluation of the hippocampus. In separate groups of CPB and sham animals, we also measured TNF-alpha and IL-6 in plasma. There were no significant differences in long-term neurocognitive performance or histological outcome between the three groups. Cytokine patterns were also similar in both operated groups. We conclude that CPB did not appear to cause long-term neurocognitive dysfunction in this model of CPB in young healthy rats. The lack of long-term deficits may be due to the absence of clinically important etiologic factors such as atheromatous and gaseous embolization in this model. Similar cytokine patterns in both operated groups suggest that surgical trauma rather than exposure of blood to extra-corporeal circuit was probably responsible for the inflammatory response.

Long-Term Neurodevelopmental Outcome and Exercise Capacity After Corrective Surgery for Tetralogy of Fallot or Ventricular Septal Defect in Infancy

BACKGROUND

The purpose of this prospective study was to assess whether neurodevelopmental status and exercise capacity of children 5 to 10 years after corrective surgery for tetralogy of Fallot or ventricular septal defect in infancy was different compared with normal children and influenced by the preoperative condition of hypoxemia or cardiac insufficiency.

METHODS

Forty unselected children, 20 with tetralogy of Fallot and hypoxemia and 20 with ventricular septal defect and cardiac insufficiency, operated on with combined deep hypothermic circulatory arrest and low flow cardiopulmonary bypass at a mean age of 0.7 +/- 0.3 years (mean +/- SD), underwent, at mean age 7.4 +/- 1.6 years, standardized evaluation of neurologic status, gross motor function, intelligence, academic achievement, language, and exercise capacity. Results were compared between the groups and related to preoperative, perioperative, and postoperative status and management.

RESULTS

Rate of mild neurologic dysfunction was increased compared with normal children, but not different between the groups. Exercise capacity and socioeconomic status were not different compared with normal children and between the groups. Compared with the normal population, motor function, formal intelligence, academic achievement, and expressive and receptive language were significantly reduced (p < 0.01 to p < 0.001) in the whole group and in the subgroups, except for normal intelligence in ventricular septal defect patients. Motor dysfunction was significantly higher in the Fallot group compared with the ventricular septal defect group (p < 0.01) and correlated with neurologic dysfunction, lower intelligence, and reduced expressive language (p < 0.05 each). Reduced New York Heart Association functional class was correlated with lower exercise capacity and longer duration of cardiopulmonary bypass (p < 0.05 each). Reduced socioeconomic status significantly influenced dysfunction in formal intelligence (p < 0.01) and academic achievement (p < 0.05). Preoperative risk factors such as prenatal hypoxia, perinatal asphyxia, and preterm birth, factors of perioperative management such as cardiac arrest, lowest nasopharyngeal temperature, and age at surgery, and postoperative risk factors as postoperative cardiocirculatory insufficiency and duration of mechanical ventilation were not different between the groups and had no influence on outcome. Degree of hypoxemia in Fallot patients and degree of cardiac insufficiency in ventricular septal defect patients did not influence the outcome within the subgroups.

CONCLUSIONS

Children with preoperative hypoxemia in infancy are at higher risk for motor dysfunction than children with cardiac insufficiency. Corrective surgery in infancy for tetralogy of Fallot or ventricular septal defect with combined circulatory arrest and low flow bypass is associated with reduced neurodevelopmental outcome, but not with reduced exercise capacity in childhood. In our experience, the general risk of long-term neurodevelopmental impairment is related to unfavorable effects of the global perioperative management. Socioeconomic status influences cognitive capabilities.

Xenon and the inflammatory response to cardiopulmonary bypass in the rat

OBJECTIVE

The purpose of this study was to investigate the effect of xenon on the inflammatory response to cardiopulmonary bypass.

DESIGN

Prospective, randomized experimental study.

SETTING

University research laboratory.

PARTICIPANTS

Sprague-Dawley rats.

INTERVENTIONS

After surgical preparation, rats were randomly divided into 4 groups: (1) SHAM rats were cannulated but did not undergo cardiopulmonary bypass; (2) cardiopulmonary bypass rats were subjected to 60 minutes of cardiopulmonary bypass using an oxygenator receiving a 30% O(2), 65% N(2), and 5% CO(2) gas mixture; (3) MK801 rats received MK801 (0.15 mg/kg intravenous) 15 minutes before 60 minutes of cardiopulmonary bypass with the same gas mixture; and (4) xenon rats underwent 60 minutes of cardiopulmonary bypass receiving a 30% O(2), 60% xenon, 5% N(2), and 5% CO(2) gas mixture.

MEASUREMENTS AND MAIN RESULTS

All bypass groups showed elevations in both cytokines compared with the SHAM-operated group. However, the inflammatory response to cardiopulmonary bypass in the group receiving xenon was no different from the other bypass groups.

CONCLUSIONS

Xenon appears to have no effect on the inflammatory response to cardiopulmonary bypass, making its previously described neuroprotective effect during cardiopulmonary bypass likely independent of any inflammation modulation.

Retrograde cerebral perfusion of oxygenated, compacted red blood cells attenuates brain damage after hypothermia circulation arrest of rat

BACKGROUND

It was proved that higher haematocrit (Hct) might improve the function of brain after hypothermia circulation arrest (HCA). In the present study we established a new rat HCA model and investigated whether retrograde cerebral perfusion of oxygenated, compacted red blood cells (RBC) could attenuate brain injury after HCA.

METHODS

A new rat HCA model was developed and rats were randomly distributed into three groups: HCA group, HCA combined with retrograde cerebral perfusion of oxygenated, compacted red blood cell group (HCArcp group), and sham operation group (sham op. group). Animals both in the HCA group and in the HCArcp group underwent HCA 90 min at 18 degrees C. Brain damage after HCA was evaluated with light microscopy and electron microscopy. Immunohistochemistry and RT-PCR techniques were used to measured the different expressions of the C-Fos, Bcl-2, Bax mRNA and protein among the groups. Additionally we measured the wet/dry ratio of the brain in order to evaluate the oedema degree after HCA.

RESULTS

The new HCA model of rat we developed was comparable to the clinical setting not only in terms of the intubation, anaesthesia method and materials employed but also in terms of the priming volume in relation to body weight. The number of injured neurones in the hippocampus CA1 and parietal cortex, but not in the thalamus of the HCA group, was significantly greater than that of the HCArcp group (P<0.05). The mean score of mitochondrion of the hippocampus CA1 in the HCA group was significantly higher than in the HCArcp group (P<0.05). The expression of C-Fos, Bax mRNA and protein in the hippocampus CA1 and/or parietal cortex area was higher in the HCA group than in the HCArcp group (P<0.05). Expression of the mRNA and protein of Bcl-2 was higher in the HCArcp group than in the HCA group (P<0.05). The degree of oedema after HCA between the HCA group and HCArcp group had no significant difference (P>0.05).

CONCLUSIONS

We established a new rat model of HCA comparable to the clinical setting. Retrograde cerebral perfusion of oxygenated, compacted RBC is a simple, effective, and safe method to protect the brain during HCA. Adjusting the gene expression in relation to apoptosis might contribute to the neuroprotective effects of a retrograde cerebral infusion of oxygenated, compacted RBC.

Differential cardiac gene expression during cardiopulmonary bypass: Ischemia-independent upregulation of proinflammatory genes

OBJECTIVE

Cardiac surgery with cardiopulmonary bypass induces both systemic and local inflammatory responses implicated in the pathogenesis of myocardial dysfunction. Multifactorial perioperative sources of myocardial injury complicate understanding of the molecular mechanisms involved. By using microarray technology, this study examines myocardial gene expression responses to cardiopulmonary bypass in the absence of cardioplegic arrest and ischemia-reperfusion injury.

METHODS

We used a unique rat model of cardiopulmonary bypass in which sternotomy, direct operations on the heart, aortic crossclamping, and cardioplegic arrest were not performed. Hearts from 6 animals randomized to either 90 minutes of cardiopulmonary bypass or sham control animals were used to perform cDNA microarray analyses of 2343 genes. Real-time quantitative polymerase chain reaction was used to confirm the microarray results for a subset of genes.

RESULTS

Compared with sham-operated control animals, myocardium from animals undergoing cardiopulmonary bypass revealed 42 differentially expressed genes. Upregulated genes include the transcription activator nuclear factor kappaB, adhesion molecules (vascular cell adhesion molecule 1 and P-selectin), and interleukin 6 receptor subunits; downregulated genes include transforming growth factor beta receptor 2, tissue inhibitor of metalloproteinase 3, and mitogen-activated protein kinase 1. Distinct proinflammatory gene cascades were confirmed by means of category overrepresentation analysis.

CONCLUSIONS

This study represents an initial report on the use of microarray technology to elucidate cardiac transcriptional programs in response to cardiopulmonary bypass-specific injury in vivo. These preliminary findings, combined with future functional genomic studies superimposing ischemia and reperfusion and other inflammatory stimuli, should improve our understanding of the molecular regulatory networks involved in myocardial responses to injury and aid in the development of novel cardioprotective and perfusion strategies.

A rat model of cardiopulmonary bypass with excellent survival

BACKGROUND

Elucidating the underlying mechanisms and developing protective strategies for the pathophysiological consequences of cardiopulmonary bypass (CPB) have been hampered due to the absence of a satisfactory long-term recovery animal model. The objective of this study was to establish a survival experimental model of CPB in rats to meet the requirement of these studies.

MATERIALS AND METHODS

Male SD rats (450-550 g) were randomly divided into CPB (n = 10) group and Sham group (n = 10). All rats were anaesthetized and mechanically ventilated. The femoral artery and vein were cannulated for continuous blood pressure recordings and fluid replacement, respectively. The CPB circuit comprised a venous reservoir, a membrane oxygenator, and a roller pump. Blood was drained from the right atrium via a jugular vein catheter and returned to the right carotid artery. Priming consisted of 8 ml of homologous blood and 8 ml of colloid. CPB was conducted for 60 min at a flow rate of 100-150 ml/kg/min in the CPB group. Haemodynamic investigations, blood gas analysis, and survival studies were performed subsequently.

RESULTS

Our data show that the rat model principally simulated the clinical setting of CPB in terms of its construction, configuration, performance, material surface area, and priming volume to blood volume ratio. All CPB rats survived and the 2-week follow-up period remained uneventful.

CONCLUSIONS

The rat model of CPB was easy to establish and was associated with excellent survival. This model should facilitate the investigation of the pathophysiological processes concerning CPB-related multiple organ dysfunction and possible protective interventions.

Cardiopulmonary bypass reduces the minimum alveolar concentration for isoflurane

OBJECTIVE

The purpose of this investigation was to determine the influence of cardiopulmonary bypass (CPB) on the minimum alveolar concentration (MAC) of isoflurane in a rat model of CPB.

DESIGN

Prospective.

SETTING

University research laboratory.

PARTICIPANTS

Sprague-Dawley rats.

INTERVENTIONS

Using tail-clamp methodology, the pre- and post-CPB MAC for isoflurane was studied.

METHODS AND MAIN RESULTS

Rats were anesthetized with isoflurane, intubated, ventilated, and surgically prepared for CPB, after which they were randomized to either Sham-operated or CPB groups. The CPB group (n = 10) underwent 90 minutes of normothermic nonpulsatile CPB. The Sham group (n = 13) were cannulated but did not undergo CPB. Pre- and post-CPB MAC determinations were compared within groups using a paired Student t test. The CPB group had a pre-CPB baseline isoflurane MAC of 1.09% +/- 0.11% versus 1.09% +/- 0.08% in the Sham group (p = 0.90). Twenty minutes after CPB, the CPB group exhibited a decrease in MAC to 0.98% +/- 0.14% (p = 0.0026, compared with baseline). The MAC in the Sham group was unchanged (p = 0.5852, compared with baseline). Two hours after CPB, the MAC in the CPB group remained lower compared with baseline at 0.99% +/- 0.14% (p = 0.0032).

CONCLUSIONS

CPB resulted in a small (10%) but significant reduction in the MAC for isoflurane. The mechanism behind this reduction in MAC is not clear but may be related to CPB-induced cerebral injury.

Neuroprotection in cardiac surgery

This article reviews past and present neuroprotective efforts and outlines a framework for the future development of techniques for neuroprotection during cardiac surgery.

Differential cerebral gene expression during cardiopulmonary bypass in the rat: evidence for apoptosis?

Cardiopulmonary bypass (CPB) is associated with a spectrum of cerebral injuries. The molecular changes in the brain that might contribute to these injuries are not clearly known. We sought to determine whether the expression of apoptotic genes is increased after CPB in the rat. Rats (n = 7) were subjected to 90 min of normothermic CPB. A group of sham-operated rats (n = 7) served as non-CPB controls. After a 3-h post-CPB period of recovery, their brains were removed, homogenized, and processed for messenger RNA (mRNA) extraction. By using a ribonuclease protection assay, the ratios of both pro- and antiapoptotic mRNA (bcl-x, bcl-2, bax, caspase 2, and caspase 3) to the housekeeping glyceraldehyde phosphate dehydrogenase (GAPDH) gene were determined. Additionally, Western immunoblotting was performed to detect the presence of activated caspase 3, a protein central in the apoptotic process. Compared with the non-CPB controls, the CPB group had significantly increased levels of apoptotic/GAPDH mRNA ratios (bcl-x, 0.414 +/- 0.152 CPB versus 0.251 +/- 0.051 non-CPB, P = 0.048; caspase 2, 0.030 +/- 0.014 CPB versus 0.018 +/- 0.005 non-CPB, P = 0.048; bax, 0.106 +/- 0.035 CPB versus 0.066 +/- 0.009 non-CPB, P = 0.009; bcl-2, 0.011 +/- 0.006 CPB versus 0.006 +/- 0.002 non-CPB, P = 0.035). However, no activated caspase 3 protein was detected in either group. Elucidating the molecular biological sequelae of CPB may aid in the understanding of the pathophysiology of cardiac surgery-associated cerebral injury and, in doing so, may be useful in identifying potential therapeutic targets for pharmacologic neuroprotection.

IMPLICATIONS

Cardiopulmonary bypass (CPB) appears to induce transcription of pro- and antiapoptotic genes in the rat brain, but caspase-mediated apoptosis itself does not appear to be activated. Elucidating the molecular biological sequelae of CPB may aid in the understanding of the pathophysiology of cardiac surgery-associated cerebral injury and, in doing so, may be useful in identifying potential therapeutic targets for pharmacologic neuroprotection.

Differential cerebral gene expression during cardiopulmonary bypass in the rat: evidence for apoptosis?

Cardiopulmonary bypass (CPB) is associated with a spectrum of cerebral injuries. The molecular changes in the brain that might contribute to these injuries are not clearly known. We sought to determine whether the expression of apoptotic genes is increased after CPB in the rat. Rats (n = 7) were subjected to 90 min of normothermic CPB. A group of sham-operated rats (n = 7) served as non-CPB controls. After a 3-h post-CPB period of recovery, their brains were removed, homogenized, and processed for messenger RNA (mRNA) extraction. By using a ribonuclease protection assay, the ratios of both pro- and antiapoptotic mRNA (bcl-x, bcl-2, bax, caspase 2, and caspase 3) to the housekeeping glyceraldehyde phosphate dehydrogenase (GAPDH) gene were determined. Additionally, Western immunoblotting was performed to detect the presence of activated caspase 3, a protein central in the apoptotic process. Compared with the non-CPB controls, the CPB group had significantly increased levels of apoptotic/GAPDH mRNA ratios (bcl-x, 0.414 +/- 0.152 CPB versus 0.251 +/- 0.051 non-CPB, P = 0.048; caspase 2, 0.030 +/- 0.014 CPB versus 0.018 +/- 0.005 non-CPB, P = 0.048; bax, 0.106 +/- 0.035 CPB versus 0.066 +/- 0.009 non-CPB, P = 0.009; bcl-2, 0.011 +/- 0.006 CPB versus 0.006 +/- 0.002 non-CPB, P = 0.035). However, no activated caspase 3 protein was detected in either group. Elucidating the molecular biological sequelae of CPB may aid in the understanding of the pathophysiology of cardiac surgery-associated cerebral injury and, in doing so, may be useful in identifying potential therapeutic targets for pharmacologic neuroprotection.

IMPLICATIONS

Cardiopulmonary bypass (CPB) appears to induce transcription of pro- and antiapoptotic genes in the rat brain, but caspase-mediated apoptosis itself does not appear to be activated. Elucidating the molecular biological sequelae of CPB may aid in the understanding of the pathophysiology of cardiac surgery-associated cerebral injury and, in doing so, may be useful in identifying potential therapeutic targets for pharmacologic neuroprotection.

Early experience with a new technique and technology designed for the study of pulsatile cardiopulmonary bypass in the rat

The benefits of pulsatile flow during the period of cardiopulmonary bypass (CPB) applied during open-heart surgery remains controversial. We have developed a rodent (rat) model of CBP that has been designed to functionally mimic the clinical setting, principally, but not solely, for the study of pulsatile CPB. The successful development of this model centres on the design of the bypass circuitry and the surgical approach employed. The entire circuit is similar to clinical equipment in terms of its construction, configuration, performance, material surface area to blood volume ratio, and priming volume to blood volume ratio. The overall priming volume of the perfusion circuitry is less than 12 ml. Early studies confirm that the pumping technology functions well, gas exchange was adequate at all times, and blood pressure exhibited a normal CPB profile and haemodynanmic response to pulsatile blood flow. We conclude that this is an effective tool for investigating the pathophysiology of pulsatile blood flow during CPB.