Microhemodynamics and leukocyte sequestration after pulmonary ischemia and reperfusion in rabbits

Correlation between Neutrophil Extracellular Traps (NETs) Expression and Primary Graft Dysfunction Following Human Lung Transplantation

Primary graft dysfunction (PGD) is characterized by alveolar epithelial and vascular endothelial damage and inflammation, lung edema and hypoxemia. Up to one-third of recipients develop the most severe form of PGD (Grade 3; PGD3). Animal studies suggest that neutrophils contribute to the inflammatory process through neutrophil extracellular traps (NETs) release (NETosis). NETs are composed of DNA filaments decorated with granular proteins contributing to vascular occlusion associated with PGD. The main objective was to correlate NETosis in PGD3 (n = 9) versus non-PGD3 (n = 27) recipients in an exploratory study. Clinical data and blood samples were collected from donors and recipients pre-, intra- and postoperatively (up to 72 h). Inflammatory inducers of NETs' release (IL-8, IL-6 and C-reactive protein [CRP]) and components (myeloperoxidase [MPO], MPO-DNA complexes and cell-free DNA [cfDNA]) were quantified by ELISA. When available, histology, immunohistochemistry and immunofluorescence techniques were performed on lung biopsies from donor grafts collected during the surgery to evaluate the presence of activated neutrophils and NETs. Lung biopsies from donor grafts collected during transplantation presented various degrees of vascular occlusion including neutrophils undergoing NETosis. Additionally, in recipients intra- and postoperatively, circulating inflammatory (IL-6, IL-8) and NETosis biomarkers (MPO-DNA, MPO, cfDNA) were up to 4-fold higher in PGD3 recipients compared to non-PGD3 (p = 0.041 to 0.001). In summary, perioperative elevation of NETosis biomarkers is associated with PGD3 following human lung transplantation and these biomarkers might serve to identify recipients at risk of PGD3 and initiate preventive therapies.

Lung ischemia-reperfusion injury: a molecular and clinical view on a complex pathophysiological process

Lung ischemia-reperfusion injury remains one of the major complications after cardiac bypass surgery and lung transplantation. Due to its dual blood supply system and the availability of oxygen from alveolar ventilation, the pathogenetic mechanisms of ischemia-reperfusion injury in the lungs are more complicated than in other organs, where loss of blood flow automatically leads to hypoxia. In this review, an extensive overview is given of the molecular and cellular mechanisms that are involved in the pathogenesis of lung ischemia-reperfusion injury and the possible therapeutic strategies to reduce or prevent it. In addition, the roles of neutrophils, alveolar macrophages, cytokines, and chemokines, as well as the alterations in the cell-death related pathways, are described in detail.

Acute effects of peritoneal dialysis solutions in the mesenteric microcirculation

Long-term peritoneal dialysis induces morphological changes that may lead to gradual functional impairment of the peritoneal membrane. These changes are characterized by progressive reduction in solute transport or ultrafiltration failure. The mechanism of the peritoneal response to dialysis fluids has not yet been fully elucidated. We used video-microscopy for in vivo evaluation of microhemodynamics and peritoneal microvascular inflammatory response, after a single intraperitoneal exposure of rats to commercial PD fluids: (1) glucose 1.5 % PD solution; (2) lactate buffered glucose 4.25% PD solution; (3) Icodextrin 7%; (4) bicarbonate buffered glucose 3.86% PD fluid; and 5) Hanks solution. Sham-control groups were not injected. A 5-h exposure of the peritoneal membrane to glucose 1.5% PD solution or to Hanks solution did not induce a significant change in leukocyte rolling and adhesion. In contrast, PD solutions containing glucose 4.25% or Icodextrin 7.5% caused a significant 2-3-fold increase in leukocyte rolling (P < 0.001) and adhesion (P < 0.001) and a significant increase in venular blood flow velocity (P < 0.01) and shear rates (P < 0.05 for glucose 4.25%, and P < 0.01 for Icodextrin). Exposure to glucose 3.86% bicarbonate buffered (Physioneal) solution was associated with the lowest values of leukocyte rolling and adhesion among the PD solutions and with extremely higher venular flow velocities and shear rates. A single exposure to conventional PD solutions with a high concentration of glucose (4.25%) or polyglucose (Icodextrin 7.5%) induces changes consistent with an early peritoneal inflammatory response that may be attenuated by the use of bicarbonate-based fluids.

Lung ischemia-reperfusion injury: implications of oxidative stress and platelet-arteriolar wall interactions

Pulmonary ischemia-reperfusion (IR) injury may result from trauma, atherosclerosis, pulmonary embolism, pulmonary thrombosis and surgical procedures such as cardiopulmonary bypass and lung transplantation. IR injury induces oxidative stress characterized by formation of reactive oxygen (ROS) and reactive nitrogen species (RNS). Nitric oxide (NO) overproduction via inducible nitric oxide synthase (iNOS) is an important component in the pathogenesis of IR. Reaction of NO with ROS forms RNS as secondary reactive products, which cause platelet activation and upregulation of adhesion molecules. This mechanism of injury is particularly important during pulmonary IR with increased iNOS activity in the presence of oxidative stress. Platelet-endothelial interactions may play an important role in causing pulmonary arteriolar vasoconstriction and post-ischemic alveolar hypoperfusion. This review discusses the relationship between ROS, RNS, P-selectin, and platelet-arteriolar wall interactions and proposes a hypothesis for their role in microvascular responses during pulmonary IR.

Subpleural microvascular flow velocities and shear rates in normal and septic mechanically ventilated rats

Changes in pulmonary microhemodynamics are important variables in a large variety of pathological processes. We used in vivo fluorescent videomicroscopy of the subpleural microvasculature in mechanically ventilated rats to directly monitor microvascular flow velocity (FV) and shear rate in pulmonary arterioles, capillaries, and venules in healthy rats and in septic rats 20 h after cecal ligation and puncture (CLP). Observations were made through a small thoracotomy after injection of fluorescent microspheres (D = 1 microm) into the systemic circulation. The FVs were calculated off-line by frame-by-frame measurements of the distance covered by individual microspheres per unit of time. In healthy rats, inspiratory FV were 1322 +/- 142 microm/s in subpleural arterioles and 599 +/- 25 microm/s in capillaries. The highest FV was found in venules (1552 +/- 132 microm/s). The calculated shear rates were 547 +/- 62/s in arterioles and 619 +/- 19/s in capillaries. The highest shear rates were detected in venules (677 +/- 59/s). No significant changes in FV and shear rates were observed throughout the 1-h observation period in any of the microvascular compartments. Pulmonary microvascular FV and shear rates found in sham-operated rats in the CLP experiments were not significantly different from values of healthy rats. The CLP caused a significant increase in leukocyte sequestration in the lungs and a mean of 27% to 34% decrease in FV in all sections of the pulmonary microvasculature (P < 0.001 in capillaries and P < 0.05 in venules). Also, CLP caused a 23% decrease in capillary shear rate that reached only borderline statistical significance (P < 0.06) and a significant 35% decrease in mean shear rate in venules (P < 0.05). Fluorescent videomicroscopy is offered as a stable and reproducible method for in vivo determinations of pulmonary microhemodynamics in clinically relevant models of sepsis.

Inflammatory response to pulmonary ischemia-reperfusion injury

Lung ischemia-reperfusion (IR) injury is one of the most important complications following lung transplant and cardiopulmonary bypass. The pulmonary dysfunction following lung IR has been well documented. Recent studies have shown that ischemia and reperfusion of the lung may each play significant yet differing roles in inducing lung injury. The mechanisms of injury involving neutrophil activation, and the release of numerous inflammatory mediators and oxygen radicals also contributes to lung cellular injury, pneumocyte necrosis, and apoptosis. We herein review the current understanding of the underlying mechanism involved in lung IR injury. The biomolecular mechanisms and interactions which lead to the inflammatory response, pneumocyte necrosis, and apoptosis following lung IR therefore warrant further investigation.

Inhibition of inducible nitric oxide synthase attenuates platelet adhesion in subpleural arterioles caused by lung ischemia-reperfusion in rabbits

Oxidative stress, induced by lung ischemia-reperfusion, leads to platelet and leukocyte activation and may contribute to decreased alveolar perfusion by platelet adhesion to the arteriolar wall. We investigated the hypothesis that ischemia-reperfusion injury increases inducible nitric oxide synthase (iNOS) activity and subsequent generation of reactive nitrogen species with P-selectin-dependent platelet-endothelial interactions and vasoconstriction during lung reperfusion. Subpleural arterioles, labeled platelets, and leukocytes were examined in anesthetized, open-chest rabbits by intravital fluorescence microscopy. Ischemia was caused by reversible occlusion of the right pulmonary artery for 1 or 2 h (1IR and 2IR groups). During 2 h of reperfusion, postischemic platelet rolling and adhesion were independent from leukocyte-arteriolar wall interactions and correlated with pulmonary arteriolar constriction in proportion to the length of ischemia. In rabbits treated with an iNOS inhibitor (1400W) before occlusion (2IR + 1400W group), platelet-arteriolar wall interactions and vasoconstriction were prevented. iNOS expression and activity in ischemic lung tissue were markedly greater than control and also were proportional to ischemia duration. NOS activity, immunochemically detected P-selectin, and nitrotyrosine expression in ischemic lung tissue from animals subjected to ischemia-reperfusion, as well as the plasma level of soluble P-selectin, were significantly higher than in nonischemic lungs and were inhibited by pretreatment with 1400W. These results show that platelet adhesion and arteriolar constriction during early reperfusion in the ventilated lung can result from increased iNOS activity and is highly correlated with reactive nitrogen species and P-selectin expression.

Protective effects of a selective neutrophil elastase inhibitor (sivelestat) on lipopolysaccharide-induced acute dysfunction of the pulmonary microcirculation

OBJECTIVE

The purpose of this study was to evaluate the effect of a neutrophil elastase inhibitor, sivelestat, on lipopolysaccharide-induced acute lung injury through analysis of hemodynamic changes in the pulmonary microcirculation.

DESIGN

Randomized animal study.

SETTING

Medical school laboratory.

SUBJECTS

Twenty-seven Wistar rats (15 rats for microspectroscopic observations, 12 rats for measurements of neutrophil elastase activity and wet-to-dry ratio).

INTERVENTIONS

Thoracosternotomy was performed on male Wistar rats under continuous anesthesia and mechanical ventilation. Rats were divided into three groups (n = 5 each groups) on the basis of the reagent used: lipopolysaccharide group (100 microg/kg lipopolysaccharide intravenously), sivelestat group (10 mg/kg sivelestat; 100 microg/kg lipopolysaccharide intravenously), and control group (saline only, intravenously).

MEASUREMENTS AND MAIN RESULTS

We measured morphologic changes and hemodynamic variables, including tissue blood flow, erythrocyte velocity, erythrocyte count, thickness of interalveolar septa, and leukocyte adhesion in the pulmonary microcirculation, with a video-rate (33 msec/frame) dual-spot microspectroscopy system (DSMSS) and a laser-Doppler flowmeter. Blood-free wet-to-dry ratio and neutrophil elastase activity in bronchoalveolar lavage fluid, serum, and supernatant of lung homogenate were measured in another set of experiments (n = 4 for each group). Sixty minutes after lipopolysaccharide administration, severe thickening of the interalveolar septa was observed in the lipopolysaccharide but not the sivelestat group. In the lipopolysaccharide group, DSMSS measurements of erythrocyte velocity and hemoglobin oxygenation in single capillaries were decreased significantly (vs. control p < .05, vs. sivelestat p < .01), whereas tissue blood flow and erythrocyte velocity measurements from laser-Doppler flowmeter were increased significantly (vs. control p < .05, vs. sivelestat p < .01). The number of adherent leukocytes was increased significantly in the lipopolysaccharide group at 30, 45, and 60 mins after lipopolysaccharide administration (vs. control p < .01, vs. sivelestat p < .05). The number of adherent leukocytes did not increase in the sivelestat group. The wet-to-dry ratio was significantly higher in the lipopolysaccharide group than in control (p < .05) and sivelestat (p < .05) groups. Neutrophil elastase activities in the bronchoalveolar lavage fluid, serum, and lung tissue were all significantly lower in the sivelestat group than in the lipopolysaccharide group (p < .05).

CONCLUSIONS

Lipopolysaccharide induces leukocyte adhesion in the pulmonary microcirculation, resulting in decreased tissue hemoglobin oxygen and alveolar and interstitial edema. The selective neutrophil elastase inhibitor sivelestat reduces neutrophil elastase activity and attenuates acute changes in the pulmonary microcirculation.

Cellular infiltrates and injury evaluation in a rat model of warm pulmonary ischemia-reperfusion

Introduction

Beside lung transplantation, cardiopulmonary bypass, isolated lung perfusion and sleeve resection result in serious pulmonary ischemia–reperfusion injury, clinically known as acute respiratory distress syndrome. Very little is known about cells infiltrating the lung during ischemia–reperfusion. Therefore, a model of warm ischemia–reperfusion injury was applied to differentiate cellular infiltrates and to quantify tissue damage.

Methods

Fifty rats were randomized into eight groups. Five groups underwent warm ischemia for 60 min followed by 30 min and 1–4 hours of warm reperfusion. An additional group was flushed with the use of isolated lung perfusion after 4 hours of reperfusion. One of two sham groups was also flushed. Neutrophils and oedema were investigated by using samples processed with hematoxylin/eosin stain at a magnification of ×500. Immunohistochemistry with antibody ED-1 (magnification ×250) and antibody 1F4 (magnification ×400) was applied to visualize macrophages and T cells. TdT-mediated dUTP nick end labelling was used for detecting apoptosis. Statistical significance was accepted at P < 0.05.

Results

Neutrophils were increased after 30 min until 4 hours of reperfusion as well as after flushing. A doubling in number of macrophages and a fourfold increase in T cells were observed after 30 min until 1 and 2 hours of reperfusion, respectively. Apoptosis with significant oedema in the absence of necrosis was seen after 30 min to 4 hours of reperfusion.

Conclusions

After warm ischemia–reperfusion a significant increase in infiltration of neutrophils, T cells and macrophages was observed. This study showed apoptosis with serious oedema in the absence of necrosis after all periods of reperfusion.

N-acetylcysteine reduces lung reperfusion injury after deep hypothermia and total circulatory arrest

OBJECTIVE

We hypothesized that the use of N-acetylcysteine would ameliorate the lung reperfusion injury observed after deep hypothermia and total circulatory arrest (DHTSA).

METHODS

Experiments were carried out on 12 adult mongrel dogs of either sex weighing 25 to 30 kg. The animals were randomly divided into two groups of six animals each. All animals were cooled to an esophageal temperature of 15 degrees C during 30 minutes and underwent 60 minutes of DHTSA, followed by the reinstitution of cardiopulmonary bypass (CPB) and rewarming. Before rewarming, while 100 mL physiologic saline solution was added into the pump in group I, 50 mg/kg N-acetylcysteine(NAC) was given in group II. Heart rate, mean arterial pressure, pulmonary arterial pressure, left atrial pressure, central venous pressure, and cardiac output were recorded. To measure lung tissue malondialdehyde (MDA), water content and polymorphonuclear leukocytes (PMNs) count, lung tissue samples were taken before CPB and after weaning CPB. In addition, alveolar-arterial oxygen difference (AaDO(2))()for tissue oxygenation was calculated by obtaining arterial blood gas samples. Dynamic lung compliance (DLC) was measured before CPB and after CPB.

RESULTS

MDA levels before CPB of 44.2 +/- 3.9 nmol/g tissue rose to 76.6 +/- 5.6 nmol/g tissue after weaning CPB in group I (p = 0.004). In group II also, the MDA levels increased from 43.5 +/- 4.2 to 57.4 +/- 5.6 nmol MDA/g tissue after weaning CPB (p = 0.006). The MDA increase in group II after CPB was found to be significantly lower than in group I (p = 0.006). The wet-to-dry lung weight ratio in the NAC group was 5.1 +/- 0.2, significantly less than in the control group (5.9 +/- 0.3), (p = 0.004). AaDO(2) significantly increased in the group I and II (p = 0.002 and p = 0.002, respectively); this elevation in group I was significant than in group II (p = 0.044). In histopathological examination, it was observed that neutrophil counts in the lung parenchyma rose significantly after CPB in both groups (p < 0.001). The increase in group I was significantly larger than group II (p < 0.001).

CONCLUSIONS

Results represented in our study indicate that addition of NAC into the pump after DHTSA can reduce lung reperfusion injury.

Importance of pulmonary artery perfusion in cardiac surgery

OBJECTIVE

To investigate the importance of pulmonary artery perfusion in cardiac surgery.

DESIGN

Prospective randomized study.

SETTING

University hospital.

PARTICIPANTS

Patients undergoing cardiac surgery.

INTERVENTIONS

Patients in whom the cross-clamp was applied only to the aorta were defined as group 1 (n = 11) and patients in whom the cross-clamp was applied to both the aorta and pulmonary artery were defined as group 2 (n = 11).

MEASUREMENT AND RESULTS

Tissue samples obtained from the lower lobe of the left lung before CPB, 20 minutes after cross-clamping, and 20 minutes after declamping were examined under light and electron microscopes. Electron microscopic examination revealed changes in the blood-air barrier, epithelial cells, pneumocytes, and basal membrane were more prominent in group 2. Changes in the leukocyte, neutrophil, and lymphocyte counts of blood samples obtained from the right atrium and right superior pulmonary vein before CPB and 5, 30, 60, and 90 minutes after the removal of clamp were also investigated. The transpulmonary difference was statistically significant at 5 and 30 minutes after declamping in group 1. In group 2, transpulmonary differences continued to be significant at 5, 30, 60, and 90 minutes after declamping. There was no difference between groups in terms of PaO(2)/F(I)O(2) ratio before CPB (group 1: 342.0 +/- 80.0 mmHg, group 2: 349.0 +/- 67.0 mmHg); however, a statistically significant difference was found between the groups 2 hours after declamping (group 1: 418.0 +/- 87.0 mmHg and group 2: 290.0 +/- 110.0 mmHg; p = 0.007).

CONCLUSION

Pulmonary artery perfusion was found to be important in cardiac surgery.

Effects of pulmonary ischemia-reperfusion on platelet adhesion in subpleural arterioles in rabbits

Reperfusion of the ischemic lung is associated with increased pulmonary vascular resistance and reduced alveolar perfusion in conjunction with an inflammatory response. To determine the contribution of platelet-endothelial interactions, we examined effects of pulmonary ischemia-reperfusion (IR) on platelet adhesion and diameter of arterioles and investigated the hypothesis that this process is P-selectin mediated. In anesthetized rabbits with open-chest and ventilated lungs, we examined subpleural arterioles by fluorescence microscopy. Ischemia was caused by reversibly occluding the right pulmonary artery for 2 h. Fluorescently labeled platelets were injected into the right atrium and the right lung was observed after 0.5, 1.0, and 2.0 h of reperfusion. Platelets rolling and adherence along arterioles occurred with a decrease in diameter that was significant during IR, but not after 3- to 5-min occlusion (control). Systemic pretreatment with Fucoidan (a ligand to P- and L-selectin) inhibited platelet rolling, adherence, and the decrease in diameter. Pretreatment of only exogenously labeled platelets with monoclonal antibody (MoAb) to P-selectin prevented platelet rolling and adherence, but not the decrease in diameter. These results indicate that in the intact lung, pulmonary IR causes platelet rolling and adhesion along arteriolar walls, and suggest that this process, which is mediated by P-selectin, contributes to vasoconstriction and hypoperfusion. Thus, it appears that platelet-endothelial interactions may contribute to the development of pulmonary IR injury.

Strategic leukocyte depletion reduces pulmonary microvascular pressure and improves pulmonary status post-cardiopulmonary bypass

Cardiopulmonary bypass (CPB) precipitates inflammation that causes marked pulmonary dysfunction. Leukocyte filtration has been proposed to reduce these deleterious effects. Other studies show an improvement with aprotinin. We proposed that a combination of these two therapies would synergistically improve pulmonary outcomes. Two hundred and twenty-five patients participated in a randomized prospective study comparing pulmonary microvascular function and pulmonary shunt fraction postcoronary artery bypass grafting (CABG). The study group underwent leukocyte depletion with aprotinin during the procedure. Pulmonary microvascular function was assessed by pulmonary microvascular pressure (PMVP), a measure of pulmonary capillary edema, and pulmonary function was evaluated by comparing pulmonary shunt fractions. Elevated PMVP and increased pulmonary shunting compromise pulmonary performance. The leukocyte-depleted group had significantly reduced PMVP and pulmonary shunt fraction for at least the first 24 hours postbypass. The combination of strategic leukocyte filtration and aprotinin therapy can effectively reduce postoperative decline in pulmonary function. Cardiopulmonary bypass precipitates a variety of inflammatory effects that can cause marked pulmonary dysfunction to the point of respiratory failure, necessitating prolonged mechanical ventilation. Leukocyte filtration has been investigated previously and appears to be beneficial in improving pulmonary outcome by preventing direct neutrophil-induced inflammatory injury. Recent studies of leukocyte reduction profiles suggest that leukoreduction via leukofiltration is short lived with filter saturation occurring 30-45 minutes after onset of filtration. This phenomenon may explain the limited utility observed with higher risk patients. These patients typically require longer pump runs, so leukocyte reduction capability is suboptimal at the time of pulmonary vascular reperfusion. To more effectively protect the lung from reperfusion injury, leukocyte filtration can be delayed so that reduction of activated neutrophils is maximal at the time of pulmonary vascular reperfusion. It is, thus, conceivable that a timely use of arterial line leukoreducing filters may improve, more substantially, pulmonary function postbypass. Two hundred and twenty-five isolated coronary revascularization patients participated in this prospective, randomized trial. The patients received moderately hypothermic CBP alone (control group: n = 110) or combined with leukocyte depletion, initiated 30 minutes before crossclamp release, with filters placed in the bypass circuit (study group: n = 115). All patients also received full Hammersmith aprotinin dosing during the operation. Pulmonary microvascular pressures were lower in the study group at three hours postbypass, and continued to fall until 24 hours postbypass. In contrast, the control group measured a rise in PMVP and a continued plateau throughout 24 hours postbypass (p < 0.028). The calculated pulmonary shunt fraction also was reduced significantly throughout the study interval, with the greatest reduction occurring approximately three to six hours post-CPB (p < 0.002). Shunt fractions eventually converged at 24 hours postbypass. Outcome measures included hospital charges and length of stay, which were also markedly reduced in the treatment group. Increasing PMVPs are a direct reflection of pulmonary capillary edema, which, in conjunction with increased pulmonary shunt ratio, lead to an overall worsening of pulmonary function. Intraoperative strategic leukocyte filtration combined with aprotinin treatment improves post-CPB lung performance by reducing significantly the reperfusion inflammatory response and its sequelae. These benefits are manifested by reductions in ventilator times, hospital stay and patient morbidity.

Intraoperative treatment strategy to reduce the incidence of postcardiopulmonary bypass atrial fibrillation

PURPOSE

Postcardiopulmonary bypass atrial fibrillation remains a constant complication associated with coronary revascularization, the incidence of which occurs from 20% to 35%. Previous studies have addressed this problem in the postoperative setting utilizing pharmacological agents, but the results have been variable. The purpose of this study was to evaluate a novel intraoperative strategy to reduce the incidence of postcardiopulmonary bypass atrial fibrillation. We theorized that leukocyte depletion by filtration with the addition of aprotinin would reduce the systemic inflammatory effects of bypass and reduce the incidence of atrial fibrillation.

METHODS

One hundred and twenty-two patients participated in this randomized study. Only isolated primary coronary revascularization procedures on cardiopulmonary bypass were included. The control group (n=55) received standard moderate hypothermic blood cardioplegia cardiopulmonary bypass. The treatment group (n=65) received similar cardiopulmonary bypass with the addition of strategic leukocyte depletion with Pall Biomedical Products (East Hills, NY) leukodepletion filters and full-dose aprotinin.

RESULTS

The intraoperative addition of leukocyte depletion by filtration with aprotinin reduced the incidence of postcardiopulmonary bypass atrial fibrillation by 72%. The incidence.of atrial fibrillation in the control group was 27% (15 of 55). In contrast, the occurrence of atrial fibrillation in the treated group was only 7.6% (5 of 65) (p<0.025).

CONCLUSIONS

This novel intraoperative treatment strategy of both mechanical (leukocyte filtration) and pharmacological (aprotinin) intervention appears to markedly reduce the incidence of postcardiopulmonary bypass atrial fibrillation. To our knowledge, this is the first study to combine these two treatment strategies. A previous study has noted a decline in atrial fibrillation with aprotinin in the animal model, but not to the extent observed in our study. The beneficial effects of the reduction of atrial fibrillation include reduced risk of emboli formation and the incidence of ischemia in the heart, lung and brain. In addition, a decrease in length of hospital stay, recovery time and overall cost occurred.

A review of leukofiltration in cardiac surgery: the time course of reperfusion injury may facilitate study design of anti-inflammatory effects

The systemic inflammatory response syndrome (SIRS) is a well-recognized phenomenon attending cardiopulmonary bypass (CPB) surgery. SIRS leads to costly complications and several strategies intended to ameliorate the symptoms have been studied, including leukocyte reduction using filtration. Although the body of work suggests that leukoreduction attenuates SIRS, discrepancies remain within the literature. The recent literature is reviewed, highlighting the areas where concordance is lacking. Investigations into many promising device-related technologies are often deterred by the high costs of clinical trials. Adding to costs is the fact that clinical end points generally require large sample sizes. An understanding, however, of the pathogenesis of reperfusion injury can guide the investigator to choose physiologic response measures that correlate well with clinical outcome, but feature low inherent variability, allowing for clinical trials with smaller sample sizes. With this goal in mind, a model for the pathogenesis of reperfusion injury is described. Using a model of reperfusion injury as underpinnings for the design of prospective pilot studies, we show that salvaged blood reinfused following CPB elicits time-dependent effects on pulmonary function as predicted by the model. Data are illustrative of principles that could expand the scope of clinical investigations designed to validate the use of physiologic response measures as correlates of clinical outcome. Such investigations would target surrogate markers of clinical outcome, measured at clinically relevant times. Once validated, these surrogate markers would, thereafter, become economical screening tools for clinical studies of device-related or pharmacological anti- inflammatory interventions.

C1-esterase inhibitor reduces reperfusion injury after lung transplantation

BACKGROUND

Activation of the complement system and polymorphonuclear neutrophilic leukocytes plays a major role in mediating reperfusion injury after lung transplantation. We hypothesized that early interference with complement activation would reduce lung reperfusion injury after transplantation.

METHODS

Unilateral left lung autotransplantation was performed in 6 sheep. After hilar stripping the left lung was flushed with Euro-Collins solution and preserved for 2 hours in situ at 15 degrees C. After reperfusion the right main bronchus and pulmonary artery were occluded, leaving the animal dependent on the reperfused lung (reperfused group). C1-esterase inhibitor group animals (n = 6) received 200 U/kg body weight of C1-esterase inhibitor as a short infusion, half 10 minutes before, the other half 10 minutes after reperfusion. Controls (n = 6) underwent hilar preparation only. Pulmonary function was assessed by alveolar-arterial oxygen difference and pulmonary vascular resistance. The release of beta-N-acetylglucosaminidase served as indicator of polymorphonuclear neutrophilic leukocyte activation. Extravascular lung water was an indicator for pulmonary edema formation. Biopsy specimens were taken from all groups 3 hours after reperfusion for light and electron microscopy.

RESULTS

In the reperfused group, alveolar-arterial oxygen difference and pulmonary vascular resistance were significantly elevated after reperfusion. All animals developed frank alveolar edema. The biochemical marker beta-N-acetylglucosaminidase showed significant leukocyte activation. In the C1-esterase inhibitor group, alveolar-arterial oxygen difference, pulmonary vascular resistance, and the level of polymorphonuclear neutrophilic leukocyte activation were significantly lower.

CONCLUSIONS

Treatment with C1-esterase inhibitor reduces reperfusion injury and improves pulmonary function in this experimental model.

Lung transplant reperfusion injury involves pulmonary macrophages and circulating leukocytes in a biphasic response

OBJECTIVE

Both donor pulmonary macrophages and recipient circulating leukocytes may be involved in reperfusion injury after lung transplantation. By using the macrophage inhibitor gadolinium chloride and leukocyte filters, we attempted to identify the roles of these two populations of cells in lung transplant reperfusion injury.

METHODS

With our isolated, ventilated, blood-perfused rabbit lung model, all groups underwent lung harvest followed by 18-hour cold storage and 2-hour blood reperfusion. Measurements of pulmonary artery pressure, lung compliance, and arterial oxygenation were obtained. Group I (n = 8) served as a control. Group II (n = 8) received gadolinium chloride at 14 mg/kg 24 hours before lung harvest. Group III (n = 8) received leukocyte-depleted blood reperfusion by means of a leukocyte filter.

RESULTS

The gadolinium chloride group had significantly improved arterial oxygenation and pulmonary artery pressure measurements compared with control subjects and an improved arterial oxygenation compared with the filter group after 30 minutes of reperfusion. After 120 minutes of reperfusion, however, the filter group had significantly improved arterial oxygenation and pulmonary artery pressure measurements compared with the control group and an improved arterial oxygenation compared with the gadolinium chloride group.

CONCLUSIONS

Lung transplant reperfusion injury occurs in two phases. The early phase is mediated by donor pulmonary macrophages and is followed by a late injury induced by recipient circulating leukocytes.

Pulmonary macrophages are involved in reperfusion injury after lung transplantation

BACKGROUND

Reperfusion injury is a perplexing cause of early graft failure after lung transplantation. Although recipient neutrophils are thought to have a role in the development of reperfusion injury, some researchers have shown that neutrophils are not involved in its earliest phase. Intrinsic donor pulmonary macrophages may be responsible for this early phase of injury. Using the macrophage inhibitor gadolinium chloride, we attempted to investigate the role of pulmonary macrophages in reperfusion injury after lung transplantation.

METHODS

Using our isolated, ventilated, blood-perfused rabbit lung model, all groups underwent lung harvest followed by 18-hour storage (4 degrees C) and blood reperfusion for 30 minutes. Group I served as a control. Group II received gadolinium chloride at 7 mg/kg 24 hours before harvest. Group III received gadolinium chloride at 14 mg/kg 24 hours before harvest.

RESULTS

Group III had significantly improved arterial oxygenation and pulmonary artery pressures compared with groups I and II after 30 minutes of reperfusion.

CONCLUSIONS

The earliest phase of reperfusion injury after lung transplantation involves donor pulmonary macrophages.

Continuous pulmonary perfusion during cardiopulmonary bypass prevents lung injury in infants

BACKGROUND

Lung injury after cardiopulmonary bypass is a serious complication for infants with congenital heart disease and pulmonary hypertension. Excessive neutrophil sequestration in the lung occurring after reestablishment of pulmonary circulation implies that interaction between neutrophils and pulmonary endothelium is the major cause of lung injury.

METHODS

Thirty infants with either ventricular septal defect or atrioventricular septal defect and with pulmonary hypertension were enrolled in this study. We performed continuous pulmonary perfusion during total cardiopulmonary bypass on 16 patients (perfused group) and conventional cardiopulmonary bypass on 14 patients (control group). PaO2/FiO2 and neutrophil counts were assessed from immediately before surgery to 24 hours after termination of cardiopulmonary bypass.

RESULTS

PaO2/FiO2 was higher in the perfused group than in the control group, and the difference was significant throughout the study period. Neutrophil counts decreased below prebypass values in both groups at 30 minutes after aortic unclamping, and the difference was significant in the control group but was not in the perfused group. Duration of postoperative ventilatory support was significantly less in the perfused group.

CONCLUSIONS

Our study demonstrates that arrested pulmonary circulation during cardiopulmonary bypass is the major risk factor of lung injury and that continuous pulmonary perfusion is effective in preventing lung injury.

Reduced neutrophil infiltration protects against lung reperfusion injury after transplantation

BACKGROUND

There is evidence that lung ischemia reperfusion injury is a result of the activation of components of the inflammatory cascade. However, the role of neutrophils in lung reperfusion injury continues to be a source of controversy.

METHODS

Using an isolated, whole blood-perfused, ventilated rabbit lung model, we sought to characterize the pattern of reperfusion injury and investigate the contribution of neutrophils to this injury. Donor rabbits underwent lung harvest after pulmonary arterial prostaglandin E1 injection and Euro-Collins preservation solution flush. Group I lungs (n = 8) were immediately reperfused without ischemic storage. Group II lungs (n = 8) were stored for 18 h at 4 degrees C before reperfusion. Group III lungs (n = 10) underwent 18 h of ischemic storage and were reperfused with whole blood that was first passed through a leukocyte-depleting filter. All lungs were reperfused for 2 h.

RESULTS

Arterial oxygenation in group III progressively improved, and was significantly higher than that of group II after 2 h of reperfusion (272.58+/-58.97 vs 53.58+/-5.34 mm Hg, p = 0.01). Both pulmonary artery pressure and pulmonary vascular resistance were significantly reduced in group III when compared with group II (27.85+/-1.45 vs 44.15+/-4.77 mm Hg, p = 0.002; and 30,867+/-2,323 vs 52,775+/-6,386 dynes x sec x cm(-5), p = 0.003, respectively). Microvascular permeability in group III lungs was reduced to 73.98+/-6.15 compared with 117.16+/-12.78 ng Evans blue dye/g tissue in group II (p = 0.005). Group III myeloperoxidase activity was 56.92+/-6.31 deltaOD/g/min compared with 102.84+/-10.41 delta0d/g/min in group II (p = 0.002).

CONCLUSIONS

Leukocyte depletion of the blood reperfusate protects against microvascular permeability and significantly improves pulmonary graft function. The neutrophil plays a major role in amplifying lung injury later during reperfusion, and this lung ischemia reperfusion injury may be reversed through the interruption of the inflammatory cascade and the interference with neutrophil infiltration.