Lung transplantation after lung volume reduction surgery.

BACKGROUND: Lung volume reduction surgery (LVRS) as a bridge to lung transplantation was first advocated in 1995 and published studies have supported the concept but with limited data. The risk-benefit tradeoffs of the combined procedure have not been thoroughly examined, although substantial information regarding LVRS has emerged. METHODS: Of 177 patients who underwent lung transplantation for end-stage emphysema between 2002 and 2009 at our center, 25 had prior LVRS (22 bilateral and 3 unilateral). Lung transplantation was performed 22.9±15.9 months after LVRS. We compared in-hospital morbidity, functional capacity, and long-term outcomes of patients who underwent LVRS before lung transplantation with a matched cohort of patients without prior LVRS to assess the influence of LVRS on posttransplantation morbidity and mortality. RESULTS: The incidence of postoperative bleeding requiring reexploration and the incidence of renal dysfunction requiring dialysis were higher in patients with LVRS before lung transplantation. Posttransplantation peak forced expiratory volume in 1 s was worse in patients with LVRS before lung transplantation (56.7% vs. 78.8%; P<0.05). Five-year survival was not significantly different (59.7% in patients with LVRS before lung transplantation vs. 66.2% in patients with lung transplantation alone). In multivariate analysis, age more than 65 years, prolonged cardiopulmonary bypass time, and severe pulmonary hypertension were significant predictors for mortality (P<0.05). CONCLUSIONS: Although LVRS remains a viable option as a bridge to lung transplantation in appropriately selected patients, LVRS before lung transplantation can impart substantial morbidity and compromised functional capacity after lung transplantation. LVRS should not be easily considered as a bridge to transplantation for all lung transplant candidates.

Human leucocyte antigen-defined microchimerism early post-transplant does not predict for stable lung allograft function.

Microchimerism is the presence of foreign cells in an individual below 1% of total cells, which can occur in the setting of solid organ transplantation. This study quantitated donor-derived cellular subsets longitudinally in human leucocyte antigen (HLA)-mismatched lung transplant recipients (LTR) during the first post-operative year and evaluated the pattern of peripheral microchimerism with clinical outcomes. Peripheral blood mononuclear cells (PBMC) isolated from non-HLA-B44 LTR who received HLA-B44 allografts were sorted flow cytometrically into three cellular subsets. Real-time quantitative polymerase chain reaction (q-PCR) demonstrated that donor-derived HLA-B44 microchimerism is a common phenomenon, observed in 61% of patients. The level of donor-derived cells varied across time and between LTR with frequencies of 38% in the B cells/monocytes subset, 56% in the T/NK cells subset and 11% in the dendritic cells (DC) subset. Observations highlighted that microchimerism was not necessarily associated with favourable clinical outcomes in the first year post-lung transplantation.

Low exercise tolerance correlates with reduced inspiratory capacity and respiratory muscle function in recipients with advanced chronic lung allograft dysfunction.

BACKGROUND: Advanced chronic lung allograft dysfunction limits survival after lung transplantation. We hypothesize that patients with chronic lung allograft dysfunction can be subdivided by exercise tolerance in two groups, and quality of life (QOL) and survival differ between the groups. METHODS: A single-center, cross-sectional, partly prospective, study was performed in our outpatient clinic between July and November 2011, including all patients with a forced expiratory volume in 1 s <50% baseline. Respiratory parameters, 6-min walk test, and QOL were measured. Patients with low exercise capacity were defined as 6-min walk test <50% predicted or use of rollator or wheelchair. RESULTS: Fifty-two patients consented to participating in the study and 22 demonstrated low exercise capacity. These patients had pathologic respiratory muscle function (P=0.005) and decreased inspiratory capacity (IC; P=0.001). QOL was significantly reduced. Multivariate analysis proved that low IC (hazard ratio, 17.9; 95% confidence interval, 2.8-111; P=0.002) and increased P0.1/Pimax (hazard ratio, 7.1; 95% confidence interval, 1.4-35.8; P=0.016) were independently associated with decrease exercise capacity. CONCLUSION: Heterogeneity of patients with advanced lung allograft dysfunction regarding exercise tolerance might result from altered IC and impaired respiratory muscle function.

Cardiopulmonary bypass during a second-lung implantation improves postoperative oxygenation after sequential double-lung transplantation.

OBJECTIVES: During sequential double-lung transplantation (DLT), the newly implanted first lung receives the entire cardiac output during the implantation of the second one. This may be responsible for the increased hydrostatic pressure that causes severe interstitial and alveolar edema that can lead to allograft dysfunction. The authors tested the hypothesis that CPB started after first graft implantation and before second recipient lung removal should improve post-transplantation oxygenation and clinical outcomes. DESIGN: Observational during 2 consecutive 1-year periods. SETTING: University hospital. PARTICIPANTS: Nine consecutive patients undergoing sequential DLT with CPB started after first graft implantation and before second recipient lung removal were compared to controls, who were 10 consecutive patients who underwent sequential DLT but without CPB the year before. MEASUREMENTS AND MAIN RESULTS: Oxygenation after transplantation was assessed. The use of CPB during the implantation of the second lung was associated with an increased mean postoperative ratio of PaO2 to the fraction of inspired oxygen at 1 hour (363±51 v 240±113, p = 0.01) and 6 hours (430±111 v 280±103, p = 0.03). The mean duration of CPB was 111±19 min. The occurrence of primary graft dysfunction and the need for extracorporeal membrane oxygenation tended to be lower, but did not reach significance. Similarly, mortality rate was comparable between both groups, as was the rate of blood transfusions. CONCLUSIONS: The authors' results suggest that the use of CPB started after first graft implantation and before second recipient lung removal appears to benefit oxygenation and reduces the occurrence of severe pulmonary edema in the first transplanted lung.

Complement-mediated microvascular injury leads to chronic rejection.

Microvascular loss may be an unappreciated root cause of chronic rejection for all solid organ transplants. As the only solid organ transplant that does not undergo primary systemic arterial revascularization at the time of surgery, lung transplants rely on the establishment of a microcirculation and are especially vulnerable to the effects of microvascular loss. Microangiopathy, with its attendant ischemia, can lead to tissue infarction and airway fibrosis. Maintaining healthy vasculature in lung allografts may be critical for preventing terminal airway fibrosis, also known as the bronchiolitis obliterans syndrome (BOS). BOS is the major obstacle to lung transplant success and affects up to 60% of patients surviving 5 years. The role of complement in causing acute microvascular loss and ischemia during rejection has recently been examined using the mouse orthotopic tracheal transplantation; this is an ideal model for parsing the role of airway vasculature in rejection. Prior to the development of airway fibrosis in rejecting tracheal allografts, C3 deposits on the vascular endothelium just as tissue hypoxia is first detected. With the eventual destruction of vessels, microvascular blood flow to the graft stops altogether for several days. Complement deficiency and complement inhibition lead to markedly improved tissue oxygenation in transplants, diminished airway remodeling, and accelerated vascular repair. CD4+ T cells and antibody-dependent complement activity independently mediate vascular destruction and sustained tissue ischemia during acute rejection. Consequently, interceding against complement-mediated microvascular injury with adjunctive therapy during acute rejection episodes, in addition to standard immunosuppression which targets CD4+ T cells, may help prevent the subsequent development of chronic rejection.

Physical activity profile of lung transplant candidates with interstitial lung disease.

PURPOSE: Little is known about physical activity in individuals with interstitial lung disease (ILD). The objectives of this study were (1) to objectively measure physical activity in lung transplant candidates with ILD, (2) to compare levels of physical activity on rehabilitation and nonrehabilitation days, and (3) to explore the relationships between physical activity and functional measures. METHODS: Twenty-four (14 men) lung transplant candidates with ILD on long-term oxygen therapy, who were enrolled in an exercise-based rehabilitation program, underwent measurements of physical activity using accelerometry (daily steps and time spent in moderate-intensity physical activity per day), functional exercise capacity (6-minute walk distance), and muscle strength (isometric quadriceps torque). RESULTS: Lung transplant candidates with ILD had reduced levels of physical activity compared to the general population but were more active on rehabilitation versus nonrehabilitation days (M ± SD) (daily steps, 3780 ± 2196 vs 2138 ± 1353; P < .001; and time spent in moderate-intensity activity per day, 4.5 [interquartile range, 1.5-17] minutes vs 2 [interquartile range, 1-3.5] minutes). The 6-minute walk distance showed the strongest correlation to daily steps (r = 0.59, P < .01) and time spent in moderate-intensity physical activity per day (r = 0.56, P < .01). CONCLUSIONS: Individuals with advanced ILD are markedly inactive; however, physical activity levels were significantly higher on rehabilitation days. The importance of physical activity as a rehabilitation outcome in ILD warrants further investigation.

Effect of positive end-expiratory pressure after porcine unilateral left lung transplant.

OBJECTIVES: To evaluate the effects of 2 different levels of positive end-expiratory pressure on pigs who had unilateral lung transplants. MATERIALS AND METHODS: A left lung transplant was performed in 12 pigs. The animals were randomized into 2 groups based on positive end-expiratory pressure: group 1 (5 cm H(2)O) and group 2 (10 cm H(2)O). Hemodynamics, gas exchange, and respiratory mechanics were measured before and after surgery. Cytokines, oxidative stress, and histologic scores were assessed in the lung tissue of each pig. RESULTS: Pigs in group 2 exhibited a significantly higher mean heart rate (P = .006), static compliance (P = .001), lower mean arterial pressure (P = .003), and airway resistance (P = .001) than did pigs in group 1. There were no postoperative differences between the groups in concentrations of thiobarbituric acid reactive substances, superoxide dismutase, and interleukin 8. At the end of the observation period, pigs in group 2 had higher levels of thiobarbituric acid reactive substances (P = .001) and interleukin 8 (P = .05), and pigs in group 1 had higher levels of superoxide dismutase (P = .05) than they did at baseline. CONCLUSIONS: After unilateral lung transplant, higher positive end-expiratory pressure was associated with improved respiratory mechanics, a negative effect on hemodynamics, a stronger inflammatory response, and increased production of reactive oxygen species, but no effect on gas exchange.

Chronic lung allograft dysfunction after lung transplantation: the moving target.

Chronic lung allograft dysfunction is a major challenge in long-term management of lung transplant recipients. Both alloimmune-dependent factors (rejection) and alloimmune-independent factors contribute to the development of chronic lung allograft dysfunction. Thus, use of the term "chronic rejection" tends to be intentionally avoided among specialists in the field, although "chronic rejection" is still an acceptable lay word understood by many patients. Several different phenotypes have been identified in chronic lung allograft dysfunction, including restrictive allograft syndrome, neutrophilic reversible allograft dysfunction, and fibrous bronchiolitis obliterans syndrome. Restrictive allograft syndrome is characterized by restrictive physiology and peripheral foci of inflammation and fibrosis, which contrasts the obstructive physiology and pathological foci in small airways in conventional bronchiolitis obliterans syndrome. Among patients with bronchiolitis obliterans syndrome, there is a subpopulation that responds relatively well to azithromycin. Because these patients show airway neutrophilia, this subtype of chronic lung allograft dysfunction was named neutrophilic reversible allograft dysfunction. Conversely, patients with bronchiolitis obliterans syndrome unresponsive to azithromycin show airway fibrosis with less inflammation (fibrous bronchiolitis obliterans syndrome). In general, restrictive allograft syndrome shows poorer survival than does bronchiolitis obliterans syndrome, and early-onset bronchiolitis obliterans syndrome (within 2 years) shows a worse prognosis than does late-onset bronchiolitis obliterans syndrome. Until preventive and therapeutic options are refined, chronic lung allograft dysfunction will remain a major life-limiting factor. It has significant psychological, physical, social, and economic impacts. Early introduction of palliative care is another important strategy to improve patients' quality of life.

Surfactant improves graft function after gastric acid-induced lung damage in lung transplantation.

BACKGROUND: The number of available donor lungs is still the limiting factor in lung transplantation. We have recently shown that diluted surfactant lavage during ex vivo lung evaluation improved the graft function after gastric acid aspiration. In the present study, we hypothesized that diluted surfactant administration would recondition and improve the graft function after acid aspiration-induced lung injury in a porcine model of pulmonary transplantation. METHODS: Left lung injury was induced by intrabronchial administration of 1 mL/kg betaine HCl and pepsin mixture. The animals were subsequently ventilated for 24 hours. After organ retrieval, the donor lungs were stored at 4°C for 4 hours. In the control group, left lung transplantation was performed without any surfactant treatment. In the surfactant group, the recipients received intratracheal diluted surfactant lavage just before reperfusion and ventilation. During 7 hours of reperfusion, the hemodynamic and respiratory variables were recorded on an hourly basis. RESULTS: Surfactant lavage resulted in lower mean pulmonary artery pressure, higher mixed venous oxygen saturation, and better oxygenation compared with the control group (p = 0.001). Bronchoalveolar lavage interleukin-6 level, protein, and neutrophil percentage at the end of the experiment were significantly higher in the control group compared with the surfactant group (p = 0.03). Minimal surface tension was significantly lower in the surfactant group compared with controls (p = 0.03). CONCLUSIONS: These results demonstrate that application of diluted surfactant before reperfusion can be used effectively to improve the graft function from donor lungs injured by gastric acid aspiration.

Tobacco smoking and solid organ transplantation.

Smoking, both by donors and by recipients, has a major impact on outcomes after organ transplantation. Recipients of smokers' organs are at greater risk of death (lungs hazard ratio [HR], 1.36; heart HR, 1.8; and liver HR, 1.25), extended intensive care stays, and greater need for ventilation. Kidney function is significantly worse at 1 year after transplantation in recipients of grafts from smokers compared with nonsmokers. Clinicians must balance the use of such higher-risk organs with the consequences on waiting list mortality if the donor pool is reduced further by exclusion of such donors. Smoking by kidney transplant recipients significantly increases the risk of cardiovascular events (29.2% vs. 15.4%), renal fibrosis, rejection, and malignancy (HR, 2.56). Furthermore, liver recipients who smoke have higher rates of hepatic artery thrombosis, biliary complications, and malignancy (13% vs. 2%). Heart recipients with a smoking history have increased risk of developing coronary atherosclerosis (21.2% vs. 12.3%), graft dysfunction, and loss after transplantation. Self-reporting of smoking is commonplace but unreliable, which limits its use as a tool for selection of transplant candidates. Despite effective counseling and pharmacotherapy, recidivism rates after transplantation remain high (10-40%). Transplant services need to be more proactive in educating and implementing effective smoking cessation strategies to reduce rates of recidivism and the posttransplantation complications associated with smoking. The adverse impact of smoking by the recipient supports the requirement for a 6-month period of abstinence in lung recipients and cessation before other solid organs.

Reconditioning lungs donated after cardiac death using short-term hypothermic machine perfusion.

BACKGROUND: Hypothermic machine perfusion (HMP) is widely used to preserve kidneys and livers for transplantation. This study investigated whether short-term HMP could improve the quality of lungs donated after cardiac death (DCD). METHODS: In a clinically relevant uncontrolled DCD model, beagles were divided into two groups (n=5 each): 4 hr warm ischemia + 14 hr static cold storage (SCS group) or 4 hr warm ischemia + 12 hr SCS followed by 2 hr HMP (HMP group). HMP was performed using centrifugal perfusion with STEEN solution at approximately 10°C. In both groups, the left lungs were then transplanted and reperfused for 4 hr to evaluate the posttransplantation lung functions. RESULTS: HMP was performed safely, not inducing any oxidative damage. The dynamic pulmonary compliance was stable during HMP, whereas the pulmonary vascular resistance significantly decreased. HMP microscopically eliminated residual microthrombi in the donor lungs just before transplantation. The lung tissue adenosine triphosphate levels 4 hr after reperfusion were significantly higher in the HMP group compared with the SCS group. The serum malondialdehyde levels and proinflammatory cytokine levels in the bronchoalveolar lavage fluid 4 hr after reperfusion were significantly lower in the HMP group than in the SCS group. The physiologic lung functions during reperfusion were significantly better in the HMP group compared with the SCS group. HMP also significantly reduced ischemia-reperfusion injury in the microscopic findings. CONCLUSIONS: Short-term HMP could resuscitate ischemically damaged DCD lungs and ameliorate ischemia-reperfusion injury.

Comparison of single lung transplant with and without the use of cardiopulmonary bypass.

OBJECTIVES: Many centres avoid using cardiopulmonary bypass (CPB) for lung transplant due to concerns over aggravated lung reperfusion injury and excessive blood loss. We reviewed our 23-years' experience of single lung transplantation. METHODS: A retrospective review of single lung transplants at our institution (1987-2010), examining differences in allograft function and postoperative complications between CPB and non-bypass (non-CPB) cases. RESULTS: Two hundred and fifty-nine single lung transplants were undertaken. Fifty-three (20.5%) with CPB. There was no difference demographically between the two groups. No difference existed in preoperative PO(2)/FiO(2). At 1 and 24 h, the postoperative PO(2)/FiO(2) ratio was no different (mean 2.95 and 3.24 in non-CPB cases; 3.53 and 3.75 in CPB patients, P = 0.18 and P = 0.34, respectively). Extubation time was not influenced by the use of CPB. Postoperative blood loss was greater in the CPB group. The usage of fresh frozen plasma and platelets was similar (P = 0.64 and 0.41, respectively). More blood was transfused during postoperative care of CPB patients (P = 0.02). CONCLUSIONS: Fears of poor postoperative lung function after CPB appear unfounded. We could detect no difference in function or extubation time. Although the use of CPB increases postoperative bleeding and the need for transfusion, it may be used safely to facilitate lung transplantation.

Effects of brain death on organ quality and transplant outcome.

The inferiority of organs from brain dead donors is reflected by impaired graft survival and patient outcome. Brain death effects hemodynamic stability, hormonal changes, and neuroimmunologic effects and unleashes a cascade of inflammatory events. Despite considerable efforts in experimental and clinical research, most of the mechanisms linked to brain death are only appreciated on a descriptive level. This overview presents our current understanding of the pathophysiology and consequences of brain death on organ injury and summarizes available therapeutic interventions.

Egr1: a novel target for ameliorating acute allograft rejection in an experimental lung transplant model.

OBJECTIVES: Acute allograft rejection is one of the significant complications occurring in lung transplant recipients. Early growth response-1 (Egr-1), zinc-finger-type transcription factor, is known as a master switch regulator of diverse chemical mediators. We used an orthotopic mouse model of left lung transplant to elucidate the function of Egr-1 in acute pulmonary rejection. METHODS: Left lung grafts retrieved from C57BL/6 wild mice or C57BL/6 Egr-1-null mice were orthotopically transplanted into BALB/c mice; the lungs were harvested at day 1, 3, 5 or 7 after lung transplantation. The grade of acute rejection was histopathologically evaluated. The intragraft gene expression levels of Egr-1 and downstream target mediators were quantitatively measured by real-time polymerase chain reaction. Immunohistochemical analysis was used to determine the location and distribution of the Egr-1 protein in the pulmonary graft. RESULTS: Severe acute rejection was observed in allografts from wild-type mice at 5 days after transplantation. Only minimal rejection was seen in the lung graft from Egr-1-null donor mice at 5 days after transplantation. Strong upregulation of Egr-1 mRNA transcripts was observed at day 1, which then decreased during the next 5 days. The mRNA of Egr-1 target mediators [interleukin-1-beta (IL-1ß), monocyte chemotactic protein-1 (MCP-1) and plasminogen activator inhibitor-1] reached maximal levels at day 5. Egr-1-null allografts exhibited significantly lower expressions of IL-1ß and MCP-1 mRNA (P < 0.05). CONCLUSIONS: Our study showed that deletion of Egr-1 in lung allografts ameliorates severe acute rejection with the reduction of expression levels of chemical mediators, implying a new possible strategy for treating acute pulmonary allograft rejection.

Factors associated with early graft dysfunction in cystic fibrosis patients receiving primary bilateral lung transplantation.

OBJECTIVES: Primary graft dysfunction (PGD) occurs in 10-25% of cases and remains responsible for significant morbidity and mortality after lung transplantation. Our goal was to explore donor and recipient variables and procedure factors that could be related to early graft failure in cystic fibrosis patients receiving bilateral lung transplantation, the PGD grade being derived from the PaO(2)/FiO(2) ratio measured at the sixth post-operative hour. METHODS: Data from 122 cystic fibrosis patients having undergone lung transplantation in six transplant centres in France were retrospectively analysed. Donor and recipient variables, procedure characteristics and anaesthesia management items were recorded and analysed with regard to the PaO(2)/FiO(2) ratio at the sixth post-operative hour. Recipients were divided into three groups according to this ratio: Grade I PGD, when PaO(2)/FiO(2) >300 mmHg or extubated patients, Grade II, when PaO(2)/FiO(2) = 200-300 mmHg, and Grade III, when PaO(2)/FiO(2) <200 mmHg or extracorporeal membrane oxygenation still required. RESULTS: Forty-eight patients were Grade I, 32 patients Grade II and 42 patients Grade III PGD. Oto's donor score, recipient variables and procedure characteristics were not statistically linked to PaO(2)/FiO(2) at the sixth post-operative hour. Ischaemic time of the last implanted graft and the lactate level at the end of the procedure are the only factors related to Grade III PGD in this group. CONCLUSIONS: Hyperlactataemia most probably reflects the severity of early PGD, which leaves graft ischaemic time as the only factor predicting early PGD in a multicentre population of cystic fibrosis lung graft recipients.

Chronic rejection pathology after orthotopic lung transplantation in mice: the development of a murine BOS model and its drawbacks.

Almost all animal models for chronic rejection (CR) after lung transplantation (LTx) fail to resemble the human situation. It was our attempt to develop a representative model of CR in mice. Orthotopic LTx was performed in allografts receiving daily immunosuppression with steroids and cyclosporine. Controls included isografts and mice only undergoing thoracotomy (SHAM). Allografts were sacrificed 2, 4, 6, 8, 10 or 12 weeks after LTx. Pulmonary function was measured repeatedly in the 12w allografts, isografts and SHAM mice. Histologically, all allografts demonstrated acute rejection (AR) around the blood vessels and airways two weeks after LTx. This decreased to 50-75% up to 10 weeks and was absent after 12 weeks. Obliterative bronchiolitis (OB) lesions were observed in 25-50% of the mice from 4-12 weeks. Isografts and lungs of SHAM mice were normal after 12 weeks. Pulmonary function measurements showed a decline in FEV(0.1), TLC and compliance in the allografts postoperatively (2 weeks) with a slow recovery over time. After this initial decline, lung function of allografts increased more than in isografts and SHAM mice indicating that pulmonary function measurement is not a good tool to diagnose CR in a mouse. We conclude that a true model for CR, with clear OB lesions in about one third of the animals, but without a decline in lung function, is possible. This model is an important step forward in the development of an ideal model for CR which will open new perspectives in unraveling CR pathogenesis and exploring new treatment options.

Spirometric obstructive lung function pattern early after lung transplantation.

BACKGROUND: An obstructive pattern in pulmonary function test is common after lung transplantation (LTx) and may be caused by multiple disorders. In this study, the impact and outcome of an obstructive spirometric pattern identified in transplant recipients early posttransplantation were investigated. METHODS: Analyzing all patients undergoing double LTx between September 1, 2007, and October 1, 2009, we separated patients with an obstructive (forced expiratory volume in 1 sec [FEV(1)]: vital capacity [VC] <0.7) and a nonobstructive pattern (FEV(1):VC ≥0.7) in pulmonary function tests 3 months after transplantation. Pulmonary function measurement, bronchoscopy, laboratory parameter, computed tomography morphology, mortality, and bronchiolitis obliterans syndrome (BOS)-free survival were analyzed up to 36 months after transplantation. In addition, information about donor lungs were collected (age, smoking history, and blood gas before lung harvesting). RESULTS: From 122 recipients included, 17 (14%) exhibited an obstructive pattern. Recipients with an early obstructive pattern were older at transplantation, had significantly decreased FEV(1), increased total lung capacity, and donor organ with lower pO(2) when ventilated with 100% oxygen before retrieval. Obstructive patients developed their best FEV(1) earlier after LTx and demonstrated a significant increase in BOS development (47% vs. 14%). CONCLUSIONS: An obstructive lung function pattern early after LTx was associated with earlier development of BOS and may have negative impact on outcome after double LTx. Early obstructive pattern after transplantation might be an indication of structural donor lung injury.

Cough reflex in lung transplant recipients.

Lung transplantation has become the standard of care for particular individuals with advanced lung disease. However, this surgical procedure involves interruption of the lower vagal nerve fibers which leads to loss of the protective cough reflex. Injury of the neural pathways involved with the sensory limb of the cough reflex is associated with an increased risk of complications involving the allograft. While loss of the cough reflex was once considered permanent, recent evidence indicates functional and structural restoration is a time-dependent process that occurs 6-12 months after lung transplantation. The implication that the cough reflex may be reestablished in lung transplant recipients provides insight into the dynamic response to airway neural injury that may lead to improvements in allograft tissue repair.