Maximum length of tracheal autografts in dogs

Replacement of a 5-cm intrathoracic trachea with a tissue-engineered prosthesis in a canine model

BACKGROUND

Critical obstacles must be addressed before clinical application of artificial tracheas. The major complications of long tracheal replacement include anastomotic dehiscence and stenosis owing to poor vascularity and incomplete re-epithelialization. The objective of this report was to clarify whether pre-incubation of the prosthesis in the omentum could be applicable for reconstruction of a long segment of the intrathoracic trachea in a canine model.

METHODS

The framework of an artificial trachea was fabricated from a polypropylene mesh tube and coated with 1% neutral atelocollagen inside and outside the lumen. The prosthesis was placed in the omentum of nine healthy male beagle dogs for 3 weeks. Then, the pedicled prosthesis was used to replace a 50 mm long section of intrathoracic trachea. Results were evaluated bronchoscopically, macroscopically, and histologically.

RESULTS

After 3 weeks of abdominal incubation, the prostheses were incorporated into the host tissue. None of the dogs showed dehiscence of the anastomosis or infection of the prostheses during the postoperative period. Seven of the nine dogs survived for more than 1 year. One dog died of a bowel obstruction resulting from a diaphragmatic hernia 3 months after replacement, and another died due to reasons unrelated to the prosthesis at 6 months. Bronchoscopic examination revealed no stenosis or dehiscence, and microscopic examination of all dogs showed that the luminal surface was covered by newly regenerated connective tissue and respiratory epithelium.

CONCLUSIONS

Pedicled omentum-prosthesis complexes may allow successful reconstruction of a long segment of the intrathoracic trachea.

Regeneration of trachea graft with cartilage support, vascularization, and epithelization

The repair and functional reconstruction of long-segment tracheal defects is always a great challenge in the clinic. Finding an ideal substitute for tracheal transplantation is the only way to solve this problem. The current study proposed a series of novel strategies for constructing a bionic living trachea substitute. For the issue of tubular cartilage support, cartilage sheet technique based on high-density culture of chondrocytes was adopted to avoid the inflammatory reaction triggered by the materials and thus formed mature cartilage-like tissue in autologous goat model. For the issue of epithelialization, the autologous transplantation of oral mucosal epithelium was used to realize mucosa coverage of the constructed trachea lumen. Finally, the flat trapezius fascia flap with double blood supply was separated by microsurgical techniques to achieve stable pre-vascularization of both the regenerated cartilage and the grafted epithelium simultaneously. By integrating the above strategies, the vascularized and epithelialized tracheal substitute with tubular cartilage support was successfully constructed in a goat model. The reconstructed trachea possessed a multiple layer structure of muscle-cartilage-fascia-mucosa comparable to the native trachea, and thus might realize stable survival and long-term airway function maintenance, providing a promising tracheal substitute for the repair and permanent functional reconstruction of long-segment tracheal defects. STATEMENT OF SIGNIFICANCE: The repair of long-segment tracheal defects is always a great challenge in the clinic. Finding an ideal substitute for tracheal transplantation is the only way to solve this problem. In the current study, by technical integration of cartilage regeneration, microsurgery, and oral mucosa transplantation, a complex tracheal substitute with satisfactory vascularization, epithelialization, and tubular cartilage support was successfully constructed in a goat autologous model. The reconstructed trachea substitute possessed a multiple layer structure of muscle-cartilage-fascia-mucosa exactly similar to native trachea, and thus might realize stable survival and long-term airway function maintenance. The current study provides feasible strategies and ideal tracheal substitutes for permanent functional reconstruction of long-segmental trachea defects.

Large animal models for long-segment tracheal reconstruction: a systematic review

BACKGROUND

The reconstruction of extensive tracheal defects is an unresolved problem. Despite decades of research, a reliable and practical substitute remains to be found. While there have been clinical reports of successful long-segment tracheal reconstruction, reproducibility and widespread applicability of these techniques have yet to be achieved. Large animals such as the dog, pig, sheep, and goat have comparable tracheal morphology and physiology to humans making them useful preclinical models to screen potential therapeutic strategies.

MATERIALS AND METHODS

The literature was reviewed to identify large animal models commonly used for tracheal reconstruction. A systematic search of PubMed and EMBASE was performed for large animal studies reporting on the reconstruction of long-segment tracheal and carinal defects. Fifty-seven studies were identified for analysis.

RESULTS

There is no standard large animal model available for tracheal research. In recent years, livestock species have gained favor over dogs as animal models in this field. The minimum requirements for successful tracheal replacement are rigidity, vascularity, and epithelial lining. Early attempts with synthetic prostheses were met with disappointing results. An autologous tracheal substitute is ideal but hindered by limited donor site availability and the lack of a dominant vascular pedicle for microsurgical reconstruction. Although tracheal allotransplantation enables like-for-like replacement, there are unresolved issues relating to graft vascularity, immunosuppression, and graft preservation. Tissue engineering holds great promise; however, the optimal combination of scaffold, cells, and culture conditions is still indeterminate.

CONCLUSIONS

Despite impressive advances in tracheal reconstruction, a durable substitute for extended tracheal defects continues to be elusive.

Successful immunosuppressant-free heterotopic transplantation of tracheal allografts in the pig

OBJECTIVES

It has been demonstrated that both heterotopic and orthotopic transplants of epithelium-denuded cryopreserved tracheal allografts are feasible in immunosuppressant-free rabbits. Validation of these results in large animals is required before considering clinical applications. We evaluated the viability, immune tolerance and strain properties of such tracheal allografts heterotopically transplanted in a pig model.

METHODS

Ten tracheal segments, 5 short (5 rings) and 5 long (10 rings), were obtained from male Landrace pigs. The tracheal segments were surgically denuded of their epithelium, then cryopreserved and stored in a tissue bank for 33 to 232 days. After thawing, tracheal segments stented with a silicone tube were wrapped in the omentum in 2 groups of 5 female recipients. The animals did not receive any immunosuppressive drugs. The animals were euthanized from Day 6 to Day 90 in both groups.

RESULTS

An effective revascularization of allografts regardless of length was observed. Lymphocyte infiltrate was shown in the early postoperative period and became non-significant after 30 days. Allografts displayed high levels of neoangiogenesis and viable cartilage rings with islets of calcification. Biomechanical measurements demonstrated strain properties similar to those of a fresh tracheal segment from Day 58.

CONCLUSIONS

Our results demonstrate the acceptability and satisfactory stiffness of epithelium-denuded cryopreserved tracheal allografts implanted in the omentum, despite the absence of immunosuppressive drugs. Since the omentum has the capability to reach the tracheal region, this approach should be investigated in the setting of orthotopic transplants in a pig model before considering clinical applications.

Successful orthotopic transplantation of short tracheal segments without immunosuppressive therapy

OBJECTIVES

Results of tracheal transplantation have been disappointing due to of ischaemia and rejection. It has been experimentally demonstrated that results of tracheal autograft/allograft transplantation were correlated with both graft length and revascularization method. Recently, we demonstrated that heterotopic epithelium-denuded-cryopreserved tracheal allograft (TA) displayed satisfactory immune tolerance. We aimed at evaluating the results of such allografts in orthotopic transplantation according to graft length and prior heterotopic or single-stage orthotopic revascularization in a rabbit model.

METHODS

Twenty New Zealand rabbits were used. Six females served as donors. Tracheal mucosa was mechanically peeled off and then the TAs were cryopreserved. Male recipients were divided into three groups receiving: (i) long TA segment with prior heterotopic revascularization (10-12 tracheal rings, n = 3); (ii) average TA segment with single-stage orthotopic revascularization (6-8 tracheal rings, n = 4); (iii) short TA segment with single-stage orthotopic revascularization (4-5 tracheal rings, n = 7). No immunosuppressive therapy was administered. Grafts were assessed bronchoscopically and upon death or sacrifice by macroscopic evaluation, histology and immunohistochemical staining for apoptosis.

RESULTS

Four animals were sacrificed from Day 33 to Day 220. The survival time of other recipients was 0-47 days (mean 19.6 ± 16.7 days). Aside from three animals that died from complications, all TA segments had satisfactory stiffness, were well vascularized, showed varying levels of neoangiogenesis and inflammatory infiltration devoid of lymphocytes, and showed evidence of only low levels of apoptosis. Varying degrees of fibroblastic proliferation originating from the lamina propria were observed in the lumen of all TAs and evolved over time into collagenized fibrosis in animals surviving over 45 days. Likewise, cartilage tracheal rings exhibited central calcification deposits, which started on Day 16 and increased over time. Epithelial regeneration was constantly observed. Intense fibroblastic proliferation led to stenosis in all animals from Groups (i) and (ii) but only one of seven animals from Group (iii).

CONCLUSIONS

Our results suggest that short segments of epithelium-denuded-cryopreserved TA may be reliable for tracheal transplantation in the rabbit model without problems related to graft stiffness or immune rejection. Before considering clinical applications, investigations should be conducted in larger mammals.

Advances in tracheal reconstruction

Summary:

A recent revival of global interest for reconstruction of long-segment tracheal defects, which represents one of the most interesting and complex problems in head and neck and thoracic reconstructive surgery, has been witnessed. The trachea functions as a conduit for air, and its subunits including the epithelial layer, hyaline cartilage, and segmental blood supply make it particularly challenging to reconstruct. A myriad of attempts at replacing the trachea have been described. These along with the anatomy, indications, and approaches including microsurgical tracheal reconstruction will be reviewed. Novel techniques such as tissue-engineering approaches will also be discussed. Multiple attempts at replacing the trachea with synthetic scaffolds have been met with failure. The main lesson learned from such failures is that the trachea must not be treated as a “simple tube.” Understanding the anatomy, developmental biology, physiology, and diseases affecting the trachea are required for solving this problem.

Advances in the use of video-assisted thoracoscopic lobectomy in lung cancer: sleeve bronchoplasty and arterioplasty

SUMMARY 

This article focuses on the technical strategies for performing sleeve bronchoplasty and pulmonary arterioplasty as advances in the application of video-assisted thoracoscopic surgery (VATS) as lobectomy with bronchovascular reconstruction is a favorable alternative to pneumonectomy in terms of the pulmonary function. When performing VATS sleeve bronchoplasty or arterioplasty, several technical issues should be discussed, including how to reduce the anastomotic tension of the airway, perform bronchial anastomosis, and clamp the pulmonary artery and select the type of vascular clamp. The traction device technique and continuous suture technique are thought to help surgeons perform VATS sleeve bronchoplasty, while cross-clamping of the pulmonary artery using thoracoscopic instruments aids in carrying out VATS arterioplasty.

Double-chamber rotating bioreactor for dynamic perfusion cell seeding of large-segment tracheal allografts: comparison to conventional static methods

Tracheal transplantation with a long-segment recellularized tracheal allograft has previously been performed without the need for immunosuppressive therapy. Recipients' mesenchymal stromal cells (MSC) and tracheal epithelial cells (TEC) were harvested, cultured, expanded, and seeded on a donor trachea within a bioreactor. Prior techniques used for cellular seeding have involved only static-seeding methods. Here, we describe a novel bioreactor for recellularization of long-segment tracheae. Tracheae were recellularized with epithelial cells on the luminal surface and bone marrow-derived MSC on the external surface. We used dynamic perfusion seeding for both cell types and demonstrate an increase in both cellular counts and homogeneity scores compared with traditional methods. Despite these improvements, orthotopic transplantation of these scaffolds revealed no labeled cells at postoperative day 3 and lack of re-epithelialization within the first 2 weeks. The animals in this study had postoperative respiratory distress and tracheal collapse that was incompatible with life.

Cryopreservation of the tracheal grafts: Review and perspective

Transplantation of the trachea may become the preferred method for the reconstruction of extensive tracheal defects, however, several unresolved problems must be addressed, such as immunosuppression, preservation and donor shortage. In this manuscript, the cryopreservation of tracheal grafts is reviewed, which potentially is associated with a lessened immunological response. Cryopreservation may be used clinically for long-term preservation and may solve the donor shortage. It is very important to confirm the immunomodulatory effect of cryopreservation on tracheal allografts in order to expand the potential clinical application of tracheal transplantation in the future. The cartilage as well as the epithelium and lamina propria serve as targets for rejection. However, the effect of cryopreservation on chondrocytes could be associated with reduced allogenicity of the trachea. The long-term cryopreservation of cartilage must be investigated in basic research models of chondrocyte viability. Growth of cryopreserved tracheal allografts is less well understood. Further studies are needed to elucidate the mechanism of synergistic effects of both cryopreservation and adequate immunosuppression for tracheal xenografts.

Successful circumferential free tracheal transplantation in a large animal model

BACKGROUND

Long segment tracheobronchial stenoses are associated with high morbi-mortality rates and difficult treatment. Transplantation hasn't proved to be useful yet. Currently, the successful results achieved in small animal models couldn't be satisfactorily accomplished or extrapolated in large mammals. We aimed to evaluate the viability of orthotopic tracheal autoimplantation in an ovine model.

METHODS

All animals underwent tracheal transplantation of 4 cm (5-7 rings) of the cervical trachea and were divided randomly in two groups: isolated autoimplantation (Group A/6) and autoimplantation with omental wrapping (Group B/6). Clinical follow up and weekly bronchoscopical examinations were performed. The grafts were macroscopically, histologically, and bacteriologically analyzed.

RESULTS

In group A, four animals achieved their planed survival and were sacrificed up to 60 days after transplantation with viable grafts. In group B, only two sheep had successful results. Graft failure with infection, necrosis and severe stenosis was observed in the rest of the animals from both groups. Pseudomonas aeruginose was isolated in all cases. The main complication of the omental pedicle was vascular congestion and peritracheal hemorrhage.

CONCLUSIONS

Contrary to the data reported to date, we found that tracheal transplantation is viable in a large mammal like the sheep. The main complication observed in this animal model was graft infection. The use of an omental pedicle with the technique applied worsened the grafts survival. The encouraging results obtained in this investigation justify further research in order to manage graft infection, leading us to establish a suitable large animal model for allotransplantation.

Animal models of tracheal allotransplantation using vitrified cryopreservation

OBJECTIVE

Tracheal reconstruction continues to pose a significant challenge in thoracic surgery. The study objective was to develop a novel method to eliminate the antigenicity of tracheal allografts by using vitrified cryopreservation and present the experimental results after cervical tracheal replacement in rabbits.

METHODS

Fifteen New Zealand rabbits, irrespective of gender, weighing 2.5 to 3.0 kg, were randomly divided into 3 groups: (A), the experimental group (n = 5), tracheal allotransplantation after 4 weeks of vitrified cryopreservation; (B), the negative control group (n = 5), fresh tracheal autotransplantation; and (C), the positive control group (n = 5), fresh tracheal segments implanted as allografts. The patency of implanted grafts, lymphocytic infiltrate, cartilage scores, and ink perfusion to evaluate revascularization were used to investigate the impact of vitrified cryopreservation on the antigenicity of tracheal grafts and vascular regeneration.

RESULTS

Rabbits in groups A and B all had uneventful postoperative courses with patent lumens and structural integrity, with obvious vascular regeneration and less lymphocytic infiltrate. Although in excellent condition, animals were sacrificed after a short-term follow-up of 4 weeks for further examination as scheduled. In group C, massive lymphocytic infiltrate and inflammatory cells without noticeable revascularization were observed, and rabbits died within 2 weeks after surgery for airway stenosis or severe obstruction.

CONCLUSION

The antigenicity of tracheal allografts was significantly decreased by using the vitrified cryopreservation method, which would be a novel alternative method to store donor trachea to make tracheal banking possible.

Revascularization of trachea in lung and tracheal transplantation

Ischemia is the primary risk factor for airway complications in double lung transplantation using tracheal anastomosis and in tracheal transplantation. Many treatment options as to revascularization for the trachea were herein described and reviewed. They include direct revascularization (using a conduit such as artery or vein), revascularization with tissue wrapping (using omentum, muscle, internal thoracic artery pedicle, pleura, or pericardial fat pad), and with drug administration (using corticosteroid hormone, prostaglandin, or angiogenic factor). As there are few organized reports including new information on revascularization for the trachea these days, this review article would help thoracic surgeons who get engaged transplantation.

Tracheal replacements: part 1

In this review, we summarize the history of tracheal reconstruction and replacement as well as progress in current tracheal substitutes. In Part 1, we cover the historical highlights of grafts, flaps, tube construction, and tissue transplants and address the progress made in tracheal stenting as a means of temporary tracheal support. This is followed in Part 2 by an analysis of solid and porous tracheal prostheses in experimental and clinical trials. We conclude Part 2 with a summary of recent efforts toward generating a bioengineered trachea. Finally, we provide an algorithm on the spectrum of options available for tracheal replacement.

Efficacy of Multiglycosidorum tripterygii for rat tracheal allografts

BACKGROUND

A new immunosuppressant must be developed because graft rejection remains the leading cause of death after lung transplantation. We evaluated the efficacy of Multiglycosidorum tripterygii as a new immunosuppressant using a heterotopic rat tracheal allotransplantation model.

METHODS

We performed short- and long-term experiments using a short-course of treatment with Multiglycosidorum tripterygii. To assess the immunosuppessive power of Multiglycosidorum tripterygii, we compared its efficacy (at 90, or 150 mg/kg/day) with that of tacrolimus (at 0.5, 1.0, or 1.5 mg/kg/day) at 4 weeks after transplantation. We then evaluated the effect of 150 mg/kg/day of Multiglycosidorum tripterygii treatment at 12 weeks after transplantation.

RESULTS

The efficacy of 150 mg/kg/day Multiglycosidorum tripterygii was superior to that of 90 mg/kg/day of the same drug and was comparable to that of 1.0 mg/kg/day tacrolimus, as demonstrated by morphologic assessment of the graft. Treatment with 150 mg/kg/day Multiglycosidorum tripterygii maintained graft morphology for 4 weeks but could not maintain graft viability for 12 weeks. Animals tolerated this dosage of Multiglycosidorum tripterygii for 12 weeks after administration.

CONCLUSIONS

We conclude that the efficacy of Multiglycosidorum tripterygii is acceptable for rat tracheal allografts. Further studies are necessary to investigate Multiglycosidorum tripterygii treatment for clinical use in humans.

Heterotopic tracheal transplantation with omentum wrapping in the abdominal position preserves functional and structural integrity of a human tracheal allograft

OBJECTIVES

Transplantation of a human trachea has been reported only twice in the literature with limited documentation of the functional and structural properties of the allograft.

PATIENTS AND METHODS

A 57-year-old patient with chronic obstructive pulmonary disease with low segment tracheal stenosis was accepted for lung transplantation and 2-stage tracheal allotransplantation. Standard bilateral sequential lung transplantation was performed with the transfer of the donor trachea into the recipient's abdomen, which was wrapped in the greater omentum and sutured into the abdominal wall, similar to a stoma. The patient received immunosuppression consisting of cyclosporine A, mycophenolate mofetil, and cortisone. Sixty days later, the tracheal allograft presented with macroscopically normal appearance with maintained elasticity and rigidity. The patient underwent a cricotracheal resection 6 months after lung transplantation. However, reconstruction with direct end-to-end anastomosis was achievable. The tracheal allograft, therefore not needed for reconstruction, was harvested and underwent complete investigations.

RESULTS

Cross-section of the graft revealed a mechanically stable and macroscopically intact trachea. Hematoxylin-eosin staining demonstrated vital cartilage covered by respiratory epithelium. Angiography, followed by corrosion studies and electromicroscopy, demonstrated excellent vascularization of the tracheal wall.

CONCLUSION

The patient is alive 31 months posttransplantation and remains in bronchiolitis obliterans syndrome stage 0. Human trachea wrapped in omentum maintains its functional and structural integrity and may be used for 2-stage allotransplantation.

The effectiveness of hyperbaric oxygen treatment in tracheal reconstruction with auricular cartilage grafts (experimental study)

PURPOSE

Tracheal stenosis or neoplastic changes, as well as, traumatic, congenital, or iatrogenic causes may require extensive tracheal resections. Complications like vascularization insufficiency and structural support problems occur nearly in all cases when end-to-end anastomosis of trachea is not feasible. Hyperbaric oxygen (HBO) treatment is a well-known method for the management of grafts and flaps that have vascularization problems. In this study, the effect of hyperbaric oxygen treatment on wound healing after tracheal reconstruction with auricular cartilage graft (ACG) has been evaluated.

METHODS

Thirty-two rabbits were divided into 2 groups: study group (n = 16) and control group (n = 16). The anterior halves of the six tracheal rings were resected, and the defects were repaired with autogenic auricular grafts. Hyperbaric 100% pure oxygen was administered to the study group at 2.4 atmospheres of absolute pressure 2 times a day for 1 week. The control group did not receive any therapy except proper control of the wound.

RESULTS

It was observed that in the study group, inflammation, fibrosis, and necrosis were less, whereas epithelialization and maturation were early and neovascularization and neochondrification were more than the control group only at specific weeks. But all tracheas in both groups showed excellent healing without graft rejection and excessive granulation tissue formation. Furthermore, there was no statistically difference between the 2 groups.

CONCLUSIONS

Auricular cartilage grafts is a valuable management method of tracheal defects, and hyperbaric oxygen treatment is a good supplementary method in healing period of cartilage autografts.

A composite tissue-engineered trachea using sheep nasal chondrocyte and epithelial cells

This study evaluates the feasibility of producing a composite engineered tracheal equivalent composed of cylindrical cartilaginous structures with lumens lined with nasal epithelial cells. Chondrocytes and epithelial cells isolated from sheep nasal septum were cultured in Ham's F12 media. After 2 wk, chondrocyte suspensions were seeded onto a matrix of polyglycolic acid. Cell-polymer constructs were wrapped around silicon tubes and cultured in vitro for 1 wk, followed by implanting into subcutaneous pockets on the backs of nude mice. After 6 wk, epithelial cells were suspended in a hydrogel and injected into the embedded cartilaginous cylinders following removal of the silicon tube. Implants were harvested 4 wk later and analyzed. The morphology of implants resembles that of native sheep trachea. H&E staining shows the presence of mature cartilage and formation of a pseudo-stratified columnar epithelium, with a distinct interface between tissue-engineered cartilage and epithelium. Safranin-O staining shows that tissue-engineered cartilage is organized into lobules with round, angular lacunae, each containing a single chondrocyte. Proteoglycan and hydroxyproline contents are similar to native cartilage. This study demonstrates the feasibility of recreating the cartilage and epithelial portion of the trachea using tissue harvested in a single procedure. This has the potential to facilitate an autologous repair of segmental tracheal defects.

The immunomodulatory effect of cryopreservation in rat tracheal allotransplantation

BACKGROUND

Cryopreservation is one solution to the problem of donor organ deficit. To investigate the effect of cryopreservation on tracheal allografts, we performed 2 experiments in rats.

METHODS

In Experiment 1, we assessed second-set graft rejection. Two weeks after primary heterotopic transplantation (Group 1, fresh isografts; Group 2, fresh allografts from Lewis rats; and Group 3, cryopreserved allografts from Lewis rats; n = 5, respectively), each animal underwent secondary heterotopic grafting with isografts and allografts from Lewis and Wistar Furth rats (n = 5, respectively). Four weeks after the secondary transplantation, all grafts were retrieved for histologic analysis. In Experiment 2, we assessed the long-term results of allograft cryopreservation, without immunosuppression therapy. Six months after transplantation of fresh (Group 4) and cryopreserved (Group 5) allografts, the tracheal segments (each group, n = 5) were histologically evaluated.

RESULTS

In Experiment 1, only the secondary allografts from Lewis rats in Group 2 did not maintain lumen structure and often showed dislocated or destroyed cartilage. Second-set graft rejection was specifically recognized in Group 2, but not in Group 1 or 3. In Experiment 2, the cryopreserved allografts appeared almost normal and lumen rigidity was preserved 6 months after transplantation. These allografts were superior to the fresh allografts in patency and in cartilage dislocation and mononuclear cell infiltration scores, but not in the viable chondrocyte ratio.

CONCLUSIONS

We conclude that cryopreservation may produce successful long-term results because of its immunomodulatory effect on tracheal allografts.

Tracheal replacement: a critical review

This review discusses the need for tracheal replacement, distinct from resection with primary anastomosis, the requirements for replacement, and the many efforts over the past century to accomplish this goal experimentally and clinically. Approaches have included use of foreign materials, nonviable tissue, autogenous tissue, tissue engineering, and transplantation. Biological problems in each category are noted.

Autologous tissue-engineered trachea with sheep nasal chondrocytes

OBJECTIVE

This study was designed to evaluate the ability of autologous tissue-engineered trachea shaped in a helix to form the structural component of a functional tracheal replacement.

METHODS

Nasal septum were harvested from six 2-month-old sheep. Chondrocytes and fibroblasts were isolated from tissue and cultured in media for 2 weeks. Both types of cells were seeded onto separate nonwoven meshes of polyglycolic acid. The chondrocyte-seeded mesh was wound around a 20-mm-diameter x 50-mm-long helical template and then covered with the fibroblast-seeded mesh. In 2 separate studies the implants were placed either in a subcutaneous pocket in the nude rat (rat tissue-engineered trachea) or in the neck of a sheep (sheep tissue-engineered trachea). Rat tissue-engineered tracheas were harvested after 8 weeks and analyzed by means of histology and biochemistry. Sheep tissue-engineered tracheas were harvested from the neck at 8 weeks and anastomosed into a 5-cm defect in the sheep trachea.

RESULTS

Sheep receiving tissue-engineered trachea grafts survived for 2 to 7 days after implantation. Gross morphology and tissue morphology were similar to that of native tracheas. Hematoxylin-and-eosin staining of rat tissue-engineered tracheas and sheep tissue-engineered tracheas revealed the presence of mature cartilage surrounded by connective tissue. Safranin-O staining showed that rat tissue-engineered tracheas and sheep tissue-engineered tracheas had similar morphologies to native tracheal cartilage. Collagen, proteoglycan, and cell contents were similar to those seen in native tracheal tissue in rat tissue-engineered tracheas. Collagen and cell contents of sheep tissue-engineered tracheas were elevated compared with that of normal tracheas, whereas proteoglycan content was less than that found in normal tracheas.

CONCLUSIONS

This study demonstrated the feasibility of recreating the cartilage and fibrous portion of the trachea with autologous tissue harvested from single procedure. This approach might provide a benefit to individuals needing tracheal resection.

Removal of cartilage rings prevents graft stenosis in extended tracheal allotransplantation with omentopexy and immunosuppression: an experimental study

BACKGROUND

One of the serious problems in longer size tracheal transplantation is severe stenosis of the graft, probably caused by an inadequate blood supply. We have previously reported that removal of some cartilage rings of the graft and omentopexy helps to provide sufficient blood flow to the graft mucosal tissue and results in satisfactory survival and non-significant graft stenosis in extended tracheal autotransplantation. However, it is unclear whether this method can be applied to extended tracheal allotransplantation that requires immunosuppression. In this report, we describe midterm results of extended tracheal allotransplantation with the technique.

METHODS

Twenty-four adult mongrel dogs were used. In 18 dogs, a nine-cartilage-ring length of the trachea was allotransplanted when five cartilage rings of the graft were removed, leaving two rings intact at both ends of the graft for simple fixing to the recipient. Two artificial tracheal rings outside the graft and a stent inside the graft were used for maintaining the lumen width. Omentopexy was done for sufficient blood supply to the graft. FK 506 (0.1 mg/kg) was given on each day after the operation in Group A (n = 10), but was not given at all in Group B (n = 8). In Group C (n = 6), a nine-cartilage-ring length of the trachea, without removal of any cartilage ring, was transplanted into the recipient dog and covered with an omental pedicle flap. The same dose of FK 506 as that used in Group A dogs was given to Group C dogs.

RESULTS

In Group A, 2 dogs died of graft stenosis within 9 weeks after surgery and 1 died of emaciation without tracheal stenosis. Seven dogs (70%) survived until time of killing. Among the 8 dogs in Group B, 6 died of graft stenosis within 9 weeks after surgery, with 1 dying of pneumonia and only 1 (13%) surviving for >1 year until killing. In Group C, all 6 dogs died of graft stenosis within 6 weeks after surgery. Survival at 16 weeks after surgery was 70% in Group A, 13% in Group B and 0% in Group C (p < 0.01, A vs B and C). No significant graft stenosis was found in 6 dogs and mild stenosis was found in 2 dogs at the time of death or killing in Group A (80%), whereas mild stenosis was found in only 2 dogs in Group B (25%) (p < 0.05). Mucosal blood flow of the graft in Group A was higher than that in Group C and was the same as that in Group B within 4 weeks after surgery; however, it remained unchanged to ultimately be higher than in Group B at 6 and 8 weeks after surgery.

CONCLUSIONS

Removal of some cartilage rings, omentopexy and immunosuppression improved blood supply to the graft and resulted in good survival and non-significant tracheal stenosis in extended tracheal allotransplantation.

Microvascular transfer of long tracheal autograft segments in the canine model

OBJECTIVE

The reconstruction of long segment tracheal defects represents an unsolved clinical dilemma. Prior attempts to directly revascularize tracheal segments have been unsuccessful. The objective of this study was to evaluate orthotopic autotransplantation of revascularized long tracheal segments in the canine model.

METHODS

Ten randomly selected mongrel dogs underwent excision, orthotopic reimplantation, and microvascular revascularization of a long segment (8.0 cm) of cervical trachea. The cranial thyroid artery and the internal jugular vein served as the vascular supply for the tracheal segment. The animals were maintained for a period of 30 days during which time graft viability was measured by routine endoscopic assessment and tracheal biopsies. Ex vivo, tracheal autografts were examined grossly for graft healing an d microscopicallyfor histologic architecture.

RESULTS

Seven of 10 dogs survived the predetermined 30-day postoperative study period without complications. Postmortem examination demonstrated that 7 dogs had healed tracheal autograft segments with normal histologic architecture, 2 dogs sustained a postoperative wound infection and tracheal dehiscence, and 1 dog sustained a fatal postoperative hematoma.

CONCLUSIONS

For the first time, we have demonstrated direct revascularization of long segment tracheal autografts in the dog model using the cranial thyroid artery and internal jugular vein as the vascular supply.

Successful allotransplantation of cryopreserved tracheal grafts with preservation of the pars membranacea in nonhuman primates

OBJECTIVE

This study was performed to confirm the feasibility of cryopreserved tracheal allotransplantation in primates, the anatomy and immunology of which are considered to be more closely related to those of humans than those of other animals.

METHODS

Cryopreserved tracheal allotransplantations were performed in 3 recipient primates. In the control group fresh tracheal allotransplantations were performed in 2 primates (control A), and a tracheal allotransplantation with a simply frozen tracheal graft was performed in 1 primate (control B). Monthly bronchoscopic examinations, histologic examinations, electron microscopic examinations, and immunohistochemical investigations were performed in each of the primates.

RESULTS

In the cryopreserved tracheal allotransplantation group, 3 recipient monkeys were killed on the 35th, 144th, and 387th postoperative days, respectively. All grafts were incorporated by the recipient trachea without stenosis in the cryopreserved group. In the control group 2 recipient monkeys were killed on the 93rd postoperative day (control A), and one was killed on the 84th postoperative day (control B). Severe stenosis was observed after the transplantation in all of the control monkeys. Immunologic reactions appeared to be attenuated by the cryopreservation, whereas T cell-mediated immunologic rejection (control A) and loss of cartilage viability (control B) were considered to be the causes of graft failure in the control group.

CONCLUSION

The immunogenicity of the tracheal allografts was reduced by cryopreservation, and cryopreserved tracheal allotransplantation was successful in our primate model. Further investigation of cryopreserved tracheal allotransplantation with regard to proper clinical applications and the limitations of the procedure should be performed.

Time necessary for neovascularization of a tracheal segment by the sternohyoid muscle

INTRODUCTION

The reimplantation of a complete tracheal segment (CTS) as an autograft or homograft often results in total or partial necrosis of the CTS. However, previous experiments suggested that when the CTS is first vascularized by the sternohyoid muscle (SM) 21 days before the reimplantation, the CTS can be reimplanted without ischemia or stenosis. However, it is not clear if the CTS requires 21 days to attain full revascularization.

GOAL

This study aims to ascertain the minimum time necessary for revascularization of the 6 rings CTS by the SM allowing reimplantation free of ischemia.

METHODS

Fifteen mongrel dogs, divided into 3 groups were submitted to 2 sequential surgical procedures. In the first procedure, a SM flap was used to envelop 6 rings CTS in all dogs. After periods of 21 days (group 1, n = 5), 14 days (group 2, n = 5) and 7 days (group 3, n = 5), the compound flaps (CTS and SM) were neovascularized. Each CTS was transected and mobilized from the trachea and then replaced again in its original site, as an autoflap.

RESULTS

After a period of at least 60 days, none of dogs presented any respiratory alteration. Macroscopic and microscopic analyses demonstrated adequate viability and no stenosis.

CONCLUSION

Our findings suggest that it is possible to neovascularize the CTS using a SM flap within a period as short as 1 week.

Tracheal allotransplantation maintaining cartilage viability with long-term cryopreserved allografts

BACKGROUND

Cartilage viability of a cryopreserved tracheal allograft seems to affect graft function and durability. We previously reported the influence of warm ischemia and cryopreservation on cartilage viability of tracheal allografts. For the clinical application of tracheal allotransplantation, it is essential to preserve grafts for a long time. In this study, we assessed cartilage viability of tracheal allografts after long-term cryopreservation in transplantation models.

METHODS

The tracheas were harvested from Lewis rats. The grafts were frozen to -80 degrees C in a programmable freezer immediately after being harvested and were then stored in liquid nitrogen (-196 degrees C) for different lengths of preservation (1, 2, 6, 9, 12, 18, and 24 months; n for each group = 8). Cartilage viability was evaluated by estimating proteoglycan synthesis. After harvest or thawing of the tracheas, the cartilage was labeled with 4 muCi/mL of Na2 35SO4. Specimens were then hydrolyzed in 0.5 mol/L NaOH, and a solution of the extracts was then counted by a liquid scintillation counter. 35Sulfur incorporation before and after cryopreservation was examined in each group. Tracheal allotransplantation was performed using Lewis rats as donors and Brown Norway rats as recipients.

RESULTS

The average 35S incorporation in the cartilage before cryopreservation was 224 +/- 17 disintegrations per minute per milligram of tissue protein. The average 35S incorporation in the cartilage after cryopreservation decreased to 67% to 76% compared with that before cryopreservation. There were no significant differences among the groups in 35S incorporations after cryopreservation. Histologic examination after transplantation revealed normal tracheal cartilage in all groups.

CONCLUSIONS

The viability of tracheal cartilage after cryopreservation decreased to 67% to 76%. There were no significant differences in viability of cartilage among the tracheas after different lengths of cryopreservation. Tracheal allotransplantation after long-term cryopreservation can be safely performed in the rat model.

Feasibility of cryopreserved tracheal xenotransplants with the use of short-course immunosuppression

OBJECTIVE

We evaluated the feasibility of discordant xenotransplantation of the cryopreserved trachea with intermittent immunosuppression to help solve the shortage of donor tracheas.

METHODS

Two experiments were performed with heterotopic transplantation models in 14 guinea pigs and 85 rats. So that the minimal dose of FK506 for viable fresh xenografts could be determined, FK506 was given in escalating doses (0, 1.5, 2.5, and 3.5 mg/kg) for recipient animals after xenogeneic transplantation. With the goal of obtaining a long-term survival of the xenografts, the effect of cryopreservation on xenografts was assessed and thereafter different cycles of immunosuppression every third week were evaluated in fresh or cryopreserved xenografts in the second experiment.

RESULTS

An FK506 dosage of more than 2.5 mg/kg per day was much more effective than smaller dosages, as demonstrated by morphologic assessment. A higher dosage of FK506 potentially delayed the rejection of xenografts and can thus maintain tracheal xenograft viability for less than 4 weeks in rat recipients. In experiment 2, the cryopreserved xenografts showed less histologic viability than fresh xenografts but greater patency of the lumen. The patency of cryopreserved xenografts was favorably maintained for a longer period than that of fresh xenografts with either the same number or more cycles of immunosuppression.

CONCLUSIONS

We conclude that the synergistic effect of cryopreservation and adequate intermittent immunosuppression may enable tracheal xenografts to remain viable over longer periods.

Limit of warm ischemia time before cryopreservation in rat tracheal isografts

BACKGROUND

The viability of cadaveric tracheal grafts undergoing cryopreservation is still unclear. We evaluated the limit of warm ischemia time before cryopreservation in rat tracheal isografts.

METHODS

Each isograft was harvested from donor rats 0 to 48 hours (0, 6, 12, 18, 24, and 48 hours) after circulatory arrest, immersed in the preservative solution, and stored in a deep freezer until reaching -80 degrees C and then was kept in liquid nitrogen for 3 months. Heterotopic transplantation into the omentum was performed after the isografts were thawed. Graft morphology 3 months after transplantation was assessed.

RESULTS

The stepwise increase of warm ischemia time significantly reduced graft survival. A prolonged period of warm ischemia had a degenerative effect on both the epithelium and cartilage. The morphology of the epithelium and cartilage in isografts undergoing warm ischemia for less than 18 hours was better preserved, whereas it deteriorated in isografts undergoing warm ischemia for more than 24 hours.

CONCLUSIONS

We thus conclude that the permissible period of warm ischemia before 3-month cryopreservation to maintain tracheal isograft viability is 18 hours in rats.

Maximal period of cryopreservation with the Bicell biofreezing vessel for rat tracheal isografts

OBJECTIVE

The maximal period of cryopreservation for the trachea is still unsolved. We assessed the maximal period of cryopreservation using the Bicell biofreezing vessel as an easy and cheap slow-freezing instrument for viable tracheal grafts in 95 rats.

METHODS

Each isograft was harvested from 17 donor rats, immersed in the preservative solution, and stored in a Bicell device in a deep freezer at -80 degrees C. The tracheal isografts were then randomly assigned to 9 groups according to cryopreservation periods ranging from 0 to 12 months. Included in the 9 groups were 2 subgroups (n = 6 per subgroup) that were observed immediately after being thawed and 1 month after heterotopic transplantation into the omentum after being thawed. Four subgroups (n = 6 per subgroup) were added according to the cryopreservation period for 1, 3, 6, and 12 months to evaluate the graft morphology 3 months after being thawed and transplanted heterotopically.

RESULTS

A prolonged period of cryopreservation had a degenerative effect on both the epithelium and cartilage. One month after transplantation, degeneration was more pronounced in the cartilage than in the epithelium, as characterized by the viable chondrocyte ratio and the epithelial score of isografts undergoing cryopreservation for more than 9 months. Three months after transplantation, the morphology of the epithelium and cartilage in isografts undergoing cryopreservation for less than 3 months was better preserved, whereas the morphology of both deteriorated in isografts undergoing cryopreservation for more than 6 months.

CONCLUSIONS

We conclude that the permissible period of cryopreservation to maintain tracheal isograft viability in this simple system using a Bicell biofreezing vessel is 3 months.

Removal of cartilage rings of the graft and omentopexy for extended tracheal autotransplantation

BACKGROUND

One of the serious problems in longer-size tracheal transplantation is infection or severe stenosis of the graft, probably caused by an inadequate blood supply even with omentopexy. For obtaining an appropriate blood supply, we experimentally developed a new technique that included removal of some cartilage rings of the graft and omentopexy.

METHODS

Twenty-one adult mongrel dogs were used. In group A (n = 11), a nine-cartilage ring length of the trachea in which six of nine rings were removed, leaving one cartilage ring at each end of the graft and another in the center, was autotransplanted with omentopexy. Two artificial tracheal rings outside the graft were used for maintaining the lumen. In group B (n = 10), a nine-cartilage ring length of the trachea was autotransplanted with omentopexy.

RESULTS

In group A, all dogs survived until being sacrificed, whereas 5 group B dogs died of graft infection and mediastinitis (p<0.05 versus group A). Mucosal blood flow of the graft in group A was normal and higher than in group B (p<0.05). Grade of the graft stenosis at death or sacrifice was 14%+/-1% in group A and 58%+/-25% in group B (p<0.05).

CONCLUSIONS

Removal of some cartilage rings improved blood supply to the graft and resulted in satisfactory survival and nonsignificant tracheal stenosis in extended tracheal autotransplantation.

Tracheal reconstruction with a vascularized cartilage flap in rabbits

The relative merits of a vascularized autogenous cartilage flap (VACF) are discussed in reconstruction of tracheal defects in rabbits. Sixteen albino Vienna rabbits were divided into two groups of eight animals each. In all rabbits, a rectangular tracheal defect was created. In the experimental group, a VACF was designed on the left auricle. This island flap was then transposed through a subcutaneous tunnel to the trachea and used to repair the defect. In the control group, tracheal defects were reconstructed with free cartilage grafts. In histologic evaluations, it was found that the reconstructed site showed a greater degree of vascularization when a VACF was used, and the gap between the trachea and flap was filled with new cartilage tissue, to a much greater extent than with the free cartilage grafts. It is concluded that use of the VACF is a relatively safe and effective procedure for repairing tracheal defects.

Anatomy and vascular perfusion territories of the superior thyroid artery in Macaca mulatta

OBJECTIVE

Currently, methods used to repair long segment tracheal stenosis are unreliable. Here, a new nonhuman primate model of tracheal transplantation is used based on its evolutionary proximity to humans.

STUDY DESIGN

Prospective dye perfusion study in Macaca mulatta.

METHODS

After anatomical characterization, Evan's blue solution was injected into the right superior thyroid artery unilaterally (n = 5). Staining of the tracheal vasculature was then examined.

RESULTS

In M mulatta, the superior thyroid artery branched from the lingual-facial trunk and was 0.64 +/- 0.18 mm in diameter. Dye staining was bilateral, with the ipsilateral side extending to 2.98 +/- 0.58 cm and the contralateral to 2.88 +/- 0.88 cm, 12.9 +/- 3.45 rings (47% of trachea).

CONCLUSIONS

The tracheal vasculature has extensive bilateral collateral vascular channels that may provide a graft survival advantage. Macaques may serve as a good model of tracheal transplantation because of the collateral vascularization of the trachea and the extensive tracheal segment supplied by the superior thyroid artery, and because the superior thyroid artery and vein are anastomosable.

Improved airway healing using basic fibroblast growth factor in a canine tracheal autotransplantation model

OBJECTIVE

We studied 22 dogs to examine the effect of basic fibroblast growth factor (bFGF) alone, in comparison with omental or muscular wrapping on airway healing in a tracheal autotransplantation model.

SUMMARY BACKGROUND DATA

Basic fibroblast growth factor is one of the most potent promoters of angiogenesis and has an ability to enhance blood supply to the ischemic airway. Topical administration of a fibrin glue enriched with 5 microg/cm2 bFGF, determined as a proportion of surface area of the tracheal grafts, improved revascularization of orthotopic canine tracheal autografts in a previous study.

METHODS

All animals received orthotopic tracheal transplantation using 6-ring autografts that occupied a distal part of the thoracic trachea. Twenty-two animals were classified randomly into the following four groups: no treatment (Group G1, n = 4), muscular wrapping (Group G2, n = 4), omental wrapping (Group G3, n = 4), and topical administration of fibrin glue enriched with 5 microg/cm2 bFGF (Group G4, n = 10). Autografts were harvested 60 days after transplantation and assessed by the percent patency and histology.

RESULTS

Devascularized tracheal autografts could not maintain their structural integrity without other treatments (Group G1). In contrast, more than half of all autografts receiving treatments remained viable, as demonstrated by gross and histologic findings (Groups G2, G3, and G4). Treatments with bFGF and omentum showed significantly better graft viability than no treatment. However, there was no statistical difference in the viability of tracheal autografts among the three treatment groups. In terms of the time performance ratio, bFGF was the best treatment for the devascularized autografts.

CONCLUSIONS

Topical administration of bFGF was superior to the omental or muscular wrapping in terms of the time performance ratio. Clinical trials will be necessary to determine whether these findings are applicable to humans.

[Perfusion of donor tissue improves the preservation of graft in heterotopic tracheal transplantation]

To assess the effect on tracheal graft preservation of perfusion of donor tissue with a Collins solution before extraction and immunosuppression of the recipient. An experimental study was performed in 36 albino rabbits with revascularized heterotopic cervical reconstruction of the trachea with omentum. The animals were distributed in four groups. Groups I (n = 9) and III (n = 9) were transplanted with non perfused donor tissue. Animals in groups II (n = 9) and IV (n = 9) received grafts perfused with Collins solution. Immunosuppression with steroids and cyclosporin was continued for 21 days in groups III and IV. In a mid portion of the trachea viewed under optical microscope, the degree of inflammation or circumferential necrosis was assessed on a scale of 0 to 9 by adding the scores for mucosa, submucosa and cartilage. The mean score for tracheal lesion was lower in group IV, with a likelihood of random difference of less than 5%. Perfusion of peritracheal tissues with Collins solution in the donor, in addition to immunosuppression decreases the extent of tissue damage in the tracheal graft.

Successful tracheal autotransplantation with two-stage approach using the greater omentum

BACKGROUND

Although many studies on reconstruction of extensive circumferential tracheal defects with a segmental trachea have been done, up to date, no reliable and satisfactory tracheal transplantation procedure has been developed. We conducted this experiment to investigate feasibility and efficacy of a staged tracheal transplantation approach for tracheal reconstruction.

METHODS

Twelve dogs were divided equally into groups I and II. A segment of cervical tracheas (six rings) was harvested as an autograft and implanted heterotopically into the greater omentum. Two weeks later, the autografts with their omental pedicles were transplanted orthotopically to the cervical (group I) or the thoracic portion of the trachea (group II). Bronchoscopic examination were performed monthly during a 5-month follow-up period. After sacrificing the dogs, we had the grafts examined macroscopically and microscopically.

RESULTS

The dogs of both groups survived well until the end of the follow-up. No abnormal findings were observed through bronchoscopy. The grafts had normal appearance, without shrinkage, granulation, or necrosis by postmortem gross examination. Histologic examination showed the structures of the grafts were intact.

CONCLUSIONS

We conclude that the two-stage tracheal transplantation approach using the greater omentum is feasible, and can facilitate the survival of a tracheal graft as well.

Reconstruction of trachea and carina with immediate or cryopreserved allografts in dogs

BACKGROUND

Grafting is required when primary reconstruction of a tracheocarinal defect is not feasible. To determine the viability of and the nature of the healing process occurring in the cryopreserved graft, we performed tracheocarinal transplantation in dogs.

METHODS

We performed 32 tracheocarinal reconstructions in dogs using autotransplanted, immediately transplanted, or cryopreserved allografts. The viability of each graft was evaluated serially by fiberoptic macroexamination and by measurement of the tracheal mucosal blood flow using a hydrogen clearance method. In group A (n = 8), the tracheal carina was removed and reimplanted immediately. In group B (n = 8), the tracheocarina was allotransplanted immediately after harvest. In group C (n = 8), allotransplantations were performed using grafts cryopreserved for 1 to 3 weeks by freeze-drying. In group D (n = 8), we attempted to achieve immunosuppression-free transplantation with the cryopreserved allografts.

RESULTS

Sufficient viability and good healing (6/8, 75%) occurred in the dogs with cryopreserved tracheocarinal allotransplants. Three of 8 dogs (38%) with cryopreserved allotransplants survived for 25 to 57 days without immunosuppression.

CONCLUSIONS

The cryopreservation of tracheocarinal allografts for 3 weeks without the use of a preservative solution was shown to be feasible. Cryopreservation prolonged the survival of nonimmunosuppressed allotransplants in dogs.

Split transplantation of the trachea: a new operative procedure for extended tracheal resection

Before tracheal transplantation can be applied clinically, several problems must be solved: immunosuppression, blood supply to grafts, and reliable long-term preservation of grafts. We have conducted experiments on tracheal transplantation to solve these problems. In the present study, we tried a new operative procedure to accomplish reliable revascularization of transplanted tracheal grafts. It has been reported that transplantation of a 10-ring length of trachea is difficult even with omentopexy. Long tracheal allografts can be transplanted with use of direct revascularization, but this technique is extremely troublesome. Thus we developed a new operative procedure, "split tracheal transplantation," in which grafts are divided at the midportion and covered with omentum, after demonstrating that the blood supply to tracheal grafts can be reestablished around the suture lines. Two groups of dogs were used. In group A (control, n = 4), a 10-ring length of trachea was autotransplanted. The anastomotic sites and grafts were covered with omental pedicles. In group B (split tracheal transplantation, n = 10), tracheal grafts 10 rings long were autotransplanted. These grafts were divided at the midportion, a piece of omentum was inserted between the two halves, and the midportion was sutured. Grafts were observed regularly by bronchoscopy and examined histopathologically after the animals died or were killed. In some animals, microangiography of the bronchial circulation was done. In the control group, necrosis, stenosis, or malacia of the grafts was observed in three of the four animals. In the split transplantation group, all animals survived for at least 2 months, all grafts were incorporated, and none showed ischemia, stenosis, or malacia. Microscopic examination and microangiography revealed that neovascularization of the graft was promoted by omentum inserted at the midportion of the graft. Split transplantation of the trachea is an easy and reliable way to extend tracheal resection.

The infeasibility of using ten-ring irradiated grafts for tracheal allotransplantation even with omentopexy

In our previous study, we demonstrated that high-dose 60Co irradiation was able to prevent rejection of canine tracheal allografts. To determine the maximum possible length of these grafts, in the present study we attempted to transplant five-ring and ten-ring tracheal allografts in two groups of five dogs each. Either five or ten rings were excised from donor tracheas and irradiated with 100,000 cGy of 60Co. The irradiated tracheal grafts were transplanted to replace either five- or ten-ring sections of the mediastinal tracheas removed from the recipient dogs. The grafts were covered with omental pedicles and no immunosuppressants were used. Graft incorporation was achieved in four of the five dogs in the five-ring groups, and three of these dogs survived for more than 700 days. However, four of the five animals in the ten-ring group died from tracheostenosis accompanied by ischemia within 3 weeks. These findings demonstrate the impossibility of performing ten-ring tracheal allotransplantation using irradiated grafts, even with omentopexy.

Magnetic resonance imaging of experimental tracheal transplantation

RATIONALE AND OBJECTIVES

We evaluated the feasibility of using contrast-enhanced magnetic resonance (MR) imaging for in vivo monitoring of tracheal transplants in rabbits.

METHODS

Plain and gadolinium-enhanced, high-resolution MR images were obtained from six rabbits 4 weeks to 6 months after an orthotopic tracheal transplantation (after heterotopic revascularization). The animals were sacrificed after the MR examination, and comparisons were made among the MR images, macroscopic observations, and histologic sections.

RESULTS

All transplants were clearly identifiable on the MR images; they produced slight-to-moderate narrowing of the airway diameter. Enhancement of the transplant tissues was clearly present. There was close correspondence between the MR morphology and the macroscopic and histologic sections.

CONCLUSION

MR imaging can be used to monitor in vivo tracheal transplantation after heterotopic revascularization.

Experimental tracheal and tracheoesophageal allotransplantation. Paris-Sud University Lung Transplantation Group

We investigated the effects of allograft perfusion with a preservative technique and of combined thyrotracheoesophageal implantation on airway epithelium of long segments of thyrotracheal grafts allotransplanted on their own vascular pedicles into immunosuppressed pigs. Four groups of five animals each underwent heterotopic (into the neck) thyrotracheal (group 1) and thyrotracheoesophageal (group 2) and orthotopic thyrotracheal (group 3) and thyrotracheoesophageal (group 4) allotransplantation. Allograft revascularization included (1) interposition of donor right subclavian artery--incorporating the inferior thyroid artery--to recipient right carotid artery (end-to-end fashion) and (2) end-to-side anastomosis of donor anterior vena cava to recipient right external jugular vein. All thyrotracheoesophageal blocks were harvested after inferior thyroid artery perfusion with 4 degrees C Euro-Collins solution. The overall lengths of tracheal and esophageal grafts were 10.7 +/- 2.7 cm and 13.4 +/- 3.6 cm, respectively. In the heterotopic groups, all allografts were viable and histologically normal at postmortem examination and the incidence and severity of airway ischemia and rejections (at equal residual levels of cyclosporine) were not different between groups 1 and 2. In the orthotopic groups, the first two pigs died of airway collapse with histologically normal grafts. In the remaining pigs, temporary airway stenting was inserted and allografts remained viable and histologically intact for their entire length 30 days after transplantation. Transplanted tracheal smooth muscles had concentration-dependent contractions and relaxations similar to those of nontransplanted (native) tracheas. This study documents the feasibility of allotransplanting long tracheal and esophageal segments on their own vascular pedicles and demonstrates that allograft preservation and thyrotracheoesophageal transplantation are equally effective in minimizing airway ischemia. Thyrotracheoesophageal transplantation does not enhance recipient alloimmune response compared with thyrotracheal transplantation alone.