Cryopreserved tracheal grafts have been used in several experimental models of long segment replacement. The clinical application of the procedure has been limited due to the fact that contradictory results have been reported. The purpose of this article is to present a review of the literature on tracheal cryopreservation. Despite the fact that most authors indicate that cryopreserved tracheal allografts retain viability and have a low immunological response, though they continue to function after transplantation with good epithelialization and patency, cryopreservation leads to significant damage to cartilage, the degree of which is based on the freezing-storage methods that affect the function and durability of a graft. The long-term storage of cartilage must therefore be investigated in more detail in basic research models of cartilage viability: the evaluation of chondrocyte apoptosis, and the use of different solutions for tracheal cryopreservation other than RPMI-1640, Dulbecco's modified Eagle's, Eurocollins, and TC-199. Furthermore, problems that involve improving the blood supply to the graft after extensive resection and immunosuppression must be resolved before tracheal cryopreservation can become a clinically established method for tracheal grafts.

Postsurgical tracheal stenosis results from fibrosis formation due to ischemia. There are healing modulators, hyaluronic acid (HA) and collagen polyvinylpyrrolidone (CPVP), which reduce collagen fibers formation. Thus we can hypothesize that the topical application of one of these modulators can diminish postsurgical tracheal scarring and stenosis. The aim of this work was to evaluate the macroscopic, microscopic, and biochemical changes of tracheal healing after the application of HA or CPVP in a canine tracheoplasty model. The study design was prospective experimental investigation in a canine model. Eighteen mongrel dogs underwent three cervical tracheal rings resection and end-to-end anastomosis. They were randomized into three groups according to treatment: group I (control group) (n = 6), topical application of saline solution on tracheal anastomosis; group II (n = 6), topical application of 15 microg HA on tracheal anastomosis; and group III (n = 6), topical application of 2.5 mg CPVP on tracheal anastomosis. They were evaluated clinical, radiological and tracheoscopically during 4 weeks. They were euthanized at the end of the study time. Macroscopic, microscopic, and biochemical changes of tracheal anastomosis healing were analyzed. Collagen formation was quantified by the Woessner method. All the animals survived the surgical procedure and study period. Macroscopic, radiologic, and endoscopic studies showed that animals in group I developed tracheal stenosis, inflammation, and firm fibrous tissue formation, and histological studies also showed severe inflammatory reaction and fibrosis formation. Groups II (HA) and III (CPVP) showed well-organized thin collagen fibers with minimal inflammatory response. Biochemical evaluation revealed a higher collagen concentration in group I animals (analysis of variance [ANOVA] p < .05 and Tukey p < .01). Thus, hyaluronic acid or collagen polyvinylpyrrolidone administered after tracheal anastomosis diminished the degree of stenosis and inflammatory reaction. Both modulators improved tracheal healing.

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Tracheal stenosis (TS) is a fibrosis originated by prolonged inflammation and increased transforming growth factor beta 1 (TGF-β1) expression and collagen deposition (CD) in the tracheal wound. Several wound-healing modulators (WHMs) have been used to modulate the tracheal healing process and prevent TS, but they have failed, justifying the need to evaluate alternative WHM. The pirfenidone (PFD) and collagen-polyvinylpyrrolidone (Collagen-PVP) decrease inflammation and fibrosis. This study assessed the effect of PFD administration and Collagen-PVP topical application on macroscopic and microscopic changes, TGF-β1 expression, and CD in an experimental model of tracheal wound healing. Forty Wistar rats underwent cervical tracheoplasty, were divided into 4 groups (n = 10), and were treated with different WHM: group I, saline solution (SS); group II, Collagen-PVP; group III, mitomycin C (MMC); and group IV, 40 mg/kg PFD. Four weeks after surgery, the macroscopic and microscopic changes, in situ TGF-β1 expression, and CD in posttracheoplasty scars were evaluated. The animals treated with Collagen-PVP and PFD developed less inflammation and fibrosis than animals in the other study groups (p < 0.05, Kruskal-Wallis) and, moreover, showed lower TGF-β1 expression and CD than animals in group I (p < 0.05, ANOVA and Tukey's test). In conclusion, PFD and Collagen-PVP decrease inflammation, fibrosis, TGFβ-1 expression, and CD in the posttracheoplasty rats' scar.

Glutaraldehyde-preserved bovine pericardium (GPBP) is evaluated as a bioprosthesis for the reconstruction of surgical defects in the thoracoabdominal wall. The mechanical properties of bovine pericardium preserved at different concentrations of glutaraldehyde were studied. Samples preserved in 0.5% glutaraldehyde showed a significantly higher tensile strength (11.7 +/- 0.8 N/mm2) than samples preserved in 2.5, 5, or 10% (similar to pericardium preserved in normal saline). The percentage of elongation was significantly lower than samples preserved in 1, 2.5, and 5% glutaraldehyde. GPBP at 0.5% was used to repair experimentally induced defects of the abdominal wall (n = 9), chest wall (n = 6), diaphragm (n = 6), and sternum (n = 7). All animals presented adequate tolerance to the material used and no case of infection or rejection of the material was seen in any of the animals. Finally, 0.5% GPBP was used clinically in a series of 40 patients: postincisional abdominal hernia (n = 30), inguinal hernia (n = 8), diaphragmatic hernia (n = 1), and congenital pelvic defect with prolapse of abdominal organs (n = 1). Surgical use showed that GPBP was a very manageable material and long-term results were good in 37 patients with a mean follow up of 18 months (range 5-35 months). Six patients presented seroma formation (all abdominal hernia patients), three of which eventually developed infection and had the GPBP patch removed at 3, 5, and 7 months postoperatively. The rest of the patients presented good scar formation with adequate resistance at the area of implantation. GPBP is a biological material with sufficient resistance to be used surgically in the repair of thoracoabdominal defects. Ideal concentration of glutaraldehyde to be used in the preparation-preservation of the material is 0.5% since higher concentration negatively affect its tensile rupture strength and elongation.

Cryopreservation has an immunomodulating effect on tracheal tissue as a result of class II antigen depletion due to epithelium exfoliation. However, not all epithelium is detached. We evaluated the role of apoptosis in the remaining epithelium of 30 cryopreserved tracheal grafts. Caspase-3 immunoreactivity of tracheal epithelium was studied in canine tracheal segments cryopreserved with F12K medium, with or without subsequent storage in liquid nitrogen at -196°C for 15 days. Loss of structural integrity of tracheal mixed glands was observed in all cryopreserved tracheal segments. Caspase-3 immunoreactivity in tracheal mucosa and in mixed glands was significantly decreased, in contrast to the control group and to cryopreserved tracheal segments in which it remained high, due to the effect of storage in liquid nitrogen (P < 0.05, ANOVA and Tukey test). We conclude that apoptosis can be triggered in epithelial cells during tracheal graft harvesting even prior to cryopreservation, and although the epithelial caspase-3 immunoreactivity is reduced in tracheal cryopreservation, this could be explained by increased cell death. Apoptosis cannot be stopped during tracheal cryopreservation

A 2.5-cm nasal septal perforation was performed in 18 pigs and repaired as follows: group I (n = 6), septal perforation without treatment; group II (n = 6), surgical repair with interpositional graft of glutaraldehyde-preserved bovine pericardium (GPBP); group III (n = 6), surgical repair with interpositional graft of lyophilized GPBP (LGPBP). The animals were evaluated clinically and radiologically (x-ray and CT scan) 2 days before surgery, daily during the first postoperative week, and weekly during the next 6 months. At the end of the study the animals were euthanized with an overdose of pentobarbital. Macroscopic and microscopic examination of the grafts and nasal septum was performed. All the animals survived the surgical procedure. Five pigs in group I showed persistence of the septal perforation. All the animals in groups II and III showed total closure of the septal perforation, with the presence of fibrotic tissue on the pericardial grafts as well as in the septal cartilage, and overall good healing. In conclusion, GPBP and LGPBP are adequate materials that can be used as interpositional grafts in the surgical closure of septal perforations in pigs

The use of dry gases during mechanical ventilation has been associated with the risk of serious airway complications. The goal of the present study was to quantify the plasma levels of TNF-alpha and IL-6 and to determine the radiological, hemodynamic, gasometric, and microscopic changes in lung mechanics in dogs subjected to short-term mechanical ventilation with and without humidification of the inhaled gas. The experiment was conducted for 24 hours in 10 dogs divided into two groups: Group I (n = 5), mechanical ventilation with dry oxygen dispensation, and Group II (n = 5), mechanical ventilation with oxygen dispensation using a moisture chamber. Variance analysis was used. No changes in physiological, hemodynamic, or gasometric, and radiographic constants were observed. Plasma TNF-alpha levels increased in group I, reaching a maximum 24 hours after mechanical ventilation was initiated (ANOVA p = 0.77). This increase was correlated to changes in mechanical ventilation. Plasma IL-6 levels decreased at 12 hours and increased again towards the end of the study (ANOVA p>0.05). Both groups exhibited a decrease in lung compliance and functional residual capacity values, but this was more pronounced in group I. Pplat increased in group I (ANOVA p = 0.02). Inhalation of dry gas caused histological lesions in the entire respiratory tract, including pulmonary parenchyma, to a greater extent than humidified gas. Humidification of inspired gases can attenuate damage associated with mechanical ventilation.