Patient-specific models of human trachea to predict mechanical consequences of endoprosthesis implantation

Nowadays, interventions associated with the implantation of tracheal prostheses in patients with airway pathologies are very common. This surgery may promote problems such as migration of the prosthesis, development of granulation tissue at the edges of the stent with overgrowth of the tracheal lumen or accumulation of secretions inside the prosthesis. Among the movements that the trachea carries out, swallowing seems to have harmful consequences for the tracheal tissues surrounding the prosthesis. In this work, a finite-element-based tool is presented to construct patient-specific tracheal models, introducing the endotracheal prosthesis and analysing the mechanical consequences of this surgery during swallowing. A complete description of a patient-specific tracheal model is given, and a fully experimental characterization of the tracheal tissues is presented. To construct patient-specific grids, a mesh adaptation algorithm has been developed and the implantation of a tracheal prosthesis is simulated. The ascending deglutition movement of the trachea is recorded using real data from each specific patient from fluoroscopic images before and after implantation. The overall behaviour of the trachea is modified when a prosthesis is introduced. The presented tool has been particularized for two different patients (patient A and patient B), allowing prediction of the consequences of this kind of surgery. In particular, patient A had a decrease of almost 30 per cent in his ability to swallow, and an increase in stresses that were three times higher after prosthesis implantation. In contrast, patient B, who had a shorter trachea and who seemed to undergo more damaging effects, did not have a significant reduction in his ability to swallow and did not present an increase in stress in the tissues. In both cases, there are clinical studies that validate our results: namely, patient A underwent a further intervention whereas the outcome of patient B's surgery was completely successful. Notwithstanding the fact that there are a lot of uncertainties relating to the implantation of endotracheal prostheses, the present work gives a new insight into these procedures, predicting their mechanical consequences. This tool could be used in the future as pre-operative planning software to help thoracic surgeons in deciding the optimal prosthesis as well as its size and positioning.

Experimental characterization and constitutive modeling of the mechanical behavior of the human trachea

BACKGROUND AND AIMS

Cartilage and smooth muscle constitute the main structural components of the human central airways, their mechanical properties affect the flow in the trachea and contribute to the biological function of the respiratory system. The aim of this work is to find out the mechanical passive response of the principal constituents of the human trachea under static tensile conditions and to propose constitutive models to describe their behavior.

METHODS

Histological analyses to characterize the tissues and mechanical tests have been made on three human trachea specimens obtained from autopsies. Uniaxial tensile tests on cartilaginous rings and smooth muscle were performed. Tracheal cartilage was considered an elastic material and its Young's modulus and Poisson's coefficient were determined fitting the experimental curves using a Neo-Hookean model. The smooth muscle was proved to behave as a reinforced hyperelastic material with two families of collagen fibers, and its non-linearity was investigated using the Holzapfel strain-energy density function for two families of fibers to fit the experimental data obtained from longitudinal and transversal cuts.

RESULTS

For cartilage, fitting the experimental curves to an elastic model, a Young's modulus of 3.33 MPa and nu=0.49 were obtained. For smooth muscle, several parameters of the Holzapfel function were found out (C(10)=0.877 kPa, k(1)=0.154 kPa, k(2)=34.157, k(3)=0.347 kPa and k(4)=13.889) and demonstrated that the tracheal muscle was stiffer in the longitudinal direction.

CONCLUSION

The better understanding of how these tissues mechanically behave is essential for a correct modeling of the human trachea, a better simulation of its response under different loading conditions, and the development of strategies for the design of new endotracheal prostheses.

[Functional outcome after resection followed by a coloanal anastomosis for cancer of the rectum]

The aim of the study was to asseses the operative, functional results of total proctectomy with coloanal anastomosis (CAA). Between 1990 and 2002, 24 patients (14 males and 10 females ) with a mean age of 50,6 years were operated on for cancer of the rectum and they underwent a total proctectomy with CAA. There was one operative death. 3 patients developed non specific complications. 4 patients experienced a supra anastomosis stenosis and underwent a new straight CAA Functional outcome were evaluated by a scoring system fonction and were considered good in 87 and 84% at 1 and 2 years respectively. Low anterior resection combined with CAA provides good treatment for mid-rectal cancers and for some distal rectal cancers. It had a good functional outcome. However Both procedures and selection of patients who underwent radiotherapy must be carefully performed.

[Colon cancer. Study of 153 cases and comparison with a series of 140 historic cases]

The authors study the epidemiological, diagnostic and therapeutic features of 153 consecutive cases of colon cancers collected between 1985 and 1998. They compare the results with those of a previous study performed in the same hospital service (140 cases between 1966 and 1984). It is a series of 79 men and 74 women (sex ratio = 1.07). The mean age was 56.6 +/- 14 years old with 13.7% of the patients who were less than 40 years old. The operability and the resectability were respectively 98.7% and 83.7% with a global operative mortality of 7.9%. According to the Dukes classification, they were 2 A stages, 73 B stages, 32 C stages and 45 D stages. Starting from 1993, 53% of the C stages an 48% of the B stages had an adjuvant chemotherapy. The comparison between our present results and those of our previous series does not show any modification in what regards the mean age, the cancer frequency in young people, the complicated forms proportion and time needed for the diagnosis by comparison to the beginning of symptomatology. The colic cancer prognostic improvement is attained through an earlier diagnosis, making it possible to reduce the developed forms and the complicated forms proportion, the consequence of which is the operative mortality decrease and the log-range survival increase.

[Neuroendocrine carcinoma in Barrett's esophagus. Report of a case]

The neuroendocrine tumours of the oesophagus are exceptional. They are a spectrum of heterogeneous tumours often not clearly defined in the literature. We report a case of moderately differentiated neuroendocrine tumour of the oesophagus arising from Barrett's mucosa in 51-year-old man treated surgically and who was free of disease 28 months after excision. We discuss about this case, the classification, the histogenesis and therapeutic approaches of these tumours.