Results for “radial basis function network” — Page 16

PubMed1981

Characterization of anisotropic elastic properties of the arteries by exponential and polynomial strain energy functions.

Three-dimensional quasi-static mechanical measurements were carried out on cylindrical segments of the dog carotid and iliac arteries for determination of the passive anisotropic elastic properties of the vessel wall. On the basis of passive characteristics of outer diameter vs. intraluminal pressure, and axial extending force vs. intraluminal pressure, picked up at various fixed initial vascular length values, the incremental Young moduli and poisson ratios of the vessel wall were calculated in the 0--33 kPa (0--250 mm Hg) pressure range. The strain energy function of the arteries was approximated by polynomial and exponential models. We found that an exponential energy function with 4-parameters gives more accurate results than the 7- or 12-parameter polynomial functions. According to the results the axial modulus reaches higher values than the tangential and radial moduli at a low tangential stretch level, while at high tangential stretch the tangential modulus is the highest in both carotid and iliac arteries. After elevation of the initial tangential stretch the increase in the tangential modulus is the most pronounced, while the values of radial and axial moduli increased less. A change in the initial axial stretch influences the axial and radial moduli to a similar extent, but has no substantial effect on the value of the tangential modulus. The values of corresponding poisson ratios depend in a similar way on the initial deformation state. The different behaviour of the two Poisson ratios characterizing the mechanical coupling between tangential and axial directions, indicates that the structural coupling between the two main directions is asymmetrical. It is assumed that this property of the passive vascular structure can be explained by the network arrangement of collagen fibres in the vessel wall.

Animals↗

PubMed2003

Use of radial forearm free flap with palmaris longus tendon in reconstruction of total maxillectomy with sparing of orbital contents.

Nasal paragangliomas are extremely rare. The most adequate treatment is total excision. After surgical excision requiring total maxillectomy, there has been no ideal technique for reconstruction. A 47-year-old man was admitted to our clinic because of recurrent epistaxis, which lasted for 2 months. He was also suffering from nasal airway obstruction. The physical examination revealed a mass originating from the medial aspect of the middle turbinate of the right nasal cavity. It invaded the anterior maxillary wall and hard and soft palate. Endoscopic examination showed that the mass pushed the nasal septum to the left side and protruded into the nasopharynx. The mass was fleshy and had a rich capillary network. Conventional paranasal sinus radiographs were normal. Computerized tomography of the skull showed the mass protruding into the nasopharynx. A total maxillectomy was performed. Histopathological evaluation showed neoplastic tissue consisting of round, oval, or slightly elongated cells, altogether of a rather monomorphous appearance, tending to arrange themselves in clusters adjacent to or around capillary blood vessels. The blood vessels were numerous and branched. Reticulum staining showed a typical Zellballen arrangement of the neoplastic cells to provide a firmer basis for the diagnosis of paraganglioma. To reconstruct the total maxillectomy defect, a radial forearm free flap with the palmaris longus tendon was elevated to inlay the nasal cavity and the oral cavity and to suspend the ocular globe. The flap was placed into the defect, and the palmaris longus tendon was medially and laterally anchored to the periosteum of the frontal bone to suspend the ocular globe in the orbital cavity. One part of the skin island was used to close the defect of the nasal mucosal cavity, and the other part was used to repair the oral mucosal defect of the palate. Consequently, speech was considered near normal; the patient was able to eat an unrestricted diet and to retain both solid and liquid food inside the oral cavity without drooling, and there was no diplopia or enophthalmos. Six months later, porous polyethylene was inserted and fixed to the zygomatic bone with a miniplate and miniscrews to restore malar contour. No further procedure was believed to be necessary later on. Two years later, a satisfactory and functional esthetic result was obtained, providing an acceptable suspension of the ocular globe and filling of the total maxillectomy defect. We believe that a total maxillectomy is indicated if it is needed in nasal paragangliomas and that microsurgical repair with the composite radial forearm-palmaris longus free flap has several advantages: 1) it can offer en bloc reconstruction of the entire defect after a total maxillectomy in terms of good function and cosmesis; 2) it can repair mucosal defects; and 3) it can anchor and suspend the ocular globe in its original anatomical location, protecting against gravity through the sling effect of the palmaris longus tendon. The composite radial forearm-palmaris longus free flap has not been described previously for suspension of the ocular globe.

Biocompatible Materials↗