Browsing by Author "Jorge, Renato M. Natal"
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- Biomechanics of the vestibular system: a numerical simulationPublication . Santos, Carla F.; Belinha, Jorge; Gentil, Fernanda; Parente, Marco; Jorge, Renato M. NatalThe vestibular system is located in the posterior portion of the inner ear. It is a key component to our sense of balance and movement. Any changes in this system can cause effects or symptoms such as dizziness, blurred vision, imbalance, and nausea, which are vertiginous syndrome indicators. Vertigo is reported as one of the most common symptoms in the world. It is considered the third most frequent complaint in medicine, transmitting a sense of inadequacy and insecurity. The aim of this work is to contribute to a better understanding of how the vestibular system works. This knowledge will help in the development of new techniques that will facilitate a more effective rehabilitation. Vestibular rehabilitation consists of a set of exercises, known as maneuvers, which can reduce and even eliminate symptoms of dizziness and imbalance associated with a vestibular disorder. In this work, a three-dimensional computational model of the vestibular system, containing the fluids promoting the body balance, will be presented. The smoothed-particle hydrodynamics (SPH) method will be used to simulate the fluid behavior. The results provide a better comprehension of the biomechanics of the vestibular system, which contribute to recover from any system disorders.
- Estudo do efeito do atrito no contacto entre os ossículos do ouvido médicoPublication . Gentil, Fernanda; Jorge, Renato M. Natal; Ferreira, António J. Mendes; Parente, Marco P. Lages; Moreira, Miguel; Almeida, Eurico deO sistema auditivo comporta complexos fenómenos, entre eles o biomecânico. O ouvido médio é constituído pelos ossículos, martelo, bigorna e estribo, dos quais derivam ligamentos, músculos e tendões. A energia sonora é captada pelo pavilhão, canal auditivo externo e tímpano, sendo transformada em energia mecânica e transmitida aos ossículos. Neste trabalho efectuou-se a modelação do ouvido médio e respectivos ligamentos pelo Método dos Elementos Finitos, sendo a ligação entre ossículos efectuada por um modelo de contacto. A modelação dos ligamentos foi realizada pela utilização de uma formulação material baseada num modelo hiperelástico. Efectuaram-se estudos relativamente aos campos de deslocamentos, na membrana timpânica e na platina do estribo, assim como, as rotações verificadas na platina do estribo. Analisou-se ainda o campo de tensões induzidas nos ligamentos ao exterior da cadeia ossicular. Os estudos foram realizados para vários coeficientes de atrito entre os ossículos e para diferentes valores de pressão aplicados à membrana timpânica. A análise dos resultados obtidos permitiu concluir que a simulação da ligação entre os ossículos pode ser abordada com base numa formulação de contacto com atrito, podendo ser considerada como uma ligação quase rígida.
- A finite element model to predict the consequencesof endolymphatic hydrops in the basilar membranePublication . Areias, Bruno; Parente, Marco P. L.; Gentil, Fernanda; Caroça, Cristina; Paço, João; Jorge, Renato M. NatalMénière's disease is an inner ear disorder, associated with episodes of vertigo,fluctuant hearing loss, tinnitus, and aural fullness. Ménière's disease is associ-ated with endolymphatic hydrops. Clinical evidences show that this disease isoften incapacitating, negatively affecting the patients' everyday life. The patho-genesis of Ménière's disease is still not fully understood and remains unclear.Previous numerical studies available in the literature related with endolym-phatic hydrops, are very scarce. The present work applies the finite elementmethod to investigate the consequences of endolymphatic hydrops in the nor-mal hearing, associated with the Ménière's disease. The obtained results forthe steady state dynamics analysis are in accordance with clinical evidences.The results show that the basilar membrane is not affected in the same inten-sity along its length and that the lower frequencies are more affected by theendolymphatic hydrops. From a clinical point of view, this work shows therelationship between the increasing of the endolymphatic pressure andthe development of hearing loss.
- Finite element modelling of the surgical procedure for placement of a straight electrode array: Mechanical and clinical consequencesPublication . Areias, Bruno; Parente, Marco P. L.; Gentil, Fernanda; Jorge, Renato M. NatalA cochlear implant is an electronic device implanted into the cochlea to directly stimulate the auditory nerve. Such device is used in patients with severe-to-profound hearing loss. The cochlear implant surgery is safe, but involves some risks, such as infections, device malfunction or damage of the facial nerve and it can result on a poor hearing outcome, due to the destruction of any present residual hearing. Future improvements in cochlear implant surgery will necessarily involve the decrease of the intra-cochlear damage. Several implant related variables, such as materials, geometrical design, processor and surgical techniques can be optimized in order for the patients to partially recover their hearing capacities The straight electrode is a type of cochlear implant that many authors indicate as being the less traumatic. From the finite element analysis conducted in this work, the influence of the insertion speed, the friction coefficient between the cochlear wall and the electrode array, and several configurations of the cochlear implant tip were studied. The numerical simulations of the implantation showed the same pattern of the insertion force against insertion depth, thus indicating the different phases of the insertion. Results demonstrated that lower insertion speeds, friction coefficients and tip stiffness, led to a reduction on the contact pressures and insertion force. It is expected that these improved configurations will allow to preserve the residual hearing while reducing surgical complications.