Browsing by Author "Parente, Marco P. L."
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- 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 sound transmission from outer to inner earPublication . Areias, Bruno; Santos, Carla; Natal Jorge, Renato M; Gentil, Fernanda; Parente, Marco P. L.The ear is one of the most complex organs in the human body. Sound is a sequence of pressure waves, which propagates through a compressible media such as air. The pinna concentrates the sound waves into the external auditory meatus. In this canal, the sound is conducted to the tympanic membrane. The tympanic membrane transforms the pressure variations into mechanical displacements, which are then transmitted to the ossicles. The vibration of the stapes footplate creates pressure waves in the fluid inside the cochlea; these pressure waves stimulate the hair cells, generating electrical signals which are sent to the brain through the cochlear nerve, where they are decoded. In this work, a three-dimensional finite element model of the human ear is developed. The model incorporates the tympanic membrane, ossicular bones, part of temporal bone (external auditory meatus and tympanic cavity), middle ear ligaments and tendons, cochlear fluid, skin, ear cartilage, jaw and the air in external auditory meatus and tympanic cavity. Using the finite element method, the magnitude and the phase angle of the umbo and stapes footplate displacement are calculated. Two slightly different models are used: one model takes into consideration the presence of air in the external auditory meatus while the other does not. The middle ear sound transfer function is determined for a stimulus of 60 dB SPL, applied to the outer surface of the air in the external auditory meatus. The obtained results are compared with previously published data in the literature. This study highlights the importance of external auditory meatus in the sound transmission. The pressure gain is calculated for the external auditory meatus.
- 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.