Conductive hearing loss (otitis media) in young children can effect speech and language development. However, little is known about the effects of conductive loss on neural activity in the auditory system. Hypothesis: Conductive hearing loss will change resting activity levels at the inner hair cell synapse, and lead to auditory deprivation of central auditory pathways. A conductive loss was produced by blocking the ear canals in mice. Resting neural activity patterns were quantified in brainstem and midbrain using c-fos immuno-labelling. Experimental subjects were compared to normal hearing controls and subjects with cochlear ablation. Conductive loss subjects showed a trend in reduction in c-fos labelled cells in cochlear nucleus and the central nucleus of inferior colliculus compared to normal controls. Results seen in this study may indicate the influence of conductive hearing loss on the developing auditory brain during early postnatal years when the system is highly plastic.

Conductive hearing loss (otitis media) in young children can effect speech and language development. However, little is known about the effects of conductive loss on neural activity in the auditory system. Hypothesis: Conductive hearing loss will change resting activity levels at the inner hair cell synapse, and lead to auditory deprivation of central auditory pathways. A conductive loss was produced by blocking the ear canals in mice. Resting neural activity patterns were quantified in brainstem and midbrain using c-fos immuno-labelling. Experimental subjects were compared to normal hearing controls and subjects with cochlear ablation. Conductive loss subjects showed a trend in reduction in c-fos labelled cells in cochlear nucleus and the central nucleus of inferior colliculus compared to normal controls. Results seen in this study may indicate the influence of conductive hearing loss on the developing auditory brain during early postnatal years when the system is highly plastic.

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Grâce à la miniaturisation de la technologie ainsi qu'a l'augmentation constante des capacités de calcul numérique, les méthodes objectives et les appareils de mesures de la physiologie auditive évoluent. C'est dans l'optique de créer de nouveaux outils diagnostics que la société Echodia a été créée en 2009. Celle-ci finance aujourd'hui mes recherches sous convention CIFRE.Les présents travaux proposent, dans une première partie, de présenter comment deux méthodes de mesures non invasives ont été mises en oeuvre pour être applicables au diagnostic de l'hydrops cochléaire. Les méthodes sont basées sur le fait que les réponses des cellules ciliées de la cochlée à des stimuli sonores dépendent de la position au repos de leur touffe de stéréocils. Or, l'hydrops cochléaire, l'une des principales caractéristiques de la maladie de Menière, est susceptible de venir perturber cet environnement. Une variation chimique ou mécanique de celui-ci peut ainsi être mise en évidence par différentes méthodes d'exploration objectives. La première est basée sur un enregistrement électrophysiologique. En étudiant le Potentiel de sommation (SP) de l'ÉlectroCochléoGraphie (ECochG), nous allons recueillir une image du tour basal de la cochlée. La deuxième méthode est basée sur un enregistrement acoustique dans le méat acoustique externe. En monitorant le déphasage des Produits de distorsion desoto-émissions acoustiques (DPOAE), nous allons enregistrer les réponses du tour apical de la cochlée.La deuxième partie est consacrée à une étude au cours de laquelle nous avons enregistré de manière concomitante le SP (basal) ainsi que le DPOAE (apical) chez 73 patients souffrant de vertiges de Menière, à proximité d'une attaque (n = 40) ou entre les attaques, sans symptômes cliniques (n = 33). Dans le cas des DPOAE, c'est la phase du produit de distorsion (PDA) à 2*f1-f2 qui a été étudiée en réponse à des sons stimulants de fréquence f1 = 1 kHz et f2 = 1,2 kHz. La puissance des deux fondamentaux a été fixée entre 70 et 75dB SPL en fonction du niveau du DPOAE. Le rapport entre SP et le Potentiel d’action global (AP) a, quant à lui, été mesuré de manière extra-tympanique en réponse à des clics de 95dB nHL. Ces deux mesures ont été effectuées plusieurs fois pendant un test de posture afin d'évaluer leur stabilité.Les limites normales de déphasage du DPOAE en réponse à la posture [-18 °, +38 °] ont été dépassées chez 75% des patients étant venus consulter à proximité d'une crise. Sur ces mêmes sujets, l'étude du ratio entre SP et AP a dépassé la valeur normale (<0,40) dans 60% des cas. De plus, chez les patients à proximité d'une crise de vertige, les deux types de mesures révèlent des fluctuations entre deux répétitions. Ces écarts mettent en évidence combien l'hydrops entrave le bon fonctionnement de la mécanique cochléaire. Le fait de constater des variations sur des échelles de temps aussi courtes pourrait expliquer la sensibilité imparfaite des tests diagnostics. En effet, les protocoles de mesure du SP ou des DPOAE nécessitent un moyennage des acquisitions qui, par définition, a tendance à niveler les fluctuations transitoires. / Thanks to technology miniaturization as well as digital computing abilities steadily increasing, objective measurement methods and their related devices evolve. Echodia company was created in 2009 with the goal to create new diagnostic tools. The company currently supports my research work through a CIFRE convention.The first part of this thesis presents two non-invasive measurement methods that have been implemented to the diagnosis of cochlear hydrops. The methods are based on the responses of cochlear hair cells to sound stimuli, depending themselves on the resting position of their stereocilia bundles. Cochlear hydrops, a hallmark of Meniere's disease, is likely to disturb this environment. A chemical or mechanical variation of this environment may be observed by various objective exploration methods. The first method is based on an electrophysiological recording. By studying the Summating Potential (SP) of the Electrocochleography (ECOG) we will register activity in the basal part of the cochlea. The second method is based on a sound recording in the external acoustic meatus. By monitoring the phase shifts of Distortion-Product OtoAcoustic Emissions (DPOAE), we will record the apical responses of the cochlea.The second part of this thesis focuses on a study in which we recorded concomitantly the SP (basal) and the DPOAE (apical) in 73 patients with Menière's disease, close to an attack (n = 40) or between attacks without clinical symptoms (n = 33). In the case of DPOAE, the phase at 2*f1-f2 has been studied in response to pure sinusoidal sounds at frequency f1 = 1 kHz and f2 = 1,2 kHz. The power of the two primary was set between 70 and 75dB SPL based on the level of the DPOAE. The SP to Action Potential (AP) ratio has been measured by extra-tympanic electrode in response to 95dB nHL clicks. These two measurements were performed several times during a postural test to evaluate their stability.The normal limit of the phase shift of the DPOAE during a postural test [-18 °, +38 °] was exceeded in 75% of patients near an attack. On these subjects, the study of the SP/AP ratio exceeded the normal value (<0.40) in 60% of cases. In addition, the two types of measurements made on patients near a vertigo attack reveal fluctuations between reiteration. These differences highlight how hydrops hinders the proper functioning of the cochlear mechanics. This short time scales fluctuations might explain the imperfect diagnostic sensitivity of SP and DPOAE tests, as averaging procedures would tend to level out transient fluctuations characteristic of hydrops.

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Inspired by the roles of hair cells in nature, this study aims to develop and characterize two new sets of novel flow sensors. One set of sensors developed and studied in this work are flow sensors fabricated using carbon nanomaterials. These sensors are made by embedding carbon nanotubes (CNT) and carbon nanohorns (CNH) into a polymeric substrate and then tested by flowing a conductive aqueous solution over the surface of the exposed CNT and CNH. In response, a flow-dependent voltage is generated. The surface coverage and the electrical relationship between the sensor and water is investigated and the voltage measurements of sensors with different levels of resistance were tested in varying fluid velocities. In response to these fluid velocities, the least resistive sensor showed small, but detectable changes in voltages, while higher resistance sensors showed less response. In addition, plasma treatment of the carbon nanomaterial/PDMS films were conducted in order to render the PDMS on the surface hydrophilic and in turn to pull more fluid towards the carbon material. This showed to improve the sensitivity of the flow sensors. This work also builds on previous research by investigating the flow dependent electrical response of a "skin"-encapsulated artificial hair cell in an aqueous flow. An artificial cell membrane is housed in a flexible polyurethane substrate and serves as the transduction element for the artificial hair cell. Flow experiments are conducted by placing the bio-inspired sensor in a flow chamber and subjecting it to pulse-like flows. This study demonstrates that the encapsulated artificial hair cell flow sensor is capable of sensing changes in flow through a mechanoelectrical response and that its sensing capabilities may be altered by varying its surface morphology. Furthermore, the sensor's response and dynamics as a function of its surface morphology and structural properties are investigated through synchronized motion tracking of the hair with a laser vibrometer and current measurements across the artificial cell membrane. / Master of Science

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