RESUMEN
BACKGROUND: Simple or non-syndromic types of oval window (OW) or round window (RW) atresia are relatively rare in clinical. Few studies have assessed bone conduction (BC) hearing in OW or RW atresia patients, with some reporting that BC hearing lies within the normal range, whereas others observing impaired BC hearing. AIMS/OBJECTIVES: This study explored the effect of blocking the OW and RW during BC in cat models. MATERIAL AND METHODS: Twenty-four cats were randomly divided into three immobilization groups (OW blockage, RW blockage, and OW + RW blockage) and control group. Each immobilization group also had the initial control state before blockage. Medical adhesive and ear mould glue were used to immobilise the stapes footplate and RW, respectively. Comparisons were made of the auditory brainstem response (ABR) thresholds before and after immobilization for the three immobilization groups during three different stimuli [air conduction (AC) click, BC click, and BC pure tones]. RESULTS: The AC click thresholds increased after immobilisation in three experimental groups compared to the control group (p < .05). The AC click thresholds increased compared to their initial control state after all three immobilization groups (p < .05). With an increase in frequency from 2 to 8 kHz, there was a general decrease in the difference between pre- and post-immobilization BC hearing thresholds in all three immobilization groups. The BC click threshold and BC tone thresholds at 2-4 kHz in both OW blockage and OW + RW blockage groups exceeded those in RW blockage group (p < .05). CONCLUSIONS AND SIGNIFICANCE: The use of medical adhesive and ear mould glue for the blockages of OW and RW, respectively in cats was feasible. The effect of blocking the OW and RW in BC hearing was larger at low frequencies than high frequencies between 2 and 8 kHz. OW blockage had a greater effect than RW blockage on BC hearing at 2-4 kHz range.
Asunto(s)
Conducción Ósea/fisiología , Ventana Oval/fisiología , Ventana Redonda/fisiología , Animales , Gatos , Distribución AleatoriaRESUMEN
Bone conduction (BC) hearing relies on sound vibration transmission in the skull bone. Several clinical findings indicate that in the human, the skull vibration of the inner ear dominates the response for BC sound. Two phenomena transform the vibrations of the skull surrounding the inner ear to an excitation of the basilar membrane, (1) inertia of the inner ear fluid and (2) compression and expansion of the inner ear space. The relative importance of these two contributors were investigated using an impedance lumped element model. By dividing the motion of the inner ear boundary in common and differential motion it was found that the common motion dominated at frequencies below 7 kHz but above this frequency differential motion was greatest. When these motions were used to excite the model it was found that for the normal ear, the fluid inertia response was up to 20 dB greater than the compression response. This changed in the pathological ear where, for example, otosclerosis of the stapes depressed the fluid inertia response and improved the compression response so that inner ear compression dominated BC hearing at frequencies above 400 Hz. The model was also able to predict experimental and clinical findings of BC sensitivity in the literature, for example the so called Carhart notch in otosclerosis, increased BC sensitivity in superior semicircular canal dehiscence, and altered BC sensitivity following a vestibular fenestration and RW atresia.
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Conducción Ósea/fisiología , Oído Interno/fisiología , Modelos Biológicos , Fenómenos Biomecánicos , Cóclea/fisiología , Impedancia Eléctrica , Humanos , Líquidos Laberínticos/fisiología , Ventana Oval/fisiología , Ventana Redonda/fisiología , VibraciónRESUMEN
The annular ligament provides a compliant connection of the stapes to the oval window. To estimate the stiffness characteristics of the annular ligament, human temporal bone measurements were conducted. A force was applied sequentially at several points on the stapes footplate leading to different patterns of displacement with different amounts of translational and rotational components. The spatial displacement of the stapes footplate was measured using a laser vibrometer. The experiments were performed on several stapes with dissected chain and the force was increased stepwise, resulting in load-deflection curves for each force application point. The annular ligament exhibited a progressive stiffening characteristic in combination with an inhomogeneous stiffness distribution. When a centric force, orientated in the lateral direction, was applied to the stapes footplate, the stapes head moved laterally and in the posterior-inferior direction. Based on the load-deflection curves, a mechanical model of the annular ligament was derived. The mathematical representation of the compliance of the annular ligament results in a stiffness matrix with a nonlinear dependence on stapes displacement. This description of the nonlinear stiffness allows simulations of the sound transfer behavior of the middle ear for different preloads.
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Ligamentos/fisiología , Modelos Biológicos , Ventana Oval/fisiología , Estribo/fisiología , Fenómenos Biomecánicos , Elasticidad , Humanos , Técnicas In Vitro , Movimiento , Dinámicas no Lineales , Presión , Estrés Mecánico , Hueso Temporal/fisiología , Factores de TiempoRESUMEN
Time-domain numerical solutions of a nonlinear active cochlear model forced by click stimuli are analyzed with a time-frequency wavelet technique to identify the components of the otoacoustic response associated with different generation mechanisms/places. Previous experimental studies have shown evidence for the presence of at least two components in the transient otoacoustic response: A long-latency response, growing compressively with increasing stimulus level, and a shorter-latency response, characterized by faster growth. The possible mechanisms for the generation of the two components are discussed using the results of the numerical simulations. The model is a one-dimensional (1-D) transmission line model with nonlinear and nonlocal active terms representing the anti-damping action of the "cochlear amplifier." The dependence on the stimulus level of latency and level was measured for the different components of the response. The generation mechanisms/places of the different components were identified by varying the stimulus level and by turning off the cochlear roughness in well-defined cochlear regions. The results suggest that reflections from roughness coming from basal regions of the cochlea may give a relevant contribution to the early otoacoustic response, whereas nonlinear mechanisms seem to produce a much smaller additional contribution.
Asunto(s)
Cóclea/fisiología , Simulación por Computador , Dinámicas no Lineales , Emisiones Otoacústicas Espontáneas/fisiología , Tiempo de Reacción/fisiología , Membrana Basilar/fisiología , Células Ciliadas Auditivas Externas/fisiología , Humanos , Ventana Oval/fisiología , Espectrografía del SonidoRESUMEN
OBJECTIVES: As prostheses and techniques related to stapes surgery develop and improve, there is a need to assess the functional outcomes of the surgery objectively. This study provides a bench test method to assess the functional results of stapes surgery by measuring volume displacement at the round window (RW), which is closely related to pressure propagation of the travelling wave inside the cochlea and thus to hearing. DESIGN: Motion of the RW membrane in fresh temporal bones was measured using a scanning laser Doppler interferometry system for normal and reconstructed conditions, and the performance of the reconstruction with stapes surgery was quantitatively assessed by comparison of the volume displacements at the RW between the two conditions. To obtain optimal measurements, reflectivity of the laser beam of the scanning laser Doppler interferometry system was improved by retroreflective beads coated onto the surface of the RW, and orientation of the RW membrane relative to the laser beam was obtained using micro-computed tomography imaging. RESULTS: From measurements in 12 temporal bones, difference in the RW volume displacement between normal ears and ears reconstructed with stapes surgery was approximately 15 dB below 2 kHz and approximately 10 dB above 4 kHz, which was comparable with air-bone gaps in patients after stapes surgery. Two different sizes of the stapes prostheses were also tested (n = 3), and a tendency toward a better outcome with a larger diameter was found. CONCLUSION: The method developed in this study can be used to assess various prostheses and surgical conditions objectively in controlled laboratory environments. It may also have potential for providing ways to assess other middle- and inner-ear surgeries, and to study other aspects of hearing science.
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Interferometría/métodos , Prótesis Osicular , Ventana Oval/fisiología , Ventana Redonda/fisiología , Cirugía del Estribo/métodos , Hueso Temporal/fisiología , Estudios de Casos y Controles , Femenino , Audición/fisiología , Pruebas Auditivas , Humanos , Masculino , Persona de Mediana Edad , Movimiento (Física) , Ventana Oval/fisiopatología , Ventana Redonda/fisiopatología , Sonido , Hueso Temporal/fisiopatologíaRESUMEN
Stapedial annular ligament (SAL) provides a sealed but mobile boundary between the stapes footplate and oval window bony wall. Mechanical properties of the SAL affect the transmission of ossicular movement into the cochlea in sound conduction. However, the mechanical properties of this tissue have never been investigated due to its complexity. In this paper, we report measurement of the viscoelastic properties of SAL on human cadaver temporal bones using a micro-material testing system with digital image correlation analysis. The measured load-deformation relations of SAL samples were converted into shear stress-shear strain relationship, stress relaxation function, and ultimate shear stress and shear strain of the SAL. The hyperelastic Ogden model was used to describe constitutive behavior of the SAL and a 3D finite element model of the experimental setup with SAL was created for assessing the effects of loading variation and measurement errors on results. The study demonstrates that the human SAL is a typical viscoelastic material with hysteresis, nonlinear stress-strain relationship and stress relaxation function. The shear modulus changes from 3.6 to 220 kPa when the shear stress increases from 2 to 140 kPa. These results provide useful information on quasi-static behavior of the SAL.
Asunto(s)
Ligamentos , Fenómenos Mecánicos , Estribo , Anciano , Anciano de 80 o más Años , Fenómenos Biomecánicos , Femenino , Análisis de Elementos Finitos , Humanos , Ligamentos/fisiología , Masculino , Ensayo de Materiales , Persona de Mediana Edad , Ventana Oval/fisiología , Estribo/fisiología , Estrés Mecánico , Hueso Temporal/fisiologíaRESUMEN
OBJECTIVE: The present study defines the extent of bone conduction loss that can be accounted for by stapes fixation. STUDY DESIGN: Prospective clinical evaluation. SETTING: Tertiary. PATIENTS: Two hundred consecutively operated cases. All patients have been operated by the first author. INTERVENTION: Posterior partial stapedectomy with a platinum-Teflon piston over a perichondral graft. MAIN OUTCOME MEASURES: The bone conduction is studied preoperatively, 1 week, 1 month, and 1 year after surgery. RESULTS: There are at least 3 postoperative gain patterns that change with time, from 1 week to 1 year after surgery. These are patients with maximum gain at 1, 2, and 4 kHz. CONCLUSION: The results suggest that these changes are due to the relation of the preoperative and postoperative oval window transfer functions. The gain in the 3 postoperative audiometric thresholds can be approximated by looking at the characteristics of the preoperative bone conduction audiogram.
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Conducción Ósea/fisiología , Otosclerosis/cirugía , Cirugía del Estribo , Adulto , Audiometría , Audiometría de Tonos Puros , Interpretación Estadística de Datos , Femenino , Humanos , Masculino , Ventana Oval/fisiología , Ventana Oval/cirugía , Resultado del TratamientoRESUMEN
In recent years, evidence has accumulated in support of a two-source model of distortion product otoacoustic emissions (DPOAEs). According to such models DPOAEs recorded in the ear canal are associated with two separate sources of cochlear origin. It is the interference between the contributions from the two sources that gives rise to the DPOAE fine structure (a pseudoperiodic change in DPOAE level or group delay with frequency). Multiple internal reflections between the base of the cochlea (oval window) and the DP tonotopic place can add additional significant components for certain stimulus conditions and thus modify the DPOAE fine structure. DPOAEs, at frequency increments between 4 and 8 Hz, were recorded at fixed f2/f1 ratios of 1.053, 1.065, 1.08, 1.11, 1.14, 1.18, 1.22, 1.26, 1.30, 1.32, 1.34, and 1.36 from four subjects. The resulting patterns of DPOAE amplitude and group delay (the negative of the slope of phase) revealed several previously unreported patterns in addition to the commonly reported log sine variation with frequency. These observed "exotic" patterns are predicted in computational simulations when multiple internal reflections are included. An inverse FFT algorithm was used to convert DPOAE data from the frequency to the "time" domain. Comparison of data in the time and frequency domains confirmed the occurrence of these "exotic" patterns in conjunction with the presence of multiple internal reflections. Multiple internal reflections were observed more commonly for high primary ratios (f2/f1 > or = 1.3). These results indicate that a full interpretation of the DPOAE level and phase (group delay) must include not only the two generation sources, but also multiple internal reflections.
Asunto(s)
Cóclea/fisiología , Emisiones Otoacústicas Espontáneas/fisiología , Estimulación Acústica , Algoritmos , Conducto Auditivo Externo/fisiología , Análisis de Fourier , Humanos , Ventana Oval/fisiología , Psicoacústica , Valores de Referencia , Procesamiento de Señales Asistido por Computador , Espectrografía del SonidoRESUMEN
In 15 cadaver ears from Norwegian cattle, sound pressure transfer functions have been measured (1) for sound input to the tympanic membrane, (2) for sound input to the oval window with the footplate in place, but with the ossicular chain removed, and (3) for sound input to the oval window with also the footplate removed. The output pressure was measured in an enclosure cemented to the round window. The data allow calculation of equivalent sound pressures at the input positions, as well as the acoustic input impedances at the oval window with intact footplate, Z(sc), and with the footplate removed, Z(c). The difference Z(s)=Z(sc)-Z(c) is the acoustic impedance contribution of the footplate and annular ligament. Z(sc) is mainly determined by the stiffness of the annular ligament at low frequencies, and by the cochlear input impedance Z(c) at higher frequencies. Z(c) is predominately resistive, a minor reactive part at low frequencies is attributed to the stiffness of the round window membrane. Z(s) and Z(c) are equal in magnitude at about 0.4 kHz. Rather close RLC fits have been obtained for all the three impedances, Z(sc), Z(s), and Z(c). The fitted values for the resistive parts of Z(sc) and Z(c) are 62.9 and 58.2 acoustic Gomega, respectively. The relatively small difference, 4.7 Gomega, is attributed to the resistance of the annular ligament. The fitted resistance of Z(s) is somewhat larger, 8.6 Gomega, but is anyway of minor importance relative to the dynamic stiffness of the annular ligament. This stiffness depends on the static pressure difference across the footplate. Each of the averaged Z(sc) corresponds to minimum stiffness. The fitted acoustic compliance is 6.89 x 10(-15) m3/Pa. The acoustic inertance plays a minor role. It is attributed to the mass of the footplate and the co-vibrating liquid in the inner ear, and has a fitted value of 4.7 x 10(5) Pa s2/m3. A sound pressure at the eardrum is equivalent to a larger pressure at the footplate, about 16 dB larger at frequencies below 100 Hz, increasing to about 30 dB at 10 kHz. In the vestibulum at the inner side of the footplate, the sound pressure at 20 Hz is about 20 dB below the equivalent pressure at the outer side. The two pressures approach toward higher frequencies, and above 1 kHz they are nearly equal.
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Pruebas de Impedancia Acústica , Oído Medio/fisiología , Ventana Oval/fisiología , Sonido , Animales , Bovinos , Modelos BiológicosRESUMEN
Changes in ambient pressure can elicit the vertigo and bodily disequilibrium known clinically as alternobaric vertigo. Our previous studies showed that changes in middle ear pressure altered the activity of the primary vestibular neuron, and the finding suggests that the pressure-induced vestibular response causes alternobaric vertigo. To investigate the roles played by the round window (RW) and the oval window (OW) in the vestibular response induced by pressure, we measured the change in perilymphatic pressure and the firing rates of primary vestibular neurons after the application of positive or negative pressure to the middle ear. We found an increase in the pressure-induced vestibular response in the group with a closed OW, and a decrease in the group with a closed RW. Measurements showed that the amplitude of the change in perilymphatic pressure in the group with a closed OW did not differ from that in the control group, whereas the amplitude of the perilymphatic pressure change in the group with a closed RW was significantly reduced. A discrepancy between the number of neurons responding and the amplitude of the perilymphatic pressure change in the closed OW group suggests that the vestibular response induced by the change in middle ear pressure was not related solely to the magnitude of the pressure change in the inner ear, but also involved the oval and round windows.
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Oído Medio/fisiología , Ventana Oval/fisiología , Ventana Redonda/fisiología , Vestíbulo del Laberinto/fisiología , Animales , Distribución de Chi-Cuadrado , Femenino , Cobayas , Neuronas/fisiología , Perilinfa/fisiología , Presión , Estadísticas no Paramétricas , Vértigo/fisiopatologíaRESUMEN
In a type IV tympanoplasty, the stapes footplate is directly exposed to incoming sound while the round window is "shielded," usually with a fascia graft. Postoperative hearing results are quite variable, with air-bone gaps ranging from 10 to 60 dB. A cadaveric human temporal bone preparation was developed to investigate the middle ear mechanics of this operation to identify causes of variable results and to test predictions of a recently described theoretic model of type IV tympanoplasty. The ear canal, tympanic membrane, malleus, and incus were removed so as to expose the stapes and round window to the sound stimulus. A "cavum minor" chamber (air space adjacent to the round window) was constructed around the round window niche. The round window could be isolated from sound by placing an acoustic shield over this chamber. The mechanical properties of the shield, cavum minor, annular ligament, and round window membrane were varied experimentally. Stapes velocity as determined by an optical motion sensor was used as a measure of hearing level. The largest stapes velocity occurred with a mobile stapes and round window, a stiff shield, and a well-aerated cavum minor. Partial fixation of the stapes or round window caused a decrease in stapes velocity. Acoustic shields of conchal cartilage or Silastic silicone rubber sheeting (approximately 1 mm thick) provided near-optimal shielding. A temporalis fascia shield resulted in a stapes velocity 10 to 20 dB less than that seen with a cartilage or Silastic silicone rubber shield at low frequencies. A cavum minor air space as small as 16 microL was sufficient for unrestricted stapes motion, provided the air was in contact with the round window membrane. These results qualitatively matched predictions of our model, but there were some quantitative differences. The clinical implications of our results are that in order to optimize postoperative hearing, the surgeon should 1) preserve normal stapes mobility, preferably by covering the footplate with a very thin split-thickness skin graft, not a fascia graft; 2) reinforce a fascia shield with cartilage or Silastic silicone rubber; 3) create conditions that promote aeration of the round window niche; and 4) preserve the mobility of the round window membrane.
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Oído Medio/cirugía , Timpanoplastia/métodos , Adulto , Anciano , Fenómenos Biomecánicos , Oído Medio/anatomía & histología , Oído Medio/fisiología , Impedancia Eléctrica , Humanos , Técnicas In Vitro , Ligamentos/fisiología , Ensayo de Materiales , Persona de Mediana Edad , Modelos Biológicos , Ventana Oval/fisiología , Presión , Valores de Referencia , Ventana Redonda/fisiología , Elastómeros de Silicona , Estribo/fisiología , Timpanoplastia/instrumentaciónRESUMEN
The assumption that the pressure difference between the cochlear windows is the stimulus that produces cochlear responses is tested experimentally in the ears of anesthetized cats. Cochlear potential is used as a measure of cochlear response. The sound pressures at the oval and round windows are individually controlled with both pressures at the same frequency and amplitude. When the angle difference between the two pressures is varied over one cycle, cochlear-potential magnitude varies by about 40 dB, with a sharp minimum occurring with the angle difference near zero. A linear model of the response to the two input pressures estimates a complex common-mode gain C and a complex difference-mode gain D; magnitude of D is about 35 dB greater than magnitude of C over the frequency range that was tested (75 to 1000 Hz). Thus, except for conditions that make the common-mode input much larger than the difference-mode input, the pressure difference between the oval and round windows is, to a good approximation, the effective acoustic stimulus for the cochlea.
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Estimulación Acústica , Acústica , Cóclea/fisiología , Ventana Oval/fisiología , Presión , Ventana Redonda/fisiología , Animales , Gatos , Humanos , Modelos TeóricosRESUMEN
A model of pitch perception, called the spatial pitch network or SPINET model, is developed and analyzed. The model neurally instantiates ideas from the spectral pitch modeling literature and joins them to basic neural network signal processing designs to stimulate a broader range of perceptual pitch data than previous spectral models. The components of the model are interpreted as peripheral mechanical and neural processing stages, which are capable of being incorporated into a larger network architecture for separating multiple sound sources in the environment. The core of the new model transforms a spectral representation of an acoustic source into a spatial distribution of pitch strengths. The SPINET model uses a weighted "harmonic sieve" whereby the strength of activation of a given pitch depends upon a weighted sum of narrow regions around the harmonics of the nominal pitch value, and higher harmonics contribute less to a pitch than lower ones. Suitably chosen harmonic weighting functions enable computer simulations of pitch perception data involving mistuned components, shifted harmonics, and various types of continuous spectra including rippled noise. It is shown how the weighting functions produce the dominance region, how they lead to octave shifts of pitch in response to ambiguous stimuli, and how they lead to a pitch region in response to the octave-spaced Shepard tone complexes and Deutsch tritones without the use of attentional mechanisms to limit pitch choices. An on-center off-surround network in the model helps to produce noise suppression, partial masking, and edge pitch. Finally, it is shown how peripheral filtering and short-term energy measurements produce a model pitch estimate that is sensitive to certain component phase relationships.
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Redes Neurales de la Computación , Percepción de la Altura Tonal , Cóclea/fisiología , Humanos , Modelos Teóricos , Ruido , Ventana Oval/fisiologíaRESUMEN
BACKGROUND: The contribution of middle-ear development to the overall development of hearing has not been explored in great detail. This presentation describes the maturation of conductive elements in the rat middle ear, and provides the basis on which future studies of middle-ear functional development will follow. METHODS: The middle-ear apparatus was examined at nine different ages (between 1 and 80 days postpartum) in Long Evans rats. At each age elements of the conducting apparatus was observed with either light or scanning electron microscopy (SEM), and quantitative measurements were made from video enhanced photomicrographs. Tympanic membrane area and cone depth, the length of the malleus and incus arms, ossicular weight, stapes foot plate and oval window areas, and bulla volume were all measured. Development of the area and lever ratios were derived from these measurements. The data were fitted to exponential equations and the time in days required to reach 90% of the adult level determined. RESULTS: The pars tensa achieved 90% of total area by 17 days. The oval window achieved the 90% criterion by 13 days, while the area ratio was within 10% of its adult size by 8 days. The ossicles took between 26 and 34 days, while bulla volume took 59 days to reach the 90% level. CONCLUSIONS: Middle-ear growth was very orderly and systematic in the data reported. When maturation of the area ratio was considered against development of the endocochlear potential or the round window compound action potential, it was clear that the growth of this important aspect of the middle ear preceded the onset of cochlear function.
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Oído Medio/crecimiento & desarrollo , Envejecimiento , Animales , Femenino , Yunque/crecimiento & desarrollo , Yunque/fisiología , Martillo/crecimiento & desarrollo , Martillo/fisiología , Microscopía Electrónica de Rastreo , Ventana Oval/crecimiento & desarrollo , Ventana Oval/fisiología , Embarazo , Ratas , Estribo/crecimiento & desarrollo , Estribo/fisiología , Membrana Timpánica/crecimiento & desarrollo , Membrana Timpánica/ultraestructuraRESUMEN
Dehiscences in the bony facial canal are comparatively common in the human adult. The highest incidence occurs in the tympanic segment of the facial nerve near the region of the oval window. Thirty-three fetal temporal bones, ranging from 16 to 40 weeks' gestation, and four from 1, 2, 4 and 12 weeks' postpartum neonates, were studied to evaluate the normal patterns of ossification of the fallopian canal of the tympanic facial nerve segment in the human. The tympanic facial nerve segment elongates three-fold during this period (from 1 mm to 3 mm). The ossification starts at 21 weeks' gestation anteriorly from apical otic ossification centers and at 26 weeks from canalicular ossification centers near the stapedius muscle. The ossification proceeds in an anterior-to-posterior direction as two periosteal shelves of bone surround the facial nerve. The superior periosteal bony ledge contributes 75% of the circumference of the fallopian canal. The anterior ossification center forms over 83% of the fallopian canal length. The two centers fuse post partum near the region of the oval window. The anatomic location of the facial nerve, nerve branching, and neural vasculature precede ossification. In 80% of the paired temporal bones, this ossification pattern appears to be symmetrical. The patterns and incidence of bony dehiscences within the tympanic fallopian canal segment can be explained by these observations. This study demonstrates that fallopian canal dehiscences are not congenital anomalies, but variations of normal developmental anatomic processes.
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Osteogénesis , Hueso Temporal/anatomía & histología , Hueso Temporal/embriología , Cartílago/anatomía & histología , Cartílago/embriología , Cartílago/fisiología , Cóclea/anatomía & histología , Cóclea/embriología , Cóclea/fisiología , Nervio Facial/anatomía & histología , Nervio Facial/embriología , Feto , Edad Gestacional , Humanos , Recién Nacido , Mesodermo/fisiología , Ventana Oval/anatomía & histología , Ventana Oval/embriología , Ventana Oval/fisiología , Periostio/anatomía & histología , Periostio/fisiología , Estribo/anatomía & histología , Estribo/embriología , Estribo/fisiología , Hueso Temporal/inervación , Hueso Temporal/fisiologíaRESUMEN
Effects of a possible inner-ear compressibility on middle-ear transfer functions are explored and a small upper bound on the magnitude of that compressibility established. Consequently. the traditional two-port representation of middle-ear mechanics remains valid to within a few percent. If the compressibility of the cochlea is small but finite, a simple phenomenological model of that compressibility correctly predicts hearing thresholds in the "middleless" ear at low frequencies. Experiments to establish the value of cochlear compressibility and to explore further its possible contributions to residual hearing in patients with missing or disarticulated middle-ear ossicles are suggested.
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Cóclea/fisiología , Audición/fisiología , Animales , Umbral Auditivo/fisiología , Fenómenos Biomecánicos , Osículos del Oído/fisiología , Humanos , Modelos Anatómicos , Ventana Oval/fisiología , Percepción de la Altura Tonal/fisiología , PsicoacústicaRESUMEN
In experiments using guinea pigs, the middle ear and perilymphatic pressures were simultaneously registered in response to pressure change in the external ear canal. In the first experiment, pressure was slowly loaded in the ear canal in the range of 200 mm H2O to -200 mm H2O. Pressure transmission to the perilymph was smaller when the bulla was open to the outside than when it was closed. It was significantly impaired by disruption of the ossicular chain and especially by closure of the round window. The data indicate that air volume in the middle ear cavity plays an important role in transmission of slowly changing atmospheric pressures. In the second experiment, the eustachian tube was closed and the pressure was changed in the range of 1000 mm H2O to -1000 mm H2O. The middle ear and perilymphatic pressures increased or decreased corresponding to the loading pressure in the range of 400 mm H2O and -200 mm H2O. Beyond these levels, response rate of the middle ear pressure decreased and perilymphatic pressure declined in spite of further increase in loading pressure. The increase in pressure difference between the middle ear and the inner ear might cause disruption of the round and/or oval windows.
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Presión Atmosférica , Oído Externo/fisiología , Oído Interno/fisiología , Oído Medio/fisiología , Perilinfa/fisiología , Animales , Barotrauma/etiología , Cobayas , Ventana Oval/fisiología , Ventana Redonda/fisiologíaRESUMEN
In clinical diagnosis bone conduction thresholds can be used to assess impaired hearing caused by pathological function of the inner ear. The effects of changed mechanical properties of the middle ear on bone conduction are usually not considered in patients who simultaneously suffer from middle ear and inner ear diseases. This procedure is only partially correct. An exact determination of the effects of altered middle ear mechanics on bone conduction in patients with otosclerosis or after middle ear operations is rather difficult, but such determinations can improve diagnostic validity. Therefore, a special electrical model was constructed to simulate the oscillation pattern of the basilar membrane for bone conduction and variable middle ear impedance. Results from the model and possible conclusions on bone conducted hearing in vivo are discussed. Further steps to ensure measurements of inner ear function in cases with modified middle ear mechanics are proposed.
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Conducción Ósea , Oído Medio/fisiología , Audición , Modelos Biológicos , Membrana Basilar/fisiología , Fenómenos Biomecánicos , Cóclea/fisiología , Conductividad Eléctrica , Humanos , Ventana Oval/fisiologíaRESUMEN
Pressure tolerance of round and oval labyrinthine windows and a cochlear segment represented by a part of the cochlear duct were investigated in experiments on cadaveric human temporal bones. The cochlear segment is less resistant than both the windows. Inner ear spaces are protected from pressure changes in the surroundings of the temporal bone by a system of narrow and comparatively long connections and some of them include also other structures strengthening the protective function (the valve described near the place where the cochlear aqueduct leads to scala tympani). Experiments with guinea pigs showed significance of inner ear integrity in protection from pressure changes. Tolerance of both windows was significantly higher in live animals than in cadaveric guinea pig bullae. Pressure tolerance of the windows was in turn higher in bullae than in isolated inner ear labyrinth. Conclusions were arrived at on the basis of the above facts that the inner ear is considerably resistant to pressure changes around it under normal circumstances. Ruptures in its parts appear only under special conditions and a number of factors participate in them. Window ruptures accompany most frequently injuries in other inner ear structures to which different degrees of hearing loss correspond. An isolated injury of windows is, from this viewpoint, rare even though it can be found and treated surgically best.
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Oído Interno/fisiología , Animales , Cobayas , Humanos , Técnicas In Vitro , Ventana Oval/fisiología , Perilinfa/fisiología , Presión , Ventana Redonda/fisiologíaRESUMEN
The effects of a conductive or mixed (conductive and sensorineural) hearing loss on anatomical and physiological properties of the chicken auditory system were examined. Animals used in the anatomical studies underwent either a columella (ossicle) removal, which produced a moderate conductive hearing loss, or an oval window puncture, which produced a severe mixed hearing loss, at 4 days posthatch. In a companion study, multiunit spike counts were obtained from 3-week-old chickens before, during, and after consecutive tympanic membrane puncture, columella removal, and oval window puncture. Tympanic membrane puncture and columella removal (conductive hearing loss) are not associated with either cell area changes in the nucleus magnocellularis or changes in spontaneous neuronal activity. Conversely, an oval window puncture (sensorineural damage) is associated with a cell area reduction of 20%, as well as a marked decline in activity within auditory nuclei.