RESUMEN
The round window (RW) membrane plays an important role in normal inner ear mechanics. Occlusion or reinforcement of the RW has been described in the context of congenital anomalies or after cochlear implantation and is applied as a surgical treatment for hyperacusis. Multiple lumped and finite element models predict a low-frequency hearing loss with air conduction of up to 20 dB after RW reinforcement and limited to no effect on hearing with bone conduction stimulation. Experimental verification of these results, however, remains limited. Here, we present an experimental study measuring the impact of RW reinforcement on the middle and inner ear mechanics with air and bone conduction stimulation. In a within-specimen repeated measures design with human cadaveric specimens (n = 6), we compared the intracochlear pressures in scala vestibuli (PSV) and scala tympani (PST) before and after RW reinforcement with soft tissue, cartilage, and bone cement. The differential pressure (PDIFF) across the basilar membrane - known to be closely related to the hearing sensation - was calculated as the complex difference between PSV and PST. With air conduction stimulation, both PSV and PSTincreased on average up to 22 dB at frequencies below 1500 Hz with larger effect sizes for PST compared to PSV. The PDIFF, in contrast, decreased up to 11 dB at frequencies between 700 and 800 Hz after reinforcement with bone cement. With bone conduction, the average within-specimen effects were less than 5 dB for either PSV, PST, or PDIFF. The inter-specimen variability with bone conduction, however, was considerably larger than with air conduction. This experimental study shows that RW reinforcement impacts air conduction stimulation at low frequencies. Bone conduction stimulation seems to be largely unaffected. From a clinical point of view, these results support the hypothesis that delayed loss of air conduction hearing after cochlear implantation could be partially explained by the impact of RW reinforcement.
Asunto(s)
Estimulación Acústica , Conducción Ósea , Cadáver , Ventana Redonda , Humanos , Ventana Redonda/fisiología , Ventana Redonda/cirugía , Presión , Anciano , Oído Medio/fisiología , Oído Medio/cirugía , Rampa Timpánica/cirugía , Rampa Timpánica/fisiología , Masculino , Femenino , Escala Vestibular/cirugía , Escala Vestibular/fisiología , Escala Vestibular/fisiopatología , Cementos para Huesos , Persona de Mediana Edad , Fenómenos Biomecánicos , Audición , Anciano de 80 o más Años , Oído Interno/fisiología , Oído Interno/fisiopatologíaRESUMEN
INTRODUCTION: Injuries to the peripheral auditory system are among the most common results of high intensity impulsive acoustic exposure. Prior studies of high intensity sound transmission by the ossicular chain have relied upon measurements in animal models, measurements at more moderate sound levels (i.e.â¯<â¯130â¯dB SPL), and/or measured responses to steady-state noise. Here, we directly measure intracochlear pressure in human cadaveric temporal bones, with fiber optic pressure sensors placed in scala vestibuli (SV) and tympani (ST), during exposure to shock waves with peak positive pressures between â¼7 and 83â¯kPa. METHODS: Eight full-cephalic human cadaver heads were exposed, face-on, to acoustic shock waves in a 45â¯cm diameter shock tube. Specimens were exposed to impulses with nominal peak overpressures of 7, 28, 55, & 83â¯kPa (171, 183, 189, & 192â¯dB pSPL), measured in the free field adjacent to the forehead. Specimens were prepared bilaterally by mastoidectomy and extended facial recess to expose the ossicular chain. Ear canal (EAC), middle ear, and intracochlear sound pressure levels were measured with fiber-optic pressure sensors. Surface-mounted sensors measured SPL and skull strain near the opening of each EAC and at the forehead. RESULTS: Measurements on the forehead showed incident peak pressures approximately twice that measured by adjacent free-field and EAC entrance sensors, as expected based on the sensor orientation (normal vs tangential to the shock wave propagation). At 7â¯kPa, EAC pressure showed gain, calculated from the frequency spectra, consistent with the ear canal resonance, and gain in the intracochlear pressures (normalized to the EAC pressure) were consistent with (though somewhat lower than) previously reported middle ear transfer functions. Responses to higher intensity impulses tended to show lower intracochlear gain relative to EAC, suggesting sound transmission efficiency along the ossicular chain is reduced at high intensities. Tympanic membrane (TM) rupture was observed following nearly every exposure 55â¯kPa or higher. CONCLUSIONS: Intracochlear pressures reveal lower middle-ear transfer function magnitudes (i.e. reduced gain relative to the ear canal) for high sound pressure levels, thus revealing lower than expected cochlear exposure based on extrapolation from cochlear pressures measured at more moderate sound levels. These results are consistent with lowered transmissivity of the ossicular chain at high intensities, and are consistent with our prior report measuring middle ear transfer functions in human cadaveric temporal bones with high intensity tone pips.
Asunto(s)
Conducción Ósea , Ondas de Choque de Alta Energía/efectos adversos , Rampa Timpánica/lesiones , Escala Vestibular/lesiones , Hueso Temporal/fisiopatología , Cadáver , Tecnología de Fibra Óptica/instrumentación , Humanos , Movimiento (Física) , Otoscopía , Presión , Medición de Riesgo , Rampa Timpánica/fisiopatología , Escala Vestibular/fisiopatología , Factores de Tiempo , Transductores de Presión , VibraciónRESUMEN
The position of the cochlear electrode array within the scala tympani is essential for optimal hearing benefit. An intraoperative neural response telemetry ratio (NRT ratio; a threshold ratio of pairs of apical and basal electrodes) has been established, which can provide information about the intracochlear electrode array position. Out of a previous collective of 85 patients, the 6-month follow-up electrophysiological NRT data of 37 patients have been included in this study. Comparing the intraoperatively estimated NRT ratio with the 6-month follow-up NRT ratio, it remained unchanged intraindividually in 92% of cases. Within this group the NRT ratio and the intracochlear position of the electrode array matched in all cases. There were two newly occurring mismatches and one new match was observed. After a period of 6 months the NRT ratio remained unchanged in most cases and showed a good correlation with the intracochlear position of the electrode array.
Asunto(s)
Cóclea/fisiopatología , Implantación Coclear/métodos , Implantes Cocleares , Sordera/rehabilitación , Fenómenos Electrofisiológicos , Pérdida Auditiva Sensorineural/rehabilitación , Rampa Timpánica/fisiopatología , Cóclea/diagnóstico por imagen , Electrodos Implantados , Estudios de Seguimiento , Humanos , Monitorización Neurofisiológica Intraoperatoria , Periodo Posoperatorio , Radiografía , Escala Vestibular/fisiopatologíaRESUMEN
OBJECTIVE: To evaluate the effect of the intracochlear electrode position on the residual hearing and VNG- and cVEMP responses. DESIGN: Prospective pilot study. STUDY SAMPLE: Thirteen adult patients who underwent unilateral cochlear implant surgery were examined with high-resolution rotational tomography after cochlear implantation. All subjects were also tested with VNG, and 12 of the subjects were tested with cVEMP and audiometry before and after surgery. RESULTS: We found that although the electrode was originally planned to be positioned inside the scala tympani, only 8 of 13 had full insertion into the scala tympani. Loss of cVEMP response occurred to the same extent in the group with full scala tympani positioning and the group with scala vestibuli involvement. There was a non-significant difference in the loss of caloric response and residual hearing between the two groups. Interscalar dislocation of the electrode inside the cochlea was observed in two patients. A higher loss of residual hearing could be seen in the group with electrode dislocation between the scalae. CONCLUSIONS: Our findings indicate that intracochlear electrode dislocation is a possible cause to loss of residual hearing during cochlear implantation but cannot be the sole cause of postoperative vestibular loss.