Hypothesis Power reflectance (PR) measurements in ears with Superior Canal Dehiscence (SCD) have a characteristic pattern, whose detection can assist in diagnosis. Background The aim of this study is to determine if PR coupled with a novel detection algorithm can perform well as a fast, non-invasive, and easy screening test for SCD. The screening test is to determine if patients with various vestibular and/or auditory symptom(s) should be further considered for more expensive and invasive tests that better define the diagnosis of SCD (and other third-window lesions). Methods PR was measured in patients diagnosed with SCD by high-resolution CT. The study included 40 ears from 32 patients with varying symptoms (e.g., with and without conductive hearing loss, vestibular symptoms, and abnormal auditory sensations). Results PR results were compared to previously published norms, and showed that SCD is commonly associated with a PR notch near 1 kHz. An analysis algorithm was designed to detect such notches and to quantify their incidence in affected and normal ears. Various notch detection thresholds yielded sensitivities of 80%–93%, specificities of 69%–72%, negative predictive value of 84%–93% and positive predictive value of 67%. Conclusion This study shows evidence that PR measurements together with the proposed notch-detecting algorithm can be used to quickly and effectively screen patients for third-window lesions such as SCD in the early stages of a diagnostic workup.

We investigated the contribution of the middle ear to the physiological response to bone conduction stimuli in chinchilla. We measured intracochlear sound pressure in response to air conduction (AC) and bone conduction (BC) stimuli before and after interruption of the ossicular chain at the incudo-stapedial joint. Interruption of the chain effectively decouples the external and middle ear from the inner ear and significantly reduces the contributions of the outer ear and middle ear to the bone conduction response. With AC stimulation, both the scala vestibuli Psv and scala tympani Pst sound pressures drop by 30 to 40 dB after the interruption. In BC stimulation, Psv decreases after interruption by about 10 to 20 dB, but Pst is little affected. This difference in the sensitivity of the BC induced Psv and Pst to ossicular interruption is not consistent with a BC response to ossicular motion, but instead suggests a significant contribution of an inner-ear drive (e.g. cochlear fluid inertia or compressibility) to the BC response.

While the cochlea is considered the primary site of the auditory response to bone conduction (BC) stimulation, the paths by which vibratory energy applied to the skull (or other structures) reaches the inner ear are a matter of continued investigation. We present acoustical measurements of sound in the inner ear that separate out the components of BC stimulation that stimulate the inner ear via ossicular motion (compression of the walls of the ear canal or ossicular inertia) from the components that act directly on the cochlea (cochlear compression or inertia, and extra-cochlear ‘third-window’ pathways). The results are consistent with our earlier suggestion that the inner-ear mechanisms play a large role in bone-conduction stimulation in the chinchilla at all frequencies. However, the data also suggest the pathways that conduct vibration to the inner ear via ossicular-motion make a significant contribution to the response to BC stimulation in the 1 to 3 kHz range, such that interruption of these path leads to a 5 dB reduction in total stimulation in that frequency range. The mid-frequency reduction produced by ossicular manipulations is similar to the ‘Carhart's notch’ phenomenon observed in otology and audiology clinics in cases of human ossicular disorders. We also present data consistent with much of the ossicular-conducted sound in chinchilla depending on occlusion of the ear canal.

While many mouse models of hearing loss have been described, a significant fraction of the genetic defects in these models affect both the inner ear and middle ears. A common method used to separate inner-ear (sensory-neural) from middle-ear (conductive) pathologies in the hearing clinic is the combination of air-conduction and bone-conduction audiometry. In this report, we investigate the use of air- and bone-conducted evoked auditory brainstem responses to perform a similar separation in mice. We describe a technique by which we stimulate the mouse ear both acoustically and via whole-head vibration. We investigate the sensitivity of this technique to conductive hearing loss by introducing middle-ear lesions in normal hearing mice. We also use the technique to investigate the presence of an age-related conductive hearing loss in a common mouse model of presbycusis, the BALB/c mouse.

Umbo velocity and Auditory Brainstem Response (ABR) measurements in aged mice suggest that there are functional changes in both the inner ear and middle ear for frequencies from 5 to 13 kHz (Doan et al., 1996). In this work, we use a combination of air conduction (AC) and bone conduction (BC) stimulation to better quantify the middle ear contribution to age-related hearing loss seen in mice. ABRs were recorded with AC and BC stimuli from BALB/c mice of four different age groups (1, 2, 8, and 12 months); mice of this strain are widely used as models for age-related hearing loss. Results show the threshold stimulus levels for both AC and BC increase as the mice get older, consistent with age-related hearing loss. At frequencies below 12 kHz, the age-related changes in thresholds for all age groups are similar for both stimuli: the AC-BC difference (the air-bone gap) is not statistically significant. This suggests in this frequency range, the hearing loss is primarily sensorineural. At 16 kHz, the air-bone gaps of the two oldest groups are statistically significant suggesting the middle ear contributes to the hearing loss. Thresholds at higher frequencies were not measurable in the two oldest groups.