RESUMO
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.
Assuntos
Condução Óssea/fisiologia , Perda Auditiva Condutiva/diagnóstico , Perda Auditiva Condutiva/etiologia , Aceleração/efeitos adversos , Estimulação Acústica , Envelhecimento/fisiologia , Animais , Modelos Animais de Doenças , Potenciais Evocados Auditivos do Tronco Encefálico/fisiologia , Perda Auditiva Condutiva/fisiopatologia , Perda Auditiva Condutiva-Neurossensorial Mista/diagnóstico , Perda Auditiva Condutiva-Neurossensorial Mista/etiologia , Perda Auditiva Condutiva-Neurossensorial Mista/fisiopatologia , Camundongos , Camundongos Endogâmicos BALB C , Camundongos Endogâmicos CBA , Presbiacusia/diagnóstico , Presbiacusia/etiologia , Presbiacusia/fisiopatologia , Especificidade da EspécieRESUMO
This study investigates the ossicular motion produced by bone-conducted (BC) sound in live human ears. Laser Doppler vibrometry was used to measure air conduction (AC)- and BC-induced umbo velocity (V(U)) in both ears of 10 subjects, 20 ears total. Sound pressure in the ear canal (P(EC)) was measured simultaneously. For air conduction, V(U) at standard hearing threshold level was calculated. For BC, ΔV was defined as the difference between V(U) and the tympanic ring velocity (an estimate of the skull velocity measured in the ear canal). ΔV and P(EC) at BC standard hearing threshold were calculated. ΔV at standard BC threshold was significantly smaller than V(U) at standard AC threshold between 500 Hz and 2000 Hz. Ear canal pressure at BC threshold tended to be smaller than for AC below 3000 Hz (with significant differences at 1000 Hz and 2000 Hz). Our results are most consistent with inertia of the ossicles and cochlear fluid driving BC hearing below 500 Hz, but with other mechanisms playing a significant role at higher frequencies. Sound radiated into the external ear canal might contribute to BC hearing at 3000 Hz and above.