Missing Links in Some Curious Auditory Phenomena: A Tale from the Middle Ear

Background: Broadband middle ear power reflectance (BMEPR) is an emerging noninvasive electroacoustic measure that evaluates transmission/reflection properties of the middle ear in high resolution. It is applicable over the entire age continuum and is rapid to perform. However, it remains to be determined if BMEPR is just an incremental step in the evolution of middle ear assessment or a major advance in the way middle ear function can be evaluated. Purpose: To evaluate effects of age, gender, ear, and frequency on BMEPR measurements in adults without a history of middle ear disease and to assess whether these factors require consideration in test development; to review how these data may influence active physiologic process within the inner ear; to consider how they reconcile with previously published results; and to suggest applications for future research. Research Design: Prospective, cross-sectional, multivariate analysis to evaluate the effects of age, gender, ear, and frequency on BMEPR in humans without a history of middle ear disease and no air-bone gaps exceeding 10 dB for any frequency. Study Sample: Fifty-six adults in two age groups (Group 1: 18-25 yr, n = 28; Group 2: >= 50 and <66 yr, n = 28). Each age group was stratified by ear and gender in a balanced design. Data Collection and Analysis: Pure tone air conduction and bone-conduction audiometry was conducted in a commercial sound booth, using a clinical audiometer with standard earphones enclosed in supra-aural ear cushions, and a standard bone-conduction oscillator and headband to evaluate for air-bone gaps. Broadband middle ear power reflectance was measured using a calibrated, commercially available computer-controlled system that incorporated a high quality probe assembly to transduce stimuli and record acoustic responses from the ear canal. Data were analyzed with a four-way (2 x 2 x 2 x 16) repeated measures analysis-of-variance (ANOVA) to evaluate the effects of age group (young vs. old), gender (male vs. female), ear (left vs. right), and frequency (258 to 5040 Hz) on BMEPR. Results: The ANOVA revealed a significant main effect of frequency. There were also gender x ear, gender x frequency, and age x gender x ear interactions. The three-way, age x gender x ear interaction captured the essence of results and revealed lowest power reflectance values in younger females and for right ears. This trend partially reversed in the older age group where higher power reflectance values were observed only in right ears of older females. Conclusions: The significant effects of age, gender, ear, and frequency on BMEPR parallel ear- and gender-related differences in hearing sensitivity, ear, and gender differences in the prevalence of spontaneous otoacoustic emissions (OAEs), gender differences in the magnitude of transient evoked OAEs, and ear differences in transient evoked contralateral OAE suppression effects reported in the literature. While original discussions of these aforementioned effects focused primarily on endocochlear and oli-vocochlear mechanisms, the BMEPR measurements reported herein suggest that middle ear transmission characteristics may also play a role.