Ear and Hearing Effects of Negative Middle Ear Pressure on Wideband Acoustic Immittance in Normal- Hearing Adults

Abstract: Objectives: Wideband acoustic immittance (WAI) measurements are capable of evaluating middle ear performance over a wide range of frequencies relevant to human hearing. It is known that static pressure in the middle ear cavity affects sound transmission to the cochlea, but only a few data sets exist to quantify the relationship between middle ear transmission and pressure level. The purpose of this study is to analyze new WAI measurements of negative middle ear pressure (NMEP), with a focus on the effects of NMEP in individual ears. Design: In this study, subjects with normal middle ear function were trained to induce consistent NMEPs, quantified by the tympanic peak pressure (TPP) and the WAI. The effects of NMEP on power absorbance are analyzed for 8 individual ears. WAI magnitude and phase quantities at the tympanic membrane (TM) are also studied by removing phase contributions from the residual ear canal (REC). Results: For the 8 ears presented here, negative TPP has the largest effect from 0.8 to 1.8 [kHz], causing less energy to be absorbed by the middle ear and cochlea. The TPP level is found to be a significant but imperfect predictor of changes in TM acoustic immittance measurements, due to individual variations in the magnitude and frequency range of the effects of NMEP on middle ear transmission. WAI estimates at the TM show pressure effects consistent with an increased stiffness in the middle ear, which could originate from the TM-malleus coupling, annular ligament, or other middle ear structures. Conclusions: The REC effect is accurately removed from the WAI magnitude and phase, allowing for direct estimation of these quantities at the TM. The effects of NMEP on WAI vary considerably in magnitude and frequency range across individual ears. TPP does not appear to be sufficiently correlated to wideband acoustic changes in the middle ear to be a reliable diagnostic. It is likely that WAI is a better predictor of changes in wideband middle ear transmission than TPP, but more data and modeling are needed to fully utilize WAI for this purpose.