Quasi-static Transfer Function of the Rabbit Middle Ear‚ Measured with a Heterodyne Interferometer with High-Resolution Position Decoder

Abstract

Due to changes in ambient pressure and to the gasexchange processes in the middle ear (ME) cavity, the ear is subject to ultra-low-frequency pressure variations, which are many orders of magnitude larger than the loudest acoustic pressures. Little quantitative data exist on how ME mechanics deals with these large quasi-static pressure changes and because of this lack of data, only few efforts could be made to incorporate quasi-static behavior into computer models. When designing and modeling ossicle prostheses and implantable ME hearing aids, the effects of large ossicle movements caused by quasistatic pressures should be taken into account. We investigated the response of the ME to slowly varying pressures by measuring the displacement of the umbo and the stapes in rabbit with a heterodyne interferometer with position decoder. Displacement versus pressure curves were obtained at linear pressure change rates between 200 Pa/s and 1.5 kPa/s, with amplitude T2.5 kPa. The change in stapes position associated with a pressure change is independent of pressure change rate (34 mm peak-to-peak at T2.5 kPa). The stapes displacement versus pressure curves are highly nonlinear and level off for pressures beyond T1 kPa. Stapes motion shows no measurable hysteresis at 1.5 kPa/s, which demonstrates that the annular ligament has little viscoelasticity. Hysteresis increases strongly at the lowest pressure change rates. The stapes moves in phase with the umbo and with pressure, but the sense of rotation of the hysteresis loop of stapes is phase inversed. Stapes motion is not a simple lever ratio mimic of umbo motion, but is the consequence of complex changes in ossicle joints and ossicle position. The change in umbo position produced by a T2.5 kPa pressure change decreases with increasing rate from 165 mm at 200 Pa/s to 118 mm at 1.5 kPa/s. Umbo motion already shows significant hysteresis at 1.5 kPa/s, but hysteresis increases further as pressure change rate decreases. We conclude that in the quasi-static regime, ossicle movement is not only governed by viscoelasticity, but that other effects become dominant as pressure change rate decreases below 1 kPa/s. The increasing hysteresis can be caused by increasing friction as speed of movement decreases, and incorporating speed-dependent friction coefficients will be essential to generate realistic models of ossicle movements at slow pressure change rates.

Biomechanics of the incudo-malleolar-joint – Experimental investigations for quasi-static loads

“…In the unloaded state the distance between the articular surfaces for all four TBs was within the range of 25 to 280 µm which is comparable to recent investigations of De Greef et al (2015). Dirckx et al (2005) proposed that friction effects are important in the quasi-static regime, but viscoelasticity may be the remaining factor at acoustic frequencies. The importance of friction was motivated by the increase of hysteresis with decreasing variation rates.…”

“…In Dirckx et al (2005) the continuous motion including the viscoelastic effects is captured by measuring the displacement using 1D-LDV. With these investigations the existence of velocity related damping mechanism in case of quasi-static low frequency excitation can be detected.…”

Wideband absorbance tympanometry using pressure sweeps: System development and results on adults with normal hearing

“…The present study aimed to: ͑1͒ shorten the dataacquisition time for wideband tympanometry by sweeping the air pressure; ͑2͒ include automatic feedback control of air pressure in the ear canal; ͑3͒ examine the effect of pressure sweeps that might affect the interpretation of results in relation to middle-ear mechanics ͑Decraemer et al., 1984;Gaihede et al, 2000;Therkildsen et al, 2005;Dirckx et al, 2006͒; and ͑4͒ maintain adequate resolution in both frequency and ear-canal pressure. New measurement procedures were developed, including new signal-processing and artifact-rejection methods.…”

A nonlinear finite-element model of the newborn middle ear

“…The mechanical deformations of the tympanic membrane ͑TM͒ in response to high static pressures have been experimentally studied in human adult ͑Elner et al, 1971;Dirckx and Decraemer 1991;Dirckx and Decraemer 1992;Vorwerk et al, 1999;Gaihede, 1999͒ andin animals ͑von Unge et al, 1993;Dirckx et al, 1997;Dirckx et al, 1998;Dirckx and Decraemer, 2001;Larsson et al, 2001;Lee and Rosowski, 2001;Rosowski and Lee, 2002;Ladak et al, 2004;Larsson et al, 2005;Dirckx et al, 2006͒. The TM in response to high static pressures has also been studied by the nonlinear finite-element method ͑Ladak et Cheng et al, 2007͒.…”