Response of the human tympanic membrane to transient acoustic and mechanical stimuli: Preliminary results

Abstract

The response of the tympanic membrane (TM) to transient environmental sounds and the contributions of different parts of the TM to middle-ear sound transmission were investigated by measuring the TM response to global transients (acoustic clicks) and to local transients (mechanical impulses) applied to the umbo and various locations on the TM. A lightly-fixed human temporal bone was prepared by removing the ear canal, inner ear, and stapes, leaving the incus, malleus, and TM intact. Motion of nearly the entire TM was measured by a digital holography system with a high speed camera at a rate of 42 000 frames per second, giving a temporal resolution of <24 μs for the duration of the TM response. The entire TM responded nearly instantaneously to acoustic transient stimuli, though the peak displacement and decay time constant varied with location. With local mechanical transients, the TM responded first locally at the site of stimulation, and the response spread approximately symmetrically and circumferentially around the umbo and manubrium. Acoustic and mechanical transients provide distinct and complementary stimuli for the study of TM response. Spatial variations in decay and rate of spread of response imply local variations in TM stiffness, mass, and damping.

The path of a click stimulus from ear canal to umbo

“…The upper frequency fell off gradually above 20 kHz in our study, and covered a substantial fraction of the ~ 60 kHz upper frequency limit of gerbil hearing. Responses to a click stimulus were recently published in a study of the human TM [25], and some of our findings in gerbil were also observed in those results.…”

“…It had also been established that the TM itself responds to sound with a highly location- and frequency-dependent motion that is much like a combination of different drum modes [11, 14]. In the time-domain, this corresponds to low-fidelity representation of the sound signal [25, 30]. This study’s primary goal was to better understand how the TM can succeed as an overall high-fidelity sound transmitter, when locally, it is a low-fidelity sound responder.…”

High-Speed Holographic Shape and Full-Field Displacement Measurements of the Tympanic Membrane in Normal and Experimentally Simulated Pathological Ears

“…and high sensitivity of the optical tools. Researchers utilized a high-speed digital holographic method to minimize these undesirable effects and made quantitative measurements on live subjects possible [24,[27][28][29][30].…”

Combined high-speed holographic shape and full-field displacement measurements of tympanic membrane

“…For example, one of the complexities of TM response is that different regions of the TM (e.g., the regions tied to the manubrium of the malleus, the four quadrants of the pars tensa, or the pars flaccida) respond differently to acoustic excitation. 15,17 Therefore, full-field-of-view measurements (i.e., simultaneous measurements over the entire surface of TM) are needed to quantify the response of the entire TM and describe how different regions of the TM interact with each other to conduct sound to the ossicular chain.…”

“…To solve this problem, high-speed digital holographic (HDH) methods were developed to measure the TM motions produced by brief acoustic transients (click response with duration of <5 ms). 17,26,29,30 The TM's responses to such brief broadband excitations (0.2 to 22 kHz) are rapid enough that they are little affected by slow in vivo physiological motions (<20 Hz), 17,26,30,31 and recording at high sampling rates (>40 kHz) provides broadband information about the TM's responses. Preliminary results on live animals show the applicability of the HDH as a quantitative full-field vibrometry tool to study TM mechanics in live ears for hearing research and the diagnosis of middle-ear disorders.…”