Laser interferometry measurements of middle ear fluid and pressure effects on sound transmission

Abstract

An otitis media with effusion model in human temporal bones with two laser vibrometers was created in this study. By measuring the displacement of the stapes from the medial side of the footplate, the transfer function of the middle ear, which is defined as the displacement transmission ratio (DTR) of the tympanic membrane to footplate, was derived under different middle ear pressure and fluid in the cavity with a correction factor for cochlear load. The results suggest that the DTR increases with increasing frequency up to 4k Hz when the middle ear pressure was changing from 0 to 20 or -20 cm H20 (e.g., +/-196 daPa) and fluid level was increasing from 0 to a full middle ear cavity. The positive and negative pressures show different effects on the DTR. The effect of fluid on DTR varies between three frequency ranges: f < 1k, between 1k and 4k, and f > 4k Hz. These findings show how the efficiency of the middle ear system for sound transmission changes during the presence of fluid in the cavity and variations of middle ear pressure.

Combined effect of fluid and pressure on middle ear function

“…The effect of middle ear pressure on TM mobility has been investigated in human temporal bones and animals (Teoh et al, 1997;Lee and Rosowski, 2001;Rosowski and Lee, 2002;Murakami et al, 1997;Dirckx and Decraemer, 1992;Huttenbrink 1998;Gan et al, 2006;Dai et al, 2007). The results of Murakami et al and Gan et al show that the middle ear pressure mainly decreased the TM movement at low frequencies (f <1k Hz).…”

“…No substantial amount of water was found in the mastoid processes of the four bones. Figure 1 shows the temporal bone experimental setup with a laser vibrometer and a tympanometer, which was similar to studies reported by Gan et al (2006) and Dai et al (2007). Briefly, the temporal bone was placed in a temporal bone holder and the bone assembly was set on a vibration isolation table.…”

“…Saline solution was selected for simulation of a serous effusion and 0.3 ml was found to be the critical amount of fluid which produced significant changes in umbo displacement in our previous studies of the OME model in human temporal bones (Gan et al, 2006;Dai et al, 2007). In those temporal bones, 0.3 ml fluid filled about half of the middle ear cavity and the fluid level was about to the umbo, which was observed under microscope.…”

“…Several studies (Goodhill and Holcomb, 1958;Majinma et al, 1988;Ravicz et al, 2004;Gan et al, 2006;Dai et al, 2007) have investigated possible mechanisms of hearing loss associated with the presence of middle ear effusions. Ravicz et al (2004) suggested that the primary mechanism responsible for hearing loss at low frequencies was the reduction of middle ear compliance by a reduction in the middle ear air volume.…”

Modeling microstructure of incudostapedial joint and the effect on cochlear input

“…90 dB SPL pure tones were applied in the ear canal at 2 mm away from the umbo and the acoustic-structure coupled FE analysis was performed between the ear canal, TM, and middle ear cavity over the frequency range of 0.2-10 kHz. Figure 2A shows the middle ear transfer function derived from the FE model of human ear (baseline model-Case 1) as the displacement-frequency curves of the TM at the umbo and the stapes footplate in comparison with the experimental measurements reported from 17 temporal bones by Gan et al [4,5]. The modelling results from the FE model without synovial ISJ are also shown in the figure.…”