Effect of middle ear fluid on sound transmission and auditory brainstem response in guinea pigs

Abstract

Combined measurements of middle ear transfer function and auditory brainstem response (ABR) in live guinea pigs with middle ear effusion (MEE) are reported in this paper. The MEE model was created by injecting saline into the middle ear cavity. Vibrations of the tympanic membrane (TM), the tip of the incus, and the round window membrane (RWM) were measured with a laser vibrometer at frequencies of 0.2-40 kHz when the middle ear fluid increased from 0 to 0.2 ml (i.e., full fill of the cavity). The click and pure tone ABRs were recorded as the middle ear fluid increased. Fluid introduction reduced mobility of the TM, incus and RWM mainly at high frequencies (f > 1 kHz). The magnitude of this reduction was related to the volume of fluid. The displacement transmission ratio of the TM to incus varied with frequency and fluid level. The volume displacement ratio of the oval window to round window was approximately 1.0 over most frequencies. Elevation of ABR thresholds and prolongation of ABR latencies were observed as fluid level increased. Reduction of TM displacement correlated well with elevation of ABR threshold at 0.5-8 kHz. Alterations in the ratio of ossicular displacements before and after fluid induction are consistent with fluid-induced changes in complex ossicular motions.

Conductive Hearing Loss Induced by Experimental Middle-Ear Effusion in a Chinchilla Model Reveals Impaired Tympanic Membrane-Coupled Ossicular Chain Movement

“…Presumably, at higher frequencies, the movement of the TM becomes more mass-dominated, so increasing the amount of fluid that is contacting the TM results in an effective increase of the TM mass, regardless of the viscosity of the fluid (Ravicz et al 2004). Our results are wholly consistent with previous studies (Ravicz et al 2004;Gan et al 2006;Dai and Gan 2008;Guan and Gan 2011;Thornton et al 2012), as we also saw a greater reduction in umbo velocity at higher frequencies (3-8 kHz) than at lower frequencies (Fig. 5).…”

“…The largest increases in CM thresholds were seen when the TM was fully covered by fluid. Similar instances of MEEinduced CM threshold elevation were observed in previous studies Petrova et al 2006;Guan and Gan 2011). Guan and Gan (2011) used auditory brainstem response (ABR) thresholds to study the peripheral auditory system response to MEEinduced CHL in guinea pigs.…”

“…6). Guan and Gan (2011) compared the effects of MEE at the level of the middle and inner ears by measuring ossicular mobility and ABR thresholds, respectively. At higher frequencies (10-20 kHz), differences between TM mobility measurements and ABR thresholds were also~6 dB.…”

Measurement of Basilar Membrane Motion During Round Window Stimulation in Guinea Pigs

“…The displacement of the incus tip in guinea pigs under acoustic stimulation in the ear canal was published by Cooper and Rhode (1995) and Guan and Gan (2011). Figure 7A shows the comparison of the incus tip displacement in forward (black line) measured in this study with the published results.…”

“…The discrepancies may be explained by the different measurement angles on the incus in these studies. In Guan and Gan (2011), the angle between the laser beam and the piston motion direction of the stapes was 40-50°. In this study, the angle was larger (60°).…”