Prospective Electrophysiologic Findings of Round Window Stimulation in a Model of Experimentally Induced Stapes Fixation

Abstract

Mechanical stimulation of the RW in an animal model of SF generates functionally similar inputs to the cochlea as normal acoustic and RW mechanical inputs but with increased thresholds. With further study, AMEIs may provide a surgical option for correction of otosclerosis and ossicular chain disruption.

A novel mechanism of cochlear excitation during simultaneous stimulation and pressure relief through the round window

“…These factors may include the shape of the transducer and the area of the RW it covers. Most significant is whether the transducer completely covers the RW, as demonstrated by other groups [27][28][29], or leaves an RW area partially free [26,[30][31][32]. The outcome of our experiments reveals that partial coverage of the RW may not affect RW impedance sufficiently to affect cochlear stimulation with the exposed portion of the RW membrane acting as a pressure shunt (figure 5).…”

“…Furthermore, where we found RW stimulation through the partially occluded RW elicited stapes displacements only at high intensities below 7 kHz, under similar stimulus conditions, Lupo et al [30] observed stapes movement in chinchillas across a wider frequency range of 0.25-16 kHz. We suggest that tighter hydromechanical coupling between the RW transducer and the stapes, and consequent changes in the hydromechanical properties of the cochlea after stapes immobilization, may account for elevation of the CAP thresholds after stapes fixation observed by Lupo et al [30]. Correspondingly, differences in transducer shape and the proportion of the RW covered may potentially account for differences in the transducer-stapes hydromechanical coupling reported in this study and by Lupo et al [30].…”

“…Our experiments demonstrate that middle ear prostheses, which partially cover the RW, can be used effectively for simultaneous cochlear stimulation and pressure relief through the RW. The existence of a 'third window' (an additional pressure shunt, Z 3,SV , Z 3,ST ; figure 10) in the cochlea has been postulated to account for the efficiency of RW stimulation because of the relatively high impedance, as seen from the cochlea, presented by the ossicles [30]. The proposed identity of the third window ranges from the vasculature of the cochlea to the cochlea and vestibular aqueducts [17,30].…”

“…The existence of a 'third window' (an additional pressure shunt, Z 3,SV , Z 3,ST ; figure 10) in the cochlea has been postulated to account for the efficiency of RW stimulation because of the relatively high impedance, as seen from the cochlea, presented by the ossicles [30]. The proposed identity of the third window ranges from the vasculature of the cochlea to the cochlea and vestibular aqueducts [17,30]. Evidence for the existence of the third window and its ability to shunt pressure is claimed from experiments in which the RW membrane is completely blocked during normal acoustic stimulation or the stapes is immobilized and the cochlea is stimulated through the RW route.…”

Controlled round-window stimulation in human temporal bones yielding reproducible and functionally relevant stapedial responses

“…1,2 In-vivo stimulation at the RW has presented a similarly confounding picture. Recently, cochlear microphonics, compound action potential and auditory brainstem response were measured in chinchilla in response to both normal auditory stimulation and RW stimulation by means of a middle-ear transducer (MET) from Otologics, equipped with a 1-mm diameter ball tip without intervening material (Lupo et al, 2009). Again, estimating the ratio of stapes displacement relative to actuator displacement at the RW, we obtain a value of 0.001 (À60 dB).…”