title: Stapes displacement and intracochlear pressure in response to very high level, low frequency sounds.
abstract: The stapes is held in the oval window by the stapedial annular ligament (SAL), which restricts total peak-to-peak displacement of the stapes. Previous studies have suggested that for moderate (<130 dB SPL) sound levels intracochlear pressure (PIC), measured at the base of the cochlea far from the basilar membrane, increases directly proportionally with stapes displacement (DStap), thus a current model of impulse noise exposure (the Auditory Hazard Assessment Algorithm for Humans, or AHAAH) predicts that peak PICwill vary linearly with DStapup to some saturation point. However, no direct tests of DStap, or of the relationship with PICduring such motion, have been performed during acoustic stimulation of the human ear. In order to examine the relationship between DStapand PICto very high level sounds, measurements of DStapand PICwere made in cadaveric human temporal bones. Specimens were prepared by mastoidectomy and extended facial recess to expose the ossicular chain. Measurements of PICwere made in scala vestibuli (PSV) and scala tympani (PST), along with the SPL in the external auditory canal (PEAC), concurrently with laser Doppler vibrometry (LDV) measurements of stapes velocity (VStap). Stimuli were moderate (∼100 dB SPL) to very high level (up to ∼170 dB SPL), low frequency tones (20-2560 Hz). Both DStapand PSVincreased proportionally with sound pressure level in the ear canal up to approximately ∼150 dB SPL, above which both DStapand PSVshowed a distinct deviation from proportionality with PEAC. Both DStapand PSVapproached saturation: DStapat a value exceeding 150 μm, which is substantially higher than has been reported for small mammals, while PSVshowed substantial frequency dependence in the saturation point. The relationship between PSVand DStapremained constant, and cochlear input impedance did not vary across the levels tested, consistent with prior measurements at lower sound levels. These results suggest that PSVsound pressure holds constant relationship with DStap, described by the cochlear input impedance, at these, but perhaps not higher, stimulation levels. Additionally, these results indicate that the AHAAH model, which was developed using results from small animals, underestimates the sound pressure levels in the cochlea in response to high level sound stimulation, and must be revised.
authors.affiliation: Department of Physiology and Biophysics, University of Colorado School of Medicine, Aurora, CO, USA; Department of Otolaryngology, University of Colorado School of Medicine, Aurora, CO, USA. Electronic address: nathaniel.greene@ucdenver.edu.
authors.forename: Nathaniel T
authors.initials: NT
authors.lastname: Greene
authors.affiliation: Department of Otolaryngology, University of Colorado School of Medicine, Aurora, CO, USA.
authors.forename: Herman A
authors.initials: HA
authors.lastname: Jenkins
authors.affiliation: Department of Physiology and Biophysics, University of Colorado School of Medicine, Aurora, CO, USA; Department of Otolaryngology, University of Colorado School of Medicine, Aurora, CO, USA.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Tollin
authors.affiliation: Cochlear Boulder LLC, Boulder, CO, USA.
authors.forename: James R
authors.initials: JR
authors.lastname: Easter
mesh_terms: D000161:Acoustic Stimulation; D000162:Acoustics; D002102:Cadaver; D003051:Cochlea / Q000502:physiology*; D004429:Ear Ossicles / Q000502:physiology; D004432:Ear, Middle / Q000502:physiology; D017097:Electric Impedance; D006309:Hearing / Q000502:physiology*; D006801:Humans; D007834:Lasers; D009998:Ossicular Prosthesis; D011312:Pressure; D016016:Proportional Hazards Models; D012405:Round Window, Ear / Q000502:physiology; D012533:Scala Tympani / Q000502:physiology*; D054738:Scala Vestibuli / Q000502:physiology*; D013016:Sound; D013199:Stapes / Q000033:anatomy & histology / Q000502:physiology*; D013701:Temporal Bone / Q000033:anatomy & histology / Q000502:physiology
keywords: High level sound; Intracochlear pressure; Laser Doppler vibrometry; Stapedial annular ligament