Abstract
Introduction: The round window membrane (RWM) acts as a pressure-relieving membrane for incompressible cochlear fluid. The reinforcement of the RWM has been used as a surgical intervention for the treatment of superior semicircular canal dehiscence and hyperacusis. The aim of this study was to investigate how RWM reinforcement affects sound pressure variations in the cochlea. Methods: The intracochlear sound pressure (ICSP) was simultaneously measured in the scala tympani (ST) and scala vestibuli (SV) of cadaveric human temporal bones (HTBs) in response to acoustic stimulation for three RWM reinforcement materials (soft tissue, cartilage, and medical-grade silicone). Results: The ICSP in the ST was significantly increased after RWM reinforcement for frequencies below 2 kHz. Between 400 and 600 Hz, all three materials demonstrated the highest median pressure increase. The higher the RWM stiffness, the larger the pressure increase: silicone (7 dB) < soft tissue (10 dB) < cartilage (13 dB). The ICSP in the SV was less affected by reinforcement. The highest median pressure increase was 3 dB. The experimental findings can be explained with numerical models of cochlear mechanics. Discussion and conclusions: RWM reinforcement increases the sound pressure in ST at lower frequencies but only has a minor influence on the SV pressure.
Highlights
The round window membrane (RWM) acts as a pressure-relieving membrane for incompressible cochlear fluid
We investigate the effects of the intracochlear sound pressure (ICSP) changes (PST, pressure measurement in the SV (PSV), and PDIFF) caused by RWM reinforcement with three clinically used materials on human temporal bones (HTBs)
Not every HTB showed an middle ear sound transfer function (METF) within the ASTM standard, the corresponding samples were still considered for the current study, as the main aim was to investigate the relative ICSP changes caused by RWM reinforcement
Summary
The round window membrane (RWM) acts as a pressure-relieving membrane for incompressible cochlear fluid. Methods: The intracochlear sound pressure (ICSP) was simultaneously measured in the scala tympani (ST) and scala vestibuli (SV) of cadaveric human temporal bones (HTBs) in response to acoustic stimulation for three RWM reinforcement materials (soft tissue, cartilage, and medical-grade silicone). The mechanical vibration of the stapes footplate at the end of the middle ear drives sound energy into the cochlea. This transmitted sound creates intracochlear sound pressure (ICSP) in the cochlear fluid, in the scala vestibuli (SV) and scala tympani (ST), which are interconnected at the apex. The round window membrane (RWM) mechanically seals the fluid-filled cochlea from the middle ear cavity at the base of the ST. The RWM with its compliant characteristics serves as a pressure release mechanism for the incompressible fluid in the cochlea, enabling the PDIFF at the basal part of the cochlea
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