Simulated otitis media with effusion reduces
intracochlear pressures comparable to umbo velocity.
Background: Otitis media with effusion is a common cause
of temporary hearing loss, particularly in children, producing
deficits of 30 to 40 dB. Previous studies measured the effects
of simulated effusion on ossicular mechanics; however, no
studies have measured cochlear stimulation directly. Here,
we compare pressures in the scala vestibuli and tympani to
umbo velocity, before and after induction of simulated
effusion in cadaveric human specimens.
Methods: Eight cadaveric, hemi-cephalic human heads were
prepared with complete mastoidectomies. Intracochlear pressures were measured with fiber optic pressure probes, and
umbo velocity measured via laser Doppler vibrometry
(LDV). Stimuli were pure tones (0.1–14 kHz) presented in
the ear canal via a custom speculum sealed with a glass
cover slip. Effusion was simulated by filling the mastoid
cavity and middle ear space with water.
Results: Acoustic stimulation with middle ear effusion
resulted in decreased umbo velocity up to 26 dB, whereas
differential pressure (PDiff) at the base of the cochlea
decreased by only 16 dB.
Conclusion: Simulating effusion leads to a frequency-dependent reduction in intracochlear sound pressure levels consistent with audiological presentation and prior reports. Results
reveal that intracochlear pressure measurements (PSV and
PST) decrease less than expected, and less than the decrease
in PDiff. The observed decrease in umbo velocity is greater
than in the differential intracochlear pressures, suggesting
that umbo velocity overestimates the induced conductive
hearing loss. These results suggest that an alternate sound
conduction pathway transmits sound to the inner ear during
effusion.