Modeling the Measurements of Cochlear Microcirculation and Hearing Function after Loud Noise

Objective: Recent findings support the crucial role of
microcirculatory disturbance and ischemia for hearing impairment
especially after noise-induced hearing loss (NIHL). The aim of this
study was to establish an animal model for in vivo analysis of
cochlear microcirculation and hearing function after a loud noise
to allow precise measurements of both parameters in vivo. Study
Design: Randomized controlled trial. Setting: Animal study.
Subjects and Methods: After assessment of normacusis (0 minutes)
using evoked auditory brainstem responses (ABRs), noise (106-dB
sound pressure level [SPL]) was applied to both ears in 6 guinea
pigs for 30 minutes while unexposed animals served as controls. In
vivo fluorescence microscopy of the stria vascularis capillaries
was performed after surgical exposure of 1 cochlea. ABR
measurements were derived from the contralateral ear. Results:
After noise exposure, red blood cell velocity was reduced
significantly by 24.3% (120 minutes) and further decreased to 44.5%
at the end of the observation (210 minutes) in contrast to stable
control measurements. Vessel diameters were not affected in both
groups. A gradual decrease of segmental blood flow became
significant (38.1%) after 150 minutes compared with controls.
Hearing thresholds shifted significantly from 20.0 ± 5.5 dB SPL (0
minutes) to 32.5 ± 4.2dB SPL (60 minutes) only in animals exposed
to loud noise. Conclusion: With regard to novel treatments
targeting the stria vascularis in NIHL, this standardized model
allows us to analyze in detail cochlear microcirculation and
hearing function in vivo.