Functional impairment of the vestibular end organ resulting from impulse noise exposure.

OBJECTIVES/HYPOTHESIS: To assess the effect of exposure t o impulse noise, known to cause damage tothe cochlea, on the vestibular part of the inner ear using short latency vestibular evoked potentials (VsEPs), which is a direct and objective test for evaluating the function of the vestibular end organs.

STUDY

DESIGN

Prospective animal study.

METHODS

Sand rats (Psammomys obesus) underwent baseline measurements of VsEPs in response to linear and angular acceleration stimuli and measurement of the auditory nerve and brainstem evoked response (ABR). The animals were then exposed to 10 gunshots generating impulse noise at an intensity of approximately 160 dB sound pressure level (SPL). Repeat measurements of the evoked potentials were conducted 2 to 4 hours, 1 week, and 6 weeks after the exposure. The amplitude and latency of the first wave of VsEPs in response to linear and angular acceleration stimuli, reflecting the function of the otolith organs and semicircular canals respectively, were compared between baseline and post-exposure measurements, as were ABR thresholds.

RESULTS

The amplitude of the first wave of the VsEPs in response to linear acceleration was significantly (P <.001) reduced and the latency significantly (P <.005) prolonged 2 to 4 hours after the exposure in comparison to baselinemeasurements. The latency prolongation persisted in follow-up measurements, whereas the amplitude showed partial recovery. The first wave of VsEPs in response to angular acceleration was unchanged long-term. ABR thresholds were elevated in the long-term by 60 dB.

CONCLUSION

It seems that impulse noise not only damages the cochlea, but also causes clear functional impairment to the vestibular end organs, mainly the otolith organs.