VESTIBULAR FINDINGS ASSOCIATED WITH CHRONIC NOISE-INDUCED HEARING IMPAIRMENT

Histological and functional derangements of the vestibular system have been reported in laboratory animals exposed to high levels of noise. However, clinical series describe contradictory results with regard to vestibular disturbances in industrial workers and military personnel suffering from noise induced hearing loss (NIHL). The purpose of the p resent study was to evaluate vestibular function in a group of subject s with documented NIHL, employing electronystagmography (ENG) and the smooth harmonic acceleration (SHA) test. Subjects were 22 men sufferin g from NIHL and 21 matched controls. Significantly lower vestibule-ocu lar reflex gain (p = 0.05), and a tendency towards decreased caloric r esponses were found in the study group. No differences: in the inciden ce of vertigo symptoms, spontaneous, positional and positioning nystag mus, directional preponderance and canal paresis in the ENG, or the SH A test phase and asymmetry parameters were observed between the groups . These results demonstrated a symmetrical centrally compensated decre ase in the vestibular end organ response which is associated with the symmetrical hearing loss measured in the study group. Statistically si gnificant correlations were found between the average hearing loss, th e decrement in the average vestibulo-ocular reflex gain (p = 0.01), an d ENG caloric lateralization (p = 0.02). These correlations might indi cate a single mechanism for both cochlear and vestibular noise-induced injury. The results imply subclinical, well compensated malfunction o f the vestibular system associated with NIHL.