HEARING LOSS INDUCED BY TRAUMA AND NOISE INTRODUCTION
Blast produces a pressure wave of phenomenal proportions at the level of the tympanic membrane. Rupture of the drum is common and, to some extent, protective of the inner ear. Transmission of a powerful shock wave to the inner ear by way of the stapes’ footplate is sufficient to cause instantaneous injury to the hair cells of the organ of Corti, with resulting deafness. It is a general rule that the hair cells of the basal turn of the cochlea are the most sensitive to traumatic injury of all kinds. The hair cells of this part of the cochlea (which may be visualised as the fattest part of the snail shell) detect high-frequency sound, and high-frequency deafness is the typical result of cochlear injury. Depending on the severity of blast damage there may be a mild to moderate loss confined to the high frequencies, or a severe deafness across the frequency range. Often one ear is more exposed than the other, but both ears may be severely deafened in survivors of explosions at close quarters. Tinnitus is a frequent accompaniment and there may be dizziness for a while after the injury.