The effects of noise during recovery from an acute acoustic trauma

Abstract

Groups of chinchillas were exposed to ten 160-dB peak SPL reverberant blast waves from a conventional shock tube at a rate of one blast per minute. Immediately following exposure, the animals were (1) returned to the quiet (approx. 40 dBA) animal colony or (2) placed in a 72-dB SPL rms broadband noise for 24 h. The broadband noise caused no temporary or permanent hearing losses nor significant sensory cell losses in a control group of six subjects. Subjects that recovered from the blast-wave exposure in the 72-dB noise averaged significantly more permanent threshold shifts than groups of animals recovering in the quiet animal colony. If the subjects were placed into the quiet animal colony for 2 h immediately following the blast-wave exposure and then allowed to recover for 24 h in the 72-dB noise, their mean permanent thresholds shifts were indistinguishable from the group that recovered in quiet only. Results indicate that there is a short period of time following an acute acoustic trauma in which the cochlea is vulnerable to stimuli that can exacerbate the hearing loss. Therefore, post-traumatic treatment protocols may be developed to reduce hearing loss. [Research supported by the Deafness Research Foundation.]