[Inner ear damage due to leisure and broadband noise. An experimental study on initial and permanent functional and morphological damage]

Abstract

The initial and permanent effects of leisure noise (toy pistols, rock music) compared to broadband noise were examined in 68 guinea pigs. Auditory threshold shifts at 1.5, 2, 3, 4, 6, 8, 12 und 16 kHz were registered before and immediately after exposure as well as on days 1, 2, 3, 5,7 and 21 post-exposure using the auditory brain stem response (ABR) technique. In order to examine cilia and hair cell damage in eight cochlear frequency regions (<0,4 kHz, 0,4-0,8 kHz, 0,8-1.5 kHz, 1.5-3 kHz, 3-5 kHz, 5-11.5 kHz, 11.5-26 kHz und >26 kHz), cytocochleograms were performed immediately after exposure and on days 1, 7 and 21.Frequency dependent functional or morphological damage was found which depended on the type of trauma tested. All results were highly significant ( P<0.001). The results show that partial recovery of hearing occurred within 3 days of acute acoustic trauma induced by toy pistols and within 1 day after exposure to rock music or broadband noise. There was no further recovery of hearing within the following 18 and 20 days, respectively. Furthermore, permanent threshold shifts after exposure to rock music or broadband noise were not associated with cilia and/or hair cell damage.