Effects of industrial noise exposure on distortion product otoacoustic emissions (DPOAEs) and hair cell loss of the cochlea - long term experiments in awake guinea pigs

Distortion product otoacoustic emissions (DPOAEs), a sensitive detector of outer hair cell (OHC) function, cochlear microphonics (CM), and hair cell l oss have been monitored in 12 awake guinea pigs before and after 2 h exposu re to specific, played-back industrial noise (105 dB SPL maximal intensity) . All animals had stable DPOAE levels before noise exposure. In the first h ours after noise exposure DPOAE levels were reduced significantly. In about 70% a partial recovery of the DPOAEs was found within 4 months after noise exposure. In 16% of the investigated ears no recovery of DPOAEs was observ ed. However, in a few ears increased DPOAEs were observed after noise expos ure. Exposure to industrial noise caused both morphological changes in the middle turns of the cochlea and electrophysiological changes in the middle frequency range. A close correlation existed between reduced DPOAE levels, loss in CM potentials, and area of damaged or lost OHCs, but not with the n umbers of damaged or lost OHCs in the cochlea. It can be concluded that con tinuous industrial noise causes a damage to OHCs which differs form the dam age caused by impulse noise. (C) 2000 Elsevier Science B.V. All rights rese rved.