EFFECTIVENESS OF INTERMITTENT AND CONTINUOUS ACOUSTIC STIMULATION IN PREVENTING NOISE-INDUCED HEARING AND HAIR CELL LOSS

Resistance to noise-induced hearing loss (NIHL) was studied in gerbils exposed either to intermittent or continuous low-level noise prior to an intense noise. Auditory-evoked brainstem response (ABR) thresholds , distortion product otoacoustic emissions (DPOAEs), Q(10 dB) dB value s from compound action potential (CAP) tuning curves, and outer hair c ell (OHC) loss were measured for each group. Subjects were exposed to A-weighted noise (octave band noise centered at 2 kHz) on an intermitt ent (80 dB, 6 h/day) or continuous schedule (74 dB, 23 h/day) for 10 d ays, allowed to rest in quiet for 2 days, then exposed to intense A-we ighted noise (107 dB, 24 h/day) for 2 days. A ''noise-only'' group was exposed only to the intense noise. Gerbils exposed in both the ''inte rmittent'' and ''continuous'' groups had less (15-30 dB) temporary thr eshold shift (TTS) than those in the noise-only group. In addition, th e continuous group had less (10-15 dB) permanent threshold shift (PTS) than the other groups. These data suggest that resistance to NIHL is evident in both the intermittent and continuous groups when TTS is mea sured, but resistance to PTS is afforded only by the continuous paradi gm, Both paradigms decreased OHC loss as compared to the noise-only gr oup, with the continuous paradigm being most effective. However, neith er paradigm conserved DPOAE amplitudes or tuning curve Q(10 dB) values relative to the noise-only group. (C) 1998 Acoustical Society of Amer ica.