Evoked Otoacoustic Emissions (EOAE's) and Inner Ear Damage from Navy Occupation Noise Exposure

摘要

In order to identify persons with early noise-induced cochlear damage and to predict susceptibility to future damage, it is desirable to develop a test that. is sensitive to effects of noise exposure on the auditory system. The aim of this project was to develop a test method applicable to the military population. Following a brief, intense noise, distortion product otoacoustic emissions (DPOAEs) were measured in normal hearing young adults for several conditions. Behavioral thresholds were measured using a Bekesy procedure. Experiment 1 involved a DPgram paradigm. F2 ranged from 1.0 to 4.0 kHz, with F2/F1=1.22. Stimulus levels were either L1=70 dB SPL, L2=60 dB SPL or L1=65 dB SPL, L2=45 dB SPL. The exposure was a 100 dB SPL, 1/3 octave band of noise centered at 1.41 KHz. Results showed a consistent decrease in behavioral thresholds at 2.0 kHz immediately following exposure. Only one of ten subjects showed a consistent decrease in DPOAE amplitude for any F2 frequency. In a second series of experiments, DFOAE input-output functions were obtained for F2-4.0 kHz, with F2/ F1=1.22 and L1=L2+15 dB, before and after exposure to a 100 dB SPL, 1/6-octave band noise centered 2.28 kHz. Pre-exposure I/O functions were very stable. In response to low to moderate level stimuli, DFOAE amplitude tended to decrease immediately post-exposure, increase and then decrease again (i.e., bounce). While for both DP paradigms the time course of the DFOAE amplitude shifts roughly paralleled threshold shifts, there was significantly inter-subject and intra-subject variability.