The effect of longitudinal noise exposure on behavioral audiograms and transient-evoked otoacoustic emissions.

The ear vulnerability of a group of combat soldiers was tested. The study initially included 84 soldiers and lasted two years. The soldiers were exposed to the noise of small-arms fire. Measurements included transient-evoked otoacoustic emissions (TEOAE) and pure-tone audiometry. Measurements, initially performed prior to the soldiers' basic training, were repeated several times during the study. In general, TEOAE levels (Em) decreased over time. About 57% of the ears developed a slight hearing loss (SHL) after two years of noise exposure. We define SHL as a threshold shift of 10 dB or greater, in at least at one of the audiometric frequencies 1000, 2000, 3000, 4000, or 6000 Hz. About 63% of the tested ears that had medium TEOAE level (1<Em<8 dB SPL) prior to the noise exposure, developed SHL. On the other hand, among the ears whose Em were either very low (Em< or =1 dB SPL) or very high (Em> or =8 dB SPL), less than 30% developed SHL. We suggest a prediction for ear vulnerability on the basis of Em prior to noise exposure.