Asymptotic threshold shift in people with sensorineural hearing loss.

Twelve men with mild to moderate sensorineural hearing loss in the frequency range of 3 to 6 kHz were exposed to 24 hours of continuous noise. The noise was an octave band centered at 4 kHz at a level of 85 dB. Hearing thresholds were measured monaurally at 11 test frequencies ranging from 250 to 10,000 Hz prior to exposure and at selected intervals during and after exposure. Temporary threshold shift (TTS) development followed a similar time course to that observed in normal hearing subjects, asymptotic levels being reached between 8 and 12 hours of noise exposure. Maximum TTS occurred at 4 and 6 kHz. The amount of TTS was less for the subjects with sensorineural hearing loss than for people with normal hearing. However, the sound pressure level required to detect pure tone (shifted thresholds) following noise exposure was greater in the group with hearing loss than was measured in the normal hearing subjects. Within the limits of this experiment, a sensorineural hearing loss does seem to exert a significant effect on change in hearing sensitivity resulting from noise exposure.