The importance of "temporal pattern'' in traumatic impulse noise exposures.
Danielson-R; Henderson-D; Gratton-MA; Bianchi-L; Salvi-R
J Acoust Soc Am 1991 Jul; 90(1):209-218
The importance of the temporal pattern during exposure to impulse noise as well as the difference between continuous and impulse noise and the relation between the number of impulses and peak level was examined. Monaural chinchillas had electrodes implanted in the inferior colliculus. Hearing was tested on 5 days at frequencies from 0.5 to 16 kilohertz (kHz) and averaged to give preexposure thresholds. The animals were then exposed to noise, and threshold measurements were repeated at 0.5, 2 and 8kHz at 0.25, 2, 8, 24 and 240 hours after exposure, and then retested 28 to 32 days postexposure. Three temporal patterns were presented: 1/second (1/s), burst, and salvo. Each pattern was presented at either 150 or 135 decibels (dB), and exposure duration was adjusted to produce the same total energy for all exposures. A continuous noise group was exposed to the same total energy as the impulse exposures, 91dB for 1 hour and 48 minutes. Burst and salvo groups had temporary threshold shifts (TTS) of 60 to 70dB, while the burst groups has less shift at 0.25 hours and no permanent shift. By 10 days, the 1/s group had recovered more than the salvo group and by 30 days had almost completely recovered while the salvo group had about 30dB of permanent shift. Low level, long duration exposures produced the least TTS in the burst group which recovered by 24 hours and the 1/s group had the greatest amount of TTS and recovered to within 20dB by 10 days after exposure. The temporal distribution was determined to be important in both TTS and permanent threshold shifts (PTS). The 150dB exposure produced the most hearing loss of the three patterns, while continuous noise exposure produced approximately the same TTS as the burst exposure. Histological examination of the right cochleae demonstrated that the pattern of hair loss parallels the PTS. The authors conclude that the equal energy hypothesis does not apply to all acoustic parameters.
NIOSH-Publication; NIOSH-Grant; Impulse-noise; Noise-induced-hearing-loss; Laboratory-animals; Auditory-system; Noise-exposure; Noise-levels; Hearing-disorders
Journal of the Acoustical Society of America
State University of New York, Buffalo, New York