Analysis of Chinchilla Temporary and Permanent Threshold Shifts Following Impulsive Noise Exposure

摘要

The analysis of the chinchilla impulsive noise exposures evaluated six potential noise exposure hazard indices (HIs) for goodness-of-fit and discrimination. The candidate HIs were the MIL-STD 1474D, A-weighted equivalent 8-hour level (LAeq8hr), Auditory Hazard Assessment Algorithm for Human (AHAAH) in the Unwarned and Warned condition, Pfander C-duration, and Smoorenburg D-duration. The Auditory Research Laboratory at State University of New York at Plattsburgh and the US Army Aeromedical Research Laboratory (Fort Rucker) collected auditory evoked potentials (AEP) from more than 900 chinchilla following exposure to impulsive noise exposures. For each exposure condition, a representative waveform was digitally recorded and archived along with the baseline AEP threshold, temporary threshold shift, permanent threshold shift and histological data from each animal. The exposures investigated the effects of peak level, number of impulses (1, 10, or 100) and temporal spacing of impulses (6, 60 or 600 seconds). The current analysis evaluated the goodness of fit through the use of mixed models that evaluated the immediate threshold shift (TS0) following exposure and the permanent threshold shift (PTS) evaluated approximately 4 weeks following exposure. The threshold shifts were evaluated using six different outcome variables: categorical classification for a 25 dB shift in hearing (permanent and temporary); categorical classification for a 15 dB shift in hearing (permanent and temporary); and as a continuous variable for threshold shift (permanent and temporary).