The effect of 'conditioning' exposures on hearing loss from traumatic exposure.
Campo-P; Subramaniam-M; Henderson-D
Hear Res 1991 Oct; 55(2):195-200
Experiments were conducted to explore the relationship between the conditioning exposure and the resultant changes in vulnerability to noise induced hearing loss. Adult chinchillas were made monaural through surgical destruction of the left cochlea. A chronic recording electrode was then stereotaxically implanted into the left inferior colliculus and a ground electrode was implanted just below the dura mater. The chinchillas were exposed to an octave band of noise centered at 0.5 kilohertz at 95 decibels (dB) for 6 hours/day for 10 days. Animals recovered to preexposure sensitivity and at 5 days after the last exposure they were reexposed to the same noise at 106dB. Thresholds recorded at various time intervals following the second exposure were compared with those recorded in a control group exposed only to the higher level noise. The results of the study showed that the experimental animals incurred less hearing loss compared to the control group when reexposed to the same noise at a higher level. The toughening effect appeared to persist even after 5 days of recovery, suggesting that the toughening phenomenon is not attributable only to temporary changes in cochlea following the low level exposures. The finding that the conditioning exposures can render the subject less susceptible to permanent threshold shift raises a number of practical and theoretical questions for the workplace.
NIOSH-Publication; NIOSH-Grant; Noise-induced-hearing-loss; Noise-exposure; Laboratory-animals; Hearing-threshold; Acute-exposure
State University of New York, Buffalo, New York