Models for Assessing Risk of Occupational Hearing Loss, Final Report;Final rept

摘要

This research project was designed to determine the ability of chemical asphyxiants, carbon monoxide and cyanide, to potentiate noise induced hearing loss. Significant findings : (1) Carbon monoxide potentiates noise induced hearing loss (NIHL); (2) The lower bound benchmark dose for such potentiation lies between 200-300 ppm CO; (3) Carbon monoxide disrupts the relationship between increasing noise duty cycle for intermittent noise and increasing auditory impairment; (4) The potentiating effect of CO on NIHL can be reduced or blocked by administration of the free radical scavenger PBN but not by the glutamate receptor blocker, MK-801; (5) Direct measurement of free radicals in cochlear tissue shows a significant increase in free radicals with combined exposure to CO and noise, but no measurable change above baseline for CO and for noise given individually; and (6) Hydrogen cyanide produces a dose dependent increase in NIHL.