Hair cell damage in the guinea pig due to different kinds of noise

Guinea pigs were exposed in groups of five animals to intense pure-tones or impulse noise, where either the intensity or the exposure duration was varied. The damage to the inner ear was analysed histologically and the loss of outer hair cells was used as damage parameter. The intensity in the pure-tone experimets was varied from 102 to 120 dB sound pressure level. The hair cell damage was not increasing proportionally over the entire intensity range. Above a certain critical level of intensity the damages started to increase more rapidly. This could be explained by theories stating that different mechanisms are responsible for the damage below and above the critical level. When the animals were exposed to impulse noise and the duration of the exposure was doubled the hair cell damage was also doubled up to an exposure time of 24 hours. At longer durations the increase of the damage seemed to level off. Animals exposed to impulse noise for 6 hours and with an equivalent sound level of 102 dB showed slightly higher mean damages than animals exposed to a corresponding continuous pure-tone. The results indicate that the total energy concept is a too simplified hypothesis concerning inner ear damage.