[Early and late reaction of the guinea pig cochlea to impulse noise]

Guinea pigs (GP) were exposed to 10 impulses of 164 dB (SPL). Measuring of cochlear microphonics (CM) at frequencies between 0.5 and 10 kHz and morphological examination of the cochlea by the surface preparation technique followed 2 hours, 2 and 6 weeks after exposure to impulse noise. During the 2 hours following noise exposure the amplitudes of CM decreased in all tested frequencies, while recovery of CM never could be observed at this time. Subsequent morphological changes in the structure of the organ of Corti could be found. They varied considerably between the tested animals. 2 and 6 weeks after exposure to 10 impulses all GP had irreversible defects in the cochlea in an extent from an incomplete pattern of outer hair cells up to a total lack of areas of the organ of Corti. Only in GP with morphological damages in a small extent CM were recordable again. A good agreement of functional and morphological results was established. It can be concluded that exposure to few single impulses with peaks of sound pressure of sufficient intensity will produce irreversible morphological defects in the cochlea, resulting in marked functional injury, if the damaged area is large enough.