Acoustic trauma effects with varying exposure times.

Guinea pigs have been exposed to 20 kHz for 2 h, 1 h, 30 min, 15 min, or 7.5 min, and the resultant damage was observed 3, 6, and 12 weeks post exposure. The areas of outer hair cell damage were statistically compared. Significant differences were obtained after a 3-week survival time with the shorter exposure times, but this difference was no longer apparent after 12 weeks. Myelinated nerve fibre and inner hair cell damage occurred only with total outer hair cell loss.