摘要
Quantitative estimation of sound transmission attenuation by different middle-ear protecting mechanisms was made with the use of a computer-based CM-cogram analyzing method (FFT of cochlear output in response to white noise) and other audiometric means. Strong reflex contraction of the middle-ear muscles in guinea pigs may cause a 5- 20 dB transmission attenuation in different frequency ranges. For impulse noise exposure, the presence of an effective reflex at the lashing of every impulse may reduce the post - exposure hearing threshold shift in 15 dB on an average.Increasing tension of the tympanic membrane by applying pressure to the ear- canal is also eflicacious.especially for frequencies below 500 Hz where attenuation of more than 10dB may result at a pressure difference of about 200mm H2O between the two sides of the membrane. Simulated opening of the eustachian tube helps only very insignificantly, with attenuation less than 5 dB. Destruction of the middle-ear structures ( drum perforation, ossicular disruption etc .) and fluid accumulation inside the tympanic cavity may buffer acoustic trauma to the cochlea to different extent depending on the amount of transmission attenuation.
Quantitative estimation of sound transmission attenuation by different middle-ear protecting mechanisms was made with the use of a computer-based CM-cogram analyzing method (FFT of cochlear output in response to white noise) and other audiometric means. Strong reflex contraction of the middle-ear muscles in guinea pigs may cause a 5- 20 dB transmission attenuation in different frequency ranges. For impulse noise exposure, the presence of an effective reflex at the lashing of every impulse may reduce the post - exposure hearing threshold shift in 15 dB on an average.Increasing tension of the tympanic membrane by applying pressure to the ear- canal is also eflicacious.especially for frequencies below 500 Hz where attenuation of more than 10dB may result at a pressure difference of about 200mm H2O between the two sides of the membrane. Simulated opening of the eustachian tube helps only very insignificantly, with attenuation less than 5 dB. Destruction of the middle-ear structures ( drum perforation, ossicular disruption etc .) and fluid accumulation inside the tympanic cavity may buffer acoustic trauma to the cochlea to different extent depending on the amount of transmission attenuation.
