The Change Of Efferent System Functions Of The Noise-induced Hearing Loss Patients

Long term exposure to excessive noise will cause noise-induced hearing loss (NIHL). NIHL has become a most common disease as the developing of the modern society. There are many causes of NIHL. The most popular factor is occupational noise exposure. In the past twenty years, the potential hearing damage hazard from exposure to non-occupational noise (leisure noise) raised intensive attentions. Non-occupational noises include listening to portable cassette player, CD player, and MP3 player and so on. NIHL can be divided into temporary threshold shift (TTS) and permanent threshold shift (PTS). The TTS can soon recover if we break away from noise exposure. The PTS cannot recover although we break away from noise exposure. The NIHL sometimes accompany tinnitus. So it is important to seek a method to detect the early noise-induced hearing loss.The investigation of the efferent system reveals that it serves an important role in accurate modulating of the cochlear functions, especially in noise environment. We should solve two problems. One is whether exposure to noise can change the functions of the efferent system, and another is whether the efferent system function test can be used as a method to detect the early NIHL.The hearing thresholds of personal listening devices users are obtained by using conventional pure-tone audiometry and extended high frequency pure-tone audiometry in present study. The NIHL patients are picked up from the subjects. The relation between the intensity of the personal listening devices and the hearing loss are investigated . The efferent system functions are tested by contralateral acoustic stimulation. The present study is composed of two parts.Part one Personal listening devices and hearing lossThe hearing thresholds of the subjects are obtained by using conventional audiometry and extended high frequency pure-tone audiometry. The results reveal that the hearing thresholds of 14.1%(34/240 ears) of the subjects have risen in some extent. The hearing thresholds of the observation group subjects are higher that of the control group subjects. The maximal available sound levels from the personal listening devices are tested by Auricle real ear test equipment. The results indicate that long-term use of the personal listening devices can cause the hearing loss. Extended high frequency audiometry can be used as a method to detect the early NIHL.Part two Efferent system and NIHLDistortion product otoacoustic emission (DPOAE) and transient evoked otoacoustic emission (TEOAE) are tested with Celesta-503 otoacoustic analyzer. The stapedius acoustic reflex is tested with GSI-33 audiometer. The amplitudes of the DPOAE and TEOAE of the observation group are lower than that of the control group. The amplitude decreases of the DPOAE and TEOAE of the observation group are lower than that of the control group. The test of efferent system functions can be used as a sensitive method to detect the early NIHL.In conclusion, this study indicates that long-term use of personal listening devices can cause NIHL. The extended high frequency audiometry and efferent system function test can be used as sensitive method to detect the early NIHL.