Bramhall Naomi F, Konrad-Martin Dawn, McMillan Garnett P, Griest Susan E
1VA RR&D National Center for Rehabilitative Auditory Research (NCRAR), VA Portland Health Care System, Portland, Oregon, USA; and 2Department of Otolaryngology/HNS, Oregon Health & Science University, Portland, Oregon, USA.
Ear Hear. 2017 Jan/Feb;38(1):e1-e12. doi: 10.1097/AUD.0000000000000370.
Recent animal studies demonstrated that cochlear synaptopathy, a partial loss of inner hair cell-auditory nerve fiber synapses, can occur in response to noise exposure without any permanent auditory threshold shift. In animal models, this synaptopathy is associated with a reduction in the amplitude of wave I of the auditory brainstem response (ABR). The goal of this study was to determine whether higher lifetime noise exposure histories in young people with clinically normal pure-tone thresholds are associated with lower ABR wave I amplitudes.
Twenty-nine young military Veterans and 35 non Veterans (19 to 35 years of age) with normal pure-tone thresholds were assigned to 1 of 4 groups based on their self-reported lifetime noise exposure history and Veteran status. Suprathreshold ABR measurements in response to alternating polarity tone bursts were obtained at 1, 3, 4, and 6 kHz with gold foil tiptrode electrodes placed in the ear canal. Wave I amplitude was calculated from the difference in voltage at the positive peak and the voltage at the following negative trough. Distortion product otoacoustic emission input/output functions were collected in each participant at the same four frequencies to assess outer hair cell function.
After controlling for individual differences in sex and distortion product otoacoustic emission amplitude, the groups containing participants with higher reported histories of noise exposure had smaller ABR wave I amplitudes at suprathreshold levels across all four frequencies compared with the groups with less history of noise exposure.
Suprathreshold ABR wave I amplitudes were reduced in Veterans reporting high levels of military noise exposure and in non Veterans reporting any history of firearm use as compared with Veterans and non Veterans with lower levels of reported noise exposure history. The reduction in ABR wave I amplitude in the groups with higher levels of noise exposure cannot be accounted for by sex or variability in outer hair cell function. This change is similar to the decreased ABR wave I amplitudes observed in animal models of noise-induced cochlear synaptopathy. However, without post mortem examination of the temporal bone, no direct conclusions can be drawn concerning the presence of synaptopathy in the study groups with higher noise exposure histories.
近期动物研究表明，耳蜗突触病变，即内毛细胞 - 听神经纤维突触部分丧失，可在无任何永久性听阈偏移的情况下因噪声暴露而发生。在动物模型中，这种突触病变与听觉脑干反应（ABR）I波振幅降低有关。本研究的目的是确定临床上纯音阈值正常的年轻人中，较高的终身噪声暴露史是否与较低的ABR I波振幅相关。
29名年轻退伍军人和35名非退伍军人（年龄在19至35岁之间），纯音阈值正常，根据他们自我报告的终身噪声暴露史和退伍军人身份被分为4组中的1组。使用置于耳道内的金箔尖端电极，在1、3、4和6kHz频率下对交替极性短音刺激进行阈上ABR测量。I波振幅通过正峰电压与随后负谷电压之差计算得出。在相同的四个频率下收集每个参与者的畸变产物耳声发射输入/输出函数，以评估外毛细胞功能。
在控制了性别和畸变产物耳声发射振幅的个体差异后，与噪声暴露史较少的组相比，报告有较高噪声暴露史的参与者组在所有四个频率的阈上水平下ABR I波振幅较小。
与报告噪声暴露史水平较低的退伍军人和非退伍军人相比，报告高水平军事噪声暴露的退伍军人和报告有任何枪支使用史的非退伍军人的阈上ABR I波振幅降低。噪声暴露水平较高组中ABR I波振幅的降低不能用性别或外毛细胞功能的变异性来解释。这种变化类似于在噪声诱导的耳蜗突触病变动物模型中观察到的ABR I波振幅降低。然而，在没有对颞骨进行尸检的情况下，无法就噪声暴露史较高的研究组中是否存在突触病变得出直接结论。
