VA RR&D National Center for Rehabilitative Auditory Research, Veterans Affairs Portland Health Care System, OR.
Department of Otolaryngology-Head & Neck Surgery, Oregon Health & Science University, Portland.
J Speech Lang Hear Res. 2023 Nov 9;66(11):4635-4652. doi: 10.1044/2023_JSLHR-23-00234. Epub 2023 Oct 27.
Animal models and human temporal bones indicate that noise exposure is a risk factor for cochlear synaptopathy, a possible etiology of tinnitus. Veterans are exposed to high levels of noise during military service. Therefore, synaptopathy may explain the high rates of noise-induced tinnitus among Veterans. Although synaptopathy cannot be directly evaluated in living humans, animal models indicate that several physiological measures are sensitive to synapse loss, including the auditory brainstem response (ABR), the middle ear muscle reflex (MEMR), and the envelope following response (EFR). The purpose of this study was to determine whether tinnitus is associated with reductions in physiological correlates of synaptopathy that parallel animal studies.
Participants with normal audiograms were grouped according to Veteran status and tinnitus report (Veterans with tinnitus, Veterans without tinnitus, and non-Veteran controls). The effects of being a Veteran with tinnitus on ABR, MEMR, and EFR measurements were independently modeled using Bayesian regression analysis.
Modeled point estimates of MEMR and EFR magnitude showed reductions for Veterans with tinnitus compared with non-Veterans, with the most evident reduction observed for the EFR. Two different approaches were used to provide context for the Veteran tinnitus effect on the EFR by comparing to age-related reductions in EFR magnitude and synapse numbers observed in previous studies. These analyses suggested that EFR magnitude/synapse counts were reduced in Veterans with tinnitus by roughly the same amount as over 20 years of aging.
These findings suggest that cochlear synaptopathy may contribute to tinnitus perception in noise-exposed Veterans.
动物模型和人类颞骨表明，噪声暴露是耳蜗突触病的一个风险因素，而耳蜗突触病可能是耳鸣的病因之一。退伍军人在服兵役期间会接触到高水平的噪声。因此，突触病可能可以解释退伍军人中噪声性耳鸣的高发病率。虽然突触病不能在活体人类中直接评估，但动物模型表明，几种生理测量对突触丢失敏感，包括听觉脑干反应（ABR）、中耳肌反射（MEMR）和包络跟随反应（EFR）。本研究的目的是确定耳鸣是否与平行于动物研究的突触病的生理相关性降低有关。
根据退伍军人身份和耳鸣报告将具有正常听力图的参与者分为组（有耳鸣的退伍军人、无耳鸣的退伍军人和非退伍军人对照组）。使用贝叶斯回归分析分别对有耳鸣的退伍军人对 ABR、MEMR 和 EFR 测量的影响进行建模。
MEMR 和 EFR 幅度的模型估计点显示，有耳鸣的退伍军人与非退伍军人相比有所减少，而 EFR 的减少最为明显。通过将 EFR 幅度与先前研究中观察到的年龄相关的 EFR 幅度和突触数量减少进行比较，使用两种不同的方法为退伍军人耳鸣对 EFR 的影响提供了背景。这些分析表明，有耳鸣的退伍军人的 EFR 幅度/突触计数减少了大约与 20 多年的衰老相同的量。
这些发现表明，耳蜗突触病可能导致噪声暴露的退伍军人出现耳鸣感知。
