振動、加速度、及共振對於耳石反射系的影響

Vibration, Acceleration and Resonance on the Otolithic Reflex System

林奎佑(Kuei-You Lin)

指導教授 ： 趙福杉

國立臺灣大學/工學院/醫學工程學研究所/博士(2021年)

https://doi.org/10.6342/NTU202100339

摘要

2005年澳洲南威爾斯大學的Rosengrens及Colebatch發表「前庭誘發眼肌電位」(ocular VEMP ，oVEMP)檢查，遂開啟了研究內耳前庭器官-橢圓囊的濫殤。另一方面加上前已發表的研究內耳前庭器官-球囊的「前庭誘發頸肌電位」cervical VEMP (cVEMP) 檢查，於是耳石器官的研究乃成為近年來神經耳科學界一熱門話題。詳細來說，oVEMP檢查主要用以檢測交叉的「前庭眼反射」(vestibulo-ocular reflex，VOR)路徑，可反映橢圓囊及上前庭神經傳導的訊息。生理學上，橢圓囊的功能在檢測垂直線性加速度，感應重心位置以穩定頭位。此功能主要藉由橢圓囊斑上密集的耳石分佈來輔佐。其機制主要透過橢圓囊斑感應加速度變化所產生的剪力(shearing force)後，進一步再藉由耳石的移動來刺激毛細胞產生電位，經由輸出神經纖維(efferent fiber)傳至中樞神經系統，進行平衡覺的整合。藉由此機轉，目前oVEMP檢查在臨床上主利用氣導音聲及骨導振動兩種刺激模式來誘發。氣導音聲的刺激源為105dBnHL，500Hz 短迴旋音；反之，骨導振動乃利用迷你振盪器(B K type 4810, Naerum, Denmark)敲擊頭顱，以144 dB force level產生y軸之最大加速度0.3g，連續刺激得到結果。然而在臨床oVEMP檢查，由於氣導音聲對橢圓囊刺激的強度較弱，因此目前際普遍認為骨導振動刺激為oVEMP檢查的較佳刺激模式。
雖然骨導振動刺激為國際共識之oVEMP檢查刺激模式，但最佳刺激位置卻仍莫衷一是。根據近年來的臨床研究，敲擊頭顱正中矢狀切面均能成功地誘生oVEMP反應，其中尤以敲擊前額(forehead)的誘發率為最高。而前額敲擊的建議位置，在健康人的實驗中則證明了眉間(Fpz)與髮線(Fz)位置均可誘發相同之結果。話雖如此，在病患族群是否如此卻仍未明，主要由於許多未解的謎題，諸如迷你振盪器振動頭顱後所產生之能量在傳遞至耳石器官的過程中會因何種因素而產生改變。由於眉間(Fpz)與髮線(Fz)之間，存在著額竇(frontal sinus)，而額竇的發育程度、頭顱密度及顱內軟組織的分佈，甚至是顱內疾病如鼻竇炎、中耳炎、乳突炎等，皆會影響能量的傳遞，進而影響前庭誘發眼肌電位的反應，造成檢查結果的變化。有鑒於此，於是進行實驗，希望能闡明敲擊振動與頭顱共振之間之關係，並進一步釐清干擾因子，使該檢查更為省時及有效，乃本計畫的最終目的。
於此博士論文中，我們進行了一系列的實驗來分析頭顱中前額竇對頭部振動之影響。主要分為兩個部分，其一是透過臨床實驗藉由比較年齡、性別以及不同前額竇發育程度在病患族群中對oVEMP檢查結果的影響；其二是設計假體模型驗證系統內空腔與周圍介質的互動是否會改變系統加速度的量測值，以進一步解釋支持臨床觀察到之現象。根據目前結果顯示，前額竇之存在的確會對前額敲擊後橢圓囊斑感受到的振動能量有所影響，並且前額竇空腔在未達一定大小或處在疾病狀態下時oVEMP反應之強度會因而減弱；且假體模型亦支持此項結論。然而，對於移除疾病狀態是否便可強化oVEMP反應以及是否可透過此結論使oVEMP檢查能成為前額竇生理狀態之臨床評估工具則有待後續實驗釐清。

關鍵字

前庭誘發眼肌電位 ； 骨振動刺激 ； 前額竇 ； 頭部加速度 ； 共振

並列摘要

As known, Colebatch and Rosengren from Australia successfully demonstrated ocular vestibular-evoked myogenic potential (oVEMP) in 2005. With the introduction of oVEMP and previously developed cVEMP, clinical neuro-otologists thus could assess otolithic organ function via subjective tools. Because of its importance, research on the VEMP test has dominated neuro-otological studies for the recent two decades. Meanwhile, applying VEMP tests in vestibular clinic is also more and more important for assessing otolithic organ function. In general, oVEMP test predominantly assesses the utricular function via crossed vestibulo-ocular reflex (VOR) pathway. Physiologically, the utricle detects head acceleration in horizontal vector, stabilizing head position and aiding postural balance. More precisely, utricular macula senses a shearing force related with the otolith displacement in response to head motion. Hence, hair cell then deflects and triggers actional potential, which transmits via efferent fibers (mainly the superior vestibular nerve) to the central nervous system for further equilibrium sensation coordination. With the feature of sensing acceleration change, there are two stimulation modes to stimulating utricle and eliciting oVEMP responses clinically, including air-conducted sound (ACS) and bone-conducted vibration (BCV). The ACS stimulation utilizes 500 Hz click sound with the intensity of 105dBnHL. For the BCV stimuli, it was generated by a vibrator placed on the subject’s head, inducing a maximal acceleration of 0.3g along the y axis, about 128dB force level. However, BCV-oVEMP is more preferred in clinical setting than ACS mode because the latter yields small response and unreliable results.
Though BCV mode serves the proper way to elicit oVEMP response, the optimal stimulation site remains unclear. According to previous studies, it is known that oVEMP could be elicited by skull tapping along the mid-sagittal plane at Fpz, Fz, Cz, and inion sites, within which, the forehead tapping results in most optimal response in terms of reflex amplitude (Lin et al., 2010). And subsequent healthy control study further demonstrated that tapping at Fpz (10% of the nasion-inion distance from nasion) and Fz (30% of the nasion-inion distance from nasion) sites both result reliable oVEMP results (Lin et al., 2012). Nevertheless, Fpz and Fz still yield inconsistent oVEMP results, probably attributed to inter-individual difference along the energy transmitting from forehead to the otolithic organ. For example, frontal sinus development, skull density, intra-cranial soft tissue distribution, even the frontal disease (e.g., frontal sinusitis) all alter acceleration profiles to some extent. Based on above, to investigate possible interfering factors in energy transmission within oVEMP elicitation is necessary to improve oVEMP test protocol.
In this dissertation, we performed a series of experiments to examine the effect of frontal sinus on head vibration. In clinical part, patients of various ages and genders together with various extents of frontal sinus development were recruited to examine possible factors affecting oVEMP responses in pathologic ears. While in laboratory part, acceleration profile change in systems with various air volume and filling materials via different dummy models was investigated. Current results revealed that the presence of frontal sinus would affect the oVEMP responses, likely via altering skull vibration profile after forehead vibration stimuli. Besides, inadequate pneumatization and pathological status of frontal sinus both lower oVEMP response rates. Our next step will focus on examining whether removing frontal sinus disease would strengthen oVEMP response and whether oVEMP response could reflect frontal sinus condition.

並列關鍵字

oVEMP ； bone vibration stimuli ； frontal sinus ； head acceleration ； resonance

參考文獻

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