振動、加速度、及共振對於耳石反射系的影響

Abstract

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. \nThough 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.\nIn 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.