Short tone-burst and mechanical vibration in eliciting ocular and cervical vestibular-evoked myogenic potentials

Autor: Shou-Jen Wang, 王守仁
Rok vydání: 2012
Druh dokumentu: 學位論文 ; thesis
Popis: 100
Similar to the cervical vestibular evoked myogenic potential (cVEMP) test, which has been widely applied in clinical practice during the past decade, the recently developed ocular VEMP (oVEMP) test has been studied extensively and used to explore vestibular disorders. Both cVEMP and oVEMP tests have been used to investigate otolithic organs and their central vestibular pathways, including the ipsilateral descending sacculo-collic reflex and a crossed ascending vestibulo-ocular reflex. First of all, this study compared the oVEMPs that are elicited in response to monaural and separately, simultaneous binaural air-conducted sound (ACS) stimulations. Twenty healthy volunteers without any previous ear disorders were enrolled in this study. Each subject underwent oVEMP testing using monaural ACS stimulation (Mon-oVEMP) with different stimulus intensities. On another day, the same volunteers underwent oVEMP testing using simultaneous binaural ACS stimulation (Bin-oVEMP). With 95 dB nHL 500Hz short tone-burst ACS stimulation, the biphasic nI–pI waveforms were recorded with maximal amplitudes from the electrodes located below the eyes contralateral to the side of acoustic stimulation while the subject was gazing upward. Significant correlations were identified between Mon-oVEMPs and Bin-oVEMPs with respect to threshold, latencies and amplitude. However, no significant difference existed between Mon-oVEMPs and Bin-oVEMPs in terms of the response rate, threshold, latency or amplitude. The Bin-oVEMP test yields the same information as the Mon-oVEMP test, but the duration of recording in the former is shorter than the latter. The Bin-oVEMP test may be a more convenient screening tool for evaluating the crossed vestibulo-ocular reflex. Subsequently, the aim of this study was to determine whether bone-conducted vibration (BCV) or ACS is the optimal mode for eliciting both oVEMPs and cVEMPs. Twelve healthy volunteers, five patients with unilateral chronic otitis media, and 10 patients with unilateral Meniere disease underwent oVEMP and cVEMP tests using ACS and BCV stimulation modes in a random order. In healthy controls, BCV mode at Fz had a significantly higher response rate and larger nI-pI amplitude of oVEMPs than that of the ACS mode. In cVEMPs, a significantly higher response rate was noted in BCV mode at inion, when compared with ACS mode. However, no significant difference was noted in the p13-n23 amplitude between these two modes. In five chronic otitis media ears, absence of oVEMPs and cVEMPs in ACS mode and presence of oVEMPs and cVEMPs in BCV mode were shown. In 10 patients with Meniere disease, BCV mode elicited higher response rates of oVEMPs and cVEMPs in the pathological ears than ACS mode did. Using BCV mode, Fz and inion may be the optimal sites for eliciting oVEMPs and cVEMPs, respectively. Thus, BCV mode can be substituted for ACS mode to elicit oVEMPs and cVEMPs in the future, especially in “mass detection.” In contrast, ACS mode provides an essential clinical merit of site selectivity. Additionally, this study compared cVEMPs and oVEMPs between ACS and BCV modes to determine whether these two stimulation modes activate the same population of primary vestibular afferents. Fifteen healthy subjects underwent cVEMP and oVEMP tests using ACS stimuli at 105dB nHL and BCV stimuli at 128 dB force level (FL). The characteristic parameters of cVEMPs and oVEMPs were compared between ACS and BCV modes. The mean p13 and n23 latencies of ACS-cVEMPs were significantly longer than those of BCV-cVEMPs. Likewise, the mean nI and pI latencies for ACS-oVEMPs were also significantly longer than those for BCV-oVEMPs. There was no significant difference in the mean amplitude of cVEMPs between the ACS and BCV modes. However, comparing the oVEMP amplitude, a relationship: (Amplitude of BCV-oVEMP) = 2.3 x (Amplitude of ACS-oVEMP) was demonstrated. In short, the population of primary vestibular afferents activated by ACS and BCV stimuli is similar for cVEMPs. In contrast with oVEMPs, BCV mode activates more number of primary vestibular afferents than ACS mode does. Finally, this study combined BCV stimulation with triaxial accelerometry to correlate the acceleration magnitudes of BCV stimuli with oVEMP test results. Fourteen healthy volunteers underwent oVEMP test using BCV stimuli with simultaneous monitoring the triaxial acceleration. All subjects exhibited clear oVEMPs in response to BCV stimuli from a vibrator. The lowest acceleration magnitudes for eliciting oVEMPs along the x-, y- and z-axes were 0.05 ± 0.01 g, 0.16 ± 0.08 g, and 0.04 ± 0.01 g, respectively, exhibiting significantly higher acceleration magnitude along the y-axis than those along the x- and z-axes. In addition, significantly positive correlations were noted between the acceleration magnitude along each axis and the oVEMP amplitude. Therefore, increasing acceleration magnitude may have more synchronization of firing of vestibular afferents, resulting in more synchronized evoked potentials and greater oVEMP amplitude.
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