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Optimizing ocular vestibular evoked myogenic potentials: electrode montage and stimulus frequency

Heijdt, J.B. van der (2017) Optimizing ocular vestibular evoked myogenic potentials: electrode montage and stimulus frequency.

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Abstract:The ocular Vestibular Evoked Myogenic Potentials (oVEMP) test is a functional vestibular test that can evaluate the function of the utricle and the superior vestibular nerve by measuring the potentials of the inferior oblique muscle. Large vibratory devices such as the minishaker can be used to evoke oVEMPs. Most literature uses the “standard” electrode montage to record the responses, an alternative, the belly-tendon montage, is hypothesized to yield larger responses than the standard montage, thereby benefiting clinical evaluation. Additionally, it is unclear with which stimulus frequency oVEMP responses can be best evoked using a minishaker setup. Objective The aim of this study is to investigate the optimal electrode montage and stimulus frequency for obtaining oVEMP responses evoked with a minishaker. Methods Two experiments were conducted, both in 15 healthy volunteers. The first experiment investigated the influence of the electrode montage (standard or belly-tendon), the second experiment investigated the optimal stimulus frequency (250, 500, 750, 1000 Hz). The main outcome parameters were response rate, threshold and n1p1 peak-to-peak amplitude. The secondary parameters were n1 and p1 latency and the inter-ocular ratio. The reproducibility and interobserver variability were examined in a subset of 8 subjects. Results There was a 100% response rate for 500 and 750 Hz stimuli with the belly-tendon montage. The response rate to 1000 Hz stimuli was 40% and no responses could be evoked to 250 Hz stimuli. Using the standard montage, no response could be evoked in one subject. The threshold to 500 Hz stimuli with the belly-tendon montage was significantly lower compared to all other conditions. The amplitude was also significantly larger compared to the standard montage. The reproducibility and interobserver variability were high, except for a 2-3 dB difference in the determined thresholds. Conclusion The belly-tendon montage yields larger amplitudes and lower threshold compared to the standard montage and is therefore the preferred method for measuring oVEMPs. The most optimal oVEMP responses are acquired with 500 Hz stimuli. 750 Hz stimuli are a good alternative, but higher or lower frequencies are unsuitable to the current setup. The most objective clinical parameter is the n1p1 amplitude at a fixed intensity, as there is a grey area in the threshold determination.
Item Type:Essay (Master)
Faculty:TNW: Science and Technology
Subject:44 medicine
Programme:Technical Medicine MSc (60033)
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