Cervical Vestibular-Evoked Myogenic Potentials Using Vibration and Sound in Normal Subjects / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: The aim of this study was to investigate and compare the incidence and the characteristics of parameters of cervical vestibular-evoked myogenic potentials (cVEMPs) using air-conducted (AC) and bone-conducted (BC) stimulations in normal subjects. SUBJECTS AND METHOD: Twenty-four normal subjects (48 ears) with normal hearing and no previous history of dizziness were included. cVEMP responses were recorded by surface electrodes on sternocleidomastiod muscles in response to AC and BC stimuli sequentially. Variances of parameters, including thresholds, amplitudes and interaural amplitude difference ratios (IADR), were analyzed and compared. RESULTS: cVEMP responses were clearly observed in all 48 ears in both AC and BC cVEMP tests. There was no significant difference in latencies (p1 and n1). However, the thresholds in BC cVEMP testing were significantly lower than those in AC cVEMP testing, when compared to the maximum stimulation level. Interaural amplitude difference ratios showed no significant difference in between the two tests, although amplitudes at maximum stimulation intensity in BC cVEMP testing were significantly larger than those in AC cVEMP testing. CONCLUSION: This study shows that BC cVEMP testing shows lower thresholds compared to AC cVEMP testing in normal subjects, suggesting that the threshold value can be used as a parameter in detecting vestibular dysfunction in the clinic. Further studies in patients with various vestibular disorders are needed.

Effects of Gaze Positions on Ocular Vestibular Evoked Myogenic Potentials / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Recent works have demonstrated the existence of ocular vestibular evoked myogenic potentials (OVEMPs), which reflects otolith-ocular reflex. The purpose of this study was to identify an appropriate gaze position to detect OVEMPs produced by air-conducted sound stimulation in healthy subjects. SUBJECTS AND METHOD: Twenty four healthy subjects (35 ears) were included in this study. Surface electromyographic activity was recorded from active electrodes placed inferior to each eye. Stimulation with 500 Hz short tone bursts was used to activate the vestibular end-organs. RESULTS: Sound stimulation evoked negative-positive biphasic responses on both ipsilateral and contralateral eyes, while responses were contralateral eye-dominant. Contralateral eye responses had higher response incidence and larger amplitudes. Altering the direction of gaze generally changed the incidence and size of the inter-peak amplitudes. The higher incidence and larger amplitudes were recorded when the eyes are directed to the superior and ipsilateral side to the sound stimulation. In that gaze position, the amplitude was 5.3 micronV, the first negative peak latency was 10.5 ms and the following positive peak latency was 15.4 ms on the average. CONCLUSION: OVEMPs can be evoked using an air-conducted 500 Hz tone burst and are best recorded contralaterally with a upward gaze towards the source of sound stimulation. Further changes of the test parameters are needed for higher and consistent responses.

Effects of Changes of Plateau and Rise/Fall Times on Ocular Vestibular Evoked Myogenic Potentials

BACKGROUND AND OBJECTIVES: The ocular vestibular evoked myogenic potential (OVEMP) is a recently discovered test of labyrinthine function, analogous to the cervical VEMP. Recent works have demonstrated the existence of OVEMPs, which likely reflect otolith-ocular reflex. The purpose of this study was to identify the optimal plateau and rise/fall times of short tone bursts to detect OVEMPs in healthy subjects. MATERIALS AND METHODS: Thirteen healthy subjects (26 ears) were included in this study. Surface electromyographic activity was recorded from active electrodes placed inferior to each eye. Stimulation with 500 Hz short tone bursts was used. We used a variety of plateau and rise/fall times. Three different plateau times (1, 2, and 3 ms) and rise/fall times (0.5, 1, and 2 ms) were used. The incidence, amplitudes and latencies were compared. RESULTS: VEMP responses were clearly observed in all 26 ears at the plateau time of 2 ms and two rise/fall times (0.5 and 1 ms). The amplitudes in the individual ears tested were lower at the rise/fall time of 2 ms than at the other conditions. The amplitudes were lower at the plateau time of 3 ms compared to the other conditions. When the rise/fall time was prolonged from 0.5 to 2 ms, the n1 and p1 latencies were prolonged in parallel. However, there was no such change in latencies according to the plateau times. CONCLUSIONS: Our findings show that the ideal stimulation pattern for evoking OVEMP is at the rise/fall times of 0.5 or 1 ms and the plateau time of 2 ms. The waveform morphology of the VEMP responses observed with this stimulation pattern was simultaneously the most constant and marked.

Changes of VEMP Responses by the Strength of SCM Muscles Contraction and Stimulation Intensities / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: The aim of this study was to investigate the effect of the strength of SCM muscle contraction and the intensity of the sound stimulation on the VEMP parameters (amplitude, latency and threshold). SUBJECTS AND METHOD: Twenty normal subjects were included. Subjects pushed with their jaw against the hand-held inflated cuff to generate cuff pressures of 20, 40 and 60 mmHg and sequential stimulation intensities were applied. Variances of each parameter were analyzed. RESULTS: There was no significant difference in terms of threshold according to the side and strength of SCM contraction. P1-N1 amplitude demonstrated no significant differences according to the side ; however, the amplitude increased significantly as the cuff pressure and stimulation intensity increased. Interaural amplitude difference ratios showed an increased difference at 20 mmHg when compared to those at 60 mmHg. There was neither a cuff pressure effect, nor stimulation intensity effect when considering the P1 latencies. As for the N1 values, there was no stimulation intensity effect but there was a delayed latency at 20 mmHg when compared to those at 40 or 60 mmHg. Interaural latency difference of N1 latencies did not differ significantly according to the cuff pressure ; however, there was an increased difference at 20 mmHg when compared to those at 40 or 60 mmHg. CONCLUSION: This study shows that VEMP response is influenced by the cuff pressure and stimulation intensity, and we recommend to get each VEMP parameter using this feedback method in the clinical setting.