Normalizing cVEMPs: Which Method Is the Most Effective?

OBJECTIVES: To determine the most effective method for normalizing cervical vestibular evoked myogenic potentials (cVEMPs). DESIGN: cVEMP data from 20 subjects with normal hearing and vestibular function were normalized using 16 combinations of methods, each using one of the 4 modes of electromyogram (EMG) quantification described below. All methods used the peak to peak value of an averaged cVEMP waveform (VEMPpp) and obtained a normalized cVEMP by dividing VEMPpp by a measure of the EMG amplitude. EMG metrics were obtained from the EMG within short- and long-duration time windows. EMG amplitude was quantified by its root-mean-square (RMS) or average full-wave-rectified (RECT) value. The EMG amplitude was used by (a) dividing each individual trace by the EMG of this specific trace, (b) dividing VEMPpp by the average RMS or RECT of the individual trace EMG, (c) dividing the VEMPpp by an EMG metric obtained from the average cVEMP waveform, or (d) dividing the VEMPpp by an EMG metric obtained from an average cVEMP "noise" waveform. Normalization methods were compared by the normalized cVEMP coefficient of variation across subjects and by the area under the curve from a receiver-operating-characteristic analysis. A separate analysis of the effect of EMG-window duration was done. RESULTS: There were large disparities in the results from different normalization methods. The best methods used EMG metrics from individual-trace EMG measurements, not from part of the average cVEMP waveform. EMG quantification by RMS or RECT produced similar results. For most EMG quantifications, longer window durations were better in producing receiver-operating-characteristic with high areas under the curve. However, even short window durations worked well when the EMG metric was calculated from the average RMS or RECT of the individual-trace EMGs. Calculating the EMG from a long-duration window of a cVEMP "noise" average waveform was almost as good as the individual-trace-EMG methods. CONCLUSIONS: The best cVEMP normalizations use EMG quantification from individual-trace EMGs. To have the normalized cVEMPs accurately reflect the vestibular activation, a good normalization method needs to be used.

Toward Optimizing VEMP: Calculating VEMP Inhibition Depth With a Generic Template.

OBJECTIVES: Cervical vestibular evoked myogenic potentials (cVEMP) indirectly reveal the response of the saccule to acoustic stimuli through the inhibition of sternocleidomastoid muscle electromyographic response. VEMP inhibition depth (VEMPid) is a recently developed metric that estimates the percentage of saccular inhibition. VEMPid provides both normalization and better accuracy at low response levels than amplitude-normalized cVEMPs. Hopefully, VEMPid will aid in the clinical assessment of patients with vestibulopatholgy. To calculate VEMPid a template is needed. In the original method, a subject's own cVEMP was used as the template, but this method can be problematic in patients who do not have robust cVEMP responses. We hypothesize that a "generic" template, created by assembling cVEMPs from healthy subjects, can be used to compute VEMPid, which would facilitate the use of VEMPid in subjects with pathological conditions. DESIGN: A generic template was created by averaging cVEMP responses from 6 normal subjects. To compare VEMPid calculations using a generic versus a subject-specific template, cVEMPs were obtained in 40 healthy subjects using 500, 750, and 1000 Hz tonebursts at sound levels ranging from 98 to 123 dB peSPL. VEMPids were calculated both with the generic template and with the subject's own template. The ability of both templates to determine whether a cVEMP was present or not was compared with receiver operating characteristic curves. RESULTS: No significant differences were found between VEMPid calculations using a generic template versus using a subject-specific template for all frequencies and sound levels. Based on the receiver operating characteristic curves, the subject-specific and generic template did an equally good job at determining threshold. Within limits, the shape of the generic template did not affect these results. CONCLUSIONS: A generic template can be used instead of a subject-specific template to calculate VEMPid. Compared with cVEMP normalized by electromyographic amplitudes, VEMPid is advantageous because it averages zero when there is no sound stimulus and it allows the accumulating VEMPid value to be shown during data acquisition as a guide to deciding when enough data has been collected.

Serial cVEMP Testing is Sensitive to Disease Progression in Ménière Patients.

OBJECTIVE: To assess the cervical vestibular evoked myogenic potentials (cVEMPs) ability to track disease progression in Ménière's disease patients over time and identify the most sensitive outcome measurement. STUDY DESIGN: Retrospective. SETTING: Large specialty hospital, department of otolaryngology. SUBJECTS: Twenty nine Ménière's patients and seven migraine associated vertigo (MAV) patients. INTERVENTION: All patients underwent two cervical vestibular evoked myogenic potential tests at 250, 500, 750, and 1000 Hz with a minimum test interval of 3 months. MAIN OUTCOME MEASURES: Threshold, peak-to-peak (PP) amplitude, interaural asymmetry ratio, and effect size. RESULTS: In affected Ménière's ears all outcome measures were worse during the second test, for threshold this difference was statistically significant at 750 and 1000 Hz compared with the first test. Compared with young healthy ears the threshold was significantly worse at all frequencies. PP amplitude was significantly decreased at the second test at 750 Hz compared with the first test. In MAV no significant difference between tests was found at any frequency in PP amplitude or threshold. In Ménière's ears, threshold showed a higher first-to-second effect size at 500, 750, and 1000 Hz compared with PP amplitude. CONCLUSION: cVEMP is able to track progression in Ménière's disease over time. Thresholds were the most effective outcome measure to both track progression and to distinguish between MAV and Ménière's patients.

Increasing the Stimulation Rate Reduces cVEMP Testing Time by More Than Half With No Significant Difference in Threshold.

OBJECTIVE: Assessing the effect of a higher stimulation rate in cervical vestibular evoked myogenic potential (cVEMP) outcome measurements. STUDY DESIGN: Prospective cohort study. SETTING: Large specialty hospital, Department of otolaryngology. SUBJECTS: Eleven healthy subjects were used in this study. INTERVENTION: All subjects underwent a cervical vestibular evoked myogenic potential test at 500, 750, and 1000 Hz using 5 and 13 Hz stimulation rates. MAIN OUTCOME MEASURES: Threshold, peak-to-peak (PP) amplitude, and interaural asymmetry ratio (IAR). RESULTS: PP cVEMP amplitudes were larger at 5/s than at 13/s. The 5/s to 13/s differences were statistically significant at 500 and 750 Hz (p < 0.02). The coefficient of variation in PP amplitudes across subjects, was not significantly different at any frequency for 5/s versus 13/s stimuli. No significant difference was found in the IAR at any frequency. The cVEMP thresholds were similar between stimulation rates. CONCLUSION: In healthy young subjects no significant differences in threshold were found between 5/s and 13/s stimulation rates, though intrasubject PP amplitude was significantly lower at the faster stimulation rate. Increasing stimulation rate reduces test time and burden. Additional studies are needed to verify that these conclusions are also true for patients.

Normalization reduces intersubject variability in cervical vestibular evoked myogenic potentials.

OBJECTIVE: Cervical vestibular evoked myogenic potentials are used to assess saccular and inferior vestibular nerve function. Normalization of the VEMP waveform has been proposed to reduce the variability in vestibular evoked myogenic potentials by correcting for muscle activation. In this study, we test the hypothesis that normalization of the raw cervical VEMP waveform causes a significant decrease in the intersubject variability. STUDY DESIGN: Prospective cohort study. SETTING: Large specialty hospital, department of otolaryngology. SUBJECTS: Twenty healthy subjects were used in this study. INTERVENTION: All subjects underwent cervical vestibular evoked myogenic potential testing using short tone bursts at 250, 500, 750, and 1,000 Hz. Both intersubject and intrasubject variability was assessed. MAIN OUTCOME MEASURES: Variability between raw and normalized peak-to-peak amplitudes was compared using the coefficient of variation. Intrasubject variability was assessed using the intraclass correlation coefficient and interaural asymmetry ratio. RESULTS: cVEMPs were present in most ears. Highest peak-to-peak amplitudes were recorded at 750 Hz. Normalization did not alter cVEMP tuning characteristics. Normalization of the cVEMP response caused a significant reduction in intersubject variability of the peak-to-peak amplitude. No significant change was seen in the intrasubject variability. CONCLUSION: Normalization significantly reduces cVEMP intersubject variability in healthy subjects without altering cVEMP characteristics. By reducing cVEMP amplitude variation due to nonsaccular, muscle-related factors, cVEMP normalization is expected to improve the ability to distinguish between healthy and pathologic responses in the clinical application of cVEMP testing.