Evaluating Fixed Single-Point Parameters When Applied to Vestibular Evoked Myogenic Potentials: The Effect of Single Point and Signal Window.

OBJECTIVES: Several studies have applied a common objective detection algorithm (fixed single point [ Fsp ]) for detection of the vestibular evoked myogenic potential (VEMP). However, fundamental parameters of Fsp , such as establishing the location and duration of a signal window, have not been examined. In addition, Fsp criterion values used for response detection have not been established for cervical VEMPs (cVEMPs) or ocular VEMPs (oVEMPs). The purpose of this article was to investigate the effect of various single points and signal windows on Fsp , as well as determining Fsp criteria to determine response presence for cVEMP and oVEMP in a group of young healthy participants. DESIGN: Twenty young healthy adults under the age of 30 and with no history of hearing or balance concerns were enrolled in the study protocol. Air-conducted cVEMPs and oVEMPs were evoked using 500 Hz tone bursts at 123 dB pSPL recorded at a fixed electromyography activation of 50 µV for cVEMPs and 35° gaze angle for oVEMPs. Responses were analyzed off-line using visual and objective detection. Fsp was applied to cVEMPs and oVEMPs using a range of single points and signal windows. RESULTS: Noise variance was lowest for cVEMPs at the latency of P1, and for oVEMPs noise variance was not significantly different across the single-point latencies. On average, extending the length of the signal window lowered the Fsp value in cVEMPs and oVEMPs. An Fsp value of 2.0 was chosen as the criterion cutoff associated with the 95th percentile during no-response conditions using group data for cVEMPs and oVEMPs, respectively. Fsp values for cVEMPs and oVEMPs were not significantly different from each other. DISCUSSION: This study established single-point latency and time-window parameters for VEMP-related applications of the Fsp detection algorithm. Fsp criteria values were established for cVEMP and oVEMP. Using these parameters, responses were detected in all participants.

Self-Reported Symptoms of Vertigo and Imbalance Are Prevalent Among Adults With Chronic Moderate-Severe Traumatic Brain Injury: A Preliminary Analysis.

PURPOSE: Dizziness and imbalance are common symptoms during the acute phase of traumatic brain injury (TBI). However, there is evidence to suggest that these symptoms persist into the chronic phase of injury. Few prospective studies have examined the frequency and type of dizziness and imbalance in adults with chronic moderate-severe TBI. The aim of this preliminary analysis was to investigate the prevalence of these symptoms in adults with chronic moderate-severe TBI. METHOD: Twenty-four adults with chronic moderate-severe TBI and a group of 19 age-, sex-, and education-matched noninjured comparison participants were recruited. Self-reported dizziness and imbalance were measured using a modified version of a standard case history form. Significant associations between group (TBI group or noninjured comparison [NC] participants) and self-reports of dizziness, imbalance, and related symptoms (endorsed "yes" or "no") were explored. RESULTS: The TBI group most reported lightheadedness (75%), vertigo (38%), and imbalance and/or falling (46%). The most common related symptom reported by the TBI group was headache (63%) and nausea (46%). Significant associations revealed that the TBI group responded "yes" in higher percentages than the NC group across all categories (dizziness, imbalance, and related symptoms). There were no statistically significant relationships among dizziness, imbalance, or headache symptoms within the TBI group. CONCLUSIONS: These preliminary findings suggest that dizziness and imbalance are prevalent in adults with chronic moderate-severe TBI. Persistent vertiginous symptoms may point to an underlying vestibular impairment. However, further research is needed to characterize vestibular function in chronic moderate-severe TBI.

The effect of EMG magnitude on the masseter vestibular evoked myogenic potential (mVEMP).

Introduction: The masseter vestibular evoked myogenic potential (mVEMP) is a bilaterally generated, electromyographically (EMG)-mediated response innervated by the trigeminal nerve. The purpose of the present investigation was to 1) determine whether subjects could accurately achieve and maintain a range of EMG target levels, 2) to examine the effects of varied EMG levels on the latencies and amplitudes of the mVEMP, and 3) to investigate the degree of side-to-side asymmetry and any effects of EMG activation. Methods: Subjects were nine neurologically and otologically normal young adults. A high-intensity tone burst was presented monaurally while subjects were seated upright and asked to match a range of EMG target levels by clenching their teeth. Recordings were made from the ipsilateral and contralateral masseter muscles referenced to the ear being monaurally stimulated. Results: We found that the tonic EMG target had no effect on mVEMP latency. Additionally, although mVEMP amplitudes "scaled" to the EMG target, there was a tendency for the subjects' EMG level to "undershoot" the EMG target levels greater than 50 µV. While some individuals did generate differences in EMG activation between sides, there were no significant differences on average EMG activation between sides. Further, while average corrected amplitude asymmetry was similar across EMG targets, some individuals demonstrated large, corrected amplitude asymmetry ratios. Conclusions: The results of this investigation suggest that, as with cVEMP recordings, the underlying EMG activation may vary between subjects and could impact mVEMP amplitudes, yet could be mitigated by amplitude correction techniques. Further it is important to be aware that even young normal subjects have difficulty maintaining large, tonic EMG activity during the mVEMP recording.

Inter-trial coherence as a measure of synchrony in cervical vestibular evoked myogenic potentials.

BACKGROUND: Cervical vestibular evoked myogenic potentials (cVEMPs) are surface-recorded responses that reflect saccular function. Analysis of cVEMPs has focused, nearly exclusively, on time-domain waveform measurements such as amplitude and latency of response peaks, but synchrony-based measures have not been previously reported. NEW METHOD: Time-frequency analyses were used to apply an objective response-detection algorithm and to quantify response synchrony. These methods are new to VEMP literature and have been adapted from previous auditory research. Air-conducted cVEMPs were elicited using a 500 Hz tone burst in twenty young, healthy participants. RESULTS: Time-frequency characteristics of cVEMPs and time-frequency boundaries for response energy were established. An inter-trial coherence analysis approach revealed highly synchronous responses with representative inter-trial coherence values of approximately 0.7. COMPARISON WITH EXISTING METHODS: Inter-trial coherence measures were highly correlated with conventional amplitude measures in this group of young, healthy adults (R2 = 0.91 - 0.94), although the frequencies at which these measures had their largest magnitude were unrelated (R2 =.02). Conventional measures of peak-to-peak amplitude and latency were consistent with previous literature. Interaural asymmetry ratios were comparable between amplitude- and synchrony-based measures. CONCLUSIONS: Synchrony-based time-frequency analyses were successfully applied to cVEMP data and this type of analysis may be helpful to differentiate synchrony from amplitude in populations with disrupted neural synchrony.

Comparison of Bone-Conducted Cervical VEMPs Elicited by B71 and B81 Bone Vibrators.

OBJECTIVE: A variety of stimulus delivery methods can elicit vestibular evoked myogenic potentials (VEMPs). The current study compared bone conduction (BC) cervical VEMPs (cVEMPs) across two different clinical bone vibrators. It was hypothesized that the B81 transducer would be more effective for producing larger BC-cVEMP peak to peak amplitudes due to its low-frequency advantages in pure-tone audiometry applications. DESIGN: Twenty young adults under the age of 40 years with no reported history of hearing or balance disorders participated in the study. BC cVEMPs were elicited using two clinical bone transducers: the Radioear B71 bone vibrator and the Radioear B81 bone vibrator. Both transducers were calibrated using the acoustic method of calibration before data collection, and the linear dynamic range of the transducers was determined. Participants were asked to sit and match a fixed electromyography (EMG) target level of 100 µV, while BC cVEMPs were recorded using stimulus frequencies of 250, 500, and 750 Hz. RESULTS: Statistically significant differences in raw amplitude at 250 and 750 Hz between the B71 and B81 were observed; the B71 produced larger peak to peak amplitudes over the B81. At 500 Hz, larger amplitudes were observed with the B71, but results were not statistically significant. The B71 produced significantly lower cVEMP thresholds at all three frequencies. Across both transducers, 500 Hz produced the largest peak to peak amplitude compared with 250 and 750 Hz. Peak to peak amplitude did not increase above 55 dB nHL for 250 and 500 Hz, but amplitude continued to increase at 750 Hz. DISCUSSION: The present study found statistically significant differences in BC-cVEMP amplitude and threshold between the B71 and B81, but results were not what we hypothesized. In general, the B71 elicited larger BC-cVEMP amplitudes and lower thresholds compared with the B81. Additionally, 500 Hz was found to be the best frequency for both BC transducers, contrasting previous studies suggesting lower frequencies yield larger BC-cVEMP amplitudes. It is possible that these average differences could also be clinically significant when looking at individual amplitude differences. Larger peak to peak amplitudes at 500 Hz may be partially due to the underlying physical levels used in the current study, as well as the output spectra of the transducers, and may explain the larger response amplitudes observed at 500 Hz compared with 250 Hz.

Diabetes and the Vestibular System.

Falls are among the most injurious, costly, and feared conditions affecting older adults. Patients with diabetes have a significantly greater risk for falling due to complications affecting the sensory systems required for balance: vision, proprioception, and vestibular. The effects of diabetes mellitus on the vestibular system are perhaps the least understood of these systems. The vestibular system is complex, includes multiple structures, and is difficult and expensive to thoroughly assess. There is pathophysiologic evidence suggesting a direct effect of diabetes mellitus complications on the vestibular system, but there is limited clinical evidence regarding which specific vestibular structures are most adversely affected. Nevertheless, large population-based studies show that patients with diabetes are more likely to have vestibular loss, have a high prevalence of a specific vestibular disorder called benign paroxysmal positional vertigo, and are at a greater risk for falling. Based on the available evidence, a balance screening and an evaluation of benign paroxysmal positional vertigo, a common but easy to treat pathology, in patients with diabetes is recommended as well as counseling on falls risk and home modifications.

Impact of Stimulus Polarity on oVEMP Response Using the Belly-Tendon Electrode Montage.

BACKGROUND: One stimulus parameter not well established with respect to the ocular vestibular evoked myogenic potential (oVEMP) is stimulus polarity. Many research studies traditionally record oVEMPs using alternating polarity primarily. PURPOSE: The purpose of this study was to evaluate the effects of stimulus polarity on the oVEMP response under three different conditions (condensation, rarefaction, and alternating) with updated but established recording procedures-the belly-tendon electrode montage. RESEARCH DESIGN: oVEMPs were assessed with changes in stimulus polarity in the seated upright position. STUDY SAMPLE: Thirty otologically normal participants (60 ears) with no history of hearing or balance disorders and normal middle ear function. DATA COLLECTION AND ANALYSIS: Five hundred-hertz air-conducted tone bursts at 95-dB nHL were used to evoke the oVEMP response while recordings were made from the contralateral eye to acoustical stimulation using the belly-tendon electrode montage. Measurements were made using three polarities: alternating, condensation, and rarefaction. Natus Bio-logic AEP hardware and software was used for all data collection and analysis. RESULTS: Condensation stimulus phase provided the largest response amplitude compared with alternating and/or rarefaction. Rarefaction provided the earliest latency among stimulus polarities. CONCLUSIONS: Condensation is a more effective stimulus polarity regarding response amplitude when recording the oVEMP. This study further supports the use of the belly-tendon electrode montage for recording the oVEMP response.