Optimization of Cervical and Ocular Vestibular Evoked Myogenic Potential Testing Using an Impulse Hammer in Adults, Adolescents, and Children.

OBJECTIVE: To characterize cervical and ocular vestibular evoked myogenic potential (c- and oVEMP) responses using an impulse hammer (IH) in adults and pediatrics at standardized force levels and evaluate: the relationship of force level on VEMP amplitude, sternocleidomastoid (SCM) contraction on cVEMP amplitude, required number of tap stimuli, and subject comfort. Using these data, optimal testing parameters were selected. STUDY DESIGN: Prospective study. SETTING: Tertiary referral center. PATIENTS: Seventy-eight healthy adults, adolescents, and children with no hearing or vestibular deficits. INTERVENTIONS: All subjects received c- and oVEMP testing using IH and 500 Hz tone burst air conduction stimuli. Adults received hard, medium, and soft force levels. Adolescents and children received medium and soft force levels. A comfort questionnaire was administered pre- and post-testing. MAIN OUTCOME MEASURES: IH VEMP response parameters (response rates, latency, cVEMP pre-stimulus SCM Electromyography [EMG], and peak-to-peak amplitude) were assessed per force level. Subjective reporting for patient comfort was also assessed. RESULTS: VEMP response rates ranged from 92 to 100%. Force had a linear relationship with VEMP amplitude. SCM contraction had a linear relationship with raw cVEMP amplitude; however, dissipated with amplitude normalization. Force level did not impact the number of taps needed. A minimum peak force of 15 to 20 N, accounting for SCM contraction, and using a lower EMG monitoring limit for cVEMP is recommended to elicit reliable responses. CONCLUSIONS: Overall, IH VEMP is appropriate and comfortable to use in adults and pediatrics and can be useful when an air conduction stimulus is contraindicated or not preferred.

Air-Conducted Vestibular Evoked Myogenic Potential Testing in Children, Adolescents, and Young Adults: Thresholds, Frequency Tuning, and Effects of Sound Exposure.

OBJECTIVES: Pediatric vestibular evaluations incorporate cervical and ocular vestibular evoked myogenic potential (c- and oVEMP, respectively) testing; however, in children, c- and oVEMP thresholds have been minimally investigated and frequency tuning is unknown. Children are also at risk for unsafe sound exposure secondary to VEMP. While it is unknown if VEMP threshold testing leads to cochlear changes, it is possible that this risk increases due to the increased number of trials needed to obtain a threshold. Obtaining VEMP thresholds at various frequencies in children provides further information for pediatric normative VEMP data. Assessing for cochlear changes after VEMP threshold testing would provide information on the safety of threshold VEMP testing in children. The objectives of this study were to (1) characterize c- and oVEMP thresholds in children, adolescents, and young adults with normal hearing using 500 and 750 Hz tone burst (TB) stimuli, (2) compare frequency tuning of 500 and 750 Hz TB, and (3) assess whether cochlear changes exist after VEMP threshold testing. It is hypothesized that children, adolescents, and young adults would not show age-related changes to the vestibular system. Therefore, reliable VEMP thresholds would be seen below maximum acoustical stimulation levels (e.g., <125 dB SPL) and frequency tuning will be similar for 500 and 750 Hz TB stimuli. DESIGN: Ten children (age 4-9), 10 adolescents (age 10-19), and 10 young adults (age 20-29) with normal hearing and tympanometry participated. All subjects received c- and oVEMP testing at maximum stimulation and threshold. To address frequency tuning, but not exceed recommended sound exposure allowance, subjects received a 500 Hz TB stimulus in one ear and a 750 Hz TB stimulus in the other ear. Subjects completed tympanometry pre-VEMP, and audiometric threshold testing, distortion product otoacoustic emission testing, and subjective questionnaire pre- and post-VEMP to study the effect of VEMP exposure on cochlear function for each stimulus frequency. RESULTS: (1) cVEMP thresholds were determined for both stimulus frequencies for children (500 Hz = 106 dB SPL; 750 Hz = 106 dB SPL), adolescents (500 Hz = 107.5 dB SPL; 750 Hz = 109.5 dB SPL), and young adults (500 Hz = 111.5 dB SPL; 750 Hz = 112 dB SPL). oVEMP thresholds were also obtained in response to both stimulus frequencies for children (500 Hz = 111.1 dB SPL; 750 Hz = 112.2 dB SPL), adolescents (500 Hz = 112.5 dB SPL; 750 Hz = 114.5 dB SPL), and young adults (500 Hz = 116 dB SPL; 750 Hz = 117 dB SPL). Similar thresholds were found between groups except for children who had significantly lower thresholds compared with adults for cVEMP (500 Hz: p = 0.002; 750 Hz: p = 0.004) and oVEMP (500 Hz: p = 0.01; 750 Hz: p = 0.02). In addition, equivalent ear-canal volume and VEMP thresholds were linearly correlated. (2) There was no significant effect of stimulus frequency on VEMP response rates, latencies, peak to peak amplitudes, or thresholds, suggesting similar frequency tuning for 500 and 750 Hz. (3) There were no significant effects of VEMP threshold testing on cochlear function for either stimulus frequency. CONCLUSIONS: Children, adolescents, and young adults show VEMP thresholds below high stimulation levels and had similar frequency tuning between 500 and 750 Hz. Use of 750 Hz could be regarded as the safer stimuli due to its shorter duration and thus reduced sound exposure. Children with smaller ear-canal volume had present responses at maximum stimulation and lower thresholds, suggesting that VEMP testing could be initiated at lower acoustic levels to minimize sound exposure and optimize testing.

Effects of High Sound Exposure During Air-Conducted Vestibular Evoked Myogenic Potential Testing in Children and Young Adults.

OBJECTIVES: Vestibular evoked myogenic potential (VEMP) testing is increasingly utilized in pediatric vestibular evaluations due to its diagnostic capability to identify otolith dysfunction and feasibility of testing. However, there is evidence demonstrating that the high-intensity stimulation level required to elicit a reliable VEMP response causes acoustic trauma in adults. Despite utility of VEMP testing in children, similar findings are unknown. It is hypothesized that increased sound exposure may exist in children because differences in ear-canal volume (ECV) compared with adults, and the effect of stimulus parameters (e.g., signal duration and intensity) will alter exposure levels delivered to a child's ear. The objectives of this study are to (1) measure peak to peak equivalent sound pressure levels (peSPL) in children with normal hearing (CNH) and young adults with normal hearing (ANH) using high-intensity VEMP stimuli, (2) determine the effect of ECV on peSPL and calculate a safe exposure level for VEMP, and (3) assess whether cochlear changes exist after VEMP exposure. DESIGN: This was a 2-phase approach. Fifteen CNH and 12 ANH participated in phase I. Equivalent ECV was measured. In 1 ear, peSPL was recorded for 5 seconds at 105 to 125 dB SPL, in 5-dB increments for 500- and 750-Hz tone bursts. Recorded peSPL values (accounting for stimulus duration) were then used to calculate safe sound energy exposure values for VEMP testing using the 132-dB recommended energy allowance from the 2003 European Union Guidelines. Fifteen CNH and 10 ANH received cervical and ocular VEMP testing in 1 ear in phase II. Subjects completed tympanometry, pre- and postaudiometric threshold testing, distortion product otoacoustic emissions, and questionnaire addressing subjective otologic symptoms to study the effect of VEMP exposure on cochlear function. RESULTS: (1) In response to high-intensity stimulation levels (e.g., 125 dB SPL), CNH had significantly higher peSPL measurements and smaller ECVs compared with ANH. (2) A significant linear relationship between equivalent ECV (as measured by diagnostic tympanometry) and peSPL exists and has an effect on total sound energy exposure level; based on data from phase I, 120 dB SPL was determined to be an acoustically safe stimulation level for testing in children. (3) Using calculated safe stimulation level for VEMP testing, there were no significant effect of VEMP exposure on cochlear function (as measured by audiometric thresholds, distortion product otoacoustic emission amplitude levels, or subjective symptoms) in CNH and ANH. CONCLUSIONS: peSPL sound recordings in children's ears are significantly higher (~3 dB) than that in adults in response to high-intensity VEMP stimuli that are commonly practiced. Equivalent ECV contributes to peSPL delivered to the ear during VEMP testing and should be considered to determine safe acoustic VEMP stimulus parameters; children with smaller ECVs are at risk for unsafe sound exposure during routine VEMP testing, and stimuli should not exceed 120 dB SPL. Using 120 dB SPL stimulus level for children during VEMP testing yields no change to cochlear function and reliable VEMP responses.

Big Stimulus, Little Ears: Safety in Administering Vestibular-Evoked Myogenic Potentials in Children.

BACKGROUND: Cervical and ocular vestibular-evoked myogenic potentials (VEMPs) have become common clinical vestibular assessments. However, VEMP testing requires high intensity stimuli, raising concerns regarding safety with children, where sound pressure levels may be higher due to their smaller ear canal volumes. PURPOSE: The purpose of this study was to estimate the range of peak-to-peak equivalent sound pressure levels (peSPLs) in child and adult ears in response to high intensity stimuli (i.e., 100 dB normal hearing level [nHL]) commonly used for VEMP testing and make a determination of whether acoustic stimuli levels with VEMP testing are safe for use in children. RESEARCH DESIGN: Prospective experimental. STUDY SAMPLE: Ten children (4-6 years) and ten young adults (24-35 years) with normal hearing sensitivity and middle ear function participated in the study. DATA COLLECTION AND ANALYSIS: Probe microphone peSPL measurements of clicks and 500 Hz tonebursts (TBs) were recorded in tubes of small, medium, and large diameter, and in a Brüel & Kjær Ear Simulator Type 4157 to assess for linearity of the stimulus at high levels. The different diameter tubes were used to approximate the range of cross-sectional areas in infant, child, and adult ears, respectively. Equivalent ear canal volume and peSPL measurements were then recorded in child and adult ears. Lower intensity levels were used in the participant's ears to limit exposure to high intensity sound. The peSPL measurements in participant ears were extrapolated using predictions from linear mixed models to determine if equivalent ear canal volume significantly contributed to overall peSPL and to estimate the mean and 95% confidence intervals of peSPLs in child and adult ears when high intensity stimulus levels (100 dB nHL) are used for VEMP testing without exposing subjects to high-intensity stimuli. RESULTS: Measurements from the coupler and tubes suggested: 1) each stimuli was linear, 2) there were no distortions or nonlinearities at high levels, and 3) peSPL increased with decreased tube diameter. Measurements in participant ears suggested: 1) peSPL was approximately 3 dB larger in child compared to adult ears, and 2) peSPL was larger in response to clicks compared to 500 Hz TBs. The model predicted the following 95% confidence interval for a 100 dB nHL click: 127-136.5 dB peSPL in adult ears and 128.7-138.2 dB peSPL in child ears. The model predicted the following 95% confidence interval for a 100 dB nHL 500 Hz TB stimulus: 122.2-128.2 dB peSPL in adult ears and 124.8-130.8 dB peSPL in child ears. CONCLUSIONS: Our findings suggest that 1) when completing VEMP testing, the stimulus is approximately 3 dB higher in a child's ear, 2) a 500 Hz TB is recommended over a click as it has lower peSPL compared to the click, and 3) both duration and intensity should be considered when choosing VEMP stimuli. Calculating the total sound energy exposure for your chosen stimuli is recommended as it accounts for both duration and intensity. When using this calculation for children, consider adding 3 dB to the stimulus level.