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ORIGINAL ARTICLE
Year : 2013  |  Volume : 19  |  Issue : 3  |  Page : 100-103

Effect of frequency on ocular vestibular evoked myogenic potential


Department of Audiology and Speech Language Pathology, Kasturba Medical College, Manipal University, Mangalore, Karnataka, India

Date of Web Publication2-Sep-2013

Correspondence Address:
Kaushlendra Kumar
Department of Audiology and Speech Language Pathology, Kasturba Medical College, Manipal University, Mangalore, Karnatka - 575 001
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0971-7749.117463

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  Abstract 

Introduction: Ocular Vestibular evoked myogenic potentials (oVEMPs) are sensitive in diagnosing clinical population with vestibular dysfunction. Aim: We aimed at comparing the oVEMP responses of normal, evoked by 500, 1000, 2000, and 4000 Hz short duration tone burst stimuli. Materials and Methods: A total of 60 subjects underwent the oVEMP testing using 500, 1000, 2000, and 4000 Hz. Single channel electrode montage was used with analysis time of 50 ms, bandpass filter of 1-1000 Hz and 200 stimuli averaging. Intensity of 99 dB normalized hearing level (nHL) evoked the responses. Results and Conclusion: oVEMP response showed no significant difference in latency of n1-p1 across the frequencies. However, the peak - peak amplitude of n1-p1 at 500 and 1000 Hz was greater than 2000 and 4000 Hz frequencies. Thus, 500 and 1000 Hz short duration tone burst stimuli can be accountable for the diagnosis of clinical population with good morphology.

Keywords: Frequency, Latency, Ocular vestibular evoked myogenic potential, Peak-peak amplitude


How to cite this article:
Dessai TD, Bhat JS, Kumar K. Effect of frequency on ocular vestibular evoked myogenic potential. Indian J Otol 2013;19:100-3

How to cite this URL:
Dessai TD, Bhat JS, Kumar K. Effect of frequency on ocular vestibular evoked myogenic potential. Indian J Otol [serial online] 2013 [cited 2019 Jul 17];19:100-3. Available from: http://www.indianjotol.org/text.asp?2013/19/3/100/117463


  Introduction Top


Vestibular evoked myogenic potentials are electromyogenic responses recorded using high acoustic stimulation. Nonphysiological vestibular stimuli like intense sound and vibration can evoke reflex ocular movements even in the absence of head displacement. [1],[2] These are short latency responses, which may be detected using surface electrodes placed over the contracted superior and inferior ocular muscles. Unlike the cervical Vestibular evoked myogenic potential (cVEMP), which assesses the descending vestibular pathway as ipsilateral sacculo-ocullic reflex, the ocular Vestibular evoked myogenic potential (oVEMP) has been validated to evaluate the ascending vestibular pathway as crossed vestibulo-ocular reflex. [3]

The normal oVEMPs are characterized by biphasic responses (negative - positive) waves. In cVEMPs, the biphasic complex obtained is labeled with short letter p1 (positive) and n1 (negative) in order to differentiate these peaks from the neurally evoked peaks. [4] However, in oVEMPs, positive peak follows the negative peak and are labeled as n1-p1. In addition, with the cVEMPs many authors claim of later peaks termed as n34-p44.

cVEMP has been extensively studied to determine the effect of different stimuli and different frequencies on normals. For the cVEMP in clinical use, optimal frequency is said to be 500 Hz. However, there are very few studies reporting on, frequency tuning of oVEMP responses. With increase in frequency there is decrease in amplitude from 1000 to 2000 Hz. [5] Amplitude of 500 and 1000 Hz were reported to be the same. Another study, reported largest responses at 1000 Hz. [6] Additionally, 1000 Hz is reported to be the optimal frequency to obtain oVEMP response. [7]

It has been observed that oVEMP studies are performed in normal subjects as well as in clinical population with either 500 Hz short duration tone bust or click stimuli. In clinical practice, the most commonly used stimulus to evoke the vestibular evoked myogenic potentials are short duration tone burst stimulus, sometimes low frequency logon stimulus. Low frequency tone burst stimuli (500 and 1000 Hz) are commonly used as the animal studies have depicted saccular nerves to be more sensitive to low frequency acoustic stimuli. [8] Hence, the present study was taken up to determine if there are any differences in response rate, latency, and peak - peak amplitude across different frequencies of short duration tone burst stimuli using oVEMP.

To use vestibular evoked myogenic response in clinical practice, a suitable stimulus parameter has to be recognized. Thus the main objective of the present study was to compare oVEMP responses elicited by 500, 1000, 2000, and 4000 Hz tone burst stimuli in healthy normal hearing subjects.


  Materials and Methods Top


A total of 60 (120 ears) subjects within the age group of 20-40 years [mean age 26 ± 5 (SD)] participated in the study. All the subjects had normal hearing sensitivity in both the ears (hearing sensitivity within 15 dB HL for air and bone conduction) and normal middle ear functioning (A type Tympanogram with bilateral reflexes present). Subjects with any history or presence of neurological or otological symptoms were excluded from the study.

At first, Puretone thresholds were estimated at octave intervals with the use of a calibrated pseudo channel clinical audiometer (GSI 61 clinical audiometer) with TDH-39 head phones and a B-71 radio ear bone vibrator. The thresholds were obtained between 250 and 8000 Hz for air conduction and between 250 and 4000 Hz for bone conduction using modified Hughson and Westlake method. [9] Second, immitanceaudimetry was carried out with the GSI Tympstar System to assess the middle ear functioning. Probe tone frequency of 226 Hz was used for the same,and so was ipsilateral and contralateral acoustic reflex thresholds at 500, 1000, 2000, and 4000 Hz. Third, uncomfortable level for speech was established using the two down one up procedure. Finally, vestibular evoked myogenic responses were evoked using an Intelligent Hearing System (Smart EP) system with an Insert ER-3A earphone. Muscle contraction was monitored between 20 and 50 μv. The following parameters were used [Table 1].
Table 1: Parameters used for oVEMP testing

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To ensure reliability, recordings were obtained twice with 500, 1000, 2000, and 4000 Hz short duration tone burst stimuli. The n1 and p1 latency and peak-peak amplitude was determined for all the waveforms.


  Results Top


oVEMP was investigated with 500, 1000, 2000, and 4000 Hz short duration tone burst stimuli in 60 healthy subjects. From [Figure 1], it is evident that n1 and p1 latencies for all the frequencies were observed more or less at the same latency. However, there was increase in peak - peak amplitude for low frequency and decrease in amplitude after 1000 Hz.
Figure 1: Shows average grand waveform for 500, 1000, 2000 and 4000Hz tone burst stimuli

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oVEMP latency and peak-peak amplitude of n1 and p1 were noted for 500, 1000, 2000, and 4000 Hz short duration tone burst stimuli. From [Figure 2], it is observed that latency of n1 and p1 across all the frequencies (500, 1000, 2000, and 4000 Hz) was same. Standard deviation is less variable across all the frequencies. One way analysis of variance (ANOVA) test revealed no significant difference for {F = (3,413) = 1.36; P = 0.25} n1 and p1 latency {F = (3, 413) = 1.03; P = 0.37}.
Figure 2: Shows mean and standard deviation of n1 and p1 latency across different frequencies

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Peak - peak amplitude of n1-p1 was obtained across all the frequencies. From [Figure 3], it is evident that mean peak-peak amplitude of 500 and 1000 Hz is 5.58 ± 2.81 (SD) μV and 5.31 ± 2.76 (SD) μV, respectively. Mean peak - peak amplitude for 2000 and 4000 Hz was 2.50 ± 1.34 (SD) μV and 1.71 ± 0.84 (SD) μv, respectively. One way ANOVA test showed main significant effect {F = (3,413) = 71.64; P = 0.00} on peak - peak amplitude across all the frequencies. Posthoc Bonferroni test was performed to observe frequency effects on peak - peak amplitude of oVEMP.
Figure 3: Shows mean and standard deviation of different frequency peak to peak amplitude

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There was no significant difference (P > 0.05) in peak - peak amplitude between 500 and 1000 Hz. When the comparison of peak - peak amplitude was made with 500-2000 and 4000 Hz; Bonferroni test showed significant difference (P < 0.05). Similarly, comparisons done with 1000 Hz showed significant difference (P < 0.05) in peak - peak amplitude of 2000 and 4000 Hz. There was no significant difference in peak - peak amplitude, between 2000 and 4000 Hz.


  Discussion Top


The present study results showed 100% response rate for 500 and 1000 Hz. Response rate was 85% and 62.5% for frequency of 2000 and 4000 Hz, respectively. Similar observations were observed when oVEMP response rate for 125, 250, 500, 750, 1000, 1500, and 2000 Hz short duration tone burst at 127 dB pSPL were compared. [10] Results showed highest response rate at 750 and 1000 Hz (100%). In the same study, the reduction in response rate to 95% at 500 Hz was obtained and at high frequencies more reduction. A similar finding with 100% oVEMP response was observed at 500 Hz short duration tone burst. [5] However, the best response rate with 1000 Hz short duration tone burst stimulus is also reported. [6],[7] oVEMP response for 500 Hz with ipsilateral and contralateral response rate were 45% and 95%, respectively. [11] As the frequency increases above 1000 Hz, there is decrease in response rate of oVEMP. Best response rate, in the present as well as the previous studies of oVEMP response was at 500 and 1000 Hz. Reduced response rate might be due to the utricle organ having resonance frequency below 1000 Hz, so when it was presented above 1000 Hz there was reduction in response rate.

Present study findings revealed that there was no change in n1 and p1 latency for 500, 1000, 2000, and 4000 Hz stimuli. In addition, 500 and 1000 Hz showed more peak - peak amplitude as compare with 2000 and 4000 Hz. Several investigators have recorded the oVEMP in response to air conducted short duration tone bursts between 400 and 1000 Hz. [6],[11],[12] Similar findings when oVEMP responses were compared with frequencies of 250, 500, 1000, and 2000 Hz in 20 normal subjects. No significant difference in latency of n1 and p1 were observed. [5] Mean amplitudes were similar across all four frequencies (3.0, 5.7, 5.7, and 3.2 μV, respectively) but an analysis of variance revealed that amplitudes at 500 and 1000 Hz were significantly larger than those at 250 and 2000 Hz. Similarly, largest oVEMP amplitude at 1000 Hz for 8 out of their 12 subjects is observed. [6] In support of this study, no significant differences for n1 and p1 latency between 500, 1000, and 2000 Hz was recorded. [13] Additionally, no significant differences in oVEMP latency at 250, 500, and 1000 Hz was reported. [14] They reported 500 Hz short duration tone burst stimuli with the highest amplitude as compared with other frequencies. Piker [10] also reported no significant difference in n1 and p1 latency of oVEMP across the different frequencies. There was no significant difference in oVEMP amplitude evoked by 500, 750, and 1000 Hz short duration tone bursts suggesting that there is no true frequency "tuning" in the vestibular system, but in fact there is a range of best frequencies evoking the VEMP response.

Hence reduced peak - peak amplitude above 1000 Hz might be due to resonance properties of utricular macula. As reported,utricular macula is "essentially floating on the fluid." [15] These differences in morphological can be reasonably hypothesized; an acoustic stimulus would deflect the saccular and utricular macula differently. The utricle is partly affixed and mostly free-floating in endolymph and is thus mass dominated. Hence, utricle will respond normally but with greater amplitude to low and mid frequency tone bursts.


  Conclusion Top


Hence, the present study showed that there were more reliable response to 500 and 1000 Hz and also peak - peak amplitude robustness were observed. At 500 and 1000 Hz 100% response rate was observed as compared to 2000 Hz and above. Hence 500 or 1000 Hz are recommended for clinical use.

 
  References Top

1.Karlberg M, Aw ST, Black RA, Todd MJ, MacDougall HG, Halmagyi GM. Vibration-induced ocular torsion and nystagmus after unilateral vestibular deafferentation. Brain 2003;26:956-64.  Back to cited text no. 1
    
2.Zhou G, Cox LC. Vestibular evoked myogenic potentials: History and overview. Am J Audiol 2004;13:135-43.  Back to cited text no. 2
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3.Iwasaki S, McGarvie LA, Halmagyi GM, Burgess AM, Kim J, Colebatch JG, et al. Head taps evoke a crossed vestibulo-ocular reflex. Neurology 2007;68:1227-9.  Back to cited text no. 3
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4.Yoshie N, Okudaira T. Myogenic evoked potential responses to clicks in man. Acta Otolaryngol Suppl 1969;252:89-103.  Back to cited text no. 4
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5.Park HJ, Lee IS, Shin JE, Lee YJ, Park MS. Frequency-tuning characteristics of cervical and ocular vestibular evoked myogenic potentials induced by air-conducted tone bursts. Clin Neurophysiol 2010;121:85-9.  Back to cited text no. 5
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6.Lewis A, Mustain W, Xu Y, Eby T, Zhou W. Frequency tuning in the tone burst-evoked myogenic potentials in extraocular muscles in normal human subjects. J Otolaryngol Head Neck Surg 2010;39:491-7.  Back to cited text no. 6
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7.Taylor RL, Bradshaw AP, Halmagyi GM, Welgampola MS. Tuning characteristics of ocular and cervical vestibular evoked myogenic potentials in intact and dehiscent ears. Audiol Neurootol 2012;17:207-18.  Back to cited text no. 7
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8.Trivelli M, Vicini C, D'Ascanio L, Greco F, Salvinelli F. The effects of logon versus click on vestibular evoked myogenic potentials. Acta Otolaryngol 2008;128:314-7.  Back to cited text no. 8
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9.Carhart R, Jerger JF. Preferred method for clinical determination of pure-tone thresholds. J Speech Hear Disord 1959;24:330-45.  Back to cited text no. 9
    
10.Picker EG. Effects of age on the frequency tuning of the cVEMP and oVEMP. Doctorate Dissertation, Graduate School of Vanderbilt University; 2012.  Back to cited text no. 10
    
11.Chihara Y, Iwasaki S, Ushio M, Murofushi T. Vestibular-evoked extraocular potentials by air-conducted sound: Another clinical test for vestibular function. Clin Neurophysiol 2007;118:2745-51.  Back to cited text no. 11
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12.Chihara Y, Shinichi C, Fujimoto C, Ushio M, Yamasoba T, Murofushi T. Frequency tuning properties of ocular vestibular evoked myogenic potentials. Neuro Report 2009;20:1491-5.  Back to cited text no. 12
    
13.Murnane OD, Akin FW, Kelly KJ, Byrd S. Effects of stimulus and recording parameters on the air conduction ocular vestibular evoked myogenic potential. J Am Acad Audiol 2011;22:469-80.  Back to cited text no. 13
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14.Winters SM, Berg IT, Grolman W, Klis SF. Ocular vetibular evoked myogenic potentials: frequency tuning to air conducted acoustic stimuli in healthy subjects and meniere's disease. Audiol Neurootol 2012;17:12-9.  Back to cited text no. 14
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15.Uzun-Coruhlu H, Curthoys IS, Jones AS. Attachment of utricular and saccula maculae to the temporal bone. Hear Res 2007;233:77-85.  Back to cited text no. 15
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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1]


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