J Am Acad Audiol 25:969-974 (2014)
Does Electrode Impedance Affect the Recording of Ocular Vestibular-Evoked Myogenic Potentials? DOI: 10.3766/jaaa.25.10.5 Rachael L. Taylor*t Mikael Schulin*f$ Samanthi Goonetillekef Miriam S. Welgampolaf
Abstract Background: In evoked potential testing, it is common practice to abrade the skin surface as a means of reducing and balancing electrode impedance. The effects of skin preparation and electrode imped ance on ocular vestibular-evoked myogenic potential (oVEMP) prevalence and amplitudes are not known. Purpose: We sought to determine whether comparable oVEMP waveforms could be recorded without excessive skin preparation. Research Design: This was a prospective study with a repeated-measures (within-subjects) design. Study Sample: The study group comprised 20 healthy participants (12 females and 8 males) ages 21-57 yr. Data Collection and Analysis: oVEMP reflexes were recorded in response to air-conducted and boneconducted (AC and BC) stimuli in three conditions. In the first condition (no skin preparation), electrodes were simply placed over the skin surface. For the second condition (moderate skin preparation), oVEMP testing was repeated after the skin had been prepared with 70% isopropyl alcohol swabs. oVEMPs recorded in these two conditions were then compared with those recorded using a third conventional protocol whereby the skin was abraded with skin preparation gel until electrode impedances were low and balanced. For BC stimuli, reflex amplitudes and latencies were compared using a repeatedmeasures general linear model. For AC stimuli, rates of reflex detection were analyzed using a gener alized estimating equation. Nonparametric Friedman tests were used to compare AC oVEMP amplitudes across the three conditions. Results: There was no significant effect of electrode impedance on reflex amplitudes, latencies, or rates of detection (p > 0.05). The results indicated significant stimulus-related artifact (>3 p,V) in 25 of 40 recordings under the high-impedance condition in response to BC stimulation. The stimulus artifact was detectable in 12 of 40 recordings after moderate skin preparation and in 5 recordings after skin abrasion. Conclusions: Comparable rates of reflex detection and oVEMP amplitudes were recorded in the three conditions, implying that rigorous rubbing of the facial skin is largely unnecessary in clinical oVEMP test ing. However, for oVEMPs recorded in response to a single-polarity stimulus, reducing and balancing electrode impedances with either isopropyl alcohol wipes or skin abrasion may help reduce unwanted stimulus artifact. Key Words: Electrode impedance, electromyography, oVEMP, vestibular function
« *Equal contribution; flnstitute of Clinical Neurosciences, Royal Prince Alfred Hospital, Central Clinical School, University of Sydney, Sydney, Sweden ;*:Departrnent of Neuroscience and Locomotion, Division of Otorhinolaryngology, Faculty of Health Sciences, Linkoping University, Linkoping Dr. Miriam S. Welgampola, Institute of Clinical Neurosciences, Royal Prince Alfred Hospital, Central Clinical School, University of Sydney NSW Australia; E-mail: [email protected] This research was funded by the Garnett Passe and Rodney Williams Memorial Foundation and the National Health and Medical Research Council of Australia.
969
J o u rn a l o f th e A m erican A cad em y o f A u d io lo g y /Volume 25, Number 10, 2014
Abbreviations: AC = air-conducted; BC = bone-conducted; cVEMP = cervical vestibular-evoked myogenic potential; oVEMP = ocular vestibular-evoked myogenic potential
INTRODUCTION
o ensure a high-quality evoked potential record ing, it is important that an optimal signal to noise ratio is achieved. For low-amplitude (
Does Electrode Impedance Affect the Recording of Ocular Vestibular-Evoked Myogenic Potentials? DOI: 10.3766/jaaa.25.10.5 Rachael L. Taylor*t Mikael Schulin*f$ Samanthi Goonetillekef Miriam S. Welgampolaf
Abstract Background: In evoked potential testing, it is common practice to abrade the skin surface as a means of reducing and balancing electrode impedance. The effects of skin preparation and electrode imped ance on ocular vestibular-evoked myogenic potential (oVEMP) prevalence and amplitudes are not known. Purpose: We sought to determine whether comparable oVEMP waveforms could be recorded without excessive skin preparation. Research Design: This was a prospective study with a repeated-measures (within-subjects) design. Study Sample: The study group comprised 20 healthy participants (12 females and 8 males) ages 21-57 yr. Data Collection and Analysis: oVEMP reflexes were recorded in response to air-conducted and boneconducted (AC and BC) stimuli in three conditions. In the first condition (no skin preparation), electrodes were simply placed over the skin surface. For the second condition (moderate skin preparation), oVEMP testing was repeated after the skin had been prepared with 70% isopropyl alcohol swabs. oVEMPs recorded in these two conditions were then compared with those recorded using a third conventional protocol whereby the skin was abraded with skin preparation gel until electrode impedances were low and balanced. For BC stimuli, reflex amplitudes and latencies were compared using a repeatedmeasures general linear model. For AC stimuli, rates of reflex detection were analyzed using a gener alized estimating equation. Nonparametric Friedman tests were used to compare AC oVEMP amplitudes across the three conditions. Results: There was no significant effect of electrode impedance on reflex amplitudes, latencies, or rates of detection (p > 0.05). The results indicated significant stimulus-related artifact (>3 p,V) in 25 of 40 recordings under the high-impedance condition in response to BC stimulation. The stimulus artifact was detectable in 12 of 40 recordings after moderate skin preparation and in 5 recordings after skin abrasion. Conclusions: Comparable rates of reflex detection and oVEMP amplitudes were recorded in the three conditions, implying that rigorous rubbing of the facial skin is largely unnecessary in clinical oVEMP test ing. However, for oVEMPs recorded in response to a single-polarity stimulus, reducing and balancing electrode impedances with either isopropyl alcohol wipes or skin abrasion may help reduce unwanted stimulus artifact. Key Words: Electrode impedance, electromyography, oVEMP, vestibular function
« *Equal contribution; flnstitute of Clinical Neurosciences, Royal Prince Alfred Hospital, Central Clinical School, University of Sydney, Sydney, Sweden ;*:Departrnent of Neuroscience and Locomotion, Division of Otorhinolaryngology, Faculty of Health Sciences, Linkoping University, Linkoping Dr. Miriam S. Welgampola, Institute of Clinical Neurosciences, Royal Prince Alfred Hospital, Central Clinical School, University of Sydney NSW Australia; E-mail: [email protected] This research was funded by the Garnett Passe and Rodney Williams Memorial Foundation and the National Health and Medical Research Council of Australia.
969
J o u rn a l o f th e A m erican A cad em y o f A u d io lo g y /Volume 25, Number 10, 2014
Abbreviations: AC = air-conducted; BC = bone-conducted; cVEMP = cervical vestibular-evoked myogenic potential; oVEMP = ocular vestibular-evoked myogenic potential
INTRODUCTION
o ensure a high-quality evoked potential record ing, it is important that an optimal signal to noise ratio is achieved. For low-amplitude (
