Ann Otol 85: 1976

TEST -RETEST RELIABILITY IN CLINICAL ELECTROCOCHLEOGRAPHY L. M.

BERGHOLTZ,

M.D.

LINKOPING, SWEDEN

R. E.

HOOPEH,

},'LD.

BRONX, NEW YORK

D. C.

MEHTA,

M.D.

BRONX, NEW YORK

SUMMARY - The intratest test-retest reliability in clinical electrocochleography was studied by measuring the difference between amplitude of the test and retest and latency of the test and retest. Eighty-four comparisons were made in 40 patients with different types of hearing losses. The type of hearing loss and whether test and retest were performed in sequence or not did not affect the variability of the amplitude, The test and retest correlation between amplitudes was good. Small amplitudes mainly found near the action potential (AP) "threshold" showed less absolute variability than larger amplitudes found at higher intensities. The correlation between the intratest latencies was excellent. The latency showed less variability at higher intensities than near AP "threshold,"

Electrocochleography has now become established as a physiological hearing test. Data is being used to establish thresholds>" often at different frequencies 1 ,2 ,5 ,8-10 and also in diagnosing the nature of the hearing loss by study of waveform and other suprathreshold parameters such as the inputoutput functions of amplitude and latency of AP response. 1 ,2 ,8 ,9,l1-13 Electrocochleography is a particularly valuable test in evaluating hearing in patients who are unable to cooperate for routine behavioral audiometry because they are very young, mentally handicapped or emotionally disturbed.I- 4 ,6 ,14 Electrocochleographic suprathreshold parameters such as the study of waveforms and input-output graphs of amplitude and latency of response may be valuable tools in diagnosing the site and type of peripheral hearing loss. However, the limitations of the method must be considered. The action potential (AP) "threshold" is usually found to be higher than the behavioral threshold. 7-9 ,15 The interpretation of frequency specific thresholds even using filtered clicks or tone bursts is difficult.

Also, some form of general anesthesia is necessary when the transtympanic technique is used in young children. I ,2,5 ,6 ,9 It is important to establish the reliability of any hearing test. The limitations and disadvantages must, therefore, be recognized before data is interpreted. This paper will report the investigation of intratest test-retest reliability in clinical electrocochleography. METHODS AND MATERlALS

Forty subjects, whose ages ranged from 20 to 74 years with a mean age of 58 years, were studied. There were 25 female and 15 male subjects. Half the group had pure tone audiograms showing low and high frequency sensorineural losses with normal or near normal hearing for at least one of the speech frequencies. The other half showed either a high frequency sensorineural loss, Hat sensorineural loss or a conductive loss. The pure tone average (PI'A) at 500, 1000 and 2000 Hz within the whole group ranged from 10 to 55 dB with a mean of 30 dB. Only the poorer hearing ear was tested in each subject. The subject, after being otoscopically examined, lies supine on a bed in a sound treated room. The tympanic membrane was anesthetized with 2% Xylocainew" with 1 :2000 parts epinephrine using an iontophoretic anesthetizer, ''''16 If the tympanic membrane was re-

.. Astra Pharmaceutical Products, Inc" Worcester, MA. .... Medicon, Portland, OR. From the Department of Otolaryngology, Albert Einstein College of Medicine, Yeshiva University, Bronx, NY. This work was supported by the Deafness Research Foundation and the International Foundation for Children's Hearing, Education and Research, Inc. 679

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680

BERGHOLTZ ET AL.

Fig. 1. Placement of the electrode. tracted or perforated, a small piece of cotton impregnated with Xylocaineeo jelly was placed on the tympanic membrane of the ear to be tested. The ground and reference electrodes were silver cup electrodes filled with electrode jelly placed on the center of the forehead and the ear lobe of the ear to be tested. The active electrode was of stainless steel, 5 em long, 0.4 mm in diameter and insulated to within 0.5 mm of its tip. It was placed transtympanically on the promontory of the middle ear, using a plastic aural speculum under microscopic control. The aim was to place this electrode halfway between the umbo and the annulus at approximately eight 0' clock.t" The electrode was secured with a rubber band on a "doughnut" placed circumaurally (Fig. 1). The DC

resistance between all three electrodes was recorded before and after testing. The aim was to keep the resistance between the surface electrodes (i.e., ground and reference electrodes less than 10,000 ohms whenever possible ) . The electrodes were connected to a preamplifier which led to the amplifier." The band pass setting was set at 32 Hz to 3.2 kHz. The signal then passed to the averager." All components are part of the electrocochleography unit" (Fig. 2). One hundred to fifteen hundred responses were averaged depending on the magnitude of the response. The averaging window was 10 msec. It was increased to 15 msec when necessary. The averager had a 200 address memory and its address time was 50 IJ,sec (75 IJ,sec for a sweep time of 15 msec). The acoustic clicks were generated by a pulse generator.... using a rectangular pulse of 0.5 msec duration. The rate of click stimulation was 10/sec made up of alternate rarefaction and condensation clicks. The stimulus pulses were fed via an attenuator v"? and audio-power amplifier] to the sound treated room. A driver speakertt was placed 70 em from the ear to be tested (Fig. 2). The maximum level of the click was 95 dB peak equivalent sound pressure level measured at the entrance of the ear canal. This corresponds to 75 dB above detection threshold as measured on ten normally hearing subjects (who all reached the same threshold), i.e., 75 dB hearing level (HL). The main energy of the stimulus was contained in the frequency range 0.5 - 2 kHz. The investigation was used clinically to establish the whole nerve AP "threshold," i.e., minimum averaged AP visual detection level of the cochlear division of the VIn nerve. The

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Fig. 3. Measurement of amplitude and latency. stimuli were initially presented at maximum intensity of 75 dB HL and the resulting response averaged and recorded. This procedure was repeated at decreasing 10 dB levels until no response was visible. Five dB decrements were used when approaching the AP "threshold." In order to analyze the intratest test-retest reliability, those tests which were repeated twice at the same intensity in the same patient were studied. The procedure for determining the AP "threshold" as described lasted approximately one hour. Test and retest were either performed in sequence or at intervals of up to one hour. An attempt was made to keep all test conditions constant during the procedure, i.e., stimulus and recording conditions remained the same and both active and reference electrodes were kept in the same position. Latency was measured on the cathode ray display of the TE 4 when the averaging was completed. It was measured from the time of the stimulus reaching external auditory canal to the point of maximum deflection of the N, or N2 when that was the only visible response (Fig. 3). Responses were recorded on the TE 4 optic recorder. The amplitude of the response was measured after the test, from the baseline to the point of maximum deflection of the N, or N2 respectively (Fig. 3). TABLE I DISTRIBUTION OF TYPES OF HEARING LOSSES IN THE SETS OF TESTS

Type of Hearing Loss Low and high frequency sensorineural loss High frequency sensorineural loss Flat sensorineural loss Conductive loss Total

No.

%

46

55

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5 10 15 20 25 30 35 40 45 50 55 dB ABOVE AP THRESHOLD

RESULTS

Eighty-four sets of tests, each set consisting of test and retest, were performed in the 40 subjects studied. The distribution of the different kinds of hearing losses is shown in Table I. Intensities at which the tests were run ranged from the AP "threshold" to 50 dB above the AP "threshold" (Fig. 4). Seven of the 84 sets of tests had a retest in which no response was recorded. These will be considered separately and only the results of the remaining 77 sets of tests (154 tests) will now be presented. The standard deviation of the differences between the amplitudes of test and retest for the 77 sets of tests was 1.0 p.v. The scattergram of the amplitudes of test and retest are shown (Fig. 5). The correlation coefficient (r ) was +0.78 (p < .001). The analysis of variance for the regression is shown in Table II. The standard deviation of the differences between the latencies of test and retest was 0.24 msec. The scattergram of the latencies of test and retest are shown (Fig. 6). The correlation coefficient was +0.93 (p < .001). The analysis of variance for the regression is shown in Table III. In order to make a more detailed study of the variability of the response amplitude and latency on test and retest, the effect of: 1) the N1 amplitude; 2) stimulus intensity; 3) type of hearing loss; and 4) whether test and retest were performed in sequence or not, were evaluated. First, the amplitude was studied. The mean of the two amplitudes in each set

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Ann Otol 85: 1976 TEST -RETEST RELIABILITY IN CLINICAL ELECTROCOCHLEOGRAPHY L. M. BERGHOLTZ, M.D. LINKOPING, SWEDEN R. E. HOOPEH, },'LD. BRONX...
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