Original Paper ORL 1992;54:133-138
Departments of a Internal Medicine and b Neurology, University Hospital, Freiburg, FRG
Key Words Electronystagmography Galvanic vestibulo-ocular reflex Evaluation of the galvanic test Response decline Threshold stimuli Psychophysical reactions
Evaluation of the Galvanic Vestibulo-Ocular Response Recorded with a Modified Electronystagmographic Technique
Abstract Previously, a simple method for recording galvanic nystagmus (GN) using conventional electronystagmography (ENG) was demonstrated. The present study reports on investigations made to examine the applicability of that tech nique. During a standard stimulus over 20 s, amplitudes and rate of saccades show no tendency to diminish. In a series of 10 repeated standard stimuli over 16 min, a parabolic relationship is observed between time on one side and on the other, the mean amplitude, the mean rate of saccades and the sum of amplitudes per stimulus duration. The threshold of GN was 1.29 mA and that of induced tilting sensation 3.64 mA. In a series of 8 repeated threshold stimu li, thresholds of GN and tilting sensation linearly increase (p < 0.001). During the slow increase of the current, the amplitudes and frequency of saccades and the slow-phase velocity linearly increase (p < 0.01). The direction of per- and poststimulatory galvanic nystagmus and tilting sensation were investigated. Several autonomic reactions and psychophysical sensations during stimula tion were noted. In conclusion, it is thought that the modified ENG technique is a valid method for further clinical use and basic research and its applicabil ity has proven to be good.
Introduction Galvanic stimulation of the labyrinths leads to mani fold reactions of the body. The most frequently investi gated reaction is the vestibulo-ocular response, the ‘gal vanic nystagmus’ (GN). This is in part due to the clear response of the vestibular stimulation which also provides an easy way of objectifying this method. Moreover, psy chophysical responses, tilting sensations (TS) and reac
Received: July 31,1991 Accepted: October 9. 1991
tions of the autonomic nervous system are interesting fea tures of the galvanic test. In an earlier study [1] we demonstrated a new tech nique for recording GN by means of conventional electro nystagmography (ENG). Now, we can report on the appli cability of this method using the standard parameters of vestibulo-ocular response and some psychophysical and vegetative reactions.
Dr. Rainer Hans Straub Department of Internal Medicine. University Hospital Hugstctterstrassc 55 D-W-7800 Freiburg (FRG)
© 1992 S. Karger AG. Basel 0301-1569/92/0543-0133 $2.75/0
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Rainer Hans Strauba Uwe Thodenb
Results
Subjects and Methods Subjects. Thirty healthy subjects of both sexes, between 20 and 45 years of age, without histories of vestibular or ocular diseases, were examined. In order to ensure vestibular normality, eye movements in the dark were recorded over 60 s, thus excluding a pathologic sponta neous nystagmus. Stimulation and Recording. A constant-current generator deliv ered single or repetitive stimuli (Tonnies, Freiburg, FRG). Two forms of electrical stimuli were used: (1) a trapezoidal electrical stimulus which has a plateau current of 4 mA, a stimulus duration of 20 s, a plateau duration of 16 s and a current slope of 2.0 mA/s (fig. 1), and (2) a stimulus with a slowly increasing current (5 mA/25 s) having a short plateau of 5 s and ending with a decreas ing current of 2.0 mA/s. TS, direct current and horizontal nystag mus were recorded simultaneously using a multichannel recorder. Nystagmus was obtained cancelling the galvanic cardiac artifact by means of the modified ENG recording technique described earlier [1], The time constant was 1 s. A stimulus isolation unit was applied (Tonnies). Calibration o f Eye Movements. The first calibration of eye move ments was carried out at the beginning of each series of stimuli in brightness. To eliminate possible changes of the corneoretinal poten tial, calibrations were carried out every 5th minute in darkness dur ing the entire examination. Calculation o f the M axim al Study Period. To avoid minimal area burns caused by the direct current it is necessary to calculate a maxi mal study period. Using our copper ring electrodes of 40 cm2 [1] we determined the following formula that should be used when stimulat ing over longer periods:
Amplitude and Frequency o f Saccades during the Pla teau o f 20 s. Figure 2 shows the tracing of a typical hori zontal nystagmus. Five hundred and fifty-nine tracings were examined with the simple linear regression model. The amplitudes of saccades did not change in 87.5% (489/559) of all stimulations, 10.4% (58/559) showed an increase and 2.1% (12/559) showed a reduction during the plateau of one trapezoidal stimulus. The frequency of saccades determined from the distance between neighbor ing saccades remained constant in 91.1 % (509/559) of all stimulations, 8.2% (46/559) showed a reduction and only 0.7% (4/559) showed an increase during the plateau of one trapezoidal stimulus. Mean Amplitude, Frequency o f Saccades and the Sum o f Amplitudes per Stimulation during 10 Repeated Stimu li. Twenty subjects were stimulated with a series of 10 tra pezoidal stimuli with a mean interval of about 60s between each other. The mean amplitude and the fre quency of saccades and the sum of amplitudes per plateau
dT = 0.375 X U X I X (tp + 1/2 X Ti/d). dT is the rise of temperature at stimulating electrodes, U is the stimu lation voltage, I the stimulating current, tp the plateau period and t,« the duration of increase and decrease of the current. In this study, we used the limit value for dT of 1.2 K, which did not lead to burns at the sites of stimulating electrodes. Furthermore, it is necessary to wet the cotton around the electrodes every 5th minute during the entire examination.
Fig. 1. Typical stimulus of 20 s with a plateau duration of 16 s, a plateau current of 4 mA and an increasing (1) and decreasing (D) cur rent of 2 mA/s.
A, mm DBNS, mm
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Evaluation of the Galvanic Vestibulo-Ocular Response
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Fig. 2. Typical tracing of GN during a stimulus over 20 s (A = amplitude of saccade, DBNS = distance between neighboring saccades, RT = running time).
Fig. 3. Mean amplitude of saccades over 16 min. Dotted line = regression line (p > 0.05), continuous line = parabolic regression line (p < 0.01). Fig. 4. Frequency of saccades over 16 min. Dotted line - regres sion line (p > 0.05), continuous line = parabolic regression line (p < 0 .01). Fig. 5. Sum o f amplitudes per stimulating time over 16 min. Dot ted line = regression line (p > 0.05), continuous line = parabolic regression line (p < 0.01).
Vertex 10 ± 3 min
10 + 3 min
5
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duration of every stimulation were calculated. The first value of the series of 10 repeated stimuli was set to 100%. the following values were calculated in percent correspond ing to the first one. Figures 3-5 show the average results of 20 subjects. Using a parabola in a nonlinear regression model the average parameter shows a diminution until the 10th minute and then an increase which was observed until the 16th minute (continuous line in fig. 3-5). The calcu lated minimum or vertex was at about 10 min. Threshold ofG N and TS. Fifteen subjects were investi gated using a slowly increasing current (5 mA/25 s, fig. 6). The subjects were instructed to press a button when the TS arose, which made a rectangular signal on the first trace in figure 6. It was found that the threshold of GN was about 1.29 mA (s = 0.5 mA, n = 15) whereas the threshold of TS was about 3.64m A (s= 1.04 mA, n= 15). In every stimulation carried out in this mode (120 stimu lations on 15 subjects) we found the threshold of GN to be higher than that of TS. Threshold o f GN and TS in a Series o f 8 Repeated Threshold Stimuli. Fifteen subjects were stimulated with a series of 8 stimuli (5 mA/25 s) with an interval of about 60 s between each other. A simple linear regression model was used to describe the relationship between the time and the threshold of GN and TS. For both thresholds, one could estimate a common correlation coefficient (CC) which differed highly significantly from zero: C C gn = 0.613 (degree of freedom = 53; p < 0.001), CCts = 0.849 (degree of freedom = 53; p < 0.001). Figures 7 and 8 show the increase in the threshold of GN and TS during several single stimulations. Amplitude o f Saccades, Frequency o f Saccades and Slow-Phase Velocity during the Slow Increase o f the Cur rent. The tracing shown in figure 6 was subdivided into 6 classes. The mean amplitude of saccades, the frequency of saccades and the mean slow-phase velocity (SPV) was cal culated in every class. Using the simple linear regression model it was found that increasing current leads to an increase in the amplitude (p < 0.01), the frequency (p < 0.01) and SPV (p < 0.01, fig. 9-11).
Fig. 6. Typical tracing of horizontal GN during a stimulus with a slowly increasing current (dizziness = TS, Diff. = horizontal deriving, n = number o f saccades per class, x = mean amplitude of saccades per class, I = mean value of the current per class, IDb = cur rent at the threshold of GN, Isu = current at the threshold of TS).
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Fig. 9. Amplitude of saccades during an increasing current (I = current, amplitude = averaged amplitude of saccades; p < 0.01). Fig. 10. Frequency of saccades during an increasing current (I = current, frequency = averaged frequency of saccades; p < 0 . 01) .
Evaluation of the Galvanic Vestibulo-Ocular Response
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Fig. 7. Threshold of GN during a series of several stimuli. Form of stimulus see figure 6. C C g n = 0.613 (p < 0.001). Fig. 8. Threshold of tilting sensation during a series of several stimuli. Form of stimulus see figure 6. C C ts = 0.849 (p < 0 . 001) .
Sensation of light in absolute darkness Existing................................. ^ ^ ^
b
Not existing......................... H B B B I ^ H ^ B M B
7 23
Tonus of muscles
Heightened.......................... B B B I ^ B
11
Unchanged..........................
19
Sensation of electrification along the edges of the tongue
Existing.................................
22
Not existing......................... ■
■
8
Increased perspiration
Existing................................. B B B B Not existing.........................
8 22
Increased swallowing I, mA
Existing.................................
Bi
Not existing.........................
3 27
Salivation
Dry mouth............................. ■
Fig. 11. SPV during an increasing current (I = current; p < O .O l).
Increased............................. ■ Unchanged...........................
2 2 26
Fig. 12. Typical autonomic and other perstimulatory reactions (n = 30).
Direction o f Per- and Poststimulatory GN. The direc tion of perstimulatory nystagmus was examined in 171 records. In 91% (156/171) one could observe horizontal nystagmus towards the cathode, in 9% (15/171) no nys tagmus, vertical nystagmus or alternating eye movements were seen. The direction of poststimulatory nystagmus was evaluated in 182 records. In 21 % (39/182) the nystag mus beats in the same direction as the perstimulatory nys tagmus, in 8% (14/182) the direction was contrary to that of the perstimulatory nystagmus, in 27% (49/182) no nys tagmus was visible, in 22% (40/182) it was directed verti cally upwards and in further 22% (40/182) one noticed only alternating eye movements. Direction ofTS. During the increase of the current 63% (19/30) felt a TS towards the side of the cathode, 20% (6/30) towards the side of the anode and 17% (5/30) were not able to delineate the impression of movement. In the course of the constant current (= plateau) 37% (11/30) could not describe the impression of movement, 37% (11/30) felt a TS to the side of the cathode, 16% (5/30) to the side of the anode and 10% (3/30) had no impression. Autonomic and Other Perstimulatory Reactions. Fig ure 12 shows typical autonomic and other perstimulatory reactions that were described by 30 subjects during the plateau of the stimulation.
12
Discussion Response Decline With reference to Singleton [2] one can distinguish between different types of response decline: (1) adapta tion is a response decline within seconds or minutes. (2) fatigue within minutes to hours and (3) habituation within days. In the First investigation no adaptation within 20 s was observed. In 1976, Swaak and Oosterveld [3] conducted galvanic bipolar binaural experiments on rabbits with a current of 15-20 mA. The provoked nys tagmus showed no tendency to diminish for more than 180 s. Benson and Jobson [4] used bipolar, monaural gal vanic stimulation and measured the body sway with a platform apparatus. During the first 5-10 s of stimulation the amplitude of the sway increased. Thereafter it re mained relatively constant until the stimulus ended. Sum ming up, there is no adaptation in the galvanic vestibular test using a current which is more than three times the threshold current. In the second investigation we examined fatigue and found a parabolic relation between nystagmus parameters and time with a minimum at about 10 min. Many investi gators who used a series of caloric or ratatory tests [5-11] described fatigue. Mittermaier [10], who used caloric stimuli, found a parabolic relation between time and
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11
amplitude of saccades with a minimum at about 30 min. Collins [8] found an oscillation of the caloric-induced nys tagmus parameter SPV with a first minimum at about 10 min. Brown and Marshall [5] also found an oscillation with a first minimum at about 15 min. From this and our own data one can postulate an oscillation of nystagmus parameters with a first minimum at 10 min and a period of 30 min. Further examinations have to be carried out to clear this phenomenon of galvanic vestibular reaction, and perhaps this will lead to a diagnostic procedure. Thresholds The threshold of GN was found to be about 1.5 mA [12-16], In agreement with Emami-Nouri [13], the threshold of TS was found to be higher than that of GN. Beyond that, the threshold become higher in a series of several threshold stimuli. Molinari and Mingrino [17] recorded the cortical response in a bipolar binaural elec trical field on an isopotential line directly from the human scalp. They found the threshold of this cortical response ranging between 2.5 and 4 mA, which is exactly the same compared with the threshold of TS in our own experi ments. Amplitude o f Saccades, Frequency o f Saccades and SPV during an Increasing Current It is generally known that an increasing current leads to an increase in the vestibulo-ocular responses [16-19],
More than that, it also leads to an increase in the ampli tude of the body sway [20], The present study confirms these results. Direction o f Per- and Poststimulatory Nystagmus Perstimulatory nystagmus is directed towards the cath ode as mentioned by several investigators [3, 13, 16, 18]. As far as poststimulatory nystagmus is concerned the examiners did not come tho the same results. It seems that the poststimulatory nystagmus is more variable than the perstimulatory nystagmus. This leads to the conclu sion that only GN during the electrical stimulation is pref erable for diagnostic purpose.
Conclusions The suitability of the modified ENG technique which allows ENG recording of GN was studied. Some experi ments were carried out to define and to standardize the method. Summing up, it may be said that the technique can be used either to make clinical diagnosis of vestibular disorders as initiated by Henriksson et al. [ 15] or to make basic research. The combination of several irritations of the vestibular system, for example electrical stimulation plus rotatory or platform tests, may be new and particu larly interesting fields of basic research.
1 Straub RH, Thoden U: A modified method of electronystagmography for recording eye movements during the galvanic vestibular test. ORL. in press. 2 Singleton GT: Relationships of the cerebellar nodulus to vestibular function: A study of the effects of nodulectomy on habituation. Laryn goscope 1967;77:1579-1620. 3 Swaak AJG. Oosterveld WJ: Galvanic vestibu lar test. ORL 1976;38:276-283. 4 Benson AJ. Jobson PH: Body-sway induced by a low frequency alternating current. Equilib rium Res 1973;3:55-61. 5 Brown JH, Marshall JE: Drug control of arousal and nystagmic habituation in the cat. Acta Otolaryngol 1967;64:345-352. 6 Brown JH: Interacting vestibular stimuli and nystagmic habituation. Acta Otolaryngol 1966; 62:341-350. 7 Brown JH. Crampton GH: Concomitant visual stimulation does not alter habituation of nys tagmic, oculogyric or psychophysical responses to angular acceleration. Acta Otolaryngol 1966; 61:80-91.
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8 Collins WE: Nystagmus responses of the cat to rotation and to directionally equivalent and non-equivalent stimulation after unilateral ca loric habituation. Acta Otolaryngol 1964:59: 247-258. 9 Crampton GH, Brown JH: Repeated vertical semicircular canal stimulation does not habit uate horizontal nystagmus in cat. Acta Otolar yngol 1964;58:441-448. 10 Mittermaier R: Über die Amplitude des experi mentell ausgelösten Nystagmus. Pract OtoRhino-Laryngol 1954;16:108-124. 11 Stahle J: Electro-nystagmography in the caloric rotatory tests. Acta Otolaryngol 1958; 137(suppl):60-72. 12 Breson K, Krag E: Galvanic pseudonystagmus. Acta Otolaryngol 1967;64:403-414. 13 Emami-Nouri M. Gedlicka W: Ein Beitrag zur galvanischen Stimulation des Vestibularapparates. Laryngol Rhinol Otol (Stuttg) !974;53: 200-204. ’
14 Hahn R. Menzio P: La valeur diagnostique de la stimulation vestibulaire galvanique dans cer tains syndromes otoneurologiqucs. Confin Neurol 1966;28:327-332. 15 Henriksson NG, Pfaltz CR. Torok N, Rubin W: Synopsis of the vestibular system. London. Sandoz, 1972. 16 Pfaltz CR: The diagnostic importance of the galvanic lest in otoneurology. Pract Oto-Rhino-Laryngol 1969;31:193-203. 17 Molinari GA. Mingrino S: Cortical evoked re sponses to vestibular stimulation in man. J Laryngol Otol 1974:88:515-521. 18 Breson K. Eberling C. Fangel J: Galvanic nys tagmography. Acta Otolaryngol 1971:71:449455. 19 Swaak T. Oosterveld WJ: The effect of gravity on galvanic nystagmus in rabbits. Acta Otolar yngol I975;(suppl 330):68—71. 20 Tanaka M. Honjo S: The double galvanic test. Equilibrium Res 1973;3:48-50.
Straub/Thoden
Evaluation of the Galvanic Vestibulo-Ocular Response
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References
Departments of a Internal Medicine and b Neurology, University Hospital, Freiburg, FRG
Key Words Electronystagmography Galvanic vestibulo-ocular reflex Evaluation of the galvanic test Response decline Threshold stimuli Psychophysical reactions
Evaluation of the Galvanic Vestibulo-Ocular Response Recorded with a Modified Electronystagmographic Technique
Abstract Previously, a simple method for recording galvanic nystagmus (GN) using conventional electronystagmography (ENG) was demonstrated. The present study reports on investigations made to examine the applicability of that tech nique. During a standard stimulus over 20 s, amplitudes and rate of saccades show no tendency to diminish. In a series of 10 repeated standard stimuli over 16 min, a parabolic relationship is observed between time on one side and on the other, the mean amplitude, the mean rate of saccades and the sum of amplitudes per stimulus duration. The threshold of GN was 1.29 mA and that of induced tilting sensation 3.64 mA. In a series of 8 repeated threshold stimu li, thresholds of GN and tilting sensation linearly increase (p < 0.001). During the slow increase of the current, the amplitudes and frequency of saccades and the slow-phase velocity linearly increase (p < 0.01). The direction of per- and poststimulatory galvanic nystagmus and tilting sensation were investigated. Several autonomic reactions and psychophysical sensations during stimula tion were noted. In conclusion, it is thought that the modified ENG technique is a valid method for further clinical use and basic research and its applicabil ity has proven to be good.
Introduction Galvanic stimulation of the labyrinths leads to mani fold reactions of the body. The most frequently investi gated reaction is the vestibulo-ocular response, the ‘gal vanic nystagmus’ (GN). This is in part due to the clear response of the vestibular stimulation which also provides an easy way of objectifying this method. Moreover, psy chophysical responses, tilting sensations (TS) and reac
Received: July 31,1991 Accepted: October 9. 1991
tions of the autonomic nervous system are interesting fea tures of the galvanic test. In an earlier study [1] we demonstrated a new tech nique for recording GN by means of conventional electro nystagmography (ENG). Now, we can report on the appli cability of this method using the standard parameters of vestibulo-ocular response and some psychophysical and vegetative reactions.
Dr. Rainer Hans Straub Department of Internal Medicine. University Hospital Hugstctterstrassc 55 D-W-7800 Freiburg (FRG)
© 1992 S. Karger AG. Basel 0301-1569/92/0543-0133 $2.75/0
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/6/2018 4:57:03 PM
Rainer Hans Strauba Uwe Thodenb
Results
Subjects and Methods Subjects. Thirty healthy subjects of both sexes, between 20 and 45 years of age, without histories of vestibular or ocular diseases, were examined. In order to ensure vestibular normality, eye movements in the dark were recorded over 60 s, thus excluding a pathologic sponta neous nystagmus. Stimulation and Recording. A constant-current generator deliv ered single or repetitive stimuli (Tonnies, Freiburg, FRG). Two forms of electrical stimuli were used: (1) a trapezoidal electrical stimulus which has a plateau current of 4 mA, a stimulus duration of 20 s, a plateau duration of 16 s and a current slope of 2.0 mA/s (fig. 1), and (2) a stimulus with a slowly increasing current (5 mA/25 s) having a short plateau of 5 s and ending with a decreas ing current of 2.0 mA/s. TS, direct current and horizontal nystag mus were recorded simultaneously using a multichannel recorder. Nystagmus was obtained cancelling the galvanic cardiac artifact by means of the modified ENG recording technique described earlier [1], The time constant was 1 s. A stimulus isolation unit was applied (Tonnies). Calibration o f Eye Movements. The first calibration of eye move ments was carried out at the beginning of each series of stimuli in brightness. To eliminate possible changes of the corneoretinal poten tial, calibrations were carried out every 5th minute in darkness dur ing the entire examination. Calculation o f the M axim al Study Period. To avoid minimal area burns caused by the direct current it is necessary to calculate a maxi mal study period. Using our copper ring electrodes of 40 cm2 [1] we determined the following formula that should be used when stimulat ing over longer periods:
Amplitude and Frequency o f Saccades during the Pla teau o f 20 s. Figure 2 shows the tracing of a typical hori zontal nystagmus. Five hundred and fifty-nine tracings were examined with the simple linear regression model. The amplitudes of saccades did not change in 87.5% (489/559) of all stimulations, 10.4% (58/559) showed an increase and 2.1% (12/559) showed a reduction during the plateau of one trapezoidal stimulus. The frequency of saccades determined from the distance between neighbor ing saccades remained constant in 91.1 % (509/559) of all stimulations, 8.2% (46/559) showed a reduction and only 0.7% (4/559) showed an increase during the plateau of one trapezoidal stimulus. Mean Amplitude, Frequency o f Saccades and the Sum o f Amplitudes per Stimulation during 10 Repeated Stimu li. Twenty subjects were stimulated with a series of 10 tra pezoidal stimuli with a mean interval of about 60s between each other. The mean amplitude and the fre quency of saccades and the sum of amplitudes per plateau
dT = 0.375 X U X I X (tp + 1/2 X Ti/d). dT is the rise of temperature at stimulating electrodes, U is the stimu lation voltage, I the stimulating current, tp the plateau period and t,« the duration of increase and decrease of the current. In this study, we used the limit value for dT of 1.2 K, which did not lead to burns at the sites of stimulating electrodes. Furthermore, it is necessary to wet the cotton around the electrodes every 5th minute during the entire examination.
Fig. 1. Typical stimulus of 20 s with a plateau duration of 16 s, a plateau current of 4 mA and an increasing (1) and decreasing (D) cur rent of 2 mA/s.
A, mm DBNS, mm
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10.95 11.95
13.35 14.85 16.21 13.95
Evaluation of the Galvanic Vestibulo-Ocular Response
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Fig. 2. Typical tracing of GN during a stimulus over 20 s (A = amplitude of saccade, DBNS = distance between neighboring saccades, RT = running time).
Fig. 3. Mean amplitude of saccades over 16 min. Dotted line = regression line (p > 0.05), continuous line = parabolic regression line (p < 0.01). Fig. 4. Frequency of saccades over 16 min. Dotted line - regres sion line (p > 0.05), continuous line = parabolic regression line (p < 0 .01). Fig. 5. Sum o f amplitudes per stimulating time over 16 min. Dot ted line = regression line (p > 0.05), continuous line = parabolic regression line (p < 0.01).
Vertex 10 ± 3 min
10 + 3 min
5
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duration of every stimulation were calculated. The first value of the series of 10 repeated stimuli was set to 100%. the following values were calculated in percent correspond ing to the first one. Figures 3-5 show the average results of 20 subjects. Using a parabola in a nonlinear regression model the average parameter shows a diminution until the 10th minute and then an increase which was observed until the 16th minute (continuous line in fig. 3-5). The calcu lated minimum or vertex was at about 10 min. Threshold ofG N and TS. Fifteen subjects were investi gated using a slowly increasing current (5 mA/25 s, fig. 6). The subjects were instructed to press a button when the TS arose, which made a rectangular signal on the first trace in figure 6. It was found that the threshold of GN was about 1.29 mA (s = 0.5 mA, n = 15) whereas the threshold of TS was about 3.64m A (s= 1.04 mA, n= 15). In every stimulation carried out in this mode (120 stimu lations on 15 subjects) we found the threshold of GN to be higher than that of TS. Threshold o f GN and TS in a Series o f 8 Repeated Threshold Stimuli. Fifteen subjects were stimulated with a series of 8 stimuli (5 mA/25 s) with an interval of about 60 s between each other. A simple linear regression model was used to describe the relationship between the time and the threshold of GN and TS. For both thresholds, one could estimate a common correlation coefficient (CC) which differed highly significantly from zero: C C gn = 0.613 (degree of freedom = 53; p < 0.001), CCts = 0.849 (degree of freedom = 53; p < 0.001). Figures 7 and 8 show the increase in the threshold of GN and TS during several single stimulations. Amplitude o f Saccades, Frequency o f Saccades and Slow-Phase Velocity during the Slow Increase o f the Cur rent. The tracing shown in figure 6 was subdivided into 6 classes. The mean amplitude of saccades, the frequency of saccades and the mean slow-phase velocity (SPV) was cal culated in every class. Using the simple linear regression model it was found that increasing current leads to an increase in the amplitude (p < 0.01), the frequency (p < 0.01) and SPV (p < 0.01, fig. 9-11).
Fig. 6. Typical tracing of horizontal GN during a stimulus with a slowly increasing current (dizziness = TS, Diff. = horizontal deriving, n = number o f saccades per class, x = mean amplitude of saccades per class, I = mean value of the current per class, IDb = cur rent at the threshold of GN, Isu = current at the threshold of TS).
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Fig. 9. Amplitude of saccades during an increasing current (I = current, amplitude = averaged amplitude of saccades; p < 0.01). Fig. 10. Frequency of saccades during an increasing current (I = current, frequency = averaged frequency of saccades; p < 0 . 01) .
Evaluation of the Galvanic Vestibulo-Ocular Response
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Fig. 7. Threshold of GN during a series of several stimuli. Form of stimulus see figure 6. C C g n = 0.613 (p < 0.001). Fig. 8. Threshold of tilting sensation during a series of several stimuli. Form of stimulus see figure 6. C C ts = 0.849 (p < 0 . 001) .
Sensation of light in absolute darkness Existing................................. ^ ^ ^
b
Not existing......................... H B B B I ^ H ^ B M B
7 23
Tonus of muscles
Heightened.......................... B B B I ^ B
11
Unchanged..........................
19
Sensation of electrification along the edges of the tongue
Existing.................................
22
Not existing......................... ■
■
8
Increased perspiration
Existing................................. B B B B Not existing.........................
8 22
Increased swallowing I, mA
Existing.................................
Bi
Not existing.........................
3 27
Salivation
Dry mouth............................. ■
Fig. 11. SPV during an increasing current (I = current; p < O .O l).
Increased............................. ■ Unchanged...........................
2 2 26
Fig. 12. Typical autonomic and other perstimulatory reactions (n = 30).
Direction o f Per- and Poststimulatory GN. The direc tion of perstimulatory nystagmus was examined in 171 records. In 91% (156/171) one could observe horizontal nystagmus towards the cathode, in 9% (15/171) no nys tagmus, vertical nystagmus or alternating eye movements were seen. The direction of poststimulatory nystagmus was evaluated in 182 records. In 21 % (39/182) the nystag mus beats in the same direction as the perstimulatory nys tagmus, in 8% (14/182) the direction was contrary to that of the perstimulatory nystagmus, in 27% (49/182) no nys tagmus was visible, in 22% (40/182) it was directed verti cally upwards and in further 22% (40/182) one noticed only alternating eye movements. Direction ofTS. During the increase of the current 63% (19/30) felt a TS towards the side of the cathode, 20% (6/30) towards the side of the anode and 17% (5/30) were not able to delineate the impression of movement. In the course of the constant current (= plateau) 37% (11/30) could not describe the impression of movement, 37% (11/30) felt a TS to the side of the cathode, 16% (5/30) to the side of the anode and 10% (3/30) had no impression. Autonomic and Other Perstimulatory Reactions. Fig ure 12 shows typical autonomic and other perstimulatory reactions that were described by 30 subjects during the plateau of the stimulation.
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Discussion Response Decline With reference to Singleton [2] one can distinguish between different types of response decline: (1) adapta tion is a response decline within seconds or minutes. (2) fatigue within minutes to hours and (3) habituation within days. In the First investigation no adaptation within 20 s was observed. In 1976, Swaak and Oosterveld [3] conducted galvanic bipolar binaural experiments on rabbits with a current of 15-20 mA. The provoked nys tagmus showed no tendency to diminish for more than 180 s. Benson and Jobson [4] used bipolar, monaural gal vanic stimulation and measured the body sway with a platform apparatus. During the first 5-10 s of stimulation the amplitude of the sway increased. Thereafter it re mained relatively constant until the stimulus ended. Sum ming up, there is no adaptation in the galvanic vestibular test using a current which is more than three times the threshold current. In the second investigation we examined fatigue and found a parabolic relation between nystagmus parameters and time with a minimum at about 10 min. Many investi gators who used a series of caloric or ratatory tests [5-11] described fatigue. Mittermaier [10], who used caloric stimuli, found a parabolic relation between time and
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amplitude of saccades with a minimum at about 30 min. Collins [8] found an oscillation of the caloric-induced nys tagmus parameter SPV with a first minimum at about 10 min. Brown and Marshall [5] also found an oscillation with a first minimum at about 15 min. From this and our own data one can postulate an oscillation of nystagmus parameters with a first minimum at 10 min and a period of 30 min. Further examinations have to be carried out to clear this phenomenon of galvanic vestibular reaction, and perhaps this will lead to a diagnostic procedure. Thresholds The threshold of GN was found to be about 1.5 mA [12-16], In agreement with Emami-Nouri [13], the threshold of TS was found to be higher than that of GN. Beyond that, the threshold become higher in a series of several threshold stimuli. Molinari and Mingrino [17] recorded the cortical response in a bipolar binaural elec trical field on an isopotential line directly from the human scalp. They found the threshold of this cortical response ranging between 2.5 and 4 mA, which is exactly the same compared with the threshold of TS in our own experi ments. Amplitude o f Saccades, Frequency o f Saccades and SPV during an Increasing Current It is generally known that an increasing current leads to an increase in the vestibulo-ocular responses [16-19],
More than that, it also leads to an increase in the ampli tude of the body sway [20], The present study confirms these results. Direction o f Per- and Poststimulatory Nystagmus Perstimulatory nystagmus is directed towards the cath ode as mentioned by several investigators [3, 13, 16, 18]. As far as poststimulatory nystagmus is concerned the examiners did not come tho the same results. It seems that the poststimulatory nystagmus is more variable than the perstimulatory nystagmus. This leads to the conclu sion that only GN during the electrical stimulation is pref erable for diagnostic purpose.
Conclusions The suitability of the modified ENG technique which allows ENG recording of GN was studied. Some experi ments were carried out to define and to standardize the method. Summing up, it may be said that the technique can be used either to make clinical diagnosis of vestibular disorders as initiated by Henriksson et al. [ 15] or to make basic research. The combination of several irritations of the vestibular system, for example electrical stimulation plus rotatory or platform tests, may be new and particu larly interesting fields of basic research.
1 Straub RH, Thoden U: A modified method of electronystagmography for recording eye movements during the galvanic vestibular test. ORL. in press. 2 Singleton GT: Relationships of the cerebellar nodulus to vestibular function: A study of the effects of nodulectomy on habituation. Laryn goscope 1967;77:1579-1620. 3 Swaak AJG. Oosterveld WJ: Galvanic vestibu lar test. ORL 1976;38:276-283. 4 Benson AJ. Jobson PH: Body-sway induced by a low frequency alternating current. Equilib rium Res 1973;3:55-61. 5 Brown JH, Marshall JE: Drug control of arousal and nystagmic habituation in the cat. Acta Otolaryngol 1967;64:345-352. 6 Brown JH: Interacting vestibular stimuli and nystagmic habituation. Acta Otolaryngol 1966; 62:341-350. 7 Brown JH. Crampton GH: Concomitant visual stimulation does not alter habituation of nys tagmic, oculogyric or psychophysical responses to angular acceleration. Acta Otolaryngol 1966; 61:80-91.
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8 Collins WE: Nystagmus responses of the cat to rotation and to directionally equivalent and non-equivalent stimulation after unilateral ca loric habituation. Acta Otolaryngol 1964:59: 247-258. 9 Crampton GH, Brown JH: Repeated vertical semicircular canal stimulation does not habit uate horizontal nystagmus in cat. Acta Otolar yngol 1964;58:441-448. 10 Mittermaier R: Über die Amplitude des experi mentell ausgelösten Nystagmus. Pract OtoRhino-Laryngol 1954;16:108-124. 11 Stahle J: Electro-nystagmography in the caloric rotatory tests. Acta Otolaryngol 1958; 137(suppl):60-72. 12 Breson K, Krag E: Galvanic pseudonystagmus. Acta Otolaryngol 1967;64:403-414. 13 Emami-Nouri M. Gedlicka W: Ein Beitrag zur galvanischen Stimulation des Vestibularapparates. Laryngol Rhinol Otol (Stuttg) !974;53: 200-204. ’
14 Hahn R. Menzio P: La valeur diagnostique de la stimulation vestibulaire galvanique dans cer tains syndromes otoneurologiqucs. Confin Neurol 1966;28:327-332. 15 Henriksson NG, Pfaltz CR. Torok N, Rubin W: Synopsis of the vestibular system. London. Sandoz, 1972. 16 Pfaltz CR: The diagnostic importance of the galvanic lest in otoneurology. Pract Oto-Rhino-Laryngol 1969;31:193-203. 17 Molinari GA. Mingrino S: Cortical evoked re sponses to vestibular stimulation in man. J Laryngol Otol 1974:88:515-521. 18 Breson K. Eberling C. Fangel J: Galvanic nys tagmography. Acta Otolaryngol 1971:71:449455. 19 Swaak T. Oosterveld WJ: The effect of gravity on galvanic nystagmus in rabbits. Acta Otolar yngol I975;(suppl 330):68—71. 20 Tanaka M. Honjo S: The double galvanic test. Equilibrium Res 1973;3:48-50.
Straub/Thoden
Evaluation of the Galvanic Vestibulo-Ocular Response
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References
