Galvanic-Induced Postural Movements As a Test of Vestibular Function in Humans

Galvanic stimulation produces postural sway and eye movements in humans. Since galvanic currents are thought to exert their effect at the trigger zone of the vestibular nerve, an intact vestibular nerve should be necessary to produce a response. We have used galvanic stimulation in humans to test the hypothesis that intact vestibular nerve fibers are required to obtain a postural sway response. Experimental subjects included normal subjects, patients who had undergone resection of an acoustic neuroma, and patients who had undergone vestibular neurectomy and surgical labyrinthectomy. Our results support the hypothesis that an intact vestibular nerve is necessary to produce a response. Moreover, two patients with recurrent vertigo following vestibular neurectomy and labyrinthectomy, who had absent ice-water caloric test responses in the operated ears, were found to have a positive galvanic response. This result suggested that their recurrent vertigo was based on intact residual vestibular nerve fibers. Although previous research has not yielded a routine clinical use for galvanic stimulation, our results suggest that galvanic stimulation of the vestibular system can provide unique and valuable diagnostic information.     

The importance of cervical muscles in responses of galvanic body sway test

Body sway in normal subjects was analyzed by means of various methods to study a role of cervical muscles in galvanic body sway test. Galvanic stimulation through the retro-auricular electrode induced an initial response and a deviation response in body sway. When the anodal stimulation was given through the right retro-auricle during standing, a deviation response toward the right side was observed. While keeping a posture weighted on one foot, the stimulation induced a similar response. The stimulation during squatting produced also a deviation response toward the right side. When the head was rotated to the right, the stimulation produced backward responses. When rotated to the left, it produced forward responses. Even without galvanic stimulation, similar responses were also induced by some other method, for example, inclining the head to one side. Galvanic stimulation while sitting resulted in slight but apparent head inclination. The results suggested that cervical muscles played an important role in galvanic body sway test. Initial and deviation responses appeared to be secondarily produced by changes in the cervical muscular tension.     

The deviation of the body's sway center with galvanic stimulation

We investigated galvanic body sway of ten healthy adults and eight patients by using the averaging program for measuring T1 and T2, which were latencies at the onset and at the cutoff of galvanic stimulation, respectively, and the plotting program, which adopted 1.73 sec as T1 and 0.39 sec as T2, for calculating the coordinates of the body's sway center. We estimated galvanic body sway with the difference between the coordinate of the body's sway center during stimulation and that during no stimulation. The deviation in lateral direction on the healthy subjects ranged from 0.7 or 0.9 to 2.1 cm at right- or left-side stimulation. One of the patients with peripheral disorders revealed differences between right- and left-side stimulation. The other patients did not reveal any differences. In antero-posterior direction six of the healthy subjects deviated backward at right-side stimulation and nine subjects deviated backward at left-side stimulation. The patients with peripheral disorders did not reveal any differences. The other patients revealed some differences. Waves computed by the averaging program do not always show the quantity of galvanic body sway. The deviation of the body's sway center shows the quantity of body sway consistently. The body's sway center is considered to be a suitable parameter in the galvanic body sway test for statistical analysis.     

Stimulation of the vestibular nerve

Introduction. The aim of this study was the development of a simple galvanic stimulator for routine clinical use, which by stimulation of the vestibular nerve helps to discriminate between labyrinthine and retro-labyrinthine lesions, as well as to localise the side (left–right) of the retro-labyrinthine function loss. Patients and methods. By way of retro-auricular electrodes 13 healthy controls and 49 patients with vestibular complaints (with and without caloric hyporeflexia) were stimulated unilaterally and bilaterally with the use of a computer-assisted stimulator. The platform on which the subject was standing recorded the body sway. Also the tendency to fall with the use of a simple battery stimulator (9V) without platform was observed. Results. Patients were more instable at rest than controls. During stimulation a significant instability increase was seen. In the patient group bilateral stimulation increases instability more than unilateral stimulation. At caloric areflexia with an intact vestibular nerve a galvanic response could be evoked. Stimulation with the battery stimulator gave comparable results. Conclusion. Galvanic stimulation by use of the simple battery driven stimulator increases the body instability and gives additional information about the function of the vestibular nerve when there is complete caloric areflexia.     

Effects of visual input on galvanic body sway test of unilateral vestibular deficiency in patients with unilateral vestibular schwannoma

OBJECTIVE: Galvanic body sway tests (GBSTs) are performed with eyes fixed and closed. However, quantitative effect of fixation on GBST has been unknown. The purpose of this study is to address this question. METHODS: We evaluated GBSTs of patients with unilateral vestibular schwannomas and normal controls, while their eyes were open and closed. We evaluated three GBST parameters: maximum amplitude of the response, velocity and latency of the onset of response. RESULTS: Closing the eyes diminished stability, resulting in increased amplitude and velocity of the responses. However, apparent contribution to the latency of response could not be found. Contribution of visual fixation seems to be greater in apparatus with vestibular hypo-function than without it. Unilateral weakness (UW) was calculated for each parameter, and significant correlation, between with eyes fixed and closed, was found only for velocity parameter. CONCLUSION: Fixation would stabilize the body of subjects, and diminish GBST responses. GBST with and without fixation can be evaluated together, using certain coefficient. On the other hand, fixation would not have any contribution to the latency of the GBST response. When we evaluate vestibular dysfunction of patients with unilateral vestibular schwannomas, velocity parameter should be employed.     

Galvanically induced body sway in the anterior-posterior plane

Anterior-posterior body sway was evoked with monopolar bi-aural galvanic stimulus of the vestibular nerves in normal subjects and recorded with a force platform, two experiments being conducted. In an experiment of paired design, 9 normal subjects showed an increase in anterior-posterior sway as compared with lateral sway when exposed to the stimulus. In a second experiment another group of 10 normal subjects were exposed to a galvanic stimulus between a neck electrode and two electrodes placed on the arms, but there was no change in the relationship between anterior-posterior and lateral body sway. It is concluded that monopolar galvanic stimulus of the vestibular nerves can induce anterior-posterior body sway, a phenomenon which can be utilised to investigate the vestibulo-spinal contribution in postural control in the anterior-posterior plane.     

Direction of galvanically-induced vestibulo-postural responses during active and passive neck torsion

The direction of a postural response induced by galvanic vestibular stimulation depends on the head and trunk position. The relative importance of afferent information (proprioception) and efferent motor command/corollary discharge is unknown. We studied the direction of body sway evoked by galvanic vestibular stimulation in 9 healthy subjects during active and passive head positioning at 0 degrees frontal position, 35 degrees to the left, and 75 degrees to the right, using a custom-built collar. At 0 degrees and 75 degrees there were no significant differences in sway direction between active and passive head positioning. The galvanic stimulation invoked sway toward the anode, mainly in the inter-aural direction. The sway direction differed significantly between active and passive positioning at 35 degrees to the side (p < 0.05). When the head was actively kept in this position, the body sway was mainly in an inter-aural direction. The sway shifted to a naso-occipital direction when the head was passively positioned at 35 degrees. Our results indicate that the afferent proprioceptive information has the largest influence on the direction of the galvanically-induced postural response, although some dependence on efferent motor commands and non-linear cervical proprioception cannot be ruled out entirely.     

Visual suppression test

The visual suppression test is one of the methods measuring the function of visual fixation. It is carried out by recording the caloric nystagmus by electronystagmography and comparing the maximum slow phase velocity of caloric nystagmus in the darkness and the slow phase velocity in the light with eyes opened. In 50 normal adults aged 16 to 31 years, the score of the visual suppression of the slow phase velocity of caloric nystagmus was 69.9 +/- 18.5%. Visual suppression was also studied in 125 cases with various kinds of vestibular diseases. The results showed that: 1. In cases with peripheral vestibular diseases, the visual suppression was normal (visual suppression over 50%). 2. In cases with cerebellar diseases, the visual suppression might be reduced (visual suppression 40%-10%) or abolished (visual suppression under 10%). It means that the flocculus or nodulus had been directly or indirectly impaired. 3. In brain stem lesions, the visual suppression might be reduced, abolished or the caloric nystagmus might even show augmentation in light (visual suppression negative). It means that the paramedian pontine reticular formation had been impaired. 4. In case of CP angle tumor, owing to compression to the vestibulo-cerebellum or brain stem, the visual suppression might be abnormal. 5. In case of congenital nystagmus, visual suppression varied from normal to abolished. Thus, the visual suppression test is useful in differential diagnosis of the central and peripheral vestibular diseases.     

Validity and limitation of detection of peripheral vestibular imbalance from analysis of manually rotated vestibulo-ocular reflex recorded in the routine vestibular clinic

We compared the results of analysis of vestibulo-ocular reflex (VOR) obtained by manual rotation in routine vestibular clinical practice with that of caloric testing, and examined the validity and limitations of VOR analysis as a test for the estimation of peripheral vestibular function and imbalance. VOR response was recorded in daily vestibular clinical examinations by manually rotating the standard clinical chair for approximately 30 s. VOR gain was slightly, but significantly, correlated with the peak slow phase velocity of caloric response (r = 0.50, p < 0.001). However, 8 out of 12 patients with no caloric response failed to exceed the range of two standard deviations of the mean value of age-matched normal subjects, indicating that it is clinically difficult to use VOR gain alone as a estimate of unilateral vestibular function. VOR directional preponderance (VOR DP%) correlated well with caloric canal paresis (CP) (CP%; r = 0.89, p < 0.001). VOR DP% was within the normal range in patients with caloric CP% < 40 and exceeded the normal range in most cases with caloric CP% > 80. VOR DP% varied widely when caloric CP% ranged between 40 and 80. The effect of vestibular compensation on VOR DP% was examined by plotting VOR DP% divided by caloric CP% (DP/CP) against the number of days since the onset of vertigo in patients with vestibular neuritis or sudden deafness with vertigo. DP/CP was large within 50 days of the onset of vestibular damage, especially when caloric CP% was < 80, and gradually decreased with time. These results indicate that determination of VOR DP% should contribute to the early diagnosis of fresh vestibular imbalance, especially in daily clinical practice, because this type of VOR recording can be performed in < 1 min in routine vestibular clinics. The decay time constant of DP/CP was larger when caloric CP% exceeded 80, indicating that vestibular compensation proceeds more slowly when the vestibular damage is severe.     

The minimal ice water caloric test compared with established vestibular caloric test procedures

Caloric testing of the vestibular labyrinth is usually performed by classical caloric test procedures (CCTP) using water warmed to 30 degrees C and 44 degrees C. Ice water irrigation (4 degrees C) is usually not performed, although it might be useful as a bedside test. To verify the validity of the Minimal Ice Water Caloric Test (MIWCT), comparative video-oculographic investigations were performed in 22 healthy subjects using ice water (0.5 ml, 1.0 ml, 2 ml), CCTP, and cold air (27 degrees C). Frequency, amplitude, slow phase velocity (SPV), the onset, and the duration of nystagmus were documented. After addition of three ice cubes, the temperature of conventional tap water (16 degrees C) fell within 13 min to 4 degrees C. In pessimum position the subjects demonstrated no nystagmus response. Compared to CCTP, MIWCT was associated with a significantly later onset of nystagmus and a significant prolongation of the nystagmus reaction. In contrast to air stimulation (27 degrees C), a significant Spearman's correlation was noted between MIWCT (1 and 2 ml) and established CCTP in respect of essential nystagmus parameters (frequency, amplitude and SPV). Furthermore, MIWCT (0.5 and 1 ml) showed a higher sensitivity and specificity with regard to the detection of canal paresis based on Jongkees' formula compared to stimulation with air 27 degrees C. Thus, MIWCT appears to be a suitable procedure for bedside investigation of vestibular function outside the vestibular laboratory, e.g. in a hospital ward, where bedridden patients with vertigo occasionally require vestibular testing.     

Direction of Galvanically-induced Vestibulo-postural Responses during Active and Passive Neck Torsion

The direction of a postural response induced by galvanic vestibular stimulation depends on the head and trunk position. The relative importance of afferent information (proprioception) and efferent motor command/corollary discharge is unknown. We studied the direction of body sway evoked by galvanic vestibular stimulation in 9 healthy subjects during active and passive head positioning at 0° frontal position, 35° to the left, and 75° to the right, using a custom-built collar. At 0° and 75° there were no significant differences in sway direction between active and passive head positioning. The galvanic stimulation invoked sway toward the anode, mainly in the inter-aural direction. The sway direction differed significantly between active and passive positioning at 35° to the side (p&lt;0.05). When the head was actively kept in this position, the body sway was mainly in an inter-aural direction. The sway shifted to a naso-occipital direction when the head was passively positioned at 35°. Our results indicate that the afferent proprioceptive information has the largest influence on the direction of the galvanically-induced postural response, although some dependence on efferent motor commands and non-linear cervical proprioception cannot be ruled out entirely.     

The status of galvanic assessment of equilibrium

The galvanic test is the only method of localising the site of the disease in the differential diagnosis between a vestibular endorgan or neuronal lesion. The galvanic nystagmus persists even after complete destruction of the inner ear but is impaired as soon as the peripheral vestibular neurone is damaged. We investigated 30 normal subjects, 10 patients with Menière's disease and 20 patients with an acoustic neuroma. The patients had a reduced caloric response on one side. All subjects were stimulated monaural-unipolar. The photoelectronystagmograms were analysed by determining slow phase velocity. For interpretation we used the "relationship of excitability" as described recently by Mulch and Scherer for the thermal test. This procedure seems to be more accurate than the calculation of side difference of excitability as a proportion of total reaction. Furthermore we suggest basing the evaluation of galvanic test by calculating expectation regions for the logarithmic values obtained by right-left stimulation. This method assumes a two dimensional symmetric normal distribution. The parameters lay within the normal range in all patients with Menière's disease whereas they were abnormal in every subject with an acoustic neuroma.     

Validity and Limitation of Detection of Peripheral Vestibular Imbalance from Analysis of Manually Rotated Vestibulo-Ocular Reflex Recorded in the Routine Vestibular Clinic

We compared the results of analysis of vestibulo-ocular reflex (VOR) obtained by manual rotation in routine vestibular clinical practice with that of caloric testing, and examined the validity and limitations of VOR analysis as a test for the estimation of peripheral vestibular function and imbalance. VOR response was recorded in daily vestibular clinical examinations by manually rotating the standard clinical chair for &#44 30 s. VOR gain was slightly, but significantly, correlated with the peak slow phase velocity of caloric response ( r = 0.50, p < 0.001). However, 8 out of 12 patients with no caloric response failed to exceed the range of two standard deviations of the mean value of age-matched normal subjects, indicating that it is clinically difficult to use VOR gain alone as a estimate of unilateral vestibular function. VOR directional preponderance (VOR DP%) correlated well with caloric canal paresis (CP) (CP%; r = 0.89, p < 0.001). VOR DP% was within the normal range in patients with caloric CP% < 40 and exceeded the normal range in most cases with caloric CP% > 80. VOR DP% varied widely when caloric CP% ranged between 40 and 80. The effect of vestibular compensation on VOR DP% was examined by plotting VOR DP% divided by caloric CP% (DP CP) against the number of days since the onset of vertigo in patients with vestibular neuritis or sudden deafness with vertigo. DP CP was large within 50 days of the onset of vestibular damage, especially when caloric CP% was < 80, and gradually decreased with time. These results indicate that determination of VOR DP% should contribute to the early diagnosis of fresh vestibular imbalance, especially in daily clinical practice, because this type of VOR recording can be performed in < 1 min in routine vestibular clinics. The decay time constant of DP CP was larger when caloric CP% exceeded 80, indicating that vestibular compensation proceeds more slowly when the vestibular damage is severe.     

Significance of pressor input from the human feet in lateral postural control. The effect of hypothermia on galvanically induced body-sway

The significance to human postural control of pressor information from the feet was investigated during vestibular disturbance in seven normal subjects who were exposed to bipolar biaural galvanic stimulation of the vestibular nerves before and after their feet were anaesthetized with hypothermia. The increase in body sway in the lateral plane induced by the galvanic stimulus was enhanced when the feet were anaesthetized, and adaptation of postural control to the galvanic stimulus was delayed. It is concluded that pressor information from the feet contributes significantly to postural control in humans and is important in compensating for vestibular disturbance.     

Extent of lesions in idiopathic sudden hearing loss with vertigo: study using click and galvanic vestibular evoked myogenic potentials

OBJECTIVE: To clarify the extent of the vestibular lesions in idiopathic sudden hearing loss with vertigo using vestibular evoked myogenic potentials (VEMPs) in response to click (click-VEMP) and galvanic (galvanic-VEMP) stimulation, as well as caloric tests. DESIGN: Retrospective study. SETTING: University hospital. PATIENTS: We enrolled 22 patients with idiopathic sudden hearing loss with vertigo in this study. All patients underwent audiometry and click-VEMP and caloric tests. Eight patients underwent a galvanic-VEMP test. RESULTS: Among the 22 patients, 17 (77%) showed an absence of click-VEMPs on the affected side. In response to caloric testing, 10 patients (45%) showed a decreased response on the affected side. All 8 patients who underwent galvanic-VEMP testing showed normal responses. Most patients with decreased caloric responses (9 [90%] of 10 patients) showed an absence of click-VEMPs, whereas 9 (53%) of the 17 patients who showed abnormal click-VEMPs showed decreased caloric responses. Initial hearing level and hearing outcome significantly correlated with abnormalities on the vestibular test results. CONCLUSIONS: The lesion site of vestibular disorders in idiopathic sudden hearing loss with vertigo appeared to be within the labyrinth on the basis of galvanic-VEMP findings. Results of the click-VEMP and caloric tests suggested that the saccule could be involved more frequently than the semicircular canals. The combined use of click-VEMP and caloric tests is useful for evaluating vestibular functions in idiopathic sudden hearing loss with vertigo because the extent of vestibular abnormalities correlated well with hearing outcome.     

Mumps virus may damage the vestibular nerve as well as the inner ear

We report a case of mumps deafness with acute vestibular symptoms secondary to both retrolabyrinthine and inner ear dysfunction. To our knowledge, no such case has been reported elsewhere. The patient was a 6-year-old girl in whom mumps deafness was initially diagnosed. Two days after onset of the hearing impairment, severe vertigo developed. Neurotologic examinations revealed spontaneous right-beating nystagmus, left canal paresis, absence of vestibular-evoked myogenic potentials in the left ear, and absence of responses to a left galvanic body sway test (GBST). The vertigo resolved 7 days after onset. However, the left hearing impairment progressed to complete deafness. Six months later, left canal paresis was still present, but bilateral GBST responses were normal, suggesting that retrolabyrinthine vestibular function had been restored. Mumps virus may affect retrolabyrinthine function as well as the inner ear.     

The dynamics of the vestibulo-ocular reflex in patients with vestibular neuritis

The dynamics of the vestibulo-ocular reflex (VOR) were studied in 14 patients at the onset of vestibular neuritis, and at follow-up 1 year later. A velocity step stimulus of 150 degrees/s was used to investigate the VOR time constant and gain, and the results were related to the caloric response. In the acute, vertiginous phase of the disease, the VOR time constant was reduced but was almost normalized 1 year later, both among patients who regained normal caloric side-difference and among those who did not. However, the increase in VOR time constant was greater among those who regained normal caloric excitability, and regression analysis showed a correlation between the prolongation of the VOR time constant and the recovery of caloric excitability. These findings suggest that VOR dynamics are modulated during the acute phase of vestibular neuritis, and that there is recovery with vestibular compensation. Furthermore, the recovery of the VOR time constant is not solely dependent on the recovery of normal caloric excitability. This implies that central storage of velocity information may be involved in the VOR, even in cases of asymmetric vestibular input after vestibular compensation.     

单侧前庭功能低下患者计时平衡试验及静态姿势描记

目的观察单侧前庭功能低下（unilateral vestibular hypofunction，UVH）患者的计时平衡试验和静态姿势描记，探讨两种方法的临床应用价值。方法65例UVH患者和92例健康志愿者进行如下静态直立试验：①标准Romberg试验；②双脚平行分开直立试验；③强化Romberg试验（踵趾足位站立）；④单足直立试验。每种测试条件下分别睁眼和闭眼站立，用秒表记录①～④试验中维持平衡的时间，同时用静态姿势描记记录①、②条件下的身体晃动平均速度。结果①计时平衡试验：UVH组采取踵趾位和单足站立时，维持平衡时间较对照组降低，差异均有统计学意义（P值均〈0．001）；②静态姿势描记：采用标准Romberg位和双脚分开站立，UVH组和对照组相比，睁眼时2组身体晃动平均速度差异无统计学意义（P值分别是0．118和0．110）。而闭眼时UVH组身体晃动平均速度较对照组增加，2组差异均有统计学意义（P值均〈0．001）；③对于UVH组和对照组，无论睁眼或闭眼，采用双脚分开站立时，身体晃动平均速度均较标准Romberg位时降低，差异有统计学意义（P值〈0．05或〈0．001）；④踵趾位和单足站立时的各计时结果与其标准Romberg站立和双足分开站立时的各身体晃动平均速度间未发现有统计学意义。结论评估UVH患者平衡功能时，踵趾位和单足直立计时平衡试验是对静态姿势描记试验的补充，两种方法可在临床中结合应用；进行静态姿势描记试验时，应考虑足位因素对测试结果的影响。     

Value of the rotation test in acute unilateral vestibular disorders

The electronystagmographically recorded response of the spontaneous nystagmus and of the per- and postrotatory nystagmus were examined in 70 patients suffering from acute unilateral vestibular disorders. Within a short time the SPN declined logarithmically compared to the reduction of the perrotatory directional preponderance. But the postrotatory nystagmus levels changed only a little in the course of time. The patient's symptoms did not correlate with results of the rotatory test or the intensity of the SPN. The graphs of both parameters (maximal velocity of the slow nystagmus phase and nystagmus frequency in culmination range) which had been analysed showed an almost identical course. Obviously two independent functions are recorded by the caloric and rotatory vestibular test: the rotatory test is said to describe the extent of the central compensation. The lack of conformity in the results of various vestibular tests, including the rotating chair, limit the reliability of the individual tests and indicate that different methods of investigation should always be carried out especially in medico-legal cases.     

Caloric test and video-head-impulse: a study of vertigo/dizziness patients in a community hospital

The head-impulse test (HIT) is an important test for examining unilateral vestibular hypofunction. The new video-head-impulse test (vHIT) is more sensitive and specific than the clinical bedside-head-impulse test (bHIT). Alternatively, one can test for vestibular hypofunction with the caloric irrigation test. Various studies showed that both tests may not always identify vestibular hypofunction; instead, the results of the tests might be contradictory. To evaluate the diagnostic value of these tests, we routinely measured patients exhibiting vertigo or dizziness at our community hospital with bithermal caloric irrigation, the bHIT and the vHIT. Only those patients (n = 172) with a pathological caloric irrigation test of more than 25 % unilateral weakness in the Jongkee’s formula were included. Out of these patients, 41 % had a pathologic vHIT. Among the subgroup with acute symptoms (symptom onset within 5 days), 63 % had a pathological video-head-impulse, whereas only 33 % of the non-acute group (symptom onset more than 5 days) tested pathological. A pathological HIT depended on the disease stage, the amount of unilateral weakness in caloric examination and on the test itself.