Adaptation of Vestibular Tone Studied with Electrical Stimulation of Semicircular Canal Afferents

Damage to one vestibular labyrinth or nerve causes a central tone imbalance, reflected by prominent spontaneous nystagmus. Central adaptive mechanisms eliminate the nystagmus over several days, and the mechanisms underlying this process have received extensive study. The characteristics of vestibular compensation when the tone imbalance is presented gradually or repeatedly have never been studied. We used high-frequency electrical stimulation of semicircular canal afferents to generate a vestibular tone imbalance and recorded the nystagmus produced when the stimulation was started abruptly or gradually and when it was repeatedly cycled on and off. In the acute-onset protocol, brisk nystagmus occurred when stimulation started, gradually resolved within 1 day, and reversed direction when the stimulation was stopped after 1 week. Repeated stimulation cycles resulted in progressively smaller nystagmus responses. In the slow-onset protocol, minimal nystagmus occurred while the stimulation ramped-up to its maximum rate over 12 h, but a reversal still occurred when the stimulation was stopped after 1 week, and repeated stimulation cycles did not affect this pattern. The absence of nystagmus during the 12 h ramp of stimulation demonstrates that central vestibular tone can rebalance relatively quickly, and the reduction in the stimulation-off nystagmus with repeated cycles of the acute-onset but not the slow-onset stimulation suggests that dual-state adaptation may have occurred with the former paradigm but not the latter.     

Head-shaking nystagmus during vestibular compensation in humans and rhesus monkeys

Nystagmus evoked after rapid horizontal head-shaking is believed to be a sensitive indication of the existence and location of a unilateral vestibular lesion. Its origin is the directional asymmetry in vestibular responses of the healthy labyrinth (Ewald's second law). For nystagmus to appear after the head has stopped moving, however, the directionally asymmetric responses must have been stored during the head-shaking to be discharged afterwards. Our results confirm the notion that head-shaking nystagmus is most likely generated by a directional preponderance in vestibular responses but only in combination with a functioning central velocity-storage mechanism. If velocity-storage is lost completely, as may occur during the acute phase of a unilateral peripheral vestibular lesion, even a large vestibular preponderance does not lead to head-shaking nystagmus. Thus, to interpret the results of the head-shaking test the condition of the velocity-storage mechanism must be taken into account.     

Electronystagmographic analysis of caloric test parameters in vestibular disorders

The electronystagmographical analysis of the eye movements provoked by caloric stimulation is an important method in the evaluation and topical diagnostic procedure of several vestibular lesions. The aim of the study was to compare the electronystagmographical results of caloric response in several vestibular disorders. The patients were divided into five groups: right and left unilateral and bilateral peripheral lesions, central vestibular dysfunction, and normal vestibular function. In the normal vestibular system group the average caloric nystagmus SPV in normal vestibular system was 17.4°/s. In the peripheral lesion groups the average slow phase velocities are decreased in the affected side, as we expected. In the compensated vestibular lesion the average ASPV of caloric nystagmus is also decreased on the unaffected side. This might be caused by the effect of the central adaptive mechanisms. According to our observations, in central dysfunctions the average caloric ASPV and the spontaneous nystagmus ASPV is increased (25.0°/s). This suggests that in central vestibular lesions the central inhibiting mechanisms of the caloric response are impaired. Our results show that electronystagmographical analysis of spontaneous and caloric nystagmus is very important in the evaluation of dizzy patients.     

Relationship of static and dynamic mechanisms in vestibuloocular reflex compensation

OBJECTIVES/HYPOTHESIS: We tested the hypothesis that recovery of dynamic oculomotor behavior (specifically the vestibuloocular reflex [VOR]) after a unilateral labyrinthectomy (UL) is independent from static deficit recovery (e.g., spontaneous nystagmus). This hypothesis predicts that VOR recovery from peripheral vestibular lesions that do not cause static symptoms, such as unilateral semicircular canal plugging (UCP), would have a similar time course and magnitude as recovery from a lesion that creates both a static and dynamic imbalance, such as UL. Furthermore, animals compensated after UCP would be expected to retain their compensated VOR response after the additional insult of ipsilateral labyrinthectomy. STUDY DESIGN: An experimental study in the Mongolian gerbil animal model. METHODS: The horizontal VOR was measured from both eyes using infrared video-oculography on gerbils before and after UCP, UL, or ipsilateral labyrinthectomy after a previous UCP. Eye movements were recorded during yaw rotation in the dark. RESULTS: UL resulted in a more severe acute deficit than the UCP. Over several weeks, the UCP animals compensated their horizontal VOR, particularly on rotation toward the intact side, quicker and more completely than the UL animals. Animals that underwent ipsilateral labyrinthectomy 8 to 11 weeks after UCP demonstrated preservation of the improved gain, particularly on rotation toward the intact labyrinth. However, the difference between the UL groups with or without precedent UCP was not retained after 72 hours, and long-term compensation was poorest in the UL after UCP group. CONCLUSIONS: Plasticity in dynamic vestibular reflexes induced by UCP is preserved after a subsequent UL. However, neurologic events during the first and second day after UL appear to limit, change, or suppress the long-term dynamic compensation of the VOR, regardless of whether the animal had a previous UCP.     

Response to galvanic vestibular stimulation in patients with unilateral vestibular loss

OBJECTIVES: This study sought to characterize various responses to galvanic vestibular stimulation (GVS) by comparing GVS-induced eye movements in healthy subjects and patients with vestibular function loss. The study also aimed to estimate the clinical significance of GVS tests. Finally, an effort was made to localize the primary excitation site of stimulation in the vestibular system. MATERIALS AND METHODS: Three parameters of response to GVS, spontaneous nystagmus, galvanic stimulating nystagmus (GSN), and postgalvanic stimulating nystagmus (PGSN), were evaluated in 20 normal subjects and 14 patients with complete unilateral vestibular function loss resulting from labyrinthectomy or vestibular neurectomy using a three-dimensional video-electronystagmography technique. RESULTS: In normal subjects, GSN was detected in all subjects and was directed toward the negative electrode. PGSN was also detected but was directed toward the opposite electrode. When the negative electrode was attached to the intact side in unilateral vestibular loss subjects, GSN was always directed toward the negative electrode and PGSN was never observed. When the negative electrode was attached to the lesion side, however, GSN was detected in only one case, and PGSN was observed and directed to the intact side in 13 patients. CONCLUSIONS: The response to GVS in vestibular loss patients differed from that in normal subjects, which suggests that GVS could be useful for estimating the extent of vestibular function loss. The fact that the patterns of GVS response differed so significantly suggests that the primary site of excitation is not central but is instead the peripheral vestibular organ.     

Diagnostic value of vibration-induced nystagmus obtained by combined vibratory stimulation applied to the neck muscles and skull of 300 vertiginous patients.

On subjects with unilateral vestibular dysfunction, the application of a vibratory stimulation (100 Hz) to the two mastoids and the vertex, and to the right and left dorsal neck muscles produces a nystagmus directed towards the good ear in 85% of patients. Fixation must be suppressed by Frenzel's glasses or video nystagmoscopy. To be significant this nystagmus must appear in at least 3 of the 5 vibratory stimulated sites. On healthy subjects nystagmus is present in 6% of cases but never in those below 30 years. In subjects affected by central vertigo, nystagmus was elicited in 10% of cases and in subjects suffering from vertigo of unknown origin in 6% of cases. Vibration nystagmus which stops immediately after stimulation differs from head shaking nystagmus which is present in only 34% of unilateral vestibular dysfunctions. Vibration occasionally produces a pseudo-caloric nystagmus which persists after stimulation. We believe that vibratory stimulation is a useful test, quick and easy to perform. In conjunction with questionnaires, clinical examination, positional testing and the results of audiometry, it gives an immediate indication of a peripheral lesion when the vertigo is seen for the first time. With unilateral deafness, a positive test leads one to suspect an acoustic neuroma. Conversely if the test becomes negative after a vestibular neuritis when it was initially positive, it is a sign of recovery.     

Recovery of postural control after an acute unilateral vestibular lesion in humans.

Postural control during stance was investigated using the EQUITEST system in 10 patients during recovery after an acute unilateral vestibular lesion and was compared to the time course of recovery of the static and dynamic vestibulo-ocular imbalance. During the acute phase the patients showed a characteristic pattern with normal upright stance as long as at least one accurate sensory input (visual or somatosensory) was provided and severe postural disturbances when they had to rely primarily on vestibular afferences. Both static vestibulo-ocular and vestibulo-spinal balance recovered very fast, showing basically normal results on postural testing within about 2 weeks after the lesion. Thereafter, no pathological pattern was detectable during postural testing even in patients with persistent complete unilateral vestibular lesions. Reflexive postural responses to unexpected rapid displacements of the support surface seemed not to be influenced by vestibular imbalance even in the acute phase of the lesion.     

Electronystagmography finding in children with peripheral and central vestibular disorders

OBJECTIVE: Dizziness and imbalance are uncommon in children, but often alarming for their families: a detailed interview and otoneurological examination are important for reaching a specific diagnosis and treatment. Children with vestibular disorders are thought to be difficult to examine: vestibular tests (caloric test, roto-acceleratory test, electronystagmography, opto-kinetic nystagmus, cranio-corpography and posturography) are used less frequently for children than in adult patients. The aim of the study was to determine whether the results of electronystagmography testing improve an emergency physician's diagnosis of dizziness in children. METHODS: Patients were selected on the basis of the following inclusion criteria: aged between 2 and 12 years and affected with vertiginous symptoms. All patients underwent the following instrumental examinations: blood tests, audiological screening, electronystagmography of spontaneous nystagmus or provoked by vestibular and optical stimulation and electroencephalogram. RESULTS: The results underlines an high incidence of central vertigo (83%): 52% of the children presented a prevailing unidirectional nystagmus at labyrinth stimulation and 48% of the children an asymmetry in the response of nystagmus at optical kinetic stimulation with quality alteration of shocks. CONCLUSIONS: Electronystagmography can register and evaluate the qualitative and quantitative characteristics of the nystagmic response and allow to distinguish between central or peripheric vertigo: different degrees and various combinations of the abnormal responses shown in optokinetic central test were the most characteristic of electronystagmography in patients with vestibular central vertigo.     

Vestibular function in experimental endolymphatic hydrops

Endolymphatic sac ablation in the guinea pig can result in a dilated membranous labyrinth and low-frequency hearing loss similar to patients with Meniere's disease. However, this animal model fails to develop analogous symptoms of a Meniere's crisis such as sudden hearing loss and marked vestibular imbalance. Possibly, factors in addition to endolymphatic hydrops must be present to result in a crisis episode. By placing animals in an inverted posture, their intralabyrinthine pressure was elevated, causing additional stress on the inner ears. Standard electronystagmographic techniques were used to monitor vestibular imbalance, which appeared as spontaneous nystagmus in the dark. Nineteen of 23 animals with unilateral endolymphatic hydrops showed spontaneous nystagmus in an inverted posture. Physiologic mechanisms explaining these results are described.     

Electronystagmographic characteristics of peripheral vestibular asymmetries in compensation development stage II

Spontaneous and reflex nystagmus of 10 patients with peripheral lesions of the vestibular system at one of the stages of vestibular dysfunction compensation development were examined. Spontaneous nystagmus (recovery) toward the sound side and asymmetry of reflex nystagmus in the form of DP toward the affected side were revealed. The period of disease characterized by the development of spontaneous and reflex nystagmus is termed compensation development stage II. This stage develops when central and peripheral compensation of vestibular dysfunction is realized simultaneously. Analysis of compensation development stage II helps to identify the compensation lesion level, side and degree of lesion of peripheral vestibular structures.     

正弦谐波加速试验的正常参考值及初步临床应用

目的 测量正弦谐波加速试验的正常参考值和常见疾病的参数值,探讨各检测参数值的临床意义.方法 正常人120例.梅尼埃病患者21例,双側外周前庭病变2例,急性单侧前庭功能受损15例,中枢病变10例,全部完成正弦谐波加速试验.结果 年龄大者的定标平均时间长.相位值随频率升高而降低,增益随频率升高而变大,低频相位值重复性好.梅尼埃病患者中7例在间歇期都正常,14例发作末期的患者均有异常,11例相位异常,3例增益异常,10例有不对称,8例患者合并2项指标的异常,不对称的患者均有自发性眼震.单侧急性前庭功能受损患者出现相位异常的11例;增益降低10例,见于0.08 Hz以上频段;不对称的有6例,其中5例有自发性眼震.双侧前庭功能受损的患者增益显著降低.中枢损伤10例中相位异常7例,低增益2例,不对称有4例,不对称者均无自发性眼震.结论 正弦谐波加速试验的正常参考值在一个比较窄的范围内,相位是其最重要的指标.     

Relation of video-head-impulse test and caloric irrigation: a study on the recovery in unilateral vestibular neuritis

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. Alternatively, one can test for vestibular hypofunction with the caloric irrigation test. Various studies have shown that both tests may not always identify vestibular hypofunction; instead, the results of the tests might be contradictory. To further explore the question, of whether vHIT and caloric irrigation test the same part of the angular horizontal vestibulo-ocular reflex (VOR), we examined patients with unilateral vestibular neuritis at different points in time. The tonic vestibular imbalance (e.g., subjective-visual-vertical, ocular torsion and spontaneous nystagmus) and dynamic dysfunction of VOR (vHIT and bithermal caloric irrigation) were measured and quantified. While parameters of the tonic vestibular imbalance were well described by single exponential decay functions, dynamic parameters were less well defined. Therefore, to better compare the time course of pairs of two different parameters, we used a linear regression analysis. No linear correlation was found in the group and individually for the gain asymmetry and the ipsilesional gain of the vHIT with the unilateral weakness of the bithermal caloric irrigation tests. Linear correlation was found for most parameters of tonic vestibular imbalance. These findings are further evidence that vHIT and caloric irrigation test different parts of the angular VOR.     

Dynamic Asymmetry of the Vestibulo‐ocular Reflex in Unilateral Peripheral Vestibular and Cochleovestibular Loss

Objective: Rotatory tests in the horizontal plane have shown various degrees of vestibulo‐ocular reflex (VOR) asymmetry in patients after surgical deafferentation of one labyrinth. The purpose of this work was to characterize dynamic horizontal VOR responses among patients presenting with a unilateral peripheral labyrinthine deficit of nonsurgical origin and to compare results in isolated vestibular loss versus cochleovestibular loss. Study Design: This study included 40 patients who presented with an acute, spontaneous unilateral peripheral labyrinthine lesion. Twenty‐two patients had vestibular loss alone (without associated hearing impairment) and 18 presented with a cochleovestibular deficit (sudden hearing loss with vertigo). The majority of these patients were part of a long‐term protocol to evaluate vestibular compensation. Methods: All patients underwent both the clockwise test and the counterclockwise rotatory test in the horizontal plane, using brief impulses of moderate intensity. Results were analyzed by a simplified model of vestibular function, allowing a parametric estimation of the response. Results: A weak and transitory horizontal VOR asymmetry was observed in the 22 patients with vestibular loss. However, the 18 patients with cochleovestibular loss demonstrated a more severe and persistent asymmetry. Conclusions: This study revealed a difference in the dynamic characteristics of the horizontal VOR between patients with vestibular loss and those with cochleovestibular loss. Our results support the presence of an extensive labyrinthine lesion in cochleovestibular deficit that involves the otolith organs. The implications of this involvement on the central mech‐ anisms of otolith‐canal interaction are discussed.     

Head-shaking nystagmus in patients with unilateral peripheral vestibular lesions

In certain patients with peripheral or central vestibular lesions, a transient nystagmus appears after shaking the head rapidly for 10 to 20 cycles. We recorded such a "head-shaking nystagmus" using the scleral eye coil in six subjects with unilateral peripheral vestibular lesions. Horizontal head shaking elicited horizontal nystagmus with slow phases that were initially directed toward the side of the lesion and upward. All subjects showed a prolonged, lower-amplitude reversal phase after the initial response following horizontal head shaking. The main features of these results can be explained by an analytic model that incorporates a central velocity-storage mechanism that perseverates vestibular inputs, Ewald's second law, and adaptation of primary vestibular afferent activity.     

Acute isolated vestibular paralysis. A clinical and electronystagmographic follow-up study in 28 patients]

Twenty-eight patients with unilateral acute vestibular paralysis (vestibular neuronitis) were examined after a period of 4-140 months. Seventeen of these patients were examined by electronystagmography with caloric stimuli at 44 degrees, 30 degrees, 17 degrees and 0 degrees C. Most were free of subjective symptoms only one-third had slight unsteadiness after sudden head movement. Subjective symptoms were independent of the presence of permanent canal paralysis or partial recovery of caloric excitability. Spontaneous nystagmus of 3-6,6% intensities was found in 11 of 17 patients. The normal limit for physiological spontaneous nystagmus should therefore be below 3 degrees/s. The most reliable parameter was the maximum velocity of the slow phase, as a mean value of the 4 caloric responses (values corrected for spontaneous nystagmus). The results were: 6 patients with persistent canal paralysis; 4 patients with considerable hypoexcitability; and 7 patients with moderate hypoexcitability. In no patient complete restoration of normal caloric response was found. This is attributed to the described method of caloric testing, which permits exact measurement of small side differences in excitability.     

Recovery of vestibular imbalances after vestibular neuritis

OBJECTIVES: To determine chronological characteristics of vestibular recovery after vestibular neuritis (VN) by using various clinical parameters. STUDY DESIGN: Prospective clinical study. METHODS: Twenty of 22 consecutive patients with acute VN underwent serial follow-ups of static (spontaneous nystagmus, subjective visual vertical, and ocular torsion) and dynamic (head-shaking nystagmus [HSN], vibration-induced nystagmus [VIN], head thrust test, and caloric test) vestibular imbalances for 1 year after symptom onset. RESULTS: Static vestibular imbalances improved more rapidly than dynamic imbalances. Among the dynamic imbalances, a trend of higher recovery rate was found in head thrust sign, HSN, and VIN than in caloric asymmetry. HSN tended to be more sensitive in detecting vestibular asymmetry than VIN and head thrust sign. Some patients showed direction reversal of HSN (n = 5, 25.0%) or VIN (n = 5, 25.0%) during follow-up. Direction of VIN changed according to the stimulation sites in four (20.0%) patients. CONCLUSIONS: In view of more rapid resolution of static vestibular imbalance after VN, evaluation of the dynamic vestibular imbalances may provide more useful information for underlying vestibulopathy, especially in the compensated phase. The different temporal profiles ofdynamic vestibular recovery may reflect different chronological characteristics of vestibular compensation according to stimulus frequency. Direction reversal of HSN and VIN during follow-up suggests that lateralization of VNbased on the direction of these nystagmus should be considered in the context of disease phase.     

Vestibular investigations in acoustic neuroma

Forty-eight patients with surgically proven acoustic neuroma were examined preoperatively with a comprehensive battery of vestibular tests. In 87% of the patients, reduced caloric responses were measured on the side of the lesion. In 60% of the patients a non-responsive labyrinth was found. Spontaneous nystagmus was observed in 29% of the patients. A significant correlation with the size of the tumour was found in the occurrence of abnormal saccades in the calibration test, pathological smooth pursuit movements and the occurrence of gaze nystagmus, respectively. There was no correlation between the magnitude of the caloric response reduction and the mean hearing loss, which suggests that the hearing loss and the vestibular function loss do not occur synchronously. This study shows that in most cases of acoustic neuroma, the peripheral part of the vestibular system is severely disturbed. Abnormalities in the central and peripheral part of the vestibular system are more easily recognized with increasing tumour size. We conclude that a complete battery of vestibular tests is essential in combination with audiometric, neurologic and radiologic analysis for the early clinical diagnosis of acoustic neuroma.     

前庭代偿动物模型的建立和评价

目的：探讨建立手术加化学方法破坏大鼠迷路的前庭代偿模型的建立及评价。方法：动物全身麻醉后行手术加化学方法建立模型，出现单侧前庭功能丧失症状后，分别于术后不同时间段记录其自发性眼震频率、头偏斜及失衡行为评分。结果：通过对动物自发性眼震、头偏斜及失衡行为的定量观察，各时间段的失衡程度随时间的推移而变化。结论：手术加化学方法破坏大鼠迷路的前庭代偿模型是一个很好的模型建立方法。     

Direction-changing positional nystagmus: incidence and meaning

Direction-changing positional nystagmus (DCPN) is a nystagmus that changes its direction with different body and head positions. Many authors consider that it indicates the presence of a central nervous system lesion. Of 1,196 patients whose abnormal electronystagmographic (ENG) traces were reviewed, 46 (3.8 per cent) showed DCPN. Of these, ten (22 per cent) had central neurologic diseases, 14 (30 per cent) had peripheral vestibular diseases, and for 22 (48 per cent) there was no definite clinical diagnosis. Nineteen patients (41 per cent) with DCPN had ENG findings suggesting a peripheral vestibular lesion, while only five (11 per cent) had ENG findings suggesting a central vestibular lesion. Four of 44 control subjects exhibited DCPN. Thus, the presence of DCPN does not necessarily indicate disease of the vestibular system and definitely does not localize the site of a lesion in the vestibular pathways, but more often indicates a peripheral vestibular site. As with spontaneous nystagmus, lack of suppression with fixation suggests a central lesion.     

Zur Unterscheidung peripherer und zentraler Vestibularisstörungen

Summary Objective equilibrium function disorders are more frequently of central than of peripheral origin in so called vestibular vertigo patients.Neuroanatomically the vestibular periphery terminates in the vestibular nuclei at the synapse from the 1st to 2nd vestibular neuron.The optimal investigation for the differentiation between peripheral and central vestibular disturbances needs the caloric tests, which nowadays should be recorded electronystagmographically. Evaluating the nystagmus beat rates by the well established butterfly chart provides us with the advantage of synoptically opposing the receptors in the horizontal and the nystagmus directions in the vertical plane of the same pattern. Inhibition as well as overactivity states can easily be read off the comparison of the characteristics with the normal range.Examples are given of patterns which represent peripheral or central equilibrium function disorders.The monolaterally inhibited butterfly indicates a peripheral disorder on the side of the inhibition.The monodirectionally inhibited butterfly shows a central nystagmus disturbance. The monolateral loss of warmfunction in combination with a contralaterally beating spontaneous nystagmus is most appearent in the phase of acute vestibular loss.The so called major butterfly expressing a total nystagmus overactivity is the most frequent pattern of a central lesion. A schedule of typical peripheral and central diseases is made after the different etiologies.