Longitudinal performance of an implantable vestibular prosthesis

Loss of vestibular function may be treatable with an implantable vestibular prosthesis that stimulates semicircular canal afferents with biphasic pulse trains. Several studies have demonstrated short-term activation of the vestibulo-ocular reflex (VOR) with electrical stimulation. Fewer long-term studies have been restricted to small numbers of animals and stimulation designed to produce adaptive changes in the electrically elicited response. This study is the first large consecutive series of implanted rhesus macaque to be studied longitudinally using brief stimuli designed to limit adaptive changes in response, so that the efficacy of electrical activation can be studied over time, across surgeries, canals and animals. The implantation of a vestibular prosthesis in animals with intact vestibular end organs produces variable responses to electrical stimulation across canals and animals, which change in threshold for electrical activation of eye movements and in elicited slow phase velocities over time. These thresholds are consistently lower, and the slow phase velocities higher, than those obtained in human subjects. The changes do not appear to be correlated with changes in electrode impedance. The variability in response suggests that empirically derived transfer functions may be required to optimize the response of individual canals to a vestibular prosthesis, and that this function may need to be remapped over time. This article is part of a Special Issue entitled .

[The analysis of nystagmus in patients with posterior canal benign paroxysmal positional vertigoin positioning test]

OBJECTIVE

To analyze and summarize nystagmus of patients with posterior canal benign paroxysmal positional vertigo (BPPV) in positioning test,and to improve the diagnosis and treatment of posterior canal BPPV (PSC-BPPV).

METHOD

The present study was conducted on 175 patients who had unilateral BPPV of the posterior semicircular canal (PSC). Their positional nystagmus recorded by videnonystagmography in Dix-Hallpike test,roll test and roll over test were analyzed to summarize the characteristics of nystagmus on nystagmograph of PSC-BP-PV.

RESULT

Of the 175 patients, lesion was located in the left PSC in 69 (39.4%) patients,the right PSC in 106 (60. 6%)patients. The nystagmus of patients with PSC-canalithiasis showed upward on the vertical phase of nystagmograph and orientated the different side on horizontal phase in the head hangging position. The horizontal phase pointed to the contralateral side in 47(26. 9%) patients, the ipsilateral contralateral side in 100(57. 1%) patients,no significant reverse ingredients in 28(16.0%) patients. When these patients returned to sit,139(79.4%) patients showed down beating positioning nystagmus, whereas 36 (20. 6%) patients with no nystagmus only had a short vertigo or dizziness. The horizontal phase of the 139 patients pointed to the contralateral side in 40(22. 9%) patients,the ipsilateral contralateral side in 68(38. 9%) patients,no significant reverse ingredients in 31(17. 7%) patients. In roll test,12 patients of the right PSC-BPPV presented an up-beating rotatory nystagmus when the head turned to right,and 5 patients of the left PSC-BPPV presented a down-beating rotatory nystagmus when the head turned to left. When the patients changed body from the left lateral position to the right lateral position in the roll over test, 74(42. 3%) patientsshowed vertical positioning nystagmus. In 30 patients who presented an up-beating nystagmus, there were 25(83. 3%) patientscame from the right PSC-BPPV. In 44 patients who presented a down-beating nystagmus, there were 36(81. 8%) patientscame from the left PSC-BPPV. The direction of the vertical nystagmus was highly correlated with the judgment about the side of the PSC-BPPV in roll over test (P<0. 01).

CONCLUSION

The patient with PSC-canalithiasis showed an uncertain direction in torsional nystagmus in Dix-Hallpike test,the diagnosis was mainly concern with the vertical nystagmus. When we found a rotatory nystagmus with much more up-beating nystagmus in roll test, it might be PSC-BPPV. We also can use the roll over test to diagnose the location of the otolith in which side of the PSC-BPPV.

[Diagnosis and therapy for horizontal semicircular canal cupulolithiasis]

OBJECTIVE

By analysing the video-nystagmography findings of positional tests,to evaluate the therapeutic effect of the patients with horikontal semicircular canal cupulolithiasis (HSC-Cup).

METHOD

A retrospective study of 36 patients with HSC-Cup. The induced nystagmus in roll tests was recorded by videonystagmography, whose direction, latency, intensity and time characteristics were analysed. All of the 36 patients were treated with lying position avoiding normal side and oral-taken betahistine mesilate tablets. A week later return visits and curative effects evaluation were made.

RESULT

Horizontal apogeotropic nystagmus was induced by turning left or right in HSC-Cup roll tests. The time of latency and duration turning to normal and lesion side were(0. 93 ± 0. 65)s and(1. 01 ± 0. 78)s, (100.58 ± 36. 56)s and (118. 65 ± 143. 71)s, which showed no statistically significant difference (P>0. 05). The duration of nystagmus was more than 60 seconds. The intensity of nystagmus turning to normal and lesion side were(45.58 ± 28.71)°/s and (20.42 ± 16. 64)°/s. The intensity turning to normal side was greater than lesion side obviously. The difference was statistically significant (P<0. 05). Twenty-three patients withright HSC-Cup, and 13 patients with left HSC-Cup were taken in count. They were treated with above methods and return visit a week later. Twenty-eight patients (77. 77%) were cured, 36 patients (100. 00%) were improved. There were 4 patients recurrence during the follow-up.

CONCLUSION

The direction and duration time of induced nystagmus are available to diagnose the HSC-Cup. The lesion side may determined according to the intensity of induced nystagmus. Lying position avoiding normal side and oral-taken betahistine mesilate tablets is an effective treatment methods for HSC-Cup.

Clinical roles of fixation suppression failure in dizzy patients in the ENT clinic

Abstract Conclusion: Any test for visual fixation suppression by itself is insufficient for screening central pathology and should be interpreted in conjunction with other neurotologic findings.

OBJECTIVES

We evaluated the correlation of visual fixation suppression (VFS) under three different test conditions (spontaneous nystagmus, caloric stimulation, and slow harmonic acceleration, SHA), as well as the diagnostic accuracy of each test for predicting central pathology, in dizzy patients.

METHODS

We retrospectively reviewed cases in a tertiary referral center; 504 consecutive dizzy patients who visited the ENT clinic were enrolled. The fixation index (FI, slow component velocity during fixation/slow component velocity before fixation × 100%) for the caloric test and spontaneous nystagmus was calculated and failure was indicated when the FI was greater than 60%. VFS during the SHA test at a frequency of 0.04 Hz was also performed and gain more than 0.2 was considered as failure of VFS.

RESULTS

The incidence of VFS failure was 5.4% in the caloric test, 3.4% in spontaneous nystagmus, and 2.3% in the SHA test, respectively. Significant correlation was found only between the caloric test and the SHA test (r = 0.341, p < 0.001). The sensitivity of VFS in different tests did not exceed 35%. The specificity of VFS was highest (96.4%) in the 0.04 Hz SHA test, and exceeded 80% in the other tests.

Comparative study of the efficacy of the canalith repositioning procedure versus the vertigo treatment and rehabilitation chair

CONCLUSION

Vertigo treatment and rehabilitation chair (TRV) may be suggested as the first choice for patients with posterior canal benign paroxysmal positional vertigo (p-BPPV).

OBJECTIVE

To investigate the short- and long-term treatment efficacy of the canalith repositioning procedure (CRP) versus TRV for patients with p-BPPV.

METHODS

A total of 165 patients with unilateral p-BPPV were assigned to either the CRP group or the TRV group. Patients were assessed at 1 week, 4 weeks, 3 months, and 6 months after their first treatment. The numbers of treatment sessions required for successful repositioning in both groups at 4 weeks, 3 months, and 6 months were recorded.

RESULTS

Treatment efficacy of patients in the TRV group was significantly better than that of patients in the CRP group 1 week after the first treatment. The number of treatment sessions needed for successful repositioning was significantly lower in the TRV group than in the CRP group at 4 weeks and 3 months after the first treatment.

Repositioning nystagmus: prognostic usefulness?

CONCLUSIONS

The presence of orthotropic nystagmus (ON), in multiple positions, appears to predict the success of canalith repositioning maneuvers (CRMs). In this sense CRMs under video-Frenzel are informative for the immediate follow-up, although not related to the degree of disability or emotional distress. Still, attention should be given to psychological assistance even in cases of clinically cured benign paroxysmal positional vertigo (BPPV).

OBJECTIVE

The aim of the study was to highlight the prognostic value of nystagmus in CRMs for BPPV and its relevance for emotional and patient-perceived disability.

METHODS

A group of 57 patients were selected from 3 balance disorders centers. CRMs were performed under video-Frenzel control. Assessment of patient disability and positional nystagmus was performed 2 months later. Emotional (Cuestionario de Impacto Emocional del Vértigo, CIEV) and quality of life (Dizziness Handicap Inventory, DHI) impact were evaluated.

RESULTS

The posterior semicircular canal (SCC) was affected in 84.2% of cases, the horizontal SCC in 10.5%, and the anterior SCC in 5.1%. Appropriate CRMs were performed. ON was present in 67% of cases. Overall resolution after the first treatment was achieved in 56% of cases. With ON present the success rate was 63% and when not observed the rate was 42%. DHI or CIEV scores were not significantly different when comparing the presence vs absence of ON. In nine patients (16%) an abnormal CIEV score was observed after treatment, even though a cured status was achieved in six of these nine patients.

On the vertigo due to static magnetic fields

Vertigo is sometimes experienced in and around MRI scanners. Mechanisms involving stimulation of the vestibular system by movement in magnetic fields or magnetic field spatial gradients have been proposed. However, it was recently shown that vestibular-dependent ocular nystagmus is evoked when stationary in homogenous static magnetic fields. The proposed mechanism involves Lorentz forces acting on endolymph to deflect semicircular canal (SCC) cupulae. To investigate whether vertigo arises from a similar mechanism we recorded qualitative and quantitative aspects of vertigo and 2D eye movements from supine healthy adults (n = 25) deprived of vision while pushed into the 7T static field of an MRI scanner. Exposures were variable and included up to 135s stationary at 7T. Nystagmus was mainly horizontal, persisted during long-exposures with partial decline, and reversed upon withdrawal. The dominant vertiginous perception with the head facing up was rotation in the horizontal plane (85% incidence) with a consistent direction across participants. With the head turned 90 degrees in yaw the perception did not transform into equivalent vertical plane rotation, indicating a context-dependency of the perception. During long exposures, illusory rotation lasted on average 50 s, including 42 s whilst stationary at 7T. Upon withdrawal, perception re-emerged and reversed, lasting on average 30 s. Onset fields for nystagmus and perception were significantly correlated (p<.05). Although perception did not persist as long as nystagmus, this is a known feature of continuous SSC stimulation. These observations, and others in the paper, are compatible with magnetic-field evoked-vertigo and nystagmus sharing a common mechanism. With this interpretation, response decay and reversal upon withdrawal from the field, are due to adaptation to continuous vestibular input. Although the study does not entirely exclude the possibility of mechanisms involving transient vestibular stimulation during movement in and out of the bore, we argue these are less likely.

Is the nystagmus pattern in hemi-labyrinthectomized subjects during positional alcohol nystagmus 2 similar to that found in patients with cupulolithiasis in the lateral semicircular canal?

CONCLUSION

A positional nystagmus pattern compatible with a condition of a heavy cupula (cupulolithiasis) in the lateral semicircular canal could be reproduced in hemi-labyrinthectomized subjects during positional alcohol nystagmus 2 (PAN 2). The nystagmus pattern was opposite to that found in the same subjects during PAN 1. The affected side could not be judged by applying Ewald's second law.

OBJECTIVES

To mimic the condition of a heavy cupula in the lateral semicircular canal by using unilaterally deafferented subjects during PAN 2 and compare (a) results reported in the literature with those of patients with cupulolithiasis, and (b) the nystagmus findings in the same subjects during PAN 1.

METHODS

Five hemi-labyrinthectomized subjects were studied during PAN 2 when they kept their heads pointed straight forward or turned sideways in the prone and supine positions, respectively.

RESULTS

When the subjects were examined with their heads turned in the supine or prone positions, the alcohol-induced nystagmus pattern was compatible with that of cupulolithiasis. When the head was pointed straight forward in the prone and supine positions, the nystagmus directions were opposite to those found during PAN 1. Directional preponderance was not seen for the apogeotropic nystagmus for either ampullofugal or ampullopetal deviation of the cupula.

Development of eye position dependency of slow phase velocity during caloric stimulation

The nystagmus in patients with vestibular disorders often has an eye position dependency, called Alexander’s law, where the slow phase velocity is higher with gaze in the fast phase direction compared with gaze in the slow phase direction. Alexander’s law has been hypothesized to arise either due to adaptive changes in the velocity-to-position neural integrator, or as a consequence of processing of the vestibular-ocular reflex. We tested whether Alexander’s law arises only as a consequence of non-physiologic vestibular stimulation. We measured the time course of the development of Alexander’s law in healthy humans with nystagmus caused by three types of caloric vestibular stimulation: cold (unilateral inhibition), warm (unilateral excitation), and simultaneous bilateral bithermal (one side cold, the other warm) stimulation, mimicking the normal push-pull pattern of vestibular stimulation. Alexander’s law, measured as a negative slope of the velocity versus position curve, was observed in all conditions. A reversed pattern of eye position dependency (positive slope) was found <10% of the time. The slope often changed with nystagmus velocity (cross-correlation of nystagmus speed and slope was significant in 50% of cases), and the average lag of the slope with the speed was not significantly different from zero. Our results do not support the hypothesis that Alexander’s law can only be observed with non-physiologic vestibular stimulation. Further, the rapid development of Alexander’s law, while possible for an adaptive mechanism, is nonetheless quite fast compared to most other ocular motor adaptations. These results suggest that Alexander’s law may not be a consequence of a true adaptive mechanism.

Invariance of vestibulo-ocular reflex gain to head impulses in pitch at different initial eye-in-orbit elevations: implications for Alexander's law

CONCLUSIONS

These findings are in line with previous data on the horizontal vestibulo-ocular reflex (VOR) from this laboratory and suggest that eye position signals do not modulate natural vestibular responses. Hence, the Alexander's law (AL) phenomenon cannot be interpreted simply as a consequence of vestibular or oculomotor nuclei activity modulation with desired gaze.

BACKGROUND

AL states that the intensity of the spontaneous nystagmus of a patient with a unilateral vestibular lesion grows with increasing gaze in the direction of the fast phase. Some of the mechanisms proposed to account for the gaze effects assume a direct modification of the normal VOR by eye position signals. We tested the validity of these assumptions and investigated the effects of gaze direction on the normal vertical human VOR in the behaviorally relevant high frequency range.

METHODS

Head and eye movements were recorded with the search coil method during passive head impulses in pitch, while subjects were asked to hold gaze at various elevation angles in 8° steps within ± 16° from the straight ahead reference position.

RESULTS

Upward and downward head rotations produced VOR gains of similar magnitude. Furthermore, the gain remained unaffected by eye-in-orbit position for both upward and downward head impulses.

[Effect of 24-hour sleep deprivation on the oculomotor reactions of human operator]

The article presents the results of oculomotor reaction investigations during 24-hour sleep deprivation of 10 normal male subjects aged 25 to 30 yrs. Video nistagmograph VNG System VO-25 was used for binocular registration of eye movements. The proposed video procedures for assessment of the functional ability of human operator are a balancing test, investigation of saccadic and smooth tracking eye movements. The balancing test is designed to determine the nystagmic activity, the saccade test, latency, peak velocity and precision of saccades, and the smooth tracking test, standard errors in tracking velocity and displacement In addition to video oculography, velocity of a simple sensorimotor reaction was measured and the self-rating scale of well-being, alertness and mood (SAN) was employed. The balancing test showed balancing nystagmus; occurrence of this nystagmus grew high with desynchronosis. Saccades registered during sleep deprivation pointed to a considerable decline of velocity, less noticeable extension of latency and degradation of precision. Sleep deprivation reduced values of the mean coefficient of gain and increased the standard error in velocity and displacement of smooth eye tracking.

Nystagmus assessments documented by emergency physicians in acute dizziness presentations: a target for decision support?

OBJECTIVES

Dizziness is a common presenting complaint to the emergency department (ED), and emergency physicians (EPs) consider these presentations a priority for decision support. Assessing for nystagmus and defining its features are important steps for any acute dizziness decision algorithm. The authors sought to describe nystagmus documentation in routine ED care to determine if nystagmus assessments might be an important target in decision support efforts.

METHODS

Medical records from ED visits for dizziness were captured as part of a surveillance study embedded within an ongoing population-based cohort study. Visits with documentation of a nystagmus assessment were reviewed and coded for presence or absence of nystagmus, ability to draw a meaningful inference from the description, and coherence with the final EP diagnosis when a peripheral vestibular diagnosis was made.

RESULTS

Of 1,091 visits for dizziness, 887 (81.3%) documented a nystagmus assessment. Nystagmus was present in 185 of 887 (20.9%) visits. When nystagmus was present, no further characteristics were recorded in 48 of the 185 visits (26%). The documentation of nystagmus (including all descriptors recorded) enabled a meaningful inference about the localization or cause in only 10 of the 185 (5.4%) visits. The nystagmus description conflicted with the EP diagnosis in 113 (80.7%) of the 140 visits that received a peripheral vestibular diagnosis.

CONCLUSIONS

Nystagmus assessments are frequently documented in acute dizziness presentations, but details do not generally enable a meaningful inference. Recorded descriptions usually conflict with the diagnosis when a peripheral vestibular diagnosis is rendered. Nystagmus assessments might be an important target in developing decision support for dizziness presentations.

[Interocular asymmetry of nystagmus and motion sickness]

Binocular video nystagmography was employed to study the human vestibulo-ocular reaction to the double rotation test used in medical flight certification to assess vestibulo-vegetative stability. Purpose of the investigation was to establish an interrelation between parameters of the nystagmus reaction to rotation and severity of motion sickness (MS). The total of 135 medically certified flying men aged 23 to 47 years were subject to testing by intermittent Coriolis accelerations accumulation according to Bryanov's procedure. The vestibulo-vegetative reaction was assessed by the criteria of vegetative reactivity and protective movements. The closed-mask binocular test was performed during and after rotation, It was shown that interocular nystagmus asymmetry is linked directly with MS severity. Asymmetry coefficients are proposed for unidirectional nystagmus during inclinations (C(ai)) and straightening (C(as)) and for time of convergent rotational nystagmus during inclinations (T(ci)) and straightening (T(cs)). Coefficients C(ai) and T(ci) were found to correlate with MS severity (p < 0.05). From the data of the investigation it was deduced that the mechanism of MS during double rotation amounts to intravestibular interlabyrinthine conflict.

Preoperative prediction of vestibular schwannoma's nerve of origin with posturography and electronystagmography

CONCLUSION

Chances of hearing preservation are better in patients with vestibular schwannoma (VS) from the superior vestibular nerve (SVN) than from the inferior vestibular nerve (IVN). Pathologic posturography and electronystagmography (ENG) findings are more common in schwannomas from the SVN compared with tumors from the IVN. In this way, computerized dynamic platform posturography (CDPP) and ENG contribute to predict the nerve of origin of VS and can be used indirectly as a prognostic factor for hearing preservation.

OBJECTIVES

To test whether preoperative CDPP or ENG results contribute to predict the nerve of origin in VS and also to evaluate the influence of the nerve of origin on hearing preservation.

METHODS

Eighty-nine patients with VS originating from the IVN and 22 patients with VS from the SVN were included. Hearing loss due to surgery was calculated on postoperative and preoperative audiograms. Caloric response was measured by ENG and condition 5 and 6 score were recorded by CDPP before surgery.

RESULTS

Hearing loss due to surgery was significantly lower in patients with tumors from the SVN than from the IVN (p = 0.011). Pathologic results in preoperative ENG (p < 0.0001) and CDPP (p = 0.025) were significantly more frequent in subjects with SVN than with IVN schwannomas.

Caloric stimulation with near infrared radiation does not induce paradoxical nystagmus

Near infrared radiation can be used for warm stimulation in caloric irrigation of the equilibrium organ. Aim of this study was to determine whether near infrared radiation offers effective stimulation of the vestibular organ, whether it is well tolerated by the patients and especially whether it is a viable alternative to warm air stimulation in patients with defects of the tympanic membrane and radical mastoid cavities. Patients with perforations of the tympanic membrane (n = 15) and with radical mastoid cavities (n = 13) were tested both with near infrared radiation and warm dry air. A caloric-induced nystagmus could be seen equally effectively and rapidly in all patients. Contrary to stimulation with warm dry air, no paradoxical nystagmus was observed following caloric irrigation with a warm stimulus (near infrared radiation). Results of a questionnaire showed excellent patient acceptance of near infrared stimulation with no arousal effects or unpleasant feeling. In conclusion, near infrared radiation proved to be an alternative method of caloric irrigation to warm dry air in patients with tympanic membrane defects and radical mastoid cavities. Near infrared radiation is pleasant, quick, contact free, sterile and quiet. With this method an effective caloric warm stimulus is available. If near infrared radiation is used for caloric stimulus no evaporative heat loss occurs.

[Spontaneous and provoked nystagmus in healthy subjects: on the so-called "vestibular" form]

A total of 25 healthy subjects were available for the study of provoked nystagmus using a series of vestibulometric functional tests affecting different component of the vestibular system. The study has demonstrates the high diagnostic value of provoked nystagmus and the importance of a series of vestibulometric functional tests as a tool for the evaluation of vestibular reactivity. Provoked nystagmus was documented in 3 cases using the full series of functional tests and was absent in 9 cases under the same conditions. It is concluded that observation of provoked nystagmus in individual tests reflects its etiology whereas its occurrence in the entire series of these tests suggests diagnosis of latent vestubular dysfunction.