[Benign paroxysmal positional vertigo with and without manifest positional nystagmus: an 18-month follow-up study of 70 patients]

BACKGROUND

In this follow-up study of approximately 18 months we assessed parameters of medical management in a sample of 70 patients suffering from benign paroxysmal positional vertigo.

METHODS

Apart from demographic data, we evaluated the time interval from the appearance of the first symptoms until a diagnostic positional manoeuvre was performed, the efficacy of liberatory manoeuvres, the prescription of medication, the use of technical diagnostic resources and the relapse rate.

RESULTS

None of the patients had received a diagnostic positioning test until then. Moreover, in one out of three cases a further unnecessary technical diagnostic procedure was carried out. There was a tendency for the right labyrinth to be more frequently affected, a fact that was statistically independent from age and sex, as well as from overall prognosis, which was characterized by a 15.6% recurrence rate. All patients with manifest positional nystagmus were successfully treated: 87.2% immediately after the repositioning manoeuvre and the rest within 10 days by self-performing Brandt-Daroff exercises. Our retrospective analysis revealed that, given a normal neuro-otological examination, a typical medical history without manifest positioning nystagmus leads safely to the correct diagnosis.

CONCLUSION

The delay between the onset of symptoms and the diagnosis of BPPV is very often unduly long. A focused medical history may be diagnostic even in the absence of nystagmus during the Dix-Hallpike manoeuvre.

Audiovestibular dysfunction in alcohol dependence. Are we worried?

PURPOSE

To study the audiovestibular function in patients of long-term alcohol dependence and compare these changes with social users of alcohol and complete abstainers.

MATERIAL AND METHODS

This was a prospective study of 20 randomly selected patients of long-term alcohol dependence fulfilling International Statistical Classification of Diseases, 10th Revision criteria of alcohol dependence. Audiovestibular function in this group was compared with social user of alcohol and complete abstainers.

RESULTS

Statistically significant elevations of thresholds were found at higher frequencies (4000 and 8000 Hz ) in the alcohol-dependent group (P < .001). Alcohol-dependent patients had elevated thresholds at 4 and 8 kHz. Brainstem-evoked response audiometry showed prolongation of latencies of waves I, III, and V alone with interpeak latencies of I-III and III-V. One third of alcohol-dependent patients had abnormal electronystagmographic (ENG) findings. Abnormal ENG findings were only seen in alcohol-dependent patients with vertigo. There was no significant correlation between duration of alcohol dependence and abnormal ENG.

CONCLUSIONS

Elevated thresholds at higher frequencies can be the only abnormality in alcohol-dependent patients. Presence of vertigo in alcohol-dependent patient may be associated with abnormal ENG findings. There is no correlation of duration of dependence and ENG abnormalities.

Clinical characteristics of benign paroxysmal positional vertigo in Korea: a multicenter study

Benign paroxysmal positional vertigo (BPPV) is characterized by episodic vertigo and nystagmus provoked by head motions. To study the characteristics of BPPV in a large group of patients in Korea, we retrospectively analyzed clinical features of 1,692 patients (women: 1,146, 67.7%; men: 54.6, 32.3%; mean age: 54.8+/-14.0 yr), who had been diagnosed as BPPV by trained neuro-otologists Dizziness Clinics. The diagnosis of BPPV was based on typical nystagmus elicited by positioning maneuvers. Posterior semicircular canal was involved in 60.9% of the patients, horizontal canal in 31.9%, anterior canal in 2.2%, and mixed canals in 5.0%. The horizontal canal type of BPPV (HC-BPPV) comprised 49.5% of geotropic and 50.5% of apogeotropic types. We could observe significant negative correlation between the proportion of HC-BPPV of each clinic and the mean time interval between the symptom onset and the first visit to the clinics (r=-0.841, p<0.05). Most patients were successfully treated with canalith repositioning maneuvers (86.9%). The high incidence of HC-BPPV in this study may be explained by relatively shorter time interval between the symptom onset and visit to the Dizziness Clinics in Korea, compared with previous studies in other countries.

Positional nystagmus and vertigo due to a solitary brachium conjunctivum plaque

The authors describe two patients suffering from demyelinating central nervous system disease who developed intense vertigo and downbeat nystagmus upon tilting their heads relative to gravity. Brain MRI revealed in both cases a single, small active lesion in the right brachium conjunctivum. The disruption of otolithic signals carried in brachium conjunctivum fibres connecting the fastigial nucleus with the vestibular nuclei is thought to be causatively involved, in agreement with a recently formulated model simulating central positional nystagmus. Insufficient otolithic information results in erroneous adjustment of the Listing's plane in off-vertical head positions, thus producing nystagmic eye movements.

Vertigo and imbalance caused by a small lesion in the anterior insula

The exact location of the vestibular cortex in humans has not yet been established. Isolated lesions in the insula are exceptional. We describe a patient with recurrent episodes of vertigo and imbalance following a small lesion in the anterior insula. Myogenic and neurogenic vestibular evoked potentials were both performed using auditory stimuli. The former was recorded from the sternocleidomastoid muscle and the latter from the parietal areas on the scalp. Brainstem auditory evoked potentials, threshold latency series, pure tone audiometry and video nystagmography were also performed, as was brain MRI. All evoked potential studies and pure tone audiometry were within normal limits, ruling out peripheral and brainstem causes for the patient's symptoms. Video nystagmography revealed high slow phase velocities bilaterally with caloric stimulation, and saccadic tracking on the smooth pursuit examination. The MRI revealed a small lesion in the right anterior insula. To our knowledge this is the first reported case of vestibular symptoms and signs from a lesion in the anterior insula on MRI. In addition, its effects on the nystagmogram suggest that this area may be part of the pathway that controls smooth pursuit.

Dynamic pitch rotation affects eye torsion

CONCLUSION

Most of the subjects studied had eye torsion responses to pitch, although the direction of torsion varied between subjects. Opposite responses may be the result of individual variation in anatomical or physiological vector orientations of hair cells in the anterior or posterior utricle or in the saccule.

OBJECTIVE

This study aimed to determine whether systematic changes in eye torsion occur when subjects are rotated in forward and backward pitch.

MATERIALS AND METHODS

Twenty-one normal subjects were seated in a dual axis human rotator, positioned so that the interaural axis was aligned with the axis of pitch rotation. Fixation LED suppressed vertical or horizontal eye movement. Recordings were carried out in darkness apart from the fixation LED, using a three-dimensional eye tracker based on CMOS image sensors. Subjects were twice tilted from upright to 90 degrees occiput down, then forward to 45 degrees face down.

RESULTS

Most subjects had eye torsion changes in response to pitch, with mean amplitudes of approximately 2 degrees to 90 degrees backward tilt and 1 degree to 45 degrees forward tilt. Ten subjects had clockwise torsion to backward pitch and counterclockwise to forward pitch; six subjects had the opposite responses. Statistical testing of the distributions of the regression slopes between these two groups were significant (p<0.001). Five subjects had unclear responses.

Reversible and controlled peripheral vestibular loss by continuous infusion of ropivacaine (Narop) into the round window niche of rats

This paper describes a method for achieving a peripheral vestibular blockade in rats by instillation of local anaesthetics over the round window membrane through a permanently implanted cannula. Being rapidly reversible, the effect of the anaesthetic drug is easily controlled by a single continuous infusion, which can be repeated at any time. The method offers a unique opportunity to study the consequence of single or repeated transient vestibular loss without any use of general anaesthetics, which may be a severe confounding factor. Such studies might shed light on balance disorders related to permanent vestibular loss or episodic vestibular dysfunction. To evaluate the method, spontaneous horizontal eye movements were recorded during the first 4 h of continuous infusion. Unilateral infusion of ropivacaine gave rise to a high-frequency spontaneous nystagmus, reaching levels that have not been documented after a surgical labyrinthectomy under general anaesthesia. This vestibulo-oculomotor behaviour is consistent with a previous report using a single intratympanic instillation of lidocaine to achieve a short-lasting vestibular blockade. In the present study, it was demonstrated that the initial high-frequency nystagmus decreased during the first 100 min of infusion before stabilizing at the same level as recorded when the effect of general anaesthesia has worn off after a surgical ablation. When the transient vestibular blockade was repeated by a second infusion during the following day, the nystagmus frequency saturated on a significantly lower level than during the first blockade. Also, serial single infusions, with recovery between each functional vestibular loss, gave rise to a less severe nystagmus. It is suggested that this phenomenon is an expression of the behavioural concept of 'vestibular habituation', the neural substrate of which is rather unknown.

Development of a vibrotactile tasking device for use in vestibular assessment

The purpose of this study was to design an automated mental alerting task that could be utilized when performing vestibular testing on a broad range of patient populations, including certain difficult-to-test populations, such as the hard-of-hearing. A device was developed that utilized vibrotactile stimuli output to two vibrators placed on the subject's left leg, and responded to activation of two momentary pushbuttons controlled by the subjects. Fourteen normal-hearing subjects without history or symptoms of vestibular involvement participated. Each participant underwent three mental-alerting conditions, defined as no task, verbal task, or vibrotactile task. Each condition involved four irrigations of the ear canals, two with warm water and two with cool water. The resultant nystagmus was recorded and analyzed using four measures to compare the effect of the mental alerting task condition. No significant difference was found between verbal and vibrotactile alerting both of which provided better responses than the no alerting task (F=8.443; df=2,13; p=0.001). Between-subjects analysis showed that the number of gaps, which are undesirable periods of absent nystagmus during test recordings, was smallest for the verbal and vibrotactile tasks, and largest for the no task condition. Overall, the results showed that the vibrotactile tasking device (VTD) is an effective alternative means of providing mental alerting during vestibular testing, specifically that of caloric examination.

[Directional preponderance of nystagmus]

The presence of directional preponderance in the peripheral and central vestibular disorders and the relation of its phenomenon to the definitive etiological factors, spontaneous nystagmus, positional nystagmus and the role of lateralization of directional preponderance were described. Directional preponderance is helpful to distinguish between peripheral and central lesions. The direction of this phenomenon is significant in the supratentorial CNS disturbances. In the peripheral lesions it is possible to estimate the progression of the disease. The coexistence of the directional preponderance, spontaneous nystagmus and positional nystagmus has the diagnostic value in neurootology.

Amplitude range analysis of otolithic organ responses

Benign paroxysmal positioning vertigo is easily diagnosed with the Dix-Hallpike maneuver. It is an ideal clinical condition in which to study the electrical response of the inner ear with electrocochleography techniques. Responses can be recorded during head tilt in roll and in pitch. With this technique we found that the amplitude range and scaling behavior of recorded raw data for the baseline resting position versus the stimulus position was statistically different in both patients and normal subjects. This can be demonstrated in the visual format of box plots. This technique promises to become a valuable addition to electrical examination techniques of the inner ear.

Triple Semicircular Canal Occlusion in Guinea Pigs with Endolymphatic Hydrops

HYPOTHESIS

Triple semicircular canal occlusion will eliminate rotatory stimulation to the vestibular peripheral system (as it blocks endolymphatic fluid movement) and therefore release rotatory vertigo attack. This surgery is safe in ears with endolymphatic hydrops.

BACKGROUND

Semicircular canal occlusion has been used as an alternative treatment of intractable benign paroxysmal positional vertigo with varied success. Triple semicircular canal occlusion in animal models blocks the responses of the semicircular canals to rotation and spares cochleae and the otolithic apparatus. This result suggests that triple semicircular canal occlusion is a prospective method in vertigo management for patients with Ménière's disease. However, the effectiveness and safety of triple semicircular canal occlusion has not been fully evaluated in ears with endolymphatic hydrops.

METHODS

Endolymphatic hydrops was established in 20 guinea pigs by endolymphatic sac obliteration. Triple semicircular canal occlusion was performed in 12 of them 120 days after endolymphatic hydrops surgery, whereas 8 others were killed for morphologic observation to confirm endolymphatic hydrops. Auditory and vestibular functions were monitored from the time before endolymphatic hydrops until 1 month after triple semicircular canal occlusion. Endolymphatic hydrops and canal occlusion were confirmed by morphologic observation.

RESULTS

Successful establishment of endolymphatic hydrops was indicated by mild elevation of the auditory brainstem response threshold and tentative asymmetry in nystagmus. Endolymphatic hydrops was confirmed by cochlear morphology in all eight animals that were killed 120 days after endolymphatic hydrops surgery. After triple semicircular canal occlusion, all 12 animals showed spontaneous nystagmus with a slow component toward the side that had been operated on, head tilt, rotated walking, and tentative asymmetry in rotatory nystagmus. The static symptoms disappeared within 1 month after triple semicircular canal occlusion. Caloric nystagmus was only slightly reduced after endolymphatic hydrops as compared with the contralateral ears but could not be elicited at all after triple semicircular canal occlusion. No significant elevation in auditory brainstem response threshold was found after triple semicircular canal occlusion. The canal occlusion and endolymphatic hydrops were confirmed in all surgical ears.

CONCLUSION

Triple semicircular canal occlusion is effective for eliminating the response of semicircular canals to rotation and caloric stimulation and is safe in ears with endolymphatic hydrops. Also, the static compensation to the disequilibrium is quick and complete. These results suggest that triple semicircular canal occlusion should be an option for controlling rotatory vertigo in Ménière's disease.

Vertigo in children

The aim of this study was to search for the reason for vertigo in children who complain of it. We tested 30 children who had been treated by a pediatrician for various diseases. We performed the detailed protocol of anamnesis, videonystagmography, posturography, and additional tests ordered by the pediatrician and then compared the results of these procedures with those of a group of 30 healthy children. Respiratory system infections, gastritis, and spondylosis were diagnosed most often by pediatricians in young people with vertigo. From videonystagmography results, we observed only four types of pathological reactions: positional nystagmus, cervical nystagmus, abnormal eye-tracking test results, and square wave abnormalities. Only 40% of children demonstrated objective signs of vertigo. Posturography results did not provide specific findings as compared with those from the healthy children. We discussed the probable reasons for vertigo, among which psychogenic origin, side effect of medications, hormonal disturbances, spondylosis, and diet errors had to be taken into consideration.

Effects of baclofen on the angular vestibulo-ocular reflex

The purpose of this study was to determine the effect of baclofen, a GABA(B) agonist on the angular vestibulo-ocular reflex (aVOR). Model studies have shown that the aVOR comprises a "direct" pathway, which determines its high frequency gain g (1), and an indirect "velocity storage" pathway, which determines its low frequency characteristics. Velocity storage can be characterized by an integrator with a dominant time constant, T (VOR), and a gain g (0) that couples afferent information from the semicircular canals to the integrator. Baclofen preferentially shortens the velocity storage time constant in monkeys, but its effect on T (VOR), g (0), and g (1) in humans is unknown. Six subjects were tested after administration of a placebo or of 10, 20, or 30 mg of baclofen in a double-blind design. The aVOR was elicited in darkness with steps of rotation at 138 degrees /s, and g (1), g (0), and T (VOR) were determined from model fits of the slow phase velocity of the per- and post-rotatory nystagmus. Baclofen significantly reduced both T (VOR) and g (0) at dosages of 20 and 30 mg, but had no effect on g (1). Small reductions in g (0) were associated with large reductions in vestibular output. Thus, baclofen does not affect the direct aVOR pathway in humans, but controls the low frequency aVOR in two ways: it limits the input to velocity storage and modulates its time constant. We speculate that pre-synaptic GABA(B) terminals in the vestibular nuclei are responsible for the control of the afferent input to velocity storage through g (0), while the post-synaptic GABA(B) terminals are responsible for altering the duration of activity that reflects the time constant. The lack of effect of baclofen on the aVOR gain suggests that only GABA(A) receptors are utilized in the direct aVOR pathway.

Diagnostic and treatment strategy of lateral semicircular canal canalolithiasis

A new strategy for the diagnosis and treatment both of geotropic and apogeotropic Lateral Semicircular Canal Benign Paroxysmal Positional Vertigo is proposed. To this end, a new strategy of approach to Lateral Semicircular Canal Benign Paroxysmal Positional Vertigo is described in order to rapidly highlight both the side and the affected canal. Thus, in the first treatment session, using the so-called "strategy of the minimum stimulus", a large percentage of cases are successfully treated, with the lowest number of vertigos for the patient. Following a review of the literature, 269 case studies, personally observed over a 4-year period, are described. The diagnostic strategy is performed by a single manoeuvre to determine whether the posterior semicircular canal or the lateral canal is affected. In the latter case, it is possible to highlight the affected sides both of the geotropic and apogeotropic forms. The therapeutic strategy comprises several liberatory manoeuvres, barbecue rotation techniques (Vannucchi-Asprella, Lempert), and Gufoni manoeuvre by continuously monitoring the ampullofugal movement of the otoliths. Almost 98% of cases are successfully treated at the first treatment diagnostic-therapeutic session. This approach to Lateral Semicircular Canal Benign Paroxysmal Positional Vertigo allows a two-fold goal to be achieved, i.e., to effect both diagnosis and treatment at the first examination. Furthermore, thanks to the philosophy of the approach to Benign Paroxysmal Positional Vertigo, called the "Strategy of the minimum stimulus", patient compliance is very good since a very small number of vertigos are produced, and few neuro-vegetative disorders.

Head position dependency of induced nystagmus to ice-water irrigation in peripheral vestibulopathy

OBJECTIVE

Evaluation of head-position dependency during the ice-water test is essential when the test is indicated. Because ice-water irrigation (IWI) in the prone position is frequently skipped in many laboratories, we investigated the importance of evaluating position dependency in an ice-water test.

DESIGN AND SETTING

Twenty-five unilateral peripheral vestibulopathy patients showing no nystagmus during warm irrigation were included. IWI was performed in supine and prone positions, and maximum slow-phase velocity and direction of nystagmus were assessed by using video nystagmography.

RESULTS

Eleven cases showed head-position dependency and were interpreted as hypofunctional. Fourteen cases showed no dependency, suggesting the absence of end organ function. In the latter group, 6 patients showing definite nystagmus in supine position could have been misinterpreted as hypofunctional, had it not been for prone-position results.

CONCLUSIONS

Evaluation of head position dependency by using IWI is important in the determination of lateral semicircular canal function.

Evaluation of the post-rotational nystagmus test (PRN) in determining alcohol intoxication

This study evaluated the accuracy of the post-rotational nystagmus test (PRN) on the basis of the results of 1006 PRN tests performed at the Institute for Forensic Medicine in Ljubljana between 1998 and 2002 during standardized medical examinations in cases of suspected drunk driving. The evaluation of PRN test results with blood alcohol concentration (BAC) as a reference was based on classification into the following categories and characteristics: true positives (TP), true negatives (TN), false positives (FP), false negatives (FN), sensitivity, specificity, positive predictive values (PPV), negative predictive values (NPV), and accuracy. An optimal cut-off value of 10 s for post-rotational nystagmus time was chosen with the help of a receiver operating characteristic (ROC) curve for the BAC limit of 0.5 g/kg. The results of the decision analyses were: TP = 584, FP = 43, FN = 229, TN = 150, sensitivity = 0.718, specificity = 0.777, PPV= 0.931, NPV= 0.396, and accuracy = 0.730. The area under the ROC curve (AUC) was 0.813. Based on the AUC, the post-rotational nystagmus test is a good test for predicting alcohol intoxication over 0.5 g/kg. As a part of the physician's examination, it contributes significantly to the description of the clinical state.

Approach to benign paroxysmal positional vertigo in old age

BACKGROUND

Benign paroxysmal positional vertigo is a common and treatable vestibular disorder characterized by attacks of positional vertigo. Although elderly patients often complain about unsteadiness, the symptom of positional vertigo is seldom reported. Several studies on BPPV in the elderly reveal a low success rate in the treatment of this entity.

OBJECTIVES

To assess the clinical characteristics and treatment outcome of BPPV in elderly patients and to compare them with those of the general population treated at our dizziness clinic.

METHODS

We reviewed the medical records of 23 patients above age 75 who were treated at our dizziness clinic for BPPV during the years 1998-2004. Their clinical data, BPPV characteristics and treatment outcome were compared with the data of 30 consecutive BPPV patients who represented the general population.

RESULTS

No differences in gender distribution, duration of BPPV, treatment responsiveness or recurrence rate were found between elderly patients as compared to the general population. The duration of the last attack of positional vertigo was found to be longer in the elderly, probably due to the delay in recognition of symptoms and accessibility of a dizziness clinic.

CONCLUSIONS

Our study shows that BPPV characteristics and treatment effectiveness, as measured by negative Dix-Hallpike maneuver, are not age-dependent and there is no need for a special approach or cautiousness in prognosis prediction. It is important to search actively for this condition since treatment leads to amelioration of unsteadiness and improved well-being in these patients.

Three-dimensional analysis of eye movements using four times high-speed video camera

In order to record and analyze the rapid eye movement non-invasively in human subjects, a four times high-speed video camera (4TC) with a new computer software was developed and utilized. Nine healthy volunteers and four patients with vestibular dysfunction participated in this study. Caloric stimulation was applied to the healthy subjects and the eye movements were recorded using a standard camera (SC) and a 4TC. In four patients, the positional and/or positioning nystagmus was recorded using SC and 4TC. Analysis of the eye speed of the quick phase of nystagmus was performed manually from the print out of the chart. The quick phase of the caloric nystagmus was adequately analyzed from the data using 4TC. However, using SC the sampling rate was not sufficiently enough for this purpose, as prospected. The adaptability of the 4TC in clinical examination is exactly similar to that of SC, because of the size and weight of the camera. Although the time taken to analyze eye movements using 4TC is about four times longer than that using SC, this system is quite useful and adequate for analyzing the quick eye movements in vestibular nystagmus, in an out-patient clinic set up.

Changes In Blood Neurotransmitter And Steroid Levels During Evoked Vertigo

HYPOTHESIS AND BACKGROUND

Experimental evidence suggests that steroids as well as various neurotransmitters are critically involved in the functioning of the vestibular system in health and disease. Yet there are no pertinent human data. We hypothesized that changes in the serum levels of cortisol and plasma levels of excitatory and inhibitory neurotransmitters may occur during evoked vertigo.

SUBJECTS AND METHODS

Ten healthy volunteers (median age 37, range 21-57) entered the study. Subjects were investigated at rest and at the time of maximal nystagmic reaction during caloric irrigation. The determination of glutamate, aspartate, and gamma-aminobutyric acid (GABA) was performed by reverse phase high-performance liquid chromatography, whereas cortisol measurements were performed with an immunoenzymatic assay with fluorescence polarization.

RESULTS

During evoked vertigo, cortisol levels increased from a baseline value of 11.86 (+/-1.272) microg/dl to 14.375 (+/-2.183) microg/dl (p < 0.01), whereas all neurotransmitter levels decreased significantly. Glutamate levels, for instance, fell from a resting value of 25.99 (+/-6.30) ng/ml to 17.40 (+/-5.50) ng/ml (p < 0.001), and aspartate and GABA decreased as well.

CONCLUSION

Evoked vertigo is consistently associated with an increase in steroid serum levels and accompanying decreases in the plasma levels of glutamate, aspartate, and GABA. The possible underlying mechanisms and the functional significance of these findings are discussed.

Artificial gravity--head movements during short-radius centrifugation: influence of cognitive effects

Short-radius centrifugation is a potential countermeasure against the effects of prolonged weightlessness. Head movements in a rotating environment, however, induce serious side effects: inappropriate vestibular ocular reflexes (VOR), body-tilt illusions and motion sickness induced by cross-coupled accelerations on a rotating platform. These are well predicted by a semicircular canal model. The present study investigates cognitive effects on the inappropriate VOR and the illusory sensations experienced by subjects rotating on a short-radius centrifuge (SRC). Subjects (N=19) were placed supine on a rotating horizontal bed with their head at the center of rotation. To investigate the extent to which they could control their sensations voluntarily, subjects were asked alternatively to "fight" (i.e. to try to resist and suppress) those sensations, or to "go" with (i.e. try to enhance or, at least, acquiesce in) them. The only significant effect on the VOR of this cognitive intervention was to diminish the time constant characterizing the decay of the nystagmus in subjects who had performed the "go" (rather than the "fight") trials. However, illusory sensations, as measured by reported subjective intensities, were significantly less intense during the "fight" than during the "go" trials. These measurements also verified an asymmetry in illusory sensation known from earlier experiments: the illusory sensations are greater when the head is rotated from right ear down (RED) to nose up (NU) posture than from NU to RED. The subjects habituated, modestly, to the rotation between their first and second sequences of trials, but showed no better (or worse) suppression of illusory sensations thereafter. No significant difference in habituation was observed between the "fight" and "go" trials.

Adaptation of VOR to Coriolis Stimulation

The vestibulo-ocular reflex (VOR) is normally characterized by the gain and phase of slow-phase velocity (SPV) relative to the stimulus velocity. Although this is perfectly satisfactory for steady-state sinusoidal oscillations about a single axis, it is less useful when applied to transient responses. The well-known decay of nystagmus following a step change of head velocity approximately follows a double exponential, with an initial amplitude (A), a long time constant (tau), and an adaptation time constant (tau(a)). We have developed a means of representing the transient response for a complex head velocity stimulus as experienced during high-speed artificial gravity (AG) experiments. When a subject, lying supine on a rotating horizontal platform, makes a yaw head movement of amplitude theta, the vertical semicircular canals experience a step in angular velocity. The pitch stimulus is equal to the change in the component of the centrifuge angular velocity (omega(c)) aligned with the interaural axis, and gives rise to a vertical VOR. The magnitude of the step change is omega(c) sin theta. The SPV is approximated by an exponential decay of amplitude A and single time constant tau, and then normalized relative to this stimulus step. MATLAB scripts filter the raw eye position data to remove noise, blinks, and saccades, differentiate the signal, and remove fast phases to obtain SPV. The amplitude of the fitted SPV exponential is divided by omega(c) sin theta to obtain the normalized SPV. A and tau are shown to behave differently as subjects adapt to repeated head movements of different amplitudes.

Falling sensation in patients who undergo the Epley maneuver: a retrospective study

The author conducted a retrospective study to determine the prevalence of a falling sensation in patients who underwent the Epley canalith repositioning maneuver for the treatment of benign paroxysmal positional vertigo. The author studied a total of 436 maneuvers performed on 412 patients and observed 58 episodes (13%) of a strong falling sensation, some very severe. In almost every case, the sensation occurred when the patient was moved to the final (sitting) position; in 1 case, the sensation occurred nearly 30 minutes later. The author recommends that physicians who perform the Epley maneuver warn patients of the risk of a falling sensation, take steps to prevent its consequences, and monitor their patients for at least 30 minutes after the completion of the procedure.

Vestibular function at the end of intratympanic gentamicin treatment of patients with Ménière's disease

The aim of this study is to analyze the effects of intratympanic gentamicin injections on vestibular function in 33 patients with unilateral Meniere's Disease (according to AAO-HNS guidelines 1995) that had been unresponsive to medical therapy for at least one year. In such patients, the results of bedside examination of vestibular function vestibular examination is compared to those from laboratory tests. Intratympanic gentamicin injections (27 mg/ml) were performed at weekly intervals until symptoms or signs of vestibular hypofunction developed in the treated ear. Vestibular function was evaluated in two different rotatory chair tests. The parameters that were specifically considered were the time constant of the vestibulo-ocular reflex (VOR) after impulse rotation with a peak chair velocity of 100 degrees s(-1), and the phase and gain of the VOR after the sinusoidal harmonic acceleration (SHA) test with a peak chair velocity of 50 degrees s(-1). After treatment, both the time constant of the VOR after rotation towards the treated side and the gain in the SHA test were significantly reduced. These reductions were in accordance with the number of additional signs observed upon bedside examination at the end of the treatment. The changes observed in the VOR correlate well with the results of bedside examination of vestibular function, which in turn reflects the damage induced by intratympanic gentamicin injection.

[Benign paroxysmal positional vertigo of the horizontal and superior semicircular canals]

The incidence of benign paroxysmal positional vertigo (BPPV) of the horizontal and superior semicircular canals is much less than that of BPPV due to affection of the posterior semicircular canal. Their diagnosis is however much more difficult and still prone to controversies. The provocative manoeuvre of the BPPV of the horizontal canal (BPPV-HSC) is the manoeuvre of rotation of the head in dorsal position. A horizontal positional nystagmus is obtained. There are two forms of BPPV-HSC: the geotropic form and the ageotropic form. In the geotropic form, the liberatory manoeuvre is a "barbecue" rotation of 180 with 360 degrees towards the healthy side. In the ageotropic form, there is no universal liberatory manoeuvre. Moreover as some cases of neurological aetiology have been recognized, it is not appropriate to apply ineffective manoeuvres. The BPPV of the superior canal (BPV-SSC) is very rare. The provocative manoeuvre is the Dix and Hallpike's manoeuvre. It causes positional torsional and vertical nystagmus with an opposite direction to that obtained for a BPPV of the contra-lateral posterior canal. The liberatory manoeuvre is a Semont manoeuvre, which is identical to that we would make for a contra-lateral BPPV of the posterior canal.

The subjective visual vertical in benign paroxysmal positional vertigo. A preliminary study

In Benign Paroxysmal Positional Vertigo (BPPV), the existence of otoconial debris in the cupula or canal explains most of the symptoms and signs characteristic of this common inner ear disorder. We have studied the ability of patients with BPPV to correctly determine the subjective visual vertical, as this is a good test to evaluate utricular function. Only 1 of 10 patients with BPPV displayed a clearly abnormal response, and there was no correlation between the side of the lesion and the perceived tilt. This might imply that the limited damage induced by the dislodged otoconia does not disrupt utricular function or that the saccule is the source of the problem.