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At least 541 records · Page 30Linked to original sources
PubMedDate not supplied

[Opto-vestibular interaction based on nystagmometric data].

Nystagmograms recorded in healthy people (270 ENG from 30 children, aged 3 to 7) were analyzed quantitatively. The velocity of the slow component of the vestibular nystagmus during caloric tests, optokinetic nystagmus in response to stimuli applied at 20 and 10 degrees/sec, as well as vestibulo-optokinetic nystagmus resulting due to the inhibitory or enhancing effect of caloric stimulation were measured. The modulation level, i.e. the change of the velocity of the slow component that accompanied the transition of the optokinetic nystagmus to the vestibulo-optokinetic nystagmus, was always less than that of the vestibular nystagmus. This disagrees with the concept about algebraic summation of intensities of the reactions. The modulation level showed a low correlation with the vestibular nystagmus slow component velocity and depended on the optokinetic nystagmus velocity: at 10 degrees/sec the inhibitory effect was smaller than the enhancing one and at 20 degrees/sec the situation was the opposite. At 20 degrees/sec the slow component velocity was twice higher than at 10 degrees/sec. It is therefore suggested that the parameter reflects the level of the residual activity of the optokinetic system which is independent of vestibular afferentation.

Caloric Tests↗
PubMed2002

Is hyperventilation-induced nystagmus more common in retrocochlear vestibular disease than in end-organ vestibular disease?

Hyperventilation-induced nystagmus (HVIN) has previously been shown by the senior author to be common in patients with both acoustic neuromas and following resection. The recurrent study's aim was to examine if HVIN was specific for retrocochlear pathology. To test this, the incidence of HVIN in 24 patients with confirmed acoustic neuroma was compared with its incidence in 38 patients with end-organ vestibular disease (defined as a greater than 25% reduction in caloric testing). Hyperventilation was carried out for 90 seconds. The results showed that 58% of the acoustic neuroma group were positive for HVIN versus 18% of the end-organ group. This difference was very significant on chi-square testing (p < .002). Hyperventilation-induced nystagmus appears to be much more prevalent in retrocochlear pathology than in end-organ pathology.

Adult↗
PubMed1996

Static tilt may modify the value of nystagmus asymmetry.

In awake pigeons (Columba livia) we investigated the horizontal cervical and ocular nystagmuses which were induced by monaural stimulation of the lateral semicircular canals by the parathreshold sinusoidal currents. The value of nystagmus asymmetry (by the average velocities of slow components) with a normal orientation of the bird's head was compared with that in static head tilts in the sagittal and frontal planes. In the normal head position depolarization of the lateral canals evoked a stronger response than hyperpolarization of an equal value indicating that Ewald's second law is justified for the weak suprathreshold stimuli. It was found that the static tilts modify the value of nystagmus asymmetry. These changes are connected with the asymmetric modifications of the otolithic activities in tilts. This feature of the canal-olithic interaction should be taken into consideration in estimation of the results of the caloric test one of the obligatory conditions of which is static tilt.

Animals↗
PubMed1977

Clinical evaluation of vertigo.

In attempting to outline the clinical evaluation of these patients with vertigo we have discussed examples which range in order from benign self-limited disease to those requiring emergency surgery or extensive diagnostic evaluation. We sought also to illustrate how the logic of hypothesis testing is generally employed by clinicians in approaching this or other diagnostic problems. The examples were chosen to illustrate the indications for, as well as the limitations of, the various diagnostic modalities--caloric testing, electronystagmography, audiometric testing, roentgenographic and nuclear medicine procedures--which may be employed by the clinician. Most of the skills discussed in our paper, though traditionally accorded to the fields of neurology and otolaryngology, would seem to be fundamental for any general physician, while the problem of vertigo is an example of how common ambulatory problems may require knowledgeable approach to sort self-limited from more serious illnesses as well as to utilize procedures with purpose and efficiency.

Adult↗
PubMedDate not supplied

Stimulation of the vestibular receptor by means of step temperature changes during continuous aural irrigation.

A technique for rapid, balanced hot/cold stimulation of the vestibular receptor is presented. During continuous aural irrigation the temperature of the irrigation fluid is switched between hot and cold values at times computed according to a mathematical model of heat conduction in the labyrinth area. As a result, the induced temperature difference across the lateral semicircular canal describes an approximately sinusoidal time course, reaching peak values of equal magnitude but opposite sign. Application of the test to 32 clinical subjects demonstrated that the heat conduction model and the analysis used in timing the sequence of thermal pulses was accurate. We expect that, with further refinements, the new technique will prove superior to conventional caloric test methods in the detection and measurement of subtle as well as gross abnormalities of the vestibular system.

Adult↗
PubMed1992

Vestibular pathophysiologic changes in experimental perilymphatic fistula.

An animal model of experimental perilymphatic fistula (EPLF) was developed in the guinea pig in order to study vestibular pathophysiology. In experimental animals, 4 microL of perilymph was suctioned from one cochlea via the round window membrane. Changes in vestibular function were as follows. 1) During the acute stage (5 hours postoperatively), spontaneous nystagmus directed toward the normal side was noted in 57.4% of the EPLF animals. This lasted less than 24 hours. 2) One week postoperatively, direction-fixed positional nystagmus toward the lesioned ear was present in 22.7% of the EPLF animals, especially when the lesioned ear was positioned inferiorly. 3) With the ice water caloric test, no response was present in 58.1% of the EPLF animals and an irregular response was found in 22.6% of them, 1 week postoperatively. These results tend to indicate that tests of vestibular function may differentiate between patients with Meniere's disease and those with perilymphatic fistula. Histologic findings indicate that a floating labyrinth is the cause of positional nystagmus and caloric irregularity. The absence of caloric responses was associated with collapse of the vestibular labyrinth.

Animals↗
PubMed2004

Effect of gravity on the caloric stimulation of the inner ear.

Robert Barany won the 1914 Nobel Prize in medicine for his convection hypothesis for caloric stimulation. Microgravity caloric tests aboard the 1983 SpaceLab 1 mission produced nystagmus results that contradicted the basic premise of Barany's convection theory. In this paper, we present a fluid structural analysis of the caloric stimulation of the lateral semicircular canal. Direct numerical simulations indicate that on earth, natural convection is the dominant mechanism for endolymphatic flow. However, in the microgravity environment of orbiting spacecraft, where buoyancy effects are mitigated, an expansive convection becomes the sole mechanism for producing endolymph motion and cupular displacement. Transient 1 g and microgravity case studies are presented to delineate the different dynamic behaviors of the 1 g and microgravity endolymphatic flows. The associated fluid-structural interactions are also analyzed based on the time evolution of cupular displacements.

Biophysical Phenomena↗
PubMed1999

Time constant of nystagmus slow-phase velocity to yaw-axis rotation as a function of the severity of unilateral caloric paresis.

OBJECTIVE: Complete unilateral loss of vestibular function results in a phase advance (reduced time constant) of the horizontal slow-phase nystagmus response to yaw-axis rotation. The objective of this study was to determine whether partial losses of lateral semicircular canal function would result in proportional reductions in the time constant. SETTING AND STUDY DESIGN: This was a retrospective study of consecutive patients' records at two tertiary referral centers for vestibular disorders. PATIENTS: Four hundred fifty-four patients who presented for evaluation of vertigo or imbalance or both and who were found to have partial or complete unilateral canal paresis on caloric testing. MAIN OUTCOME MEASURES: In 372 patients, the gain and time constant of the horizontal nystagmus response was measured using a 5-second velocity ramp of constant yaw-axis acceleration. Caloric responses to standard bithermal irrigations at 30 degrees and 44 degrees were obtained using an open-loop irrigation system. In a second group of 82 patients, the gain and time constant of the horizontal vestibulo-ocular reflex were measured using a sum-of-sines (pseudorandom) yaw-axis acceleration. The caloric response was measured using a closed-loop system. RESULTS: In both groups, the peak gain of the nystagmus response was independent of the level of the canal paresis. However, the time constant of the response both toward and away from the lesioned side decreased proportionally with increasing canal paresis. CONCLUSION: This result supports the hypothesis that bilateral symmetrical peripheral vestibular input is a necessary condition for the mechanisms or processes underlying normal horizontal slow-phase velocity storage.

Caloric Tests↗
PubMed2003

Vibration-induced nystagmus in patients with vestibular disorders.

OBJECTIVE: Our goal was to clarify the clinical significance of vibration-induced nystagmus (VIN). METHODS: One hundred patients with unilateral vestibulocochlear disorders were enrolled into this study. However, patients with spontaneous nystagmus were excluded. Vibratory stimuli (approximately 100 Hz) were presented to the mastoids and the forehead. Patients also underwent caloric testing and vestibular evoked myogenic potential testing. RESULTS: Of the 100 patients, 60 (60%) showed VIN. The nystagmus was mainly horizontal. VIN was more frequently evoked on the mastoids than the forehead. In the majority of patients, the direction of VIN was toward the healthy side, whereas some patients, especially patients with Meniere's disease, showed nystagmus toward the affected side. VIN was frequently evoked in patients with severe unilateral vestibular damages (canal paresis >50%) (39 of 43, or 90%). CONCLUSION: VIN testing is a simple and sensitive clinical test that indicates unilateral vestibular dysfunction.

Adolescent↗
PubMedDate not supplied

Head-shaking nystagmus: associations with canal paresis and hearing loss.

In 108 patients referred for caloric testing, head-shaking nystagmus (HSN) was noted in 37 electronystagmography (ENG) recordings. A canal paresis was found in 31 patients and a sensorineural or mixed hearing loss in one or both ears was found in 45 patients. Both HSN and canal paresis were insensitive predictors of either hearing loss or of each other. HSN was less sensitive as well as less specific than canal paresis for hearing loss. These data suggest that HSN is not as powerful a test as canal paresis in detecting lesions of the 8th nerve.

Adult↗
PubMed1992

[New indications for the rotating chair test for side localization and determination of central compensation in vestibular function disorder].

The horizontal vestibulo-ocular reflex was studied in normals and 35 patients with an acute or compensated unilateral peripheral vestibular deficit (PVD) in order to determine the efficacy of different response measures obtained from a rotating chair test in localizing the deficit side and defining its central compensation. The profiles of chair velocity and the visual fixation period were chosen in such a way that the slow phase velocity profiles were comparable to those obtained during caloric tests. Mean slow phase eye velocity measured during the culmination period elicited by constant chair acceleration of 5 degrees/s2 over 40 s was significantly reduced for rotations towards the side of an acute or compensated PVD. Per-rotatory gain asymmetry (after correcting for spontaneous nystagmus) was not always specific for the side of the deficit and often not significantly different from normal values in the compensated stage of the deficit. In combination both parameters (SPV and gain asymmetry) were reliable indicators (sensitivity 88%) of the underlying pathology and correctly localized the deficit side during the compensated state. The decay of post rotatory SPV followed a more rapid time course than normal during acute and compensated stages of the deficit. It may be concluded from those results that the rotating chair test is a valuable indicator of the presence and side of a peripheral vestibular deficit even when it has been centrally compensated.

Caloric Tests↗
PubMed1986

Experiences with the butterfly chart.

The bithermal caloric test remains, four decades after its first description, the single most valuable test of vestibular function. However, there are several variations described in the exact procedure of caloric stimulation and in the method of evaluating and representing the test results. For the past 10 years, we have followed a procedure using a constant standardized stimulus and a particular system for caloric nystagmus representation, viz., the Butterfly Chart, and have found it to be very satisfactory. This paper describes our experience with the use of the Butterfly Chart and its clinical application in over 4,500 cases.

Adult↗
PubMedDate not supplied

Normal values in a routine ENG test.

A total of 50 normal subjects were examined by electronystagmography for spontaneous and positional nystagmus. In this way the normal limit of the speed of the slow phase was determined to be 6.5 degrees/sec. By examining 15 of the subjects twice, the normal limit of the mean value of the two results was determined to be 4.5 degrees/sec. Forty-nine of the subjects were calorically tested, using 30 degrees and 44 degrees C stimulation. The results were calculated as indices expressing the degree of unilateral hypofunction and directional preponderance relative to the total caloric excitability. The results were evaluated for the duration of and for the maximum eye speed of the slow phase. The normal limits were determined as the mean value +/- twice the standard deviation. Our results indicate that a left-side hypofunction is a normal phenomenon and that duration and maximum eye speed of the slow phase reflect different aspects of the vestibular function.

Adolescent↗
PubMed1986

The caloric response in the contralateral ear in acoustic neuroma.

The caloric test response from the unaffected ear in a case of acoustic neuroma may be normal, hypoactive or hyperactive; each has a different pathophysiological connotation: a normal response is the anticipated finding; a hyperactive contralateral response is due to the presence of a large neuroma with brainstem compression; and a hypoactive response may result from several factors, such as lack of mental alertness during the test, drugs like barbiturates, raised intracranial tension, or the presence of bilateral neuromas.

Caloric Tests↗
PubMed2001

Three-dimensional analysis of post-caloric nystagmus caused by postural change.

In order to record caloric nystagmus (CN) using three-dimensional videonystagmography (3D VNG) 14 subjects were placed in the supine position with the head tilted up 30 degrees relative to the earth's horizontal plane. After the primary-phase CN had terminated, the subjects were repositioned from a supine to a sitting position, with the head anteflexed 30 degrees for recording the post-caloric nystagmus (PCN). In addition, 8 of the original subjects were placed in the supine position but with the head turned 40 degrees to the left so that the irrigated (right) ear was oriented upwards. After the primary-phase CN had terminated, the subjects were rotated by 180 degrees so that the irrigated ear was oriented downwards to record PCN. The results indicated that both methods successfully provoked horizontal and vertical CN. For torsional CN, the irrigated ear up/down method produced a higher provocation rate (75%) than the supine/sitting method (50%), but the difference was not significant. Comparing the provocation rate of the PCN for the horizontal component revealed that the two methods do not differ significantly. However, when comparing the provocation rates of PCN for the vertical component, the irrigated ear up/down method showed a higher rate (82%) than the supine/sitting method (18%). Thus using 3D VNG coupled with postural change during caloric testing, the horizontal or vertical components of PCN can be successfully provoked.

Adult↗
PubMed1979

Pitfalls in detecting vestibular decruitment with air calorics.

Vestibular decruitment is a pathological finding which indicates retrolabyrinthine disease. In the overwhelming majority of cases, it is consistent with posterior fossa pathology. Weak and strong caloric stimulations must be applied with precision for detecting decruitment. Air-caloric stimulation has inherent limitation in regards to reproducing the strength of the stimulus. Thus, it is inadequate for decruitment detection. It is, therefore, advisable to use water-caloric testing to assess vestibular decruitment or recruitment as one of the most revealing diagnostic clues in our neurotologic armamentarium.

Air↗
PubMed1995

Effects of semicircular canal plugging on caloric nystagmus recorded in three dimensions.

In Rhesus monkeys, distinct eye movement response components in the planes of the semicircular canals (canal plane vectors, CPV) were identified by 3-dimensional recordings of caloric nystagmus elicited in different head positions relative to gravity. Surgical plugging of single semicircular canals (SCC) was used to identify the generators of these response components. The lateral CPV is a sinusoidal function of head position, compatible with a thermovective mechanisms in this canal. Surgical plugging of the lateral SCC leaves only a small head position independent, lateral CPV, probably due to direct temperature effects on lateral SCC afferents. The posterior and anterior CPVs are complex responses composed of various components of which the present plugging experiments identified two generators: i) effects of thermovection in the lateral SCC, demonstrated by modifications of posterior and anterior CPVs after occlusion of the lateral SCC; and ii) thermovection in the vertical SCCs, demonstrated by effects of plugging a single vertical SCC exclusively on the corresponding CPV. This is the first definite identification of the vertical SCCs as contributors to the generation of nystagmus induced by caloric irrigation of the outer ear canal. It may provide a basis for the development of a modified caloric test measuring more than only lateral canal function in human patients.

Animals↗
PubMed1985

Rotational testing in patients with bilateral peripheral vestibular disease.

We performed quantitative low and high frequency rotational testing in 17 patients with bilateral peripheral vestibular deficits. A characteristic pattern of decreased gain and increased phase lead at low frequencies of sinusoidal stimulation and decreased time constant to impulsive stimulation was observed in most patients. The results of caloric testing correlated with the results of low frequency rotational testing but not with the results of high frequency testing. Only 2 patients complained of oscillopsia at the time of testing and both of these had decreased vestibulo-ocular reflex gain at low and high frequencies of sinusoidal rotation.

Adult↗