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Correlations between hearing thresholds and caloric responses among a heterogeneous sample of dizzy patients.
Auditory and vestibular function were compared in a heterogeneous sample of dizzy patients (N = 52). Hearing thresholds for the conventional audiometric frequencies were measured for each patient and parceled into two frequency ranges, 0.25-1 kHz and 2-8 kHz. Hearing thresholds also were measured for each patient over an extended high-frequency range that included the frequencies 10, 12, and 14 kHz. Bithermal caloric responses for these patients were available and were grouped for unilateral weakness (UW) or no unilateral weakness (NOUW). Hearing thresholds ipsilateral to the side of unilateral weakness (UW) yielded significant (p less than .05) modest correlations (r = .39-.52) with UW for all three audiometric frequency ranges (N = 35). These findings do not suggest a strong tonotopic relation between the audiometric and UW data. Hearing thresholds for the frequency range 10-14 kHz, but not for the conventional audiometric frequencies, correlated with slow-phase eye velocity (SPV) when SPV was averaged across the four caloric conditions for each of 17 NOUW patients. The latter finding indicates a subtle trend for eye velocity to increase as a function of increasing hearing threshold.
[The vestibulospinal reflex and its tests].
Examination of vestibulospinal reflexes is an integral part of investigation of the balance apparatus activity. Four tests were selected to verify its utility and reliability, i.e. Romberg (stand II) and Hautant's tests for examining tonic reflexes, Fukuda's stepping test and writing test to monitor how the vestibular apparatus affects coordinated movement. The latter was, however, eliminated from clinical usage due to its unreliability. The final assessment of vestibulospinal reflexes is made more precise by simultaneous evaluation of the three remaining tests.
Closed-loop caloric, harmonic acceleration and active head rotation tests: norms and reliability.
Norms and test-retest data from 20 persons with normal hearing and balance function were obtained for bithermal caloric (BC) using a closed-loop irrigator, sinusoidal harmonic acceleration (SHA) and active head rotation (AHR) tests. Each subject was tested twice with each test, with at least 24 hours between retest. Results of BC testing indicate that a unilateral weakness of 30% should be present to confidently identify a significant inter-ear difference when using a closed-loop irrigator for stimulus. Test-retest correlations of unilateral weakness were extremely poor, reflecting the potential for considerable variability with this test. With the exception of asymmetry measures at 0.01 and 0.02 Hz, SHA gain, phase, and asymmetry are very similar to previously published norms. Test-retest correlations were generally better than BC correlations, with phase measures having the highest test-retest correlations. AHR norms were obtained in three conditions, with eyes open and starting at a stationary target (AHR-EO), with eyes closed (AHR-EC), and with eyes open and fixated on a target moving synchronously with the head (AHR-FX). AHR-EO mean gain and phase were slightly less than that reported by other researchers, possibly as a result of differences in analysis algorithms, and had the poorest test-retest correlations. AHR-EC gain and phase were much more variable than AHR-EO between subjects, but showed very high test-retest correlations. AHR-FX gain, phase, and asymmetry are similar to those reported previously and have slightly better test-retest correlations than AHR-EO.
[Static function tests. 2. Diagnosis based on the results of Romberg, Mann and Goniometer tests].
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Sensorimotor postural rearrangement after unilateral vestibular deafferentation in patients with acoustic neuroma.
Unilateral vestibular lesion, as acoustic neuroma and its surgical removal, leads to impaired balance control. After initial vertigo and postural instability corresponding to unilateral vestibular deafferentation, improvement in symptoms and global balance functions occurs by a process called vestibular compensation. In this respect, this prospective study aimed to assess the differential contribution of sensory inputs to the regulation of posture during the recovery process after acoustic neuroma removal. Twenty-seven patients with acoustic neuroma underwent vestibular and posturographic testings, shortly before and 8 days, 1 month and 3 months after surgical removal of the tumour. Immediately after vestibular deafferentation, vestibular function was asymmetrical, postural performances were altered, especially in eyes closed conditions and in sensory challenged situations. One month, and more particularly 3 months after surgery, restoration and even improvement of vestibular and balance performances occurred, associated with a lower number of falls, development of more appropriate sensorimotor strategies and better resolution of sensorial conflicts. Postural perturbations are related to erroneous vestibular afferences, leading to incoherence in information about head position and interference with somatosensory and visual pathways. The time-course implementation of central adaptive mechanisms, characterized by substitution by other sensory afferences and new behavioural strategies, leads to an improvement of balance performance.
[Value of symmetrical directional preponderance for evaluation of the function of the organ of equilibrium].
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Effects of six conditions of ocular fixation on caloric nystagmus.
Caloric tests were performed on 20 normal volunteers under the following six conditions of ocular fixation: (1) eyes open with lighted +20-diopter lenses; (2) eyes open with lighted +20-diopter lenses plus strobe lighting; (3) eyes open in darkness; (4) eyes closed in darkness; (5) eyes closed in a dimly lighted room; and (6) eyes open with unlighted +20-diopter lenses plus strobe lighting. Latency, amplitude, frequency, duration, and speed of the slow component were measured from a permanent recording. Significant differences were found between the lighted +20-diopter lens conditions and all others for all variables except latency. Tests performed with lighted +20-diopter lenses should be cautiously interpreted due to the noticeable response suppression noted in these conditions. The present procedure of performing caloric tests with the eyes closed in a dimly lighted room was found to be unqeustionably preferable.
Electrocochleography and low-frequency harmonic acceleration in Meniere's disease.
We evaluated a series of 31 consecutive cases of Meniere's disease using electrocochleography (ECochG) and low-frequency harmonic acceleration (HA). The ECochG was positive for endolymphatic hydrops in 74% of the cases. A positive ECochG was strongly related to the degree of hearing loss. The results of harmonic acceleration were consistent with peripheral vestibular disorder in 80% of the cases. Five illustrative cases are also presented.
Caloric diagnosis maximum stimulus and suppression of habituation effects.
The relation between randomized caloric stimuli of 30 degrees - 5 degrees C to the parameters: duration, maximum frequency and maximum intensity was electronystagmographically examined on 25 persons. The duration and the maximum frequency showed only a slight correlation to the stimulus. There was a linear correlation to the maximum intensity and the stimulus between 30 degrees and 15 degrees C. But with temperatures below 15 degrees C the reaction did not increase. So the maximum intensity corresponds best to the characteristics of the temperature wave in the petrous bone and thus to the cupula deviation. By mathematical correction of the randomized stimulus sequence it was possible to show that habituation effects can be suppressed by certain test conditions, e.g. a constant degree of alertness of the subject and free head movements in the intervals. It is recommended to replace the 30 degrees C stimulus by a 17 degrees C stimulus: by this strong stimulus extra-vestibular interference and the influence of a latent spontaneous nustagmus are relatively suppressed and hypoexcitability is more accurately determined. Temperatures below 15 degrees C are not recommendable: the vestibular stimulus is not stronger but more painful and pseudocaloric effects are accentuated. When ascertaining correctly a spontaneous nystagmus we propose to refrain from the determination of directional preponderance, the value of which seems questionable.
The caloric vestibular test in weightlessness.
Although the theoretical background for the caloric vestibular test was assumed to be known, recent studies in weightlessness have thrown doubts on the original theory of its mechanism. It is most likely that several mechanisms are involved in the generation of caloric nystagmus in addition to the convection current theory. Experiments with the caloric test in humans conducted during parabolic flight are described. These results are compared with the results of similar experiments performed in orbital missions.
Thermal stimulation of the vestibular labyrinth during orbital flight.
During the European Spacelab mission (SL1) in 1983, caloric testing was performed for the first time in long-term weightlessness. After 2 days into orbital flight an unequivocal caloric nystagmus was observed in both subjects tested which corresponded in both quality and intensity with that measured in one-g conditions on Earth. The subsequent D1 mission enabled the experiment to be repeated on further subjects and with improved measurement procedures. As with the SL1 findings, the observed caloric nystagmus response proved to be equivalent to that measured during baseline testing on Earth. Renewed consideration of peripheral and central mechanisms, which might be involved in the elicitation of the caloric response--both in one-g and zero-g environments--has led to the reopening of a number of associated issues. One important observation which has been addressed by various research groups concerns the influence of the labyrinth's orientation to the gravity vector on the caloric response. The present authors have examined a group of healthy subjects in various body positions in the sagittal plane. The interindividual variability in the response behavior was found to be high; indeed single cases were observed in which the nystagmus response did not invert from the supine to the prone positions. These findings are discussed together with earlier reports in the literature.
Quantification of the vestibulo-ocular reflex and visual-vestibular interaction for the purpose of clinical diagnosis.
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The investigation of acoustic neuroma.
Gadolinium-enhanced magnetic resonance (GdMR) is the long awaited, easy and definitive investigation for imaging or excluding small acoustic neuromas. However, on the grounds of cost alone it is unrealistic to submit every patient with mild unilateral sensorineural deafness to GdMR. A screening regime is described which combines simple but effective imaging studies of the internal auditory meatus with clinical testing of vestibular function and objective audiometry. The 'two out of three positive' approach based on these tests has proved to be a reliable screening regime for selecting patients for GdMR.
Vestibular testing: the current position.
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[New diagnostic insights into the region of the eighth cerebral nerve (nervus statoacusticus)].
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Superior canal dehiscence: review of a new condition.
A new cause of sound and pressure induced vertigo, superior canal dehisence, is described. Auditory manifestations include hyperacusis to bone-conducted sounds and conductive hearing loss with normal acoustic reflexes. The diagnosis is reached by a directed history, documentation of upward and torsional nystagmus evoked by sound and pressure, and radiology. Acoustic reflexes and VEMP (vestibular evoked myogenic potentials) aid in the identification of patients with an apparent conductive loss with normal acoustic reflexes or have an asymptomatic dehiscense on radiology. Treatment involves avoidance of the precipitating stimuli. Surgical treatment, by resurfacing the dehiscence, is considered in patients with more severe symptoms.
Results of cupulometry in 150 patients with vertigo.
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