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Does the vestibulo-ocular reflex (VOR) merit redefinition?
The VOR has historically been described by parameters of the slow phase of nystagmus while fast phases have been systematically ignored. However, ample neurophysiologic and theoretical evidence suggests that fast phases are an integral part of the VOR and are not to be discarded in evaluation of vestibular function. In a series of experiments, normal subjects and compensated patients with total or partial loss of unilateral peripheral vestibular function were tested. They were exposed to sinusoidal oscillations (20 degrees, 60 degrees, and 120 degrees/second at 1/6 Hz and 25 degrees/second at 1 Hz) with no actual or imaginary visual targets (doing mental arithmetic) and the usual slow-phase parameters (gain, phase, etc.) were computed. The gaze (total eye position, slow and fast phase of nystagmus vs. head + head position in space) was also plotted vs. head position in space. It was found that in patients, fast phases of nystagmus are unequally (right vs. left) produced, extending the linear range of VOR function. It was also found that in normal subjects and patients, gaze essentially tracks the head in the absence of visual targets. It is concluded that fast phases of nystagmus contribute to gaze control during head rotations in darkness and that the definition and the testing of the VOR have to be modified to accommodate these observations.
Cisplatin ototoxicity in the guinea pig: vestibular and cochlear damage.
The aim of the present study was to investigate both vestibular and cochlear cisplatin toxicity. Twelve albino guinea pigs were divided into an experimental (n=8) and a control saline group (n=4) and were treated with cisplatin at a daily dose of 2.5 mg/kg for 6 consecutive days. Vestibular dysfunction was evaluated by computing the gain of the vestibular ocular reflex (VOR) evoked by stimulation in the horizontal (HVOR) and vertical (VVOR) planes. Changes in cochlear function were characterised as compound action potential threshold shifts. After the functional testing, tympanic bullae were removed and processed for morphological examination of the sensorineural epithelium. The onset of vestibular functional impairment was observed on the third day, although the VOR gain decrease was not significant. The impairment of the vestibular function progressed until the sixth day becoming statistically significant particularly at VVOR mid frequencies of stimulation. At these frequencies both macula and crista ampullaris functions are involved. Concomitantly a progressive auditory threshold shift was observed at all stimulus frequencies. The decline of the auditory function was statistically significant from the third day of treatment and it was more evident at high frequencies. Morphological observations showed a massive loss of outer hair cells and a degeneration of the organ of Corti in the basal/middle turns and only a slight loss of hair cells of the cristae ampullares and maculae. In conclusion, functional and morphological data provide evidence that the toxic effect of cisplatin is more pronounced in the organ of Corti than in the vestibular epithelium.
Clinical assessment of postural stability.
It is important to evaluate both vestibulo-oculomotor and vestibulospinal pathways in patients with balance disorders. While moving-platform posturography can assess vestibulospinal function, the cost and time required to perform this test may limit its clinical use. A clinical office vestibulospinal evaluation that could be done quickly and inexpensively would be of benefit. In this study we used foam posturography to prospectively evaluate 50 patients with vestibular complaints to determine its predictive value in comparison with moving-platform posturography results. Our results demonstrate a significant correlation (p < 0.005) with a sensitivity and specificity of 95 percent and 90 percent, respectively, between the clinical office assessment using foam posturography and the results of moving-platform posturography. The ability of patients to utilize vestibular cues to maintain posture may be accurately assessed in a clinical office examination and should be useful to otolaryngologists to evaluate the vestibulospinal system.
Audiovestibular manifestations in giant cell arteritis: a prospective study.
Giant cell arteritis (GCA) is a multisystemic vasculitis of elderly people that involves large and medium-sized blood vessels with predisposition to the cranial arteries. Some cranial ischemic manifestations, in particular permanent visual loss, have been widely described. Audiovestibular manifestations have been less commonly reported. In the present study we assessed the frequency and outcome of audiovestibular manifestations in a series of GCA and isolated polymyalgia rheumatica (PMR) patients examined prospectively between June 1999 and May 2001 at the single hospital for a defined population. Patients were included in the study if a temporal artery biopsy had been performed and they were examined within a week after beginning corticosteroid treatment. Patients with abnormal otoscopy or tympanogram, history of cerebrovascular complications, syphilis, Ménière and other vestibular syndromes, infections involving the inner ear, barotrauma, or being treated with ototoxic drugs were excluded. During the study period 44 patients with GCA and 10 patients with biopsy-negative isolated PMR were examined. Patients with isolated PMR were younger. Audiovestibular dysfunction was significantly more frequent in GCA patients than in those with isolated PMR and matched controls. Almost 90% of the GCA patients had vestibular dysfunction, which was generally reversible after several days of steroid treatment; after 3 months of treatment, vestibular dysfunction was observed in only 13 (29.6%) of the 44 GCA patients. These patients with persistent vestibular dysfunction were more likely to have persistent head-shaking nystagmus. Twelve (27.3%) of the 44 GCA patients had hearing improvement after 3 months of therapy. After 6 months of therapy, only 1 of the 44 GCA patients had abnormal vestibular tests. However, no additional improvement in hearing function was observed. The present study confirms a high frequency of audiovestibular manifestations in GCA. It also suggests that audiovestibular damage may be reversible in some patients with GCA.
Caloric tests.
The caloric test is still the most useful vestibular test by far. Rotatory tests may allow more accurate control of the stimulus and the response parameters may vary less in normal individuals, but only the caloric test allows individual testing of each ear. By various means described in this article, it is possible to minimize potential sources of error and thus maximize the reliability of the test. Although the test allows a good measure of horizontal semicircular canal function and, by inference, an estimate of labyrinthine disease, the fact that the reflex arc traverses the vestibular nerve and brain stem renders this pathway liable to damage by central vestibular disease. Thus the electronystagmographic recording of the caloric nystagmus response may show a variety of changes, depending on the site and nature of the central vestibular lesion. Some of these changes are discussed.
The Quix test.
Professor Doctor F.H. Quix, of Utrecht, was a keen student of macular function, who published extensively at the beginning of this century. He described many useful tests for otolithic function, and one in particular has continued to be fairly widely used. The so-called "Quix Test" is performed with the patient standing, feet slightly apart, arms outstretched, index fingers extended, and the examiner assumes a similar mirror-image posture, such that the fingertips almost touch. The patient is then requested to close his eyes, and the index fingers are observed for drift. The lateralizing value of this sign of vestibular disease is discussed.
[Vestibulo-ocular reactions by infants and young children (author's transl)].
Neurootological research demonstrated significantly different vestibulo-ocular reactions by infants and young children as compared to adults. Neurohistological research has demonstrated that the vestibular apparatus is developed by birth and therefore should be fully functional. Fifty full-term and healthy infants and children between 9 days and 24 months of age were placed on an electrically controlled rotating chair in order to determine the functional development of the vestibular system. The rotational test program consisted of a supraliminal acceleration stimulus of 3 degrees/s2, a constant rotation at 90 degrees/s for 3 minutes, and a final abrupt deceleration stimulus. The frequency and amplitude of the per- and post-rotatory nystagmus reaction were analysed from the electronystagmogram. The nystagmus frequencies demonstrate a low level in the first month. The per- and post-rotatory deviate clearly from each other in the following months. The amplitude values also start out low in the first month then climb thru the 7th month and finally stabilize or drop slightly in both the per- and post-rotatory phases. The accumulated results will be discussed and typical examples will be demonstrated.
A method for evaluating vestibular control of posture.
Tests that measure the patient's ability to control his posture generally have failed to yield clinically useful information about vestibular function. The primary reason for this failure is that postural control does not depend on vestibular function when visual and proprioceptive cues are available. To test vestibular function, one should use a procedure that forces the patient to rely on vestibular cues by eliminating cues from these other sensory systems. Such a procedure is described. Vision is eliminated by eye closure, and proprioceptive cues are minimized by rotating the supporting surface to null changes in ankle angle. Data are presented which show that postural responses are complex, but that they appear to conform to the pattern originally observed by Nashner. A method potentially capable of separately evaluating semicircular canal and otolith function is described.
[Irritability test of the vestibular apparatus by means of a calorization funnel].
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[Giratory threshold test in cranial injuries].
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Lateralization of hearing loss and vestibular nystagmus in test pilots.
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Normative study of Spacelab preflight/postflight vestibular test battery.
A study was designed to establish baseline normative responses to the MIT/Canadian Spacelab vestibular test battery. Three tests used a linear acceleration sled to measure otolith function: 1) perception of linear motion (threshold determination); 2) compensatory eye movements (linear VOR); 3) closed-loop nulling, in which the blindfolded subject nulls his velocity with a joystick under the influences of a pseudorandom sled disturbance. Rotational VOR was measured at 0.3 and 0.8 Hz in the dark and the light. Static visual-vestibular interaction was tested with a standard rod and frame apparatus, while dynamic interaction was assessed by susceptibility to roll vection induced by a rotating peripheral visual field. Two examples are presented of how results from this study can aid in the interpretation of data from preflight/postflight testing of Space Shuttle/Spacelab crews on these same experiments.
Inexpensive thermostat for the Hallpike test.
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The pendular-platform-test (P.P.T.).
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[ngle of displacement in the stepping test].
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Sources of error in interpretation of caloric tests.
Caloric testing plays a prominent role in evaluating the vestibular system. A unilateral reduced vestibular response (RVR) is a common abnormality and is consistent with peripheral vestibular pathology. An erroneous interpretation of RVR may be made due to the following circumstances: laboratory technique, the influence of directional preponderance (DP) on monothermal tests (MT), unilateral hyperactivity, or pseudocaloric (PC) nystagmus. These errors in interpretation may be avoided by (1) repeating any single irrigation that is significantly different from the other three, to rule out laboratory technical error; (2) performing bithermal (BT) testing exists, to eliminate the effects of directional preponderance; (3) observing that a right/left (R/L) difference is not due to unilateral hyperactivity, by noting absolute slow phase (SP) velocity; and (4) by demonstrating bidirectional sensitivity of the cupula before concluding that residual caloric function exists instead of no function.
[Frequency response of the semicircular canals--on semicircular canal function test by pendular rotation].
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