Poster
# 1
Poster |
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6th Internet World Congress for Biomedical Sciences |
J. Javier Mata(1), Jaime Marco (2), Juan M. Jiménez (3), Amparo Postigo(4), Francisco Delgado Moreno(5)
(1)Department of Neuro-otology. Centro Audiológico, S.L. - Sevilla. Spain
(2)Department of Otolaryngology. University Hospital - Valencia. Spain
(3)Department of Otolaryngology. "V. Valme" University Hospital - Sevilla. Spain
(4)Department of Audiology. Centro Audiologico, S.L - Sevilla. Spain
(5)Department of Otolaryngology. "V.del Rocio" University Hospital - Sevilla. Spain
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[Physiology] |
[Otorhinolaryngology] |
For more than twenty years ago, work is being done on the objective register of an evoked response of the vestibular branch of VIII pair which can be accurately measured, as it is the one obtained after sound stimulation and registering of bioelectrical activity by means of surface electrodes.
The relationship between the register of these responses and the nervous activity in the vestibular nerve as well as its different nuclei and minor vestibular neurones, has been demonstrated with animals (1). The main problems stem from both the adaptation of the stimulus to be employed and the achievement of a reliable response above the numerous contaminated registers (2). Nevertheless, up to now the short activity and middle latency register after angular acceleration impulses, seems to be the most reliable (3).
Another major problem to be born in mind is the sole origin of the obtained response as well as and mainly, the implication of other kinds of responses in the obtained register (4).
Highly controversial as these types of registers are, our aim here is to show and obtained bioelectrical response based on the angular stimulation technique. The usual methodology for electronystagmography with caloric stimulation has been used, and we have tried to neglect all the polluting responses that, due to other types of non-vestibular stimuli, could interfere with the responses to be analysed. These will be compared to the ones obtained by other authors who used an angular acceleration technique of stimulation.
We have worked with 36 adults, aged between 18 and 43 (average 32,3), not showing either otologic pathologies or alterations in the vestibular study carried out. This study is reported below.
AMPLAID MK15 multisensorial equipment has been used to register the bioelectrical responses. A previous electro-oculographic study had been carried out with its vestibular exploratory software. We registered the spontaneous oculomotor activity, conducted a saccadic, pendular and horizontal optokinetic monitoring, followed a classical positional manoeuvres and performed electronystagmographies after caloric stimulation with horizontal (binocular derivation) and vertical (monocular derivation) registers. As a stimulus we used 47ºC air coming from a Life-Tech caloric stimulator.
In order to register the bioelectrical activity, the aim of our study, we placed silver-silver chloride electrodes over the skin. The ipsilateral mastoid being the reference, the forehead the active one and the contralateral mastoid being considered as indifferent. The above-mentioned register was made coincide with that of the nystagmic response at maximum response stage -between 60 and 90 seconds- with closed eyes (table 1). To make the absence of auditory stimuli sure, the patient was provided with approved muffling headphones during this stage. The test was carried out in a specially soundproofed room, where the noise level didn’t go over 25 dB A.
Considering the obtained results from a morphological point of view, the coincidence regarding the obtained response during the first 20 ms. shows itself in the way of a series of positive and negative deflections from the basic isoelectrical line. They alternate until they reach a total of five positive deflections -which have been consecutively numbered as P waves- an four negative ones, numbered as N. (See figure 1).
With regard to the latency values that appear after averaging out the registers achieved, we find a response margin ranging from about 2 to 17 ms. (Table 2)
After analysing the results, we agree with others authors about the difficulty of obtaining registers from which a reliable response without somatosensorial, ocular or auditory response interference (4). The register technique must take this possibility into account and try and prevent it.
Regarding the assessment of early potentials like those obtained by some authors (5), we objectify certain identification difficulties, although in a first approach the registers, as far as latency and morphology are concerned, coincide with those obtained in humans’ beings with linear acceleration stimuli. When comparing them, our P5 wave matches up with P1 concerning middle latency vestibular potentials, and at the same time, P1 and P2 match up with their homonyms of short latency vestibular potentials (6).
Due to the fact that we have carefully prevented the results were polluted by auditory registers, we think the response may tally with some activity generated by the vestibular nerve. At the same time, we bear in mind that the only activity that could interferes -oculomotor activity- does not seem to meddle with the short latency response, in spite of the fact that the first middle latency positive wave could be interfered with (7). We, nevertheless, have to mention that all this has given rise to considerable controversy and that it is still being studied.
It is then obvious the greater difficulty of the register if compared with that of nystagmic register when using a caloric stimulus. For that reason its clinical application should be assessed according to the estimated advantages of both, the nystagmic response, well studied and know, and those of the vestibular potentials. When comparing this assessment with the one extracted from the analysis of the registers with auditory evoked potentials, some data should be obtained which would be closer to the vestibular nerve’s physiological function on its way from the start to the brainstem. This seems to have already been demonstrated from the analysis of registers with acceleration stimuli (8-9). However, caloric stimulation would allow the obtaining of a coincident register of vestibular evoked potentials and classical nystagmic response, and it would provide, at least in theory, with a more complete assessment.
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[Physiology] |
[Otorhinolaryngology] |
