Nonlinear analysis of orthostatic posture in patients with vertigo or balance disorders.

The stabilometry signals involve irregular and unpredictable components. In order to identify the hidden dynamics that underlie the multi-link networks consisted of the multiple sensory systems, motor components and central integration, we applied a nonlinear analysis to these signals. We evaluated the postural control differences between eyes open and closed by means of the dynamical closeness between two states, known as similarity index, for the patients with vestibular disorders. We were able to demonstrate that some patients (eight of 21) showed a difference between the conventional and nonlinear measures. Especially, the similarity index tended to reflect the clinical course of the vestibular compensation and the findings in the patients with benign paroxysmal positional vertigo (BPPV) demonstrated that its vestibular function may include various pathologies besides canalithiasis. These results suggest that nonlinear analysis can elucidate the complex postural control networks and this procedure may also be able to provide the new findings of the stabilometry examinations.

[Static balance is controlled by a non-linear dynamic system]. / L'équilibre statique est contrôlé par un système dynamique non-linéaire.

Different techniques of stabilometric signal analysis have been used in order to study the adaptation of the fine postural control system to the wearing of corrective glasses with or without prisms. The comparison between the results obtained with conventional techniques and those obtained with non-linear dynamic methods demonstrates the better efficiency of the latter. These results confirm that the postural system behaves as a non-linear dynamical system and may explain the outstanding sensitivity of the fine postural system to small perturbations.

Orthostatic postural control in vestibular neuritis: a stabilometric analysis.

Posturographic data for 182 vestibular neuritis patients were recorded on a static posturographic platform (stabilometry) with the patients' eyes both open and closed. Three of the parameters studied are presented here: mean position of the center of pressure, area of the statokinesigram, and Romberg's quotient. Vestibular neuritis modifies the performance of the fine-postural system in unpredictable ways, varying with the subject. It may disturb either the mean position of the center of pressure or the integration of visual input. Sixty of the patients in this study did not use visual input to stabilize their position in relation to their surroundings. The value of stabilometry as a method for observing the integration of visual input in the control of orthostatic posture is discussed.

Non-vestibular dizziness and static posturography.

In patients complaining of dizziness attributable neither to vestibular disorders nor to any neurological cause, static posturographic recordings can reveal signs consistent with the symptoms. These posturographic abnormalities are a sign, not of impairment of some other input of the fine-postural system, but of faulty integration of the multimodal sensory information that contributes to the control of orthostatic posture.

[Visual contribution to the postural system: a clinical approach to the study of vision]. / L'entrée visuelle du système postural fin: une approche clinique de la vision.

The clinician posturologist studies vision as one of the sources of informations about the small movements of the body relative to its environment, informations which enable controlling postural stability. But this way of working, very restrictive indeed, acquires a great clinical dimension because visual information must be integrated with all the other postural informations, and it appears that this integration is not always satisfactory and that its disorders can be detected and cured in many illnesses.

[Can corrective lenses change the precision of postural control?]. / Les verres correcteurs peuvent-ils altérer la précision du contrôle postural?

The wearing of corrective lens may disturb the functioning of the fine postural system, at least in some circumstances which have to be specified. The first condition of this deleterious effect could supplying of badly centered lenses. But this clinical hypothesis have to be tested experimentally.