Utricular Function Testing in Healthy Subjects and Patients with Unilateral Deafferentiation: Sinusoidal Lateral Displacement Versus Steady State Unilateral Testing
- Paper number
IAC-07-A1.2.03
- Author
Prof. Floris Wuyts, University of Antwerp, Belgium
- Year
2007
- Abstract
Astronauts experience often space motion sickness during g-level transitions. This is partly due to the intra-vestibular conflict, that originates in the unloading of the utricles while the semi-circular canals still sense the angular accelerations during head rotations. Few tests exist to investigate the utricular system side by side. We investigated the utricular function during the past years, based on the protocol as described in Wuyts et al, (2003), that is an extension of the methodology as developed by Clarke et al (1998). In this so called unilateral centrifugation test, subjects are rotated about an earth vertical axis at a velocity of 400 degrees per second. First, subjects are accelerated at 3 degrees per second square, followed by a 90 second dwell period to damp any canal influences. Then during the ongoing rotation the subject is translated along an inter-aural axis over a distance of 4 cm first to the right at a translation speed of 0.2 cm per second. At this position one utricle becomes aligned with the axis of rotation. This position is maintained for a period of 30 seconds. Then the chair translates back to its initial center position, followed by a translation to the left for the same time periods, before the chair returns to the initial position and decelerates. At each eccentric position, the contra-lateral utricle is exposed to the combination of gravity and a centrifugal acceleration of 0.4g, corresponding to an apparent roll-tilt of 21.7 degrees. This stimulus induces ocular counter rolling (OCR) which is measured on-line using three-dimensional video-oculography. Not only these extreme positions are taken into account for the analysis, but also all intermediate positions of the rotation axis. As long as the axis of rotation is positioned in between both utricles, the response, i.e. the ocular counter rolling, appears linear. The slope and intercept of this linear response as a function of the eccentricity of the head center (midpoint between both labyrinths), are a measure of the utricular response, i.e. sensitivity and preponderance. In some cases however, while the axis is positioned over one otolith, shifts occur of the ocular counter roll despite the 30s period of constant stimulation. Moreover, a slow delay is present that suggests hysteresis of the response. Therefore, a new stimulation paradigm has been used where a slow sinusoidal lateral translation (0.0125 Hz) of the rotation axis is imposed on each subject, while the chair rotates at 400 degrees per second. Four cycles of sinusoidal translation are obtained per subject. By means of a Matlab program, we apply different methods for analyzing the transfer function between stimulus and response, yielding measures for gain, phase, bias shift as well as an trend. 30 healthy volunteers (with signed informed consent) have undergone the initial steady state test as well as the sinusoidal paradigm. 10 patients who had acoustic neuroma surgery were also tested to validate the model for unilateral deafferentiation. The results of this paired study design will be presented. Knowledge of the behavior of the utricle allows a better insight to investigate effects of medication or other countermeasures against effects of spaceflight such as otolith deconditioning.
Authors: ROBBY VANSPAUWEN, PIERRE-FRANCOIS MIGEOTTE#, PAUL VAN DE HEYNING AND FLORIS L. WUYTS Antwerp University Research Center for Equilibrium and Aerospace (AUREA), Groenenborgerlaan 171, 2020 Antwerp, Belgium. #Biomedical Physics Laboratory. Universite Libre de Bruxelles, Floris.Wuyts@ua.ac.be
- Abstract document