Abstract 189, Date 1:00 pm, Sunday, February 20, 2005 (24 hours) Session : D16: Vestibular: Clinical
Reliance on Dynamic Visual Cues for Postural Control: Effect of Age is More Important Than History of Unilateral Vestibular Hypofunction
*Patrick J. Sparto, Joseph Furman, Mark S. Redfern
Background:</B> Young adult subjects with unilateral vestibular hypofunction (UVH) and healthy older adults demonstrate greater visually-induced sway than healthy young adult control subjects. The purpose of this study was to determine if the combination of advanced age and UVH synergistically result in even greater reliance on dynamic visual cues. Methods:</B> Four groups of subjects were tested: four young adults (22-39 years) and eight older adults (58-80 years) with a history of UVH, and 4 young and 8 older age- and gender-matched controls. Eleven of the twelve subjects with UVH had a unilaterally absent caloric response; 1 had 6% loss. Subjects viewed sinusoidal anterior-posterior optic flow in a full field of view environment while standing on both a fixed and a sway-referenced platform. The optic flow consisted of nine trials each using a single frequency (0.1, 0.25, or 0.4 Hz) and a single amplitude (4, 8 or 12 cm). Anterior-posterior head sway was digitized at 20 Hz. Data were processed using a phaseless digital bandpass filter centered at the stimulus frequency of the optic flow. The root-mean-square (RMS) of the head sway was used to measure postural response. Results:</B> Analysis of Variance revealed a significant effect of age on the magnitude of sway in response to optic flow (p = 0.005); older subjects swayed 64% more than young adult subjects. There was no effect of UVH nor were there interaction effects with age. Additional significant effects were found for type of support surface, frequency, and amplitude (p < 0.001) Conclusion:</B> Age was a greater determinant of visually-induced sway than the presence of UVH. Moreover, the combination of advanced age and UVH did not result in a significantly greater reliance on dynamic visual cues than that associated with advanced age alone. This study was supported by NIH grant K25-AG001049.