Studies on the Largest Lyapunov Exponents of the Standing Posture in Patients with Unilateral Vestibular Dysfunction

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  • Mizuta Keisuke
    Department of Otolaryngology, Graduate School of Medicine, Gifu University
  • Tokita Takashi
    Department of Otolaryngology, Graduate School of Medicine, Gifu University
  • Ito Yatsuji
    Department of Otolaryngology, Graduate School of Medicine, Gifu University
  • Aoki Mitsuhiro
    Department of Otolaryngology, Graduate School of Medicine, Gifu University
  • Kuze Bunya
    Department of Otolaryngology, Graduate School of Medicine, Gifu University

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Other Title
  • 一側迷路障害例の重心動揺における最大リアプノフ指数の検討
  • イッソク メイロ ショウガイレイ ノ ジュウシン ドウヨウ ニ オケル サイダイ リアプノフ シスウ ノ ケントウ
  • Studies on the largest Lyapnov exponents of the standing posture in patients with unilateral vestibular dysfunction

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In the present study, we investigated the body sway in patients with unilateral vestibular dysfunction by the largest Lyapunov exponents using a chaotic time series analysis. The largest Lyapunov exponent is regarded as a parameter indexing an orbital instability.<br>Materials and Methods: Subjects consisted of 55 normal healthy subjects, 11 patients diagnosed as having vestibular neuritis (VN), 6 patients diagnosed as having sudden deafness (SD) with vertigo, 23 patients diagnosed as having Meniere disease (MD), 11 patients diagnosed as having benign paroxysmal positional vertigo (BPPV) and 14 patients diagnosed as having other vestibular disorders. Using a stabilometer, the sway of the body center of gravity in an upright standing position was recorded with eyes open and closed for 60 seconds under each condition. From the time series data obtained, the largest Lyapunov exponents were calculated using a chaos analysis program.<br>Results: In normal healthy subjects and patients with unilateral vestibular dysfunction, the largest Lyapunov exponents on right-left sway were larger than those on forward-backward sway with eyes open and closed. The largest Lyapunov exponents in patients with unilateral vestibular dysfunction on forward-backward sway with eyes closed were significantly larger than those in normal healthy subjects. A few patients with the instability of standing posture judged from conventional analysis (area of sway, locus length per time) showed higher values of the LLE. We investigated the variation of the values of the largest Lyapunov exponents in patients with unilateral vestibular dysfunction at each stage during recovery from their vestibular damage. The largest Lyapunov exponents at the early stage with stable standing posture were significantly higher than those at the late stable stage with stable standing posture. Some patients at the very early stage had lower values of the largest Lyapunov exponents.<br>Conclusion: We speculate that the orbital instability indicated by the values of the largest Lyapunov exponents has a different significance from instability of standing posture indicated by a conventional analysis. We propose that the largest Lyapunov exponents may be an useful subsidiary measure to evaluate postural stability and its change due to vestibular dysfunction.

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