Abstract
To clarify the features of labyrinthine equilibrium disturbances, body sway in the upright standing posture was studied by a time series analysis with a 5-dimensional feedback model.
Sways of the head, shoulder and hip and activities of the nuchal and rural muscles during upright standing were recorded polygraphically and stored in the memory of a PDP-11 computer. Data processing with a 5-dimensional feedback model was performed in a specially designed program. The results were displayed on a cathode ray tube and teletype as determinant of noise correlation matrix, power spectrum, correlogram, transfer function (Bode plot) and relative power contribution.
1. The determinant of noise correlation matrix on upright standing with eyes closed was 0.49 using linear movement of the head agdinst 0.73 using angular movement of the head. The vestibulo-spinal system has a good feedback when angular movement is used as head sway.
2. Power spectrum and correlogram of head movement indicated that head movement was a slow irregular sway with marked decrease of power in a frequency exceeding 1 Hz. The results indicate that the vestibulo-spinal system controls body sway of low frequency.
3. The transfer function calculated with head movements as input and the nuchal muscle activities as output indicated an increase of the gain in the frequency range from 0.02 to 1 Hz. The gain obtained from the sural muscle activities as output was flat. These features of the Bode plots suggest the dynamic characteristics of the vestibulo-spinal reflex. However, more than half of the subjects showed different features in their Bode plots.
4. In the relative power contribution, the proportion induced by the head movement in the autopower spectra of the nuchal and sural muscle was from 1% to 14% in the frequency range from 0.2 to 1 Hz.
The vestibulo-spinal system regulates body sways of low frequency during upright standing. However, the proportion of the contribution of the vestibulospinal system is low in the whole control of standing posture.
