Significance of Body Sway Velocity-Power-Spectrum Analysis in Postural Equilibrium Dysfunction

Abstract

The method and objective of the analysis of equilibrium dysfunction based on the indices of gravitudinal fluctuations as well as the expression of the body sway in mathematical values have contributed in the diagnosis of the location of disturbance and the classification of diseases.The power spectrum analysis of deviation is one of the analytical methods which have gained much popularity in practice in recent years.We have recently conducted a power spectrum analysis of body sway velocity. It was not possible to analyze the directional component of a body sway by this method, but observation of sways in terms of velocity was possible. Formerly, it was difficult to analyse the high frequency of the body sway in terms of the power spectrum : however, by converting the body sway into the velocity power spectrum, the analysis of the high frequency body sway could be easily be performed.We used this method for the analysis of 19 cases of spinocerebellar degeneration, seven cases of Parkinson's disease, 22 cases of hemiplegia, and eight cases of Meniere's disease.For basic data, tetanic stimulation of lower limb muscles was given by connecting plate electrodes to the tibial nerves bilaterally below the knees to induce body movements.In this experiment, a peak was observed which coincided with the loaded frequency in the sway velocity power spectrum. It was discovered also in this experiment that the velocity component of body sway in the normal person was a noise which was inversely proportional to the Feurier's frequency, which is said to be Schottky effect (by Johnson 1925, 1/f noise).When various neurological diseases was analysed using this method, a distinct finding was observed at higher frequencies, i.e. a deviation in the slope of the spectrum from that of the 1/f noise.How a method like this can be utilized for the analysis of body movements was discussed.