Aasen T, Nordahl SHG, Goplen FK and Knapstad MK
Background: A method for detecting the critical time frame for reacting to postural sway in order to maintain balance has been previously proposed. However, this method requires subjective assessment, which reduces cost-efficiency and could introduce bias. In this article, we present a simple and robust algorithm to estimate the time window length, the turning point, during which the regulating functions for maintaining the upright position come into action.
Methods: Postural sway was measured using a static balance platform across four conditions (eyes open/closed, standing on bare platform/rubber foam) in a group of healthy subjects and a group of patients suffering from dizziness. The Hurst exponent is a measure of long-term memory of a time series. The turning point is estimated as the time where the derivative, the stepwise difference of the slope, of the Hurst scaling series crosses from higher to lower than 0.5 (i.e. switching from a positive to negative correlation).
Results: The turning point was increased in patients when standing on the bare platform with eyes open and closed.
Conclusion: An increased turning point may indicate delayed compensatory action to postural sway in some patients suffering from dizziness. This paper presents a new algorithm for estimating the turning point without the need for subjective data evaluation, increasing cost efficiency and reducing the potential for bias. The method is feasible for evaluating postural control and discriminates between patients with dizziness and healthy controls.
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