Model-Based Posturographic Sleepiness Monitor Tested on 20 Subjects

A previous posturographic force platform study verified that human balance deteriorates as a function of time awake (TA) [1, 2]. It was found that TA can be estimated with plusmn2.5 h accuracy using 30 s trial length. For a fast, reliable and convenient sleepiness monitor even better TA estimation accuracy and shorter trial length is needed. We continued this quest by modeling the quiet stance test situation with a single-link inverted pendulum model (SLIPM). The center-of-mass (COM) trace in the AP (anterior-posterior) direction was calculated from the measured center-of-pressure (COP) trace. The sway angle thetas, ankle torque tau and the horizontal force F acting on the COM were calculated from the SLIP equations - each analyzed with 13 different sway measures, i.e. variables that correlate with TA. The effect of circadian rhythm was separated from the sway measures. Twenty subjects´ sway measures were analyzed. The SLIPM-based posturographic averaged TA estimation accuracy improved to plusmn2.3 h. The trial length could be shortened to 21 s.