RANDOMIZED PERTURBED POSTUROGRAPHY - METHODOLOGY AND EFFECTS OF MIDAZOLAM SEDATION

To study quiescent stance without applying external disturbances is no t a theoretically appealing way to unveil the dynamic properties of hu man equilibrium. Methods to disturb equilibrium range from standing on foam surface, attaching vibrators to the calves to interfere with som atosensation, and exposure to body-position tracking environments, as in dynamic posturography (EquiTest). The EquiTest apparatus was modifi ed by a menu-driven software to allow arbitrary movements of the suppo rt surface and visual surround, and force data were recorded for subse quent analysis. The support surface was randomly moved in the antero-p osterior direction. First equilibrium was studied on the stable suppor t surface, then low (RMS 1.3 cm) and high (RMS 2.6 cm) amplitude movem ents were used. Vision was either present or absent at all test amplit udes. Equilibrium was evaluated by the confidence (61%) ellipse sway a rea and average sway velocity during 45 s. Eleven healthy subjects age d 23-36 years (mean 29) were sedated with a short acting sedative, mid azolam 0.1 mg/kg. Randomized perturbed posturography was conducted at baseline, and at about 60, 120 and 180 min after injection. Psychomoto r tests were conducted at baseline, and at 30, 90, 150 and 210 min. La rge interindividual variations were found. One subject could not be te sted at all at 60 min due to sleepiness, whereas some subjects felt ne arly full awake at 30 min. Sway areas were larger at 60 min, but not s ubsequently. At 60 min, sway velocities with open eyes were higher, ju st as when vision was absent and low amplitude movements were used. La ter no effects could be shown. All psychomotor tests had deteriorated at 30, and some also at 90 min. In conclusion, the randomized perturbe d posturography evaluates the dynamics of disturbed equilibrium, and t he modified EquiTest apparatus allows the study of several aspects of dynamic equilibrium control. Balance disturbances due to midazolam sed ation were quantified and correlated to psychomotor tests.