Evaluation of a controlled-energy-dissipation orthosis for tremor suppression

Abstract

The purpose of this study was to assess the effectiveness of the CEDO 1, a prototype Controlled Energy-Dissipating Orthosis for persons disabled by pathological intention tremor. Conventional neurological practice is generally unsuccessful in restoring independent upper extremity function to persons with debilitating tremors. The CEDO 1 was built to determine whether an alternative approach to tremor management, namely the application of velocity-dependent resistive loads to tremorous limbs, is a feasible means of attenuating intention tremor without degrading purposeful movement. The CEDO 1 mounts to a wheelchair or table, permits the three degrees of freedom needed for 'table-top' activities, and generates resistive loads by means of computer-controlled magnetic particle brakes whose torques are transmitted to the user's forearm via a stiff low-inertia linkage. In this investigation, five tremor-disabled and five able-bodied subjects were given computer-mediated pursuit tracking tasks in two degrees of freedom to verify that damping loads applied by the CEDO 1 do selectively attenuate upperextremity intention tremor. Experiments were also done to determine the range of damping loads needed in a tremor-suppressing orthosis and whether non-linear (velocity-squared) loads offer any advantages over linear (viscous) loads. Subjectively, all disabled subjects offered positive remarks on the effect of damping. Objectively, data from four of the five disabled subjects, processed using spectral analysis techniques, demonstrated that linear and non-linear damping loads can selectively reduce subjects' tremors by statistically significant amounts (P values <0.001). These results have allowed design specifications for tremor-suppressing orthoses to be refined, and planning for the CEDO 2 -a functionally improved version of the CEDO 1-is underway.