Measuring functional recovery of hemiparetic subjects during gentle robot therapy

This paper presents a pilot, proof-of-concept study of robot arm therapy (RT) with a treatment protocol specifically designed for severe hemiparetic patients and integrated with a suitable performance measurement protocol. The robot is a planar haptic manipulandum, with low inertia, low friction and impedance control. The task is reaching, with targets arranged in the horizontal plane, in such a way to induce full extension of the arm. Targets are represented haptically, by means of an attractive force field applied by the manipulandum, and visually, by means of circles on a computer screen. The force field is smoothly activated until it reaches a preset intensity that is maintained until the target is reached. Such level of assistance is selected initially as the minimum level that allows each patient to fulfill the task. In each training session, two blocks of trials are alternated (with open and closed eyes, respectively). In the course of training, the level of assistance is reduced as performance improves. Functional recovery is evaluated by processing the kinematic measurements in order to express in quantitative terms the smoothness of the targeting movements. In particular, we defined four performance indicators or outcome measures: (1) the mean speed of the movements; (2) the number of sub-movements in which reaching is decomposed, (3) the remaining error after the first sub-movement, (4) the relative time of the first sub-movement with respect to the total reaching time. For these indicators we identified a measurement scale from the performance of a population of normal subjects performing the same task. The statistical analysis of the responses shows that the proposed protocol is capable to induce significant improvements in all the patients and the performance indicators are sufficiently stable to be chosen as candidates of future adaptive RT protocols in which the training and measurement protocols are designed in an integrated way.