Evaluation of upper extremity robot-assistances in subacute and chronic stroke subjects

Abstract

Background: Robotic systems are becoming increasingly common in upper extremity stroke rehabilitation. Recent studies have already shown that the use of rehabilitation robots can improve recovery. This paper evaluates the effect of different modes of robot-assistances in a complex virtual environment on the subjects' ability to complete the task as well as on various haptic parameters arising from the human-robot interaction.

Methods: The MIMICS multimodal system that includes the haptic robot HapticMaster and a dynamic virtual environment is used. The goal of the task is to catch a ball that rolls down a sloped table and place it in a basket above the table. Our study examines the influence of catching assistance, pick-and-place movement assistance and grasping assistance on the catching efficiency, placing efficiency and on movement-dependent parameters: mean reaching forces, deviation error, mechanical work and correlation between the grasping force and the load force.

Results: The results with groups of subjects (23 subacute hemiparetic subjects, 10 chronic hemiparetic subjects and 23 control subjects) showed that the assistance raises the catching efficiency and pick-and-place efficiency. The pick-and-place movement assistance greatly limits the movements of the subject and results in decreased work toward the basket. The correlation between the load force and the grasping force exists in a certain phase of the movement. The results also showed that the stroke subjects without assistance and the control subjects performed similarly.

Conclusions: The robot-assistances used in the study were found to be a possible way to raise the catching efficiency and efficiency of the pick-and-place movements in subacute and chronic subjects. The observed movement parameters showed that robot-assistances we used for our virtual task should be improved to maximize physical activity.

Figure 1

Rehabilitation system. A subject performing the virtual rehabilitation task. The subject performs the task using the robot (1) and grasping device (2) while his/her arm is gravity compensated (3). The screen (4) shows an inclined table, a ball (5) and a basket (6).

Figure 2

Deviation error. Deviation error of the pick-and-place movement with respect to the predefined central curve line. The results are shown for subacute, chronic and control group without tunnel assistance (dTA) as well as for subacute and chronic group with tunnel assistance (TA).

Figure 3

Measured movement parameters. Comparison of measured parameters in a subacute dTA subject (a), a subacute TA subject (b) and a control subject (c). The end-effector force, the movement velocity, the work toward target (WTT) and the work away from target (WAT) are shown. The parameters are observed in the tangential direction on the central curve line. The lines represent different trials for the same subject.

Figure 4

Work toward the target. Comparison of the performed work toward the target during pick-and-place movement for the subacute, chronic and control group with disabled tunnel assistance (dTA). The results of chronic and subacute group with tunnel assistance (TA) are also shown.

Figure 5

Work away from the target. Comparison of the performed work away from the target during pick-and-place movement for the subacute, chronic and control group with disabled tunnel assistance (dTA). The results of chronic and subacute group with tunnel assistance (TA) are also shown.

Figure 6

The grasping force and the load force. The grasping force and the load force during pick-and-place movement for grasping phase (gPh), transport phase (tPh) and release phase (rPh). The movements were performed by a subacute subject who had no grasping assistance. Each line represents the force during single pick-and-place movement.

Figure 7

The correlation between the grasping force and the load force. Correlation between the grasping force (F_g ) and the load force (F_l) for each phase separated: grasping phase (gPh), transport phase (tPh) and release phase (rPh). The load force is the vertical component of the measured force on the end-effector. The results are shown for subacute, chronic, and control group who had no grasping assistance (dGA).