Bioengineering
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Isokinetic Robotic Device to Improve Test-Retest and Inter-Rater Reliability for Stretch Reflex Measurements in Stroke Patients with Spasticity
Chapters
Summary June 12th, 2019
Using a robotic isokinetic device with electromyography (EMG) measurements, this protocol illustrates that isokinetic motion itself can improve inter-rater reliability for the angle of catch measurements in stroke patients with mild elbow flexor spasticity.
Transcript
This protocol improves the reliability of spasticity measurement compared to the conventional method. The stretch reflex is measured while considering the effect of standardized isokinetic motion on the reliability of angle of catch. Using this technique angle of catch illustrated by the stretcher press can be measured using the standardized manner, both in the isokinetic and the manual motions by measuring the surface and the activity from the biceps brachii.
Demonstrating the procedure will be Seo Hyun Park, a occupational therapist from my laboratory. Begin by asking the patient to sit in a chair with a straight back. Also inform them that they should keep their shoulder position stable throughout the experiment.
Next, unfasten the fixation block on the linear slider so that the cuff can be moved freely. Then place the subject's hemiparetic arm lightly on the robot manipulandum without fastening the strap. Adjust the height of the robot using the lab jack until the patient's shoulder is abducted 90 degrees and confirm this using a goniometer.
Fasten the straps of the forearm cuff. Next, instruct the subject to hold the handle and fasten their hand to the handle with straps. Align the rotation axis of the robot with the anatomical axis of the patient's elbow joint.
Now flex and extend the subject's elbow joint so that the position of the cuff can be readjusted naturally in an optimal position without generating resistance during movement. Then fasten the fixation block to fix the position of the cuff. Finally, attach the surface EMG electrodes on the biceps brachii muscle in the hemiparetic arm.
To begin measurements first input the patient's hemiparetic side information into the program. Then confirm that the elbow is flexed to 90 degrees using a goniometer and press the 90 degree set button on the graphic interface panel. Press the Finish set button to switch the robot to the actuating state.
Then, click the buttons on the motor run panel on the left side of the graphic interface in order from top to bottom. Now set the speed to one degree per second, then click the Run button. The robot will extend the elbow slowly at one degree per second from a 90-degree flexed posture until the reaction torque reaches a certain threshold level, or extends by 170 degrees.
Next, change the speed to negative one degree per second and again select Run. The robot will flex the elbow slowly until the reaction torque reaches the threshold level. Before beginning measurements, perform inertia effect compensation.
First, click the Back button on the control panel and the robot will flex the elbow to the minimum angle posture. Now set the speed to 150 degrees per second, select Inertia Test and then click the Run button. The robot will apply a short perturbation of five degrees to the patient at this rate.
The peak torque and period value of each trial are automatically stacked and displayed on the GUI panel. Repeat this inertia test two more times, then determine a proper peak torque value and period value from the measured data and enter the value on the program GUI. Here we see an example of inertia effect compensation.
The green line indicates the raw torque. The dotted line indicates the inertial force model, and the red line indicates the inertial torque compensation result. Next run the familiarization step.
Click the Back button to flex the elbow to the minimum angle posture. Then inform the subject that the robot will move before clicking the Run button. The robot will extend the patient's elbow at a rate of 150 degrees per second until a maximum angle is reached or the reaction torque reaches threshold.
Repeat the familiarization procedure two more times. Then take a five-minute rest before starting the test. To begin isokinetic MTS measurement again press the Back button to return to minimum angle posture.
This time however, click the Run button without informing the subject. The robot will again extend the patient's elbow at the same rate. Time, angle, reaction torque and trigger signal data will be stored by the system during the test.
Repeat the isokinetic MTS measurement two more times with two minutes breaks between sets. Then take a five-minute rest after performing all three measurements. For the manual MTS experiment, try to extend the subject's arm at the maximum constant speed according to the ideal MTS performance condition.
Next, perform manual MTS measurement. After returning to the minimum angle, press the Free Run button and the robot will change to manual operation mode. Now hold the handle of the manipulandum and stretch the subject's arm.
During operation the rater should generate a constant speed of 150 degrees per second. At this point, turn off the Free Run mode and have the subject take a two-minute break. Then repeat the manual MTS measurement two more times.
After finishing the entire experiment with the first rater have the subject rest for 10 minutes. Then repeat all MTS measurements with a different rater. To perform isokinetic MTS experiment data analysis, first synchronize the EMG data and robot angle data using the trigger signals of each data set.
Then determine the angle of catch manually as the starting point of the root mean square EMG upsurge as seen here. For angle of catch evaluation using the torque data draw one regression line beginning with the point where the trigger signal goes up and draw another regression line from the point where the trigger signal goes down. Now compare the slopes of these two regression lines.
If they show a significant difference, angle of catch can be determined at the intersection of the two regression lines. This figure shows an example of angle of catch evaluation using EMG data for a manual MTS case. As done in the isokinetic case, the angle of catch is determined as the angle when a clear upsurge of the EMG occurs.
Here we see variables for the normalized assessment motion index. Intuitively, index value is the ratio of the area under the velocity graph to the area of the gray box. Most basic kinetic movements show values closer to one.
The most critical step in this technique is the angle of catch selection. Also experiment conditions should remain constant to reduce noise since these experiments are performed quickly. Following this procedure, more comprehensive state evaluation are possible using the measured reaction torque and the EMG data, such as evaluating patient rigidity using the slope of the regression line.
Standardization and the quantification of the assessment tool in this protocol can provide a basis for more efficient treatment, and may enable the development of a new method, such as evoked variation. Be aware that the rapid movement of the robotic device may make the patient nervous, and this can affect the muscle tone. Therefore, familiarization is necessary before beginning the experiment.
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