Stroke Clinical Trial
Official title:
Reaching Training Based on Robotic Hybrid Assistance for Stroke Patients
Stroke is the third most common cause of death and the main cause of acquired adult
disability in high-income countries. The most common deficit after stroke is motor
impairment of the contralateral arm, with more than 80% of stroke survivors experiencing
this condition in the acute phase, and only half regaining some useful upper limb function
after six months.
Within the European project RETRAINER (grant agreement No 644721), the consortium developed
a platform for the rehabilitation of the upper limb after stroke, which combines a passive
arm exoskeleton for weight relief supporting both shoulder and elbow movements, Functional
Electrical Stimulation (FES) of the two-most impaired muscles of the affected side,
interactive objects, and voluntary effort. The system also provides a graphical user
interface which helps the therapist set the training session and save the training data and
parameters, and provides the subject a visual feedback about his/her active involvement in
the exercise. The training consists of the execution of a series of exercises involving the
affected arm during daily life activities. Typical exercises are anterior reaching on a
plane or in the space, moving an object on a plane or in the space, moving the hand to the
mouth, with or without an object in the hand, and lateral elevation of the shoulder.
The aim of this clinical study it to evaluate the efficacy of this novel training platform
on patients between two weeks and nine months after their first stroke, who preserved at
least a visible muscle contraction for the arm and shoulder muscles. Participants are
randomized in an experimental and a control group. The control group is trained with an
advanced rehabilitative program, including physical training, occupational therapy, FES, and
virtual reality, while the experimental group is trained with the RETRAINER system for about
30 minutes, in addition to the same program of the control group. The daily training time is
the same for the two groups. The intervention consists of three sessions a week for nine
weeks. Patients are assessed at baseline, soon after the end of the intervention, and in a
4-week follow-up visits. It is planned to recruit 68 subjects for this study.
Since the RETRAINER platform was built on the up-to-date theory of motor re-learning, which
supports task-oriented repetitive training, a close temporal association between motor
intention and stimulated motor response, and an intensive and frequent training paradigm,
the study's hypothesis is that the experimental group shows a greater treatment effect than
the control group.
This is multi-center randomized controlled trial designed according to the CONSORT Statement
recommendations. A total of 68 patients will be recruited in the two centers. This sample
size was a-priori calculated as capable to detect a clinically important between-group
difference of 5.7 points in the primary endpoint Action Research Arm Test, considering a
standard deviation of 12.5, a type I error of 5%, and a power of 80%.
More technical details on the RETRAINER platform for the rehabilitation of the arm are here
reported.
The experimental setup consists of a lightweight passive arm exoskeleton for weight
compensation, a current-controlled stimulator with 2 channels of stimulation and 2 channels
of EMG recordings developed by Hasomed GmbH, and interactive objects, which are daily life
objects equipped with RFID (Radio Frequency Identification) tags used to identify the target
positions so as to drive the execution of the rehabilitation exercises. A suitable reader is
embedded in the exoskeleton with the antenna on the wrist joint. The control system is
shared between an Embedded Control System (ECS), running on a BeagleBoneBlackTM, for
real-time operation, and a Windows-based table (Microsoft Surface 3 running Windows 8),
which provides a graphical user interface (GUI) for the therapist and the patient.
The exoskeleton is characterized by four degrees of freedom (DOFs): three of them, e.g.
shoulder elevation, shoulder rotation in the transversal plane and elbow flex-extension, are
equipped with angle sensors (Vert-X 13 E, ConTelec AG) to measure the position and
electromagnetic brakes to avoid the fatiguing and unnecessary use of FES to hold a target
position once reached. The additional DOF is provided by an inclination module, which
enables the patient to move the trunk 20° forward without constriction. In addition to the 4
DOFs, the humeral rotation, the prono-supination as well as the length of the forearm and
the upper arm can be adjusted at the beginning of the training session at subject-specific
positions. The gravity compensation modules for upper arm and forearm consist of a carbon
fiber-tube with springs inside whose pre-tension can be adjusted at the beginning of the
training session in order to change the level of compensation. Thanks to the adjustability
of the lengths and the level of compensation, the exoskeleton can fit and support patients
within 5th and 95th female/male percentile. The exoskeleton can be mounted on the user's
wheelchair or on a normal chair by means of a universal clamping mechanism which assures
easy and stable mounting. The exoskeleton weights about 4kg plus 2kg for the clamping
mechanism.
In addition to the support provided by the exoskeleton, EMG-triggered FES is delivered to
two muscles, selected by the therapist based on the subject-specific needs. For each
stimulated muscle, the residual volitional EMG signal is detected and used to trigger the
onset of a predetermined stimulation sequence applied to the muscle itself. In case the
muscle does not reach the pre-defined threshold, the stimulation sequence is automatically
started after a time-out. EMG signals are acquired at 4kHz, the stimulation frequency is set
at 25Hz, the pulse width is fixed at 300µs, while the stimulation intensity is set at the
beginning of the training session on each muscle individually at a value tolerated by the
subject and able to induce a functional movement. Separate EMG and stimulation (Pals®
electrodes, Axelgaard Manufacturing Ltd) are placed over each muscle belly. When the
stimulation starts, EMG signals are continuously measured in order to provide a visual
feedback about the patient's volitional involvement at the end of the execution of each
task. An adaptive linear prediction filter is used to estimate the volitional EMG during
hybrid muscle contractions. If the mean value of the volitional EMG estimate during the
stimulation phase is over a pre-defined threshold, a happy emoji is shown to the patient
through the GUI; conversely, if it is below the pre-defined threshold a sad emoji is shown
in order to promote the active involvement of the subject. A fast and automatic calibration
procedure is required before the beginning of each session. This procedure aims at setting
the current amplitude and the EMG threshold values. During the procedure the subject is
asked to be relaxed. Specifically, three thresholds are set on each muscle: two of them are
used to trigger the stimulation, one in case the muscle is activated as first and one in
case the muscle is activated as second one; the third threshold is used to define the
subject's active involvement in the task. The thresholds are defined as twice the mean
volitional EMG during a phase of no stimulation (first threshold), during a phase of
stimulation of the other muscle (second threshold), and during a phase of simultaneous
stimulation of the two muscles (third threshold).
The control interface of the system, implemented in .Net 4.6, provides a GUI including
multiple software tools to organize rehabilitation exercises and monitor rehabilitation
progress. The heart of the control interface is a State Machine, which drives both the
parameterization and the execution of the exercises. Each exercise is divided into single
tasks: the State Machine drives the exercise execution throughout the tasks, while the
execution of each single task is controlled by the ECS. The ECS controls all the modules
requiring real time constraints, such as the stimulator, the FES controller and the
exoskeleton sensors. To keep the control interface and the ESC synchronized, a strict master
slave concept using a custom made communication protocol was implemented, meaning that the
ECS must not act independently, but only reacts to commands sent by the high level control.
Transitions between states of the state machine and thus tasks of the exercise are triggered
by angle sensors data, RFID data or a timer (depending on the task). Transitions have to
fulfill certain conditions, so called guards. These guards are predefined for each task and
have to be parameterized as described in the Section D. The GUI guides the user through the
training by providing visual instructions and feedback.
The workflow of a typical training session consists of four main phases: the setting,
donning and parameterization of the system, and the training following a pre-defined
sequence of exercises. The control interface supports the therapist and the patient
throughout all the phases via the GUI.
The setting starts with the therapist creating a new user, or selecting an existent one, and
selecting the exercises. Afterwards, the donning phase starts with the placement of the EMG
and stimulation electrodes. Once the electrodes placement is checked, the therapist should
adjust the exoskeleton lengths to fit with the patient and let the patient don the
exoskeleton. The following step is the calibration of the FES controller by means of the
automatic procedure previously described. The therapist sets the gravity compensation both
at the arm and forearm level and saves the final exoskeleton settings. On the following
training days, the setting and donning procedure is partly simplified since the therapist
can load the settings of the previous day and eventually adjust them.
The parameterization step is designed to set the guards of the State Machine. In this
process the GUI guides the patient and the therapist through each task of the selected
exercises without stimulation. The patient-specific parameters for each task, such as the
target positions, the desired time for the execution of each task, and the time of the relax
phases, are determined. At the end of the parameterization phase, all the parameters are
stored and the training session can start.
The training consists of the execution of a series of exercises involving the arm during
daily life activities. Typical exercises are anterior reaching on a plane or in the space,
moving an object on a plane or in the space, moving the hand to the mouth, with or without
an object in the hand, and lateral elevation of the shoulder. The execution of the exercises
is controlled by the control interface which leads the patient throughout the single tasks
by means of both visual and audio messages via the GUI.
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