Functional electrical stimulation for flexion-extension and grasping movements of upper limbs in rehabilitation (2023)

INTRODUCTION

Functional Electrical Stimulation (FES) is a technique based on the application of low-energy electrical pulses to neuromuscular structures to produce movements or sensations. FES is used in individuals who have been paralyzed by central nervous system injury but retain residual peripheral neuromuscular innervation.

FES is usually delivered by applying regular pulse waves made of monophasic or biphasic pulses. Monophasic waveforms consist of repeated identical pulses (Figure 1), usually cathodic. Biphasic waveforms (Fig. 2) are made up of repeated biphasic pulses, each consisting of a cathodic phase followed by an anodic phase. The second phase pulse aims to reverse the electrochemical processes caused by the first phase pulse, which can occur at the tissue-electrode interface and damage the skin.

The pulse waveform should be selected considering the following: the desired physiologic effect (action potential), any tissue damage, and possible electrode degradation. Biphasic waveforms are used more than monophasic in FES and are generally made up of square pulses. The short rise time of the pulses can impede the accommodation of the muscle fibers. An interface time delay must be applied between the cathodic and anode pulses to allow full propagation of the action potential along the nerve. Furthermore, limiting the amplitude of the second pulse can prevent electrode potential and its corrosion.

The application of FES in a clinical setting encompasses both patient care and rehabilitation. FES can be used in patients with damage to the central nervous system, where the propagation of stimuli to peripheral structures is disrupted due to injury or cerebral palsy. To achieve results, the stimulated muscles and nerves must be intact and completely healthy.

The main goal of FES is to continue training healthy muscles and voluntary functions by inducing physiological changes [1-3]. The main results obtained with FES are: reduction of spasticity and associated pain; improve local blood circulation; local soft tissue mobilization; bone stress; stop atrophy and increase muscle mass; improving the posture of the extremities.

The FES intervention aims to complement the functions, both sensory and motor, altered and damaged by neurological pathologies. It stimulates neuronal reorganization for the restoration of motor control, taking advantage of the plasticity of the cerebral cortex. In the case of the upper extremities, for example, the goal of FES is to restore to the patient (usually a C5 and C6 level hemiplegic or paraplegic) the ability to grasp, hold and hold objects and tools, manipulate and release them. various ways, restoring your self-confidence in daily activities.

The aim of this study is to establish a clinical FES protocol for the rehabilitation of the upper limbs to support and train the performance of complex movements, such as wrist and finger flexion extension and palmar grip strength. The benefits derived from the application of the new FES protocol have been evaluated by comparing specific quantitative electromyographic parameters evaluated before and after treatment.

Methods and materials

A. Study population

A group of five subjects with different neuromotor disorders of the upper extremities and different muscular degenerations, with no previous experience in FES training, was recruited from the Department of Neurology, ICS Maugeri Institute for Scientific Care and Research, Telese Terme (BN, Italy). . Written informed consent was obtained from each of the subjects prior to their participation in the study.

The characteristics of the subjects are summarized in Table I.

Despite their different diagnosis, all patients are characterized by spastic muscles in the affected upper limbs that are treated.

B. Functional Electrical Stimulator - MotionStim 8

MotionStim8 from Medel Medicine Electronics is a device designed for FES as adjunctive therapy after central nervous system disorders (Fig. 3). The system is designed to integrate exercise therapy with FES, for damaged and/or paralyzed muscles to activate trophic recovery and muscle effort and restore lost functionality.

The device has 8 channels, to which 2 electrodes each can be connected. It measures 186 x 38 x 155 millimeters, weighs 550 grams, and contains an internal battery for wireless operation, providing power supply and drain. The treatment time is adjustable from 0 to 10 hours. Stimulation is performed by a biphasic square pulse. The width of the current pulse can be set from 1 to 125 milliamps, with a frequency of 1 to 99 Hertz and a pulse duration of 10 to 500 µseconds [4]

MotionStim8 comes with Motionsoft, the PC software dedicated to creating functional protocols for electrical stimulation. The software development environment has intuitive interfaces that make learning how to use it very fast for the user. They can effectively develop custom FES programs through an editor to create electrostimulation protocols.

C. BTS FREEEMG 300

BTS FREEEMG 300 is a diagnostic device for surface dynamic electromyography analysis. The BTS FREEEMG 300 is completely based on wireless technologies and uses 16 miniaturized probes (Fig. 4) with active electrodes weighing less than 9 grams for signal acquisition and transmission. The probes amplify the EMG signals, digitize them, and communicate with the compact, light-receiving unit, which is a Microsoft Windows-based Pocket PC.

BTS FREEEMG 300 comes with Myolab, the intelligent and easy-to-use software developed by BTS for EMG signal acquisition, visualization and first level processing.

D. FES Clinical Protocol

We have developed a new clinical protocol to support and train the execution of complex upper limb movements, based on asynchronous FES. The protocol consists of 2 attempts.

1. The first test is aimed at retraining the muscles of the upper extremities in flexion-extension movements of the wrist and fingers.
2. The second test is aimed at retraining the muscles of the upper extremities in palmar grip movements.

Table II lists the muscles involved in the first trial. For each muscle, the following information is reported: MotionStim8 channel to which the muscle is connected, current pulse width, current pulse width, delay time from the first pulse delivered on channel 1, and stimulation rate. Pulse amplitude and width are the parameters used to adjust the number of motor units involved and the force of muscle contraction. The increase in any of these parameters produces an increase in the energy delivered to the muscle, activating a greater number of motor units, and consequently a greater muscular strength. Otherwise, the pulse rate has no effect on the force of muscle contraction. Pulse rate values ​​less than 15 Hz can cause muscle tremors, values ​​greater than 50 Hz cause rapid muscle fatigue, while rate values ​​between 15 Hz and 50 Hz have little or no effect on muscle strength. Therefore, the stimulus frequency is set to a constant value (20 Hz) as low as possible to avoid premature muscle fatigue and minimize skin discomfort.

Transcutaneous electrodes have been used in the FES protocol. They are placed on the motor points of the muscles, the stimulation site that produces the strongest and most isolated contraction, at the lowest level of stimulation. The advantages of surface electrodes are their non-invasiveness, low cost, and relative technological simplicity. However, the disadvantages are not lacking: it is problematic to achieve isolated contractions or activate the muscles in depth; repeated electrode placement is difficult to replicate; finally, electrical stimulation on sensitive skin can cause painful sensations due to the activation of pain receptors in the skin. fig. 5 shows the placement of the electrodes. In this test, oval Flextrode electrodes (4 × 6 cm) were used for all muscles involved.

The duration of the first test is 22 minutes, with an initial warm-up time of 2 minutes, during which the amplitude of the current pulses is gradually increased to the value chosen for stimulation. For the next 20 minutes, 10-second stimulation phases alternate with 5-second pause phases, during which no pulses are delivered. The stimulation phase begins with activation of the extensor carpi ulnaris in channel 1, followed by the extensor digiti minimi in channel 2 after 100 ms. This type of stimulation allows extension of the fingers and wrist and remains active for 5 seconds. Subsequently, channels 3 and 4 simultaneously activate the flexor muscles, flexing the wrist and fingers during the last 5 seconds of the stimulation phase.

Table III lists the muscles involved in the second test. fig. 6 shows the placement of the electrodes. In this test, 6 oval Flextrode electrodes (4×6 cm) and 8 round Flextrode electrodes (Ø25 mm) were used. The duration of the second test is 22 minutes, with an initial warm-up time of 2 minutes. For the next 20 minutes, 11-second stimulation phases alternate with 5-second pause phases, during which no pulses are delivered. The stimulation phase begins with activation of the extensor carpi ulnaris in channel 1, followed by the extensor digiti minimi in channel 2 after 100 ms and the flexor digitorum superficialis of both channels 3 and 4 after 1.9 seconds. This type of stimulation allows the closing phase of the prehensile hand. Following this, channels 5 and 6 sequentially activate the palmar lumbrical muscles to better control movement. Finally, after 300 ms, the flexor carpi ulnaris is activated in channel 7 to maintain the grip. All involved muscles remain active for 8 seconds, after which the extensor muscles relax first, followed by the hand and flexor muscles.

Patients performed the FES protocol once a day for at least one week during their rehabilitation treatment at the Department of Neurology at the ICS Maugeri Institute.

E. EMG acquisition protocol

Electromyographic evaluations of the patients were performed before and after FES treatment to assess the outcome of rehabilitation. Electromyography (EMG) has been performed using the BTS Free EMG system on the following muscles: Extensor Carpi Ulnaris (ECU), Extensor Digiti Minimi (ECM), Flexor Carpi Ulnaris (FCU), Flexor Digitorum Superficialis (FDS). Before applying the probes, the patient's skin is shaved and cleaned with alcohol. Bipolar electrodes on each muscle are placed with a 20 mm electrode gap and orientation parallel to the muscle fibers. fig. 7 shows the location of the EMG probes.

The EMG measurement session consists of 5 consecutive phases of 1 minute each, with a total duration of 5 minutes. At each stage, the patient is asked to perform a different task:

1. Rest
2. Maximum Wrist Extension (MWE)
3. Maximale polsflexie (MWF)
4. Maximum Finger Extension (MFE)

Each subject performed at least 2 sessions. The EMG signals are further processed with Matlab. Signals are extracted and then filtered using a Butterworth bandpass filter (cutoff frequencies 10 to 500 Hz). The Root Mean Square (RMS) of the signal was evaluated for each muscle and for each recording task. In order to be able to compare the RMS values ​​of the different phases and muscles, they are normalized to the RMS value assumed for the same muscle from the same subject during the resting phase. In this way, the RMS values ​​are expressed as a percentage of the corresponding rest phase.

Result and discussion

EMG measurements were performed to assess the outcome of the rehabilitation caused by the FES protocol. In Table IV, the results are expressed in terms of RMS range, that is, the range between the minimum and maximum nominal values. Results are reported for each patient and for each active task phase of the EMG acquisition protocol. RMS ranges are expressed as a percentage of the corresponding RMS value evaluated during the rest phase. For each task, the results are divided into RMS sets of the agonist and antagonist muscles. A cohort of 3 healthy subjects performed the same EMG protocol to assessnormative rangesfor the measures evaluated. Normative ranges are reported in the last row of the table. Significant differences between the ranges before and after RMS are shown in bold.

The first task involves extension of the wrist. Significant differences were found between the pre and post measurement in all patients, both for agonist and antagonist muscles. RMS ranges for agonistic muscles increase after rehabilitation, indicating an increase in muscle tone. Antagonist muscles have tighter RMS ranges after rehabilitation, which means better control of muscle activation.

The second task, relating to wrist extension, showed similar results. The RMS ranges in the agonistic muscles obtain higher values ​​and closer to the normative values ​​in the subsequent measurements. Better control of the antagonist muscles is evidenced by the tighter ranges adopted after rehabilitation.

No significant differences were made in the extension of the fingers.

Finally, 4 out of 5 patients improved their finger flexion performance with FES rehabilitation. Due to the severe disease state and minimally conscious state characteristic of Patient 4, no significant flexion or extension of the fingers was observed.

According to the results presented, it can be said that the new proposed asynchronous FES protocol achieved effective improvements in 4 out of 5 patients. It should be noted that the numerical limitation of the study population makes this work a preliminary study and an exploratory study. research with biotechnological value. To demonstrate significant clinical results, it would be desirable to expand the study to as large a cohort of patients as possible.

CONCLUSION and PERSPECTIVE

In conclusion, two important aspects emerged from this work. The method carried out demonstrated the efficacy and usefulness of a Functional Electrostimulation protocol in the therapeutic treatment of certain neuromotor pathologies.

On the other hand, although simple devices for FES exist commercially, it is difficult to establish their specific implementation in rehabilitation protocols in clinical practice. The main obstacle lies in the gap between bioengineering skills and the needs of physicians, physiotherapists and neuropathophysiology technicians. Overcoming this obstacle is possible by seeking a high degree of integration and synergy between the professional figures involved; The engineer must have the ability to establish a beneficial relationship of mediation and mutual cooperation with doctors, physiotherapists and therapists, promoting and enabling the configuration of technology in the clinical protocols of the rehabilitation program.

REFERENCES

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3. H. Weingarden, g. Vela, R. Heruti, J. Shemesh, a. Oh one. Give, ged. Katz, R. Nathan and one. Smith, "Functional Hybrid System of Upper Extremity Electrical Stimulation Orthoses: Effects on Spasticity in Chronic Stable Hemiplegia," am j phys med rehabili, vol. 77, no. 4, pp. 276-281, 1998.
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