Stimulation map for control of functional grasp based on multi-channel EMG recordings
Introduction
Electrical stimulation of paretic and paralyzed upper limbs was introduced many years ago, yet the clinical evidence is still not sufficiently convincing to make this technique widely used [1], [2]. Functional electrical therapy (FET), i.e., intensive functional exercise combined with surface electrical stimulation of the paretic arm, promoted greater recovery of motor control and function in acute stroke patients [3] compared with the same treatment applied in chronic stroke patients [4]. However, in both acute and chronic stroke, the difficulty of determining the most effective positions for the stimulating electrodes remains a major challenge [5].
Selective activation of the muscles that control each finger and the wrist with electrical stimulation is a challenge that was initially addressed by Nathan [6]. The technology that has allowed fabrication of array electrodes for stimulation and the development of advanced electronic stimulators has provided a basis for determining how selective stimulation of the forearm muscles can be achieved [e.g., [7], [8], [9], [10]]. These studies led to two major conclusions: 1) small electrodes that are positioned appropriately can improve the selectivity of stimulation [11], [12], [13], [14] and 2) stimulation delivered asynchronously through several small electrodes at a lower frequency (approximately 10 pulses per second) rather than a single large electrode at a high frequency (approximately 30 pulses per second) allows prolonged stimulation that results in fused contraction [15], [16], [17]. A remaining challenge is how to easily and quickly select the number of electrodes and their relative positions with respect to the excitable tissue to produce adequate prehension and a safe and strong grasp with minimal wrist interference.
The hypothesis that we introduce is that by comparing EMG maps recorded while the patient performs the target function (hand opening, hand closing, holding an object for various types of grasp) using the nonparetic and paretic arm, one can determine the positions (regions) over the peripheral sensory-motor systems that can be stimulated. Thus, by mimicking the activation map of the nonparetic arm, we can replicate on the paretic side the complex and hardly predictable neural interplay that is unique to each individual. The quasi-normal activation of neural systems is likely to influence the motor control system and contribute to the development of synergies that can facilitate more effective and efficient movements and possibly re-train the brain so the patient no longer depends on the FES (carryover effect). Our hypothesis testing was facilitated by the availability of a practical and easy-to-use multi-channel recording system (Smarting [18]) and new array electrodes with quick contacts [19]. The results we present here come from the experimental work in clinical tests with stroke patients. The variables we used to quantitatively assess the achieved function (hand opening and grasping) were the differences in the achieved joint angles and grasping forces between the non-paretic (without stimulation) and paretic hands when stimulated.
Section snippets
Patients
The proposed method was tested as a case series study with three sub-acute stroke patients (Table 1).
The inclusion criteria for the study were as follows: response to electrical stimulation applied via surface electrodes, nonfunctional volitional prehension and grasp, first ever stroke, stable blood pressure and heart rhythm, no implanted stimulators, no known epileptic condition, not participating in other therapy that uses electrical stimulation, and ability to understand and follow
Procedure
The subjects were informed about the experimental procedure and signed the informed consent form approved by the local ethics committee.
Subjects sat in front of a desk with their forearm supported and the elbow joint maintained at an angle of approximately 110°. Two EMG array electrodes were positioned on the dorsal and volar side of the nonparetic forearm, covering the innervation zones of wrist and fingers flexors and extensors (Fig. 4, left panel). The skin was cleaned and prepared with an
Results and discussion
Figs. 5 and 6 show the envelopes of EMG signals from all 48 electrodes, EMG maps at the selected moments and data from the kinematic sensors for the hand-opening and hand-closing task, respectively.
Fig. 7 shows the zones with significant differences between the EMG activity in the nonparetic and paretic arms during the same functional task. If a particular zone on the EMG map of the paretic arm is blue and the corresponding zone on the nonparetic arm is red, then this is a clear indication
Summary
We developed a method for determining the regions over the motor system that can be stimulated for selective functional activation of the hand that is based on a comparison between the EMG activity of the nonparetic and paretic forearms. The actual implementation is foreseen as a two-phase operation (Fig. 11) that includes 1) multi-channel EMG recordings and data processing and 2) stimulation via electrode pads placed at locations selected according to significant differences in the EMG maps
Contributions of the authors
Lana Popović Maneski contributed to the development of the stimulation electrodes, methodology of stimulation and designed the protocol for the study; Ivan Topalović, PhD student, contributed to the EMG recordings and data processing; Nenad Jovičić developed the stimulators, Suzana Dedijer, MD, supervised the measurements and assisted in data analysis, Ljubica Konstantinović, MD, selected patients and supervised the clinical work; and Dejan B. Popović contributed to the idea of using EMG maps
Conflicts of interest
Authors declare no conflicts of interest.
Acknowledgments
The work on this project was partly supported by the Grants III 44008 and TR35003 from the Ministry of Education, Science and Technological Development of Serbia. We thank the company “Tecnalia Serbia” in Belgrade, Serbia for generously providing the electrodes used for the EMG recordings. We thank the company “mBrainTrain” in Belgrade, Serbia for providing us with the Smarting amplifiers and appropriate software support. We thank the company “Axelgaard Manufacturing Co” in Lystrup, Denmark for
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