A Wearable System for Attenuating Essential Tremor Based on Peripheral Nerve Stimulation

Abstract

Objective: Currently available treatments for kinetic tremor can cause intolerable side effects or be highly invasive and expensive. Even though several studies have shown the positive effects of external feedback (i.e., electrical stimulation) for suppressing tremor, such approaches have not been fully integrated into wearable real-time feedback systems. Method: We have developed a wireless wearable stimulation system that analyzes upper limb tremor using a three-axis accelerometer and that modulates/attenuates tremor using peripheral-nerve electrical stimulation with adjustable stimulation parameters and a real-time tremor detection algorithm. We outfitted nine subjects with tremor with a wearable system and a set of surface electrodes placed on the skin overlying the radial nerve and tested the effects of stimulation with nine combinations of parameters for open-and closed-loop stimulation on tremor. To quantify the effects of the stimulation, we measured tremor movements, and analyzed the dominant tremor frequency and tremor power. Results:Baseline tremor power gradually decreased over the course of 18 stimulation trials. During the last trial, compared with the control trial, the reduction rate of tremor power was 42.17 ± 3.09%. The dominant tremor frequency could be modulated more efficiently by phase-locked closed-loop stimulation. The tremor power was equally reduced by open-and closed-loop stimulation. Conclusion: Peripheral nerve stimulation significantly affects tremor, and stimulation parameters need to be optimized to modulate tremor metrics. Clinical Impact: This preliminary study lays the foundation for future studies that will evaluate the efficacy of the proposed closed-loop peripheral nerve stimulation method in a larger group of patients with kinetic tremor. INDEX TERMS Essential tremor, kinetic tremor, tremor measurement, tremor modulation, wearable peripheral nerve electrical stimulation.

Intramuscular Stimulation of Muscle Afferents Attains Prolonged Tremor Reduction in Essential Tremor Patients

“…The tremor reduction results observed at the end of IntraStim sessions (short-term effect) are in line with the results reported by others using SurfStim [10]- [12], [28]. All patients who received SATS during IntraStim session (6 out of 6) reduced their tremor during the assessment after the experiment (post-ASSESS), and some of them held this reduction even 24 h after the stimulation session (post24-ASSESS).…”

Peripheral electrical stimulation to reduce pathological tremor: a review

“…Among the review articles, ten studies reported the effects of peripheral electrical stimulation results on patients with ET [18][19][20][21][22][23][24][25][26][27] while ten studies reported on patients with PD [28][29][30][31][32][33][34][35][36][37] and seven studies included both patients with ET and patients with PD [16,17,[38][39][40][41][42]. In order to compare electrical stimulation strategies, some studies also included healthy volunteers that either mimicked tremorgenic activity during experimentation or were subject to artificially induced tremors for experimentation [31,38,41].…”

“…There are two outliers for the minimum stimulation frequency, Spiegel et al [37], who tested at 2 Hz, 3 Hz, and 5 Hz, and Munhoz et al [18], who tested at 5 Hz, 10 Hz, 50 Hz, and 100 Hz. Certain studies have tested varying the stimulation frequencies while maintaining other stimulation parameters in order to determine optimal tremor reduction values [18,25]. The pulse width is another stimulation parameter and is defined as the duration of each electrical stimulus applied.…”

“…Lin et al [23] and Pahwa et al [24] applied a duty cycle equivalent to half of the tremor period. Dideriksen et al [42] and Kim et al [25] tested the effect of several duty cycle values: 20% and 40%; and 12.5%, 25% and 37%; respectively.…”

“…Alternatively, electrical stimulation of the nerves has been explored instead of stimulation of the muscle belly. The main nerves stimulated were the distal branches of the radial nerve at the hand [25,31,32], median nerve at the elbow [38], median and ulnar nerves at the wrist [37], median and radial nerves at the arm [27], or a combined stimulation of radial and median nerves in the same session through a wearable device at the wrist [23,24,26].…”