Variation of Finger Activation Patterns Post-stroke Through Non-invasive Nerve Stimulation

Way too many big words used to have any clue on how to explain this to therapists and doctors for our use.  I see no objective damage diagnosis that would point to which patients this would work on. Without that, this research is not repeatable and thus useless. 

Variation of Finger Activation Patterns Post-stroke Through Non-invasive Nerve Stimulationh

Henry Shin, Yang Zheng and Xiaogang Hu^*

• Joint Department of Biomedical Engineering, University of North Carolina at Chapel Hill and North Carolina State University, Raleigh, NC, United States

Purpose: A transcutaneous proximal nerve stimulation technique utilizing an electrode grid along the nerve bundles has previously shown flexible activation of multiple fingers. This case study aimed to further demonstrate the ability of this novel stimulation technique to induce various finger grasp patterns in a stroke survivor.

Methods: An individual with chronic hemiplegia and severe hand impairment was recruited. Electrical stimulation was delivered to different pairs of an electrode grid along the ulnar and median nerves to selectively activate different finger flexor muscles, with an automated electrode switching method. The resultant individual isometric flexion forces and forearm flexor high-density electromyography (HDEMG) were acquired to evaluate the finger activation patterns. A medium and low level of overall activation were chosen to gauge the available finger patterns for both the contralateral and paretic hands. All the flexion forces were then clustered to categorize the different types of grasp patterns.

Results: Both the contralateral and paretic sides demonstrated various force clusters including single and multi-finger activation patterns. The contralateral hand showed finger activation patterns mainly centered on median nerve activation of the index, middle, and ring fingers. The paretic hand exhibited fewer total activation patterns, but still showed activation of all four fingers in some combination.

Conclusion: Our results show that electrical stimulation at multiple positions along the proximal nerve bundles can elicit a select variety of finger activation patterns even in a stroke survivor with minimal hand function. This system could be further implemented for better rehabilitative training to help induce functional grasp patterns or to help regain muscle mass.

Introduction

Following a stroke, a majority of individuals have paresis due to a loss of excitatory input and subsequent complications, such as disuse atrophy (1) and altered spinal organization (2–4). This loss of voluntary control of muscle activation often limits activities of daily living. Neuromuscular electrical stimulation (NMES) has been widely utilized both in the clinic and in research settings to help restore atrophied muscle and lost functions (5–7). Electrical stimulation has been particularly successful with post-stroke survivors for functional recovery (8–10). Research in NMES also aims to restore functional activation of muscles, such as the restoration of hand grasps (11).

Traditionally, NMES uses large electrode pads, targeting the distal branches of the nerve, known as the motor point stimulation (12). Although stimulation of the motor point is straightforward methodologically, NMES is limited to localized muscle activation, which limits its functional efficacy and also leads to rapid muscle fatigue (13). Advances in NMES techniques to alleviate these issues involve various multi-electrode techniques, which can stimulate multiple small regions of the muscle to help distribute the current and potentially activate more muscle fibers (14, 15). Crema et al. has also demonstrated flexible activation of multiple fingers using a multi-electrode array across the forearm and hand (16). Other approaches to NMES involve stimulation of the nerve bundle prior to branching and innervating a muscle, which has shown to allow for a larger area of muscle activation and potentially reduce long-term fatigue effects (17–19).

Recent developments have demonstrated the capabilities of an alternative non-invasive transcutaneous electrical nerve stimulation method targeting the ulnar and median nerves proximal to the elbow to flexibly activate individual and multiple fingers (20, 21). In addition, this technique shows the ability to delay the force decline (22, 23). A stimulation electrode grid placed along the two nerves allows us to activate different muscles or muscle portions to elicit varied desired movements, but manually switching between different electrode pairs is time-consuming. To shorten this process, an automated electrode pair searching method has been developed and tested on intact control subjects (24). This new method can further categorize the total available sets of finger activation patterns across the entire electrode grid, providing valuable information on electrode selection and the force generation capacity of stroke muscles. However, the efficiency of this method has not been tested on stroke survivors. Therefore, this case study recruited a control subject and a stroke survivor with severe weakness of the right arm, and evaluated the available finger activation patterns of the subjects. Our results showed varied activation of multiple fingers from both subjects. Further development of this stimulation technique can provide valuable alternatives to current rehabilitation for the restoration of hand movements.