Automatic determination of parameters for multipad functional electrical stimulation: Application to hand opening and closing

Abstract

Transcutaneous functional electrical stimulation (FES) is a method used for rehabilitation of patients having suffered a stroke or spinal cord injury. When applying FES a common problem is that stimulation electrodes have to be placed with great care in order to avoid activation of muscles close to the target muscles. A promising approach to circumvent this problem is to employ multipad FES, i.e. to employ electrode arrays containing many small electrodes allowing selective activation of muscles. In this work an algorithm is presented which automatically determines subsets of active electrodes and stimulation currents such that movements with user-specified amplitudes are induced. Using a recently developed portable multipad FES system and a virtual reality dataglove, the algorithm was tested with seven able-bodied subjects. Stimulation with parameters determined by the algorithm led to movements with a median deviation of between 0° and 5° from the specified wrist angle and between 0% and 12% from the specified degree of finger flexion.

User-centered practicability analysis of two identification strategies in electrode arrays for FES induced hand motion in early stroke rehabilitation

“…This intelligent procedure might be the right choice when it comes to FES systems in home-use, as it assists the patient in the decision making. The presented automatic search strategy combines algorithm features of previous methods by Hoffmann et al [12] and Schill et al [14]. Our algorithm consists of two phases as illustrated in Fig.…”

“…In heuristic a), the element combinations for testing consisted of all eleven possible combinations of the four best single elements (cf. [12]). The maximum number of elements in an element combination selected with heuristic a) thus is four.…”

“…In most approaches, the evoked motion via twitch or step stimulation is registered and evaluated in a cost function for each tested element or element combination. Such a function can be the fit with a reference trajectory, which was derived from the movement of healthy people [10], the achievement of predefined constraints for the joint angles [11], or the maximum registered joint angle amplitude [12] together with additional restrictions [13]. The existing methods often evaluate only a small number of stimulation intensities [12, 14] and interpolate the outcome with higher stimulation intensities.…”

“…The presented automatic search strategy is examined as an example for the practicability of such approaches in everyday clinical practice. It is an extension and combination of algorithm features from previously published methods by Hoffmann et al [12] and Schill et al [14] for hand movements. A cost function is defined on joint angle constraints and calculated for the stimulation of single elements, and element combinations.…”

Automatic calibration of electrode arrays for dexterous neuroprostheses: a review

“…Also, the inter-subject variability due to never depth, fat thickness, and other intrinsic factors influence the overall stimulation outcome. Hence, it remains an optimization problem to identify suitable electrode combinations and stimulation parameters to customize stimulation delivery that can elicit the desired response [3,9].…”