Development and evaluation of a two-dimensional electrocutaneous cognitive feedback system for use in paraplegic standing

Abstract

Fatigue of electrically activated paralysed muscles is a major factor limiting the duration of functional electrical stimulation (FES) supported paraplegic standing. Fatigue can be significantly delayed by changing the posture. Since paralysed individuals are deprived of proprio- and exteroception from the lower limbs they are not aware of the posture and loading of their paralysed legs. If suitable cognitive feedback (CF) information about posture in the sagittal and frontal planes is provided, they might be able to successfully exercise posture switching. A two-dimensional electrocutaneous CF system was developed. Relative limb loading and the location of the weighted centre of pressure were selected as informational variables. Discrete encoding schemes in the form of spatial and frequency codes were employed and the informational signals were divided into three sub-regions. The ability to correctly interpret the CF was investigated using one- and two-dimension tracking tests in three paralysed subjects, each of whom were studied over five consecutive days. All three subjects were able to use the CF in one-dimension tests. Two subjects could do the same also in two-dimension tests. The encoding scheme which was developed to communicate the selected biomechanical variables proved to be easily understood and thus appropriate for use in paraplegic standing.

Restoring standing capabilities with feedback control of functional neuromuscular stimulation following spinal cord injury

“…The typical neuroprosthesis user would have uncompromised visual feedback, but in tact sensory feedback would be restricted to portions of the body innervated above the level of injury. Studies investigating cognitive feedback about whole-body leaning using electrocutaneous [Matjacic, Jensen et al 23] and vibrotactile [Kadkade, Benda et al 24] stimulation to just the skin surface have shown improvement in balance performance. Such findings motivate the development of balance prostheses that augment sensory capabilities of the user such as touch and proprioception in relation to the lower extremities and facilitate the integration of that feedback for whole-body FNS standing control.…”