Functional electrical stimulation using microstimulators to correct foot drop: a case study.

This paper presents a case study that tested the feasibility and efficacy of using injectable microstimulators (BIONs) in a functional electrical stimulation (FES) device to correct foot drop. Compared with surface stimulation of the common peroneal nerve, stimulation with BIONs provides more selective activation of specific muscles. For example, stimulation of the tibialis anterior (TA) and extensor digitorum longus (EDL) muscles with BIONs produces ankle flexion without excessive inversion or eversion of the foot (i.e., balanced flexion). Efficacy was assessed using a 3-dimensional motion analysis of the ankle and foot trajectories during walking with and without stimulation. Without stimulation, the toe on the affected leg drags across the ground. BION stimulation of the TA muscle and deep peroneal nerve (which innervates TA and EDL) elevates the foot such that the toe clears the ground by 3 cm, which is equivalent to the toe clearance in the less affected leg. The physiological cost index (PCI) measured effort during walking. The PCI equals the change in heart rate (from rest to activity) divided by the walking speed; units are beats per metre. The PCI is high without stimulation (2.29 +/- 0.37, mean +/- SD) and greatly reduced with surface (1.29 +/- 0.10) and BIONic stimulation (1.46 +/- 0.24). Also, walking speed increased from 9.4 +/- 0.4 m/min without stimulation to 19.6 +/- 2.0 m/min with surface and 17.8 +/- 0.7 m/min with BIONic stimulation. These results suggest that FES delivered by a BION is an alternative to surface stimulation and provides selective control of muscle activation.

RF-powered BIONs for stimulation and sensing.

Virtually all bodily functions are controlled by electrical signals in nerves and muscles. Electrical stimulation can restore missing signals but this has been difficult to achieve practically because of limitations in the bioelectric interfaces. Wireless, injectable microdevices are versatile, robust and relatively inexpensive to implant in a variety of sites and applications. Several variants are now in clinical use or under development to perform stimulation and/or sensing functions and to operate autonomously or with continuous coordination and feedback control.

BIONic WalkAide for correcting foot drop.

The goal of this study was to test the feasibility and efficacy of using microstimulators (BIONs) to correct foot drop, the first human application of BIONs in functional electrical stimulation (FES). A prototype BIONic foot drop stimulator was developed by modifying a WalkAide2 stimulator to control BION stimulation of the ankle dorsiflexor muscles. BION stimulation was compared with surface stimulation of the common peroneal nerve provided by a normal WalkAide2 foot drop stimulator. Compared to surface stimulation, we found that BION stimulation of the deep peroneal nerve produces a more balanced ankle flexion movement without everting the foot. A 3-D motion analysis was performed to measure the ankle and foot kinematics with and without stimulation. Without stimulation, the toe on the affected leg drags across the ground. The BIONic WalkAide elevates the foot such that the toe clears the ground by 3 cm, which is equivalent to the toe clearance in the unaffected leg. The physiological cost index (PCI) was used to measure effort during walking. The PCI is high without stimulation (2.29 +/- 0.37; mean +/- S.D.) and greatly reduced with surface (1.29 +/- 0.10) and BION stimulation (1.46 +/- 0.24). Also, walking speed is increased from 9.4 +/- 0.4 m/min. without stimulation to 19.6 +/- 2.0 m/min. with surface and 17.8 +/- 0.7 m/min. with BION stimulation. We conclude that functional electrical stimulation with BIONs is a practical alternative to surface stimulation and provides more selective control of muscle activation.

Mesencephalic projections to the first cervical segment in the cat.

Mesencephalic neurons projecting to the upper cervical spinal cord were examined by mapping the distributions of labeled cells after injecting fluorescent tracers or wheat-germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the C1 segment. Injections into the central or deep regions of the ventral horn produced retrograde labeling in cells of several mesencephalic regions. The majority of cells were found contralaterally in the superior colliculus and red nucleus, and ipsilaterally in and around the interstitial nucleus of Cajal (INC), in the cuneiform region, and in the fields of Forel. Smaller numbers of cells were located in the periaqueductal gray matter, nucleus annularis, and magnocellular nucleus of the posterior commissure. Dorsomedial injections in the ventral horn near the ventral commissure labeled only a subset of these projections, including cells in the mesencephalic reticular formation adjacent to the INC and in the nucleus annularis. Dorsolateral injections labeled some cells in the superior colliculus and were particularly effective at labeling cells in the red nucleus. These results suggest that at least ten different cell groups project to the ventral horn of the first cervical segment. Most, but not all, groups originate from regions implicated previously in the control of eye or head movements.