Su Ling Chong

Long-Term Therapeutic and Orthotic Effects of a Foot Drop Stimulator on Walking Performance in Progressive and Nonprogressive Neurological Disorders

Background. Stimulators applying functional electrical stimulation (FES) to the common peroneal nerve improve walking with a foot drop, which occurs in several disorders. Objective. To compare the orthotic and therapeutic effects of a foot drop stimulator on walking performance of subjects with chronic nonprogressive (eg, stroke) and progressive (eg, multiple sclerosis) disorders. Methods . Subjects with nonprogressive (41) and progressive (32) conditions used a foot drop stimulator for 3 to 12 months while walking in the community. Walking speed was measured with a 10-m test and a 4-minute figure-8 test; physiological cost index (PCI) and device usage were also measured. The subjects were tested with FES on and off (orthotic effect) before and after (therapeutic effect) stimulator use. Results. After 3 months of FES use, the nonprogressive and progressive groups had a similar, significant orthotic effect (5.0% and 5.7%, respectively, P < .003; percentage change in mean values) and therapeutic effect with FES off (17.8% and 9.1%, respectively, P < .005) on figure-8 walking speed. Overall, PCI showed a decreasing trend ( P = .031). The therapeutic effect on figure-8 speed diverged later between both groups to 28.0% (P < .001) and 7.9% at 11 months. The combined therapeutic plus orthotic effect on figure-8 speed at 11 months was, respectively, 37.8% (P < .001) and 13.1% (P = .012); PCI decreased 18.2% (P = .038) and 6.5%, respectively. Conclusions. Subjects with progressive and nonprogressive disorders had an orthotic benefit from FES up to 11 months. The therapeutic effect increased for 11 months in nonprogressive disorders but only for 3 months in progressive disorders. The combined effect remained significant and clinically relevant.

Does Functional Electrical Stimulation for Foot Drop Strengthen Corticospinal Connections

Background. Long-term use of a foot-drop stimulator applying functional electrical stimulation (FES) to the common peroneal nerve improves walking performance even when the stimulator is off. This “therapeutic” effect might result from neuroplastic changes. Objective. To determine the effect of long-term use of a foot-drop stimulator on residual corticospinal connections in people with central nervous system disorders. Methods. Ten people with nonprogressive disorders (eg, stroke) and 26 with progressive disorders (eg, multiple sclerosis) used a foot-drop stimulator for 3 to 12 months while walking in the community. Walking performance and electrophysiological variables were measured before and after FES use. From the surface electromyogram of the tibialis anterior muscle, we measured the following: (1) motor-evoked potential (MEP) from transcranial magnetic stimulation over the motor cortex, (2) maximum voluntary contraction (MVC), and (3) maximum motor wave (Mmax) from stimulating the common peroneal nerve. Results. After using FES, MEP and MVC increased significantly by comparable amounts, 50% and 48%, respectively, in the nonprogressive group and 27% and 17% in the progressive group; the changes were positively correlated (R 2 = .35; P < .001). Walking speed increased with the stimulator off (therapeutic effect) by 24% (P = .008) and 7% (P = .014) in the nonprogressive and progressive groups, respectively. The changes in Mmax were small and not correlated with changes in MEP. Conclusions. The large increases in MVC and MEP suggest that regular use of a foot-drop stimulator strengthens activation of motor cortical areas and their residual descending connections, which may explain the therapeutic effect on walking speed.

Intermittent electrical stimulation redistributes pressure and promotes tissue oxygenation in loaded muscles of individuals with spinal cord injury

Deep tissue injury (DTI) is a severe form of pressure ulcer that originates at the bone-muscle interface. It results from mechanical damage and ischemic injury due to unrelieved pressure. Currently, there are no established clinical methods to detect the formation of DTI. Moreover, despite the many recommended methods for preventing pressure ulcers, none so far has significantly reduced the incidence of DTI. The goal of this study was to assess the effectiveness of a new electrical stimulation-based intervention, termed intermittent electrical stimulation (IES), in ameliorating the factors leading to DTI in individuals with compromised mobility and sensation. Specifically, we sought to determine whether IES-induced contractions in the gluteal muscles can 1) reduce pressure in tissue surrounding bony prominences susceptible to the development of DTI and 2) increase oxygenation in deep tissue. Experiments were conducted in individuals with spinal cord injury, and two paradigms of IES were utilized to induce contractions in the gluteus maximus muscles of the seated participants. Changes in surface pressure around the ischial tuberosities were assessed using a pressure-sensing mattress, and changes in deep tissue oxygenation were indirectly assessed using T₂*-weighted magnetic resonance imaging (MRI) techniques. Both IES paradigms significantly reduced pressure around the bony prominences in the buttocks by an average of 10-26% (P < 0.05). Furthermore, both IES paradigms induced significant increases in T₂* signal intensity (SI), indicating significant increases in tissue oxygenation, which were sustained for the duration of each 10-min trial (P < 0.05). Maximal increases in SI ranged from 2-3.3% (arbitrary units). Direct measurements of oxygenation in adult rats revealed that IES produces up to a 100% increase in tissue oxygenation. The results suggest that IES directly targets factors contributing to the development of DTI in people with reduced mobility and sensation and may therefore be an effective method for the prevention of deep pressure ulcers.

Effects of Intermittent Electrical Stimulation on Superficial Pressure, Tissue Oxygenation, and Discomfort Levels for the Prevention of Deep Tissue Injury

The overall goal of this project is to develop effective methods for the prevention of deep tissue injury (DTI). DTI is a severe type of pressure ulcer that originates at deep bone–muscle interfaces as a result of the prolonged compression of tissue. It afflicts individuals with reduced mobility and sensation, particularly those with spinal cord injury. We previously proposed using a novel electrical stimulation paradigm called intermittent electrical stimulation (IES) for the prophylactic prevention of DTI. IES-induced contractions mimic the natural repositioning performed by intact individuals, who subconsciously reposition themselves as a result of discomfort due to prolonged sitting. In this study, we investigated the effectiveness of various IES paradigms in reducing pressure around the ischial tuberosities, increasing tissue oxygenation throughout the gluteus muscles, and reducing sitting discomfort in able-bodied volunteers. The results were compared to the effects of voluntary muscle contractions and conventional pressure relief maneuvers (wheelchair push-ups). IES significantly reduced pressure around the tuberosities, produced significant and long-lasting elevations in tissue oxygenation, and significantly reduced discomfort produced by prolonged sitting. IES performed as well or better than both voluntary contractions and chair push-ups. The results suggest that IES may be an effective means for the prevention of DTI.

The Effects of Intermittent Electrical Stimulation on the Prevention of Deep Tissue Injury: Varying Loads and Stimulation Paradigms

A pressure ulcer is a medical complication that arises in persons with decreased mobility and/or sensation. Deep pressure ulcers starting at the bone-muscle interface are the most dangerous, as they can cause extensive damage before showing any signs at the skin surface. We previously proposed a novel intervention called intermittent electrical stimulation (IES) for the prevention of deep tissue injury (DTI). In this study, we tested the effects of four paradigms of IES and one conventional pressure relief paradigm in preventing the formation of deep pressure ulcers in rats. Loading equivalent to 18, 28, or 38% of the body weight (BW) of each rat was applied to the triceps surae muscle in one hind limb. Treatment groups received IES every 10 min for either (i) 5 or 10 s with moderate or maximal contraction, or (ii) complete pressure removal every 10 min for 10 s (conventional pressure relief). The results showed that conventional pressure relief, emulating a wheelchair push-up every 10 min, was inadequate for the prevention of DTI. In contrast, all IES paradigms were equally effective in significantly reducing the extent of deep muscle damage caused by 28 or 38% BW pressure application. These findings suggest that, in conjunction with existing techniques, IES may be an effective intervention for the prophylactic prevention of DTI.

Modulation of corticospinal input to the legs by arm and leg cycling in people with incomplete spinal cord injury

The spinal cervico-lumbar interaction during rhythmic movements in humans has recently been studied; however, the role of arm movements in modulating the corticospinal drive to the legs is not well understood. The goals of this study were to investigate the effect of active rhythmic arm movements on the corticospinal drive to the legs (study 1) and assess the effect of simultaneous arm and leg training on the corticospinal pathway after incomplete spinal cord injury (iSCI) (study 2). In study 1, neurologically intact (NI) participants or participants with iSCI performed combinations of stationary and rhythmic cycling of the arms and legs while motor evoked potentials (MEPs) were recorded from the vastus lateralis (VL) muscle. In the NI group, arm cycling alone could facilitate the VL MEP amplitude, suggesting that dynamic arm movements strongly modulate the corticospinal pathway to the legs. No significant difference in VL MEP between conditions was found in participants with iSCI. In study 2, participants with iSCI underwent 12 wk of electrical stimulation-assisted cycling training: one group performed simultaneous arm and leg (A&L) cycling and the other legs-only cycling. MEPs in the tibialis anterior (TA) muscle were compared before and after training. After training, only the A&L group had a significantly larger TA MEP, suggesting increased excitability in the corticospinal pathway. The findings demonstrate the importance of arm movements in modulating the corticospinal drive to the legs and suggest that active engagement of the arms in lower limb rehabilitation may produce better neural regulation and restoration of function.NEW & NOTEWORTHY This study aimed to demonstrate the importance of arm movements in modulating the corticospinal drive to the legs. It provides direct evidence in humans that active movement of the arms could facilitate corticospinal transmission to the legs and, for the first time, shows that facilitation is absent after spinal cord injury. Active engagement of the arms in lower limb rehabilitation increased the excitability of the corticospinal pathway and may produce more effective improvement in leg function.

NON-GAIT SPECIFIC INTERVENTION FOR THE REHABILITATION OF WALKING AFTER SCI: ROLE OF THE ARMS

Arm movements modulate leg activity and improve gait efficiency; however, current rehabilitation interventions focus on improving walking through gait-specific training and do not actively involve the arms. The goal of this project was to assess the effect of a rehabilitation strategy involving simultaneous arm and leg cycling on improving walking after incomplete spinal cord injury (iSCI). We investigated the effect of 1) non-gait-specific training and 2) active arm involvement during training on changes in over ground walking capacity. Participants with iSCI were assigned to simultaneous arm-leg cycling (A&L) or legs only cycling (Leg) training paradigms, and cycling movements were assisted with electrical stimulation. Overground walking speed significantly increased by 0.092 ± 0.022 m/s in the Leg group and 0.27 ± 0.072m/s in the A&L group after training. Whereas the increases in the Leg group were similar to those seen after current locomotor training strategies, increases in the A&L group were significantly larger than those in the Leg group. Walking distance also significantly increased by 32.12 ± 8.74 m in the Leg and 91.58 ± 36.24 m in the A&L group. Muscle strength, sensation, and balance improved in both groups; however, the A&L group had significant improvements in most gait measures and had more regulated joint kinematics and muscle activity after training compared with the Leg group. We conclude that electrical stimulation-assisted cycling training can produce significant improvements in walking after SCI. Furthermore, active arm involvement during training can produce greater improvements in walking performance. This strategy may also be effective in people with other neural disorders or diseases. NEW & NOTEWORTHY This work challenges concepts of task-specific training for the rehabilitation of walking and encourages coordinated training of the arms and legs after spinal cord injury. Cycling of the legs produced significant improvements in walking that were similar in magnitude to those reported with gait-specific training. Moreover, active engagement of the arms simultaneously with the legs generated nearly double the improvements obtained by leg training only. The cervico-lumbar networks are critical for the improvement of walking.

The Effect of Cervico-lumbar Coupling on Spinal Reflexes during Cycling after Incomplete Spinal Cord Injury

Spinal networks in the cervical and lumbar cord are actively coupled during locomotion to coordinate arm and leg activity. The goals of this project were to investigate the intersegmental cervicolumbar connectivity during cycling after incomplete spinal cord injury (iSCI) and to assess the effect of rehabilitation training on improving reflex modulation mediated by cervicolumbar pathways. Two studies were conducted. In the first, 22 neurologically intact (NI) people and 10 people with chronic iSCI were recruited. The change in H-reflex amplitude in flexor carpi radialis (FCR) during leg cycling and H-reflex amplitude in soleus (SOL) during arm cycling were investigated. In the second study, two groups of participants with chronic iSCI underwent 12 wk of cycling training: one performed combined arm and leg cycling (A&L) and the other legs only cycling (Leg). The effect of training paradigm on the amplitude of the SOL H-reflex was assessed. Significant reduction in the amplitude of both FCR and SOL H-reflexes during dynamic cycling of the opposite limbs was found in NI participants but not in participants with iSCI. Nonetheless, there was a significant reduction in the SOL H-reflex during dynamic arm cycling in iSCI participants after training. Substantial improvements in SOL H-reflex properties were found in the A&L group after training. The results demonstrate that cervicolumbar modulation during rhythmic movements is disrupted in people with chronic iSCI; however, this modulation is restored after cycling training. Furthermore, involvement of the arms simultaneously with the legs during training may better regulate the leg spinal reflexes. NEW & NOTEWORTHY This work systematically demonstrates the disruptive effect of incomplete spinal cord injury on cervicolumbar coupling during rhythmic locomotor movements. It also shows that the impaired cervicolumbar coupling could be significantly restored after cycling training. Actively engaging the arms in rehabilitation paradigms for the improvement of walking substantially regulates the excitability of the lumbar spinal networks. The resulting regulation may be better than that obtained by interventions that focus on training of the legs only.