Mechanical and metabolic changes in gait permormance with spinal cord stimulation and reflex-FES

In a previous study, we demonstrated that the application of lumbar epidural spinal cord stimulation (ESCS) produced marked improvements in walking performance of a tetraplegic with incomplete spinal cord injury (ISCI). The present study seeks to extend these results, as well as to compare the enhancement in walking performance provided by ESCS with that offered by reflex functional electrical stimulation (FES). A 48 year old ISCI participant (T8, ASIA C, 8 years post-injury) was provided with several months of partial weight bearing therapy (PWBT) with and without FES, followed by over-ground training assisted by ESCS and FES. Over-ground walking performance and metabolic response was subsequently evaluated under four conditions: no stimulation (NS), FES, ESCS, and ESCS+FES. Performance measures included: gait kinematics, average walking speed, maximum walking distance, pulmonary gas exchange, and the reliance on assistive devices. Stimulation of any type markedly improved locomotion, and reduced the O² cost of transport. FES was associated with a dramatic improvement in limb motion unilaterally, enhancing limb swing, and step length; walking speed and endurance were improved by factors of 2 and 4, respectively, while the O² cost of transport was reduced by 45% versus the NS condition. Despite less significant improvements in movement kinematics, ESCS resulted in further improvements in walking speed and endurance, a 57% reduction in the O² cost of transport, and a reduction in the reliance on the instrumented walker for body weight support. ESCS resulted in a respiratory exchange ratio (RER) suggesting marked reliance on fat oxidation for energy, similar to able-bodied walking at preferred speed. In contrast, FES elicited a CO² production consistent with carbohydrate dependence roughly similar to the NS condition. Superimposing FES on ESCS improved walking speed and endurance while reducing the participant's reliance on the walker for support, but apparently at the expense of greater carbohydrate dependence. We conclude that stimulation of the peripheral and central nervous system can facilitate walking in individuals with ISCI. Further, ESCS may facilitate a neural activation pattern that favors fat metabolism in a manner which more-closely resembles that operating in the able-bodied population.