Neuromodulation for restoration of spinal autonomic functions that increase exercise capacity after spinal cord injury: a systematic scoping review

Abstract

Spinal cord injury results in varying degrees of motor and autonomic dysfunction. Cardiovascular and metabolic diseases are much more prevalent with an earlier onset in persons with spinal cord injury compared to the general population. Physical activity is widely accepted method for maintaining appropriate body weight, composition and overall health. Unfortunately, those living with a cervical or high thoracic spinal cord injury experience mild to severe dysautonomia, limiting their exercise performance and subsequent health benefits. Electrical spinal cord stimulation has been a therapeutic strategy investigated in recent years and has demonstrated beneficial effects on motor function as well as autonomic functions related to bladder, bowel and sexual function. Within the last 15 years, spinal stimulation studies aimed at improving motor function began to include anecdotal reports of improved autonomic functions, such cardiovascular control, metabolism, and exercise performance. This area of research is relatively new, and the neural mechanisms mediating these positive effects and the optimal parameters and stimulus locations have yet to be elucidated. We therefore performed a systematic scoping review to identify what has been reported about the effects of spinal cord stimulation on autonomic functions related to exercise outcomes to help identify knowledge gaps. A total of 1815 unique records were screened for eligibility following an electronic database search of Medline, EMBASE, Scopus, CINAHL and SportDiscus. Based on our inclusion criteria, 21 studies were included in this review. Of these 21 articles, 9 were transcutaneous stimulation studies and 12 were epidural stimulation studies. Improvements in blood pressure regulation, exercise output, thermoregulation, and body composition were reported in multiple studies. However, stimulation locations and parameters were highly variable and the number of participants relatively small. Therefore, further pre-clinical mechanism-based research and studies systematically testing different stimulus locations and parameters with larger numbers of participants are necessary to establish optimal stimulation interventions to improve exercise related autonomic functions.