Evaluation of respiratory muscle activation in individuals with chronic spinal cord injury

This study was undertaken to physiologically characterize respiratory muscle control in eighteen individuals with spinal cord injury (SCI) through comparison with 14 matched non-injured (NI) subjects. Standard pulmonary function measures (FVC, FEV1, PImax and PEmax) were obtained along with surface electromyographic (sEMG) recording from respiratory muscles. A vector analysis of sEMG was used to calculate Similarity Index (SI) values relating SCI subject sEMG patterns to those produced by NI subjects. SI values for inspiratory and expiratory tasks were very consistent within the NI group, 0.92 ± 0.03 and 0.93 ± 0.04 (mean ± SD), respectively. Altered multi-muscle patterns in the SCI group produced SI values that trended lower 0.84 ± 0.11 for inspiratory tasks and were significantly lower, 0.59 ± 0.22 for expiratory tasks. SI values for expiratory tasks were also significantly correlated with SCI levels and pulmonary function measures. These results suggest that pulmonary function after SCI is dependent upon the degree to which multi-muscle activation patterns are disrupted.