Compensatory muscle activation during forced respiratory tasks in individuals with chronic spinal cord injury

When lesions in the spinal cord occur, the neural activation of respiratory muscles is compromised (De Troyer and Heilporn, 1980; De Troyer et al., 1986, 1990; Estenne et al., 2000a) resulting in significant respiratory dysfunction (De Troyer and Heilporn, 1980; Linn et al., 2000, 2001; Yokoba et al., 2003). However the underlying mechanisms that contribute to this dysfunction remain unclear. The aims of this study were: (1) to investigate whether a correlation exists between pulmonary function and the International Standards for the Neurological Classification of Spinal Cord Injury (ISNCSCI) examination scores for sensory and motor function; (2) to evaluate whether compensatory muscle activation plays a role in pulmonary function after spinal cord injury (SCI). We recorded Forced Vital Capacity (FVC); Forced Expiratory Volume in 1s (FEV1); and electromyography (EMG) of respiratory muscles during maximum respiratory tasks in 36 with SCI and 15 neurologically intact participants. Results indicate that pulmonary function (FVC, FEV1) was strongly correlated with motor and sensory scores from the ISNCSCI exam and maximal expiratory pressure (MEP) was also significantly related to ISNCSCI sensory scores (ρ=0.73, p<.001) and moderately, but significantly correlated to motor scores (ρ=0.41, p=.04). After SCI, there is a compensatory recruitment of accessory muscles upper trapezius during maximal inspiratory pressure (MIP) and pectoralis and latissimus dorsi during MEP that is significantly higher than in non-injured (p<.001).