Longitudinal association between respiratory muscle strength and cough capacity in persons with spinal cord injury: An explorative analysis of data from a randomized controlled trial

Objective: To assess the longitudinal association between respiratory muscle strength and cough capacity in persons with recent spinal cord injury. Design: Longitudinal analyses. Subjects: Forty persons with recent spinal cord injury and impaired pulmonary function. Methods: Measurements were performed 4 weeks after the start of rehabilitation, 9 and 17 weeks after the first measurement, and one year after discharge from inpatient rehabilitation. Peak cough flow was measured with a spirometer. Maximum inspiratory and expiratory pressures (MIP and MEP), expressed in cmH₂O, were measured at the mouth. Results: Both MIP and MEP were significantly positively associated with peak cough flow. After correction for confounders and time 10 cmH₂O higher MIP was associated with a 0.32 l/s higher peak cough flow, and a 10 cmH₂O higher MEP was associated with a 0.15 l/s higher peak cough flow. The association between MIP and peak cough flow was mainly based on within-subject variance. The association between MIP and peak cough flow was stronger than between MEP and peak cough flow. Conclusion: Improvement in respiratory muscle strength is associated with improvement in cough capacity in persons with recent spinal cord injury who have impaired pulmonary function.