Impact of respiratory muscle training on sleep disordered breathing in people with tetraplegia: A sub-analysis of a randomised controlled trial

Study Design: Sub-analysis of a randomised controlled trial. Objectives: Respiratory muscle training (RMT) in people with tetraplegia yields marked improvements in inspiratory muscle strength. The present study investigated whether RMT also modifies sleep disordered breathing (SDB) and daytime sleepiness. Setting: Independent research institute in Sydney, Australia. Methods: Sixty-two adults with tetraplegia underwent six weeks of supervised RMT. The active-RMT group trained the respiratory muscles through progressive threshold loading to a mean intensity of 50% maximal inspiratory pressure whereas the sham-RMT group experienced the same training protocol, but their device had no progressive threshold load. Primary measures of SDB were obtained using level II ambulatory polysomnograms and daytime sleepiness was assessed using the Epworth Sleepiness Score (ESS). Results: Forty-eight participants completed two home-based polysomnograms. Maximal inspiratory pressure (primary outcome) increased more after active intervention than sham, between-group difference 11.8cmH2O (95%CI, 5.2 to 18.4, p=0.001). There were no between group differences for any SDB parameter from baseline to 6-weeks (p=0.173 to p=0.935; e.g. mean apnoea-hypopnea index (±SD): active 46 ± 21 vs. 45 ± 22 events/h; sham 44 ± 25 vs. 40 ± 25 events/h; p=0.553) and ESS: active 9.5 ± 5.7 vs. 9.2 ± 6.7; sham 10.8 ± 6.2 vs. 10.1 ± 5.8; p=0.952. Conclusions: Despite significant increases in inspiratory muscle strength, 6 weeks of supervised respiratory muscle training at a mean intensity of 50% maximal inspiratory pressure does not reduce SDB or daytime sleepiness in people with tetraplegia and severe SDB.