Effect of Respiratory Muscle Training on the Perception of Inspiratory Resistive Loads in People with Chronic Tetraplegia
Authors List
Billy L. Luu1, R.H. Chaminda Lewis1,2,3, Rachel A. McBain1, Simon C. Gandevia1,2,3, Claire L. Boswell-Ruys1,2,3, and Jane E. Butler1,2.
1. Neuroscience Research Australia, Randwick, NSW, Australia. 2. University of New South Wales, Sydney, NSW, Australia. 3. Prince of Wales Hospital, Randwick, NSW, Australia.
The loss of respiratory muscle strength in tetraplegia leads to impaired breathing, but it is not clear whether sensations of breathing are also impaired. Two separate studies were performed. In both studies, sensations of breathing were quantified by first determining the detection threshold of an added resistance during inspiration and then having participants report the perceived magnitudes of six suprathreshold loads using a modified Borg scale of effort ratings.
Fifteen people with chronic tetraplegia and fifteen matched, able-bodied controls participated in the first study. The tetraplegia group had a higher detection threshold of 1.17 cmH2O/l/s (95% CI, 1.00 to 1.34) compared to 0.78 cmH2O/l/s (95% CI, 0.61 to 0.95) for able-bodied controls (p = 0.004). Larger loads were perceived to be more effortful by both participant groups, with Borg rating increasing linearly with peak inspiratory pressure (force).
This linear relationship was steeper in participants with tetraplegia than able-bodied controls (p = 0.001), but there was no difference between groups when pressure was divided by maximal inspiratory pressure (PImax) to account for differences in contraction intensity (p = 0.95). In the subsequent study, a secondary analysis was performed on thirty-two people with chronic tetraplegia who participated in a randomised controlled trial based on a six-week intervention of respiratory muscle training. The active group who underwent progressive threshold loading increased their PImax by 32% (95% CI, 18 to 45) whereas the sham group who trained with a fixed threshold load of 3.6 cmH2O showed no change in PImax (p = 0.51).
The training intervention had no effect on detection thresholds in the active (p = 0.24) or sham (p = 0.77) groups. Increased inspiratory muscle strength reduced the slope of the linear relationship between Borg rating and peak inspiratory pressure (p = 0.003), but not when pressure was divided by PImax (p = 0.92). These findings suggest that the higher detection threshold in people with chronic tetraplegia is not related to their weaker inspiratory muscles.
Differences in the sensitivity (slope) of perceived magnitudes for a given change in peak inspiratory pressure between people with tetraplegia and able-bodied controls, as well as in people with tetraplegia after their inspiratory muscle strength improved, were accounted for when peak inspiratory pressure was expressed relative to PImax to reflect contraction intensity.
This suggests that the ability to estimate the magnitude of an added inspiratory load is not impaired in chronic tetraplegia, and that the perceived magnitude is related to the maximal, and not absolute, inspiratory muscle force.
Funding sources: National Health and Medical Research Council of Australia and the Prince of Wales Hospital Foundation.
Billy L. Luu1, R.H. Chaminda Lewis1,2,3, Rachel A. McBain1, Simon C. Gandevia1,2,3, Claire L. Boswell-Ruys1,2,3, and Jane E. Butler1,2.
1. Neuroscience Research Australia, Randwick, NSW, Australia. 2. University of New South Wales, Sydney, NSW, Australia. 3. Prince of Wales Hospital, Randwick, NSW, Australia.
The loss of respiratory muscle strength in tetraplegia leads to impaired breathing, but it is not clear whether sensations of breathing are also impaired. Two separate studies were performed. In both studies, sensations of breathing were quantified by first determining the detection threshold of an added resistance during inspiration and then having participants report the perceived magnitudes of six suprathreshold loads using a modified Borg scale of effort ratings.
Fifteen people with chronic tetraplegia and fifteen matched, able-bodied controls participated in the first study. The tetraplegia group had a higher detection threshold of 1.17 cmH2O/l/s (95% CI, 1.00 to 1.34) compared to 0.78 cmH2O/l/s (95% CI, 0.61 to 0.95) for able-bodied controls (p = 0.004). Larger loads were perceived to be more effortful by both participant groups, with Borg rating increasing linearly with peak inspiratory pressure (force).
This linear relationship was steeper in participants with tetraplegia than able-bodied controls (p = 0.001), but there was no difference between groups when pressure was divided by maximal inspiratory pressure (PImax) to account for differences in contraction intensity (p = 0.95). In the subsequent study, a secondary analysis was performed on thirty-two people with chronic tetraplegia who participated in a randomised controlled trial based on a six-week intervention of respiratory muscle training. The active group who underwent progressive threshold loading increased their PImax by 32% (95% CI, 18 to 45) whereas the sham group who trained with a fixed threshold load of 3.6 cmH2O showed no change in PImax (p = 0.51).
The training intervention had no effect on detection thresholds in the active (p = 0.24) or sham (p = 0.77) groups. Increased inspiratory muscle strength reduced the slope of the linear relationship between Borg rating and peak inspiratory pressure (p = 0.003), but not when pressure was divided by PImax (p = 0.92). These findings suggest that the higher detection threshold in people with chronic tetraplegia is not related to their weaker inspiratory muscles.
Differences in the sensitivity (slope) of perceived magnitudes for a given change in peak inspiratory pressure between people with tetraplegia and able-bodied controls, as well as in people with tetraplegia after their inspiratory muscle strength improved, were accounted for when peak inspiratory pressure was expressed relative to PImax to reflect contraction intensity.
This suggests that the ability to estimate the magnitude of an added inspiratory load is not impaired in chronic tetraplegia, and that the perceived magnitude is related to the maximal, and not absolute, inspiratory muscle force.
Funding sources: National Health and Medical Research Council of Australia and the Prince of Wales Hospital Foundation.
