Dear Dr. Chan
We would like to thank you for the opportunity to respond to the issues raised in the Letter. We would also like to express our appreciation to Dr. West and Mr. Gee for the interest in our work.
The objective of the reported study was to investigate if our original reciprocal respiratory training approach, already reported to be effective in improving blood pressure regulation in individuals with SCI-induced orthostatic hypotension2, can affect baroreflex function which is often deconditioned in the general SCI population. Study groups intentionally included participants with different levels and severity of injury with a variety of respiratory-cardiovascular functional states. Since respiratory motor function was not the primary point of interest, maximum airway pressure values were not reported, but will be when we address specific mechanisms related to respiratory motor control in future publications.
As acknowledged, the sample of participants in the intervention and control groups was functionally heterogeneous, with a variety of levels and severity of injury. That is why, in order to control for variability within groups, a multivariate linear regression model was used to test for significance. A simple Student’s t-test is not appropriate in this case. The role played by level and severity of injury on changes in pulmonary function, baroreflex, and heart rate variability outcomes after training was elucidated in Table 3.
It is correct that only a few individuals in our sample exhibited orthostatic intolerance at baseline and it was not significantly changed after training. However, orthostatic intolerance is not the only marker of cardiovascular dysfunction.
We appreciate the recognition that “the data provided speaks to a fascinating area of research on the interaction of the cardiovascular and respiratory systems following SCI”. Indeed, impaired baroreflex and decreased heart rate variability are predictors for future cardiac events3,4. We found significant improvement to baroreflex sensitivity and heart rate variability induced by respiratory training. Therefore, these findings suggest respiratory training is a promising direction in respiratory-cardiovascular rehabilitation for patients with chronic SCI.
References
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