To the Editor:
In the November 1999 issue of Physical Therapy, Lin et al1 published an interesting article about the cough threshold in people with spinal cord injuries (SCIs). They justified the investigation based on the fact that interruption of sympathetic outflow in these people conducts to an unopposed vagal tone, possibly resulting in an increase in cough sensitivity. They concluded that there is a decrease in the cough threshold in individuals with SCI, besides the additional information that smoking could also increase this sensitivity.
Unfortunately, to completely validate their results and conclusions, the authors omitted 2 important questions about the studied population: the specific level of lesion and the use of baclofen. They reported that they studied 26 people with SCI—13 with cervical spinal cord lesions and 13 with thoracic spinal cord lesions (C4–T12). It is essential to know the exact level of the lesion in the people with paraplegia because we know that the imbalance between vago-sympathetic components occurs only in lesions above the T6 level.2
As for baclofen, a potent gamma-aminobutyric acid (GABA) agonist frequently used by people with SCIs to control spasticity, recent studies have demonstrated its antitussive activity3 and inhibition of bronchial hyperresponsiveness to methacholine in people with quadriplegia.4 In a recent survey in our SCI ward, 60% (30/50) of the patients were using baclofen. We would appreciate knowing the specific level of lesion and baclofen use of the subjects in the study by Lin et al.
- Physical Therapy
References
Author Response:
In response to the letter from Dr Beraldo and colleagues, I appreciate that they have raised 2 important questions about our study. I would like to make some clarification of our study. First, it is true that the sympathetic nerve supplying to the lung originates from the upper thoracic segments, but the sympathetic preganglionic neurons are located between the first thoracic and third lumbar segments of the spinal cord.1 We just wonder whether the cough threshold is different in individuals with lower thoracic lesions. Actually, 11 of 13 subjects with paraplegia in our study were injured at or above the T7 level. The other 2 subjects with paraplegia were injured at the T10 and T12 levels, and both of them were smokers. When the data of those 2 subjects are excluded, the mean cough threshold concentration of citric acid in the patients with spinal cord injuries (SCIs) who smoked was 224 mmol, which was close to the previously reported value of 209 mmol. Accordingly, our data do not show that there was a markedly different cough threshold between subjects with lower thoracic lesions who smoked and subjects with upper thoracic lesions who smoked.
Second, the effect of baclofen (GABA-agonist) on cough threshold should be considered. In our study, all 26 subjects with SCIs (13 with quadriplegia and 13 with paraplegia) did not take baclofen for control of spasticity during the study period. Therefore, our results were not confounded by baclofen. Further studies are suggested to evaluate the effect of baclofen on cough threshold in patients with SCIs.
