The “immediate” effect is a relative term. Assessment
at “10 min” after an intervention could be reasonably
called “immediate” with reference to the delayed
analgesic effect observed at the 4-week follow-up visit
after a 5-day tDCS intervention (6).
In this study, each subject received a “sham” or
“active” tDCS conditioning intervention prior to the
BreEStim treatment, but on different days. Therefore,
this is a sham-controlled study. As shown in Fig. 1, we
compared measures before and after each intervention.
It is also a pre-post sham-controlled study.
The authors questioned “the intervention was given
for at least 3 days” and randomization. To clarify, we
explicitly mentioned in the study that “each combined
intervention was given at least 3 days apart and in a
randomized order.” This means that the order of each
combined intervention was randomized. Each subject re-
ceived only one session of each combined intervention.
Two combined interventions were at least 3 days apart.
In addition to VAS assessment, we performed secon-
dary outcome measures, including electrical sensation
threshold and electrical pain threshold. As reported in
Clinicaltrials.gov, there were great variations in both
measures. Given the impaired sensation in subjects
with SCI, we were not sure how informative this set of
data was. It was reported on Clinicaltrials.gov, but not
in the article. The primary goal was whether combined
tDCS and BreEStim could yield additive analgesic ef-
fects. VAS was appropriate for this goal.
BreEStim was applied to the median nerve in this
study. However, we do not agree with the authors that
623
BreEStim produces analgesic effects only for the arm.
Our recent series of experiments has provided evidence
that BreEStim has central analgesic effects in pain-
free healthy subjects (7–9) and in subjects with SCI
(10, 11). This study provided further evidence for this
central analgesic effect.
The authors questioned the use of the term “ap-
proximately” to describe the duration of BreEStim
treatment. In contrast to tDCS treatment, the duration
of which was pre-set by the experimenter, electrical
stimulation was triggered by voluntary breathing of the
subjects in the BreEStim treatment. Subjects performed
BreEStim at their own pace. As explicitly described,
sufficient rest was allowed during the BreEStim treat-
ment. Due to this methodology, the best way to standar-
dize the dose or “duration” of the BreEStim treatment
was to control the number of electrical stimuli, rather
than the duration. In this study, every subject received
160 electrical stimuli during BreEStim; approximately
20 min with rest.
With regard to the statistical analysis, we were aware
that VAS is an ordinal scale. We provided the rationale
for this, with literature support, in the study.
Shengai Li, Argyrios Stampas, Joel Frontera, Matthew Davis
and Sheng Li
From the Department of Physical Medicine and Rehabilita-
tion, McGovern Medical School, University of Texas, Health
Science Center, 77025 Houston, USA.
E-mail: [email protected]
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Letter to the Editor
J Rehabil Med 51, 2019