Respiratory muscle training with NH for patients with chronic SCI
tion parameters. A study by Mueller et al. found that
FEV 1 , PEF and maximal expiratory muscle pressure
generating capacity increased only during inpatient
rehabilitation, but not thereafter (18). However, this
study failed to explore the effect of the rehabilitation
programme, especially the influence of RMT during
inpatient rehabilitation and thereafter. We reasoned
that training of muscle endurance might be more
suitable for patients with chronic SCI, given the slow
progression of hypercapnic respiratory failure, while
training of muscle strength might be more suitable for
those with acute SCI. The improvement in MVV in
the NH group also suggested better endurance com-
pared with the control group (Table II). Two previous
studies have shown the training effects of NH in SCI
with a post-injury time between 2 and 8 months (4, 6).
Mueller et al. found that inspiratory resistance training
is more advantageous than NH regarding maximal
inspiratory pressure, which was not surprising, since
inspiratory resistance training focused on inspiratory
muscle strength (6). To our knowledge, no study has
examined the effect of NH on chronic SCI with a longer
period after injury. Kim et al. considered training of
both thoracic and abdominal muscles to be important
for respiratory function (5). Their study included pa-
tients with SCI with a time post-injury > 3 years. The
combined training showed a greater improvement
compared with RMT focused on muscle strength
alone. Although we did not include a group subjected
to combined training, our results indicate that RMT
with NH might have induced similar improvement as
the combined training, given that the training period
in our study was shorter (4 vs 8 weeks).
Several limitations were identified in the present
study. The patients were not blinded to their group
assignment, which is critical with respect to subjective
evaluations with the questionnaires. Psychological
influences on PROMs were not clear. In addition, the
CAT and SGRQ were not validated in patients with
SCI. Furthermore, no data from previous studies could
be used to assess the sample size for comparing the
effects on lesion levels. Hence, the number of patients
for each lesion level was not considered in the randomi-
zation process. It may be more reasonable to divide
the lesion levels into high, low cervical and thoracic.
However, due to the limited number of patients, the
comparison may not be adequate. Comparison with
other RMT or combined training could be beneficial,
but this was beyond the objective of this study. Further
comparison with other RMT should be considered in
future studies. Last, but not least, the sample size was
small in this randomized study and the current findings
need to be confirmed in a larger one. Nevertheless, the
differences in lung function and quality of life between
619
groups can be used for sample size estimation in future
larger randomization studies.
Conclusion
We suggest that patients with chronic SCI could
consider receiving RMT with NH, even a long period
after injury. NH training may reduce the incidence of
respiratory symptoms, improve pulmonary function
and quality of life, and reduce depression in patients
with chronic SCI, regardless of their neurological level
of injury, even at more than 24 months after injury.
ACKNOWLEDGEMENT
This work was financially supported by the project Beijing
Rehabilitation Hospital of Capital Medical University (No.
2018–16).
Conflicts of interest
Zhanqi Zhao receives a consulting fee from Dräger Medical.
Inéz Frerichs reports funding by the European Union’s 7 th Fram-
ework Program for Research and Technological Development
(WELCOME, Grant Number 611223), the European Union’s
Framework Program for Research and Innovation Horizon2020
(CRADL, Grant Number 668259) and reimbursement of spea-
king fees, congress and travel costs by Dräger Medical. The
other authors declare no conflicts of interest.
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