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J. Xi et al.
I. A summary of the determined pulmonary function
parameters and the PROMs taken before the study and
at the end of the 4-week study period are presented in
Table II. FVC, forced expiratory volume in 1 s (FEV 1 ),
and maximal voluntary ventilation (MVV) were signi-
ficantly higher in the NH group, but not in the control
group at the end of the study period. All 4 PROMs
revealed significant improvement in patients’ status
in the post-study results for the NH group. Incidence
of respiratory symptoms (e.g. sputum, shortness of
breath, wheezing) were reduced compared with pre-
study evaluation. There were significant differences
in the improvement ratio between the NH and control
groups for all investigated parameters, except total lung
capacity (TLC) and diffusing capacity of the lung for
carbon monoxide (DLCO). Significant differences in
FVC and Borg score were found between high- and
low-level lesions, both pre- and post-study (FVC in
high vs low levels 53.6 ± 10.8 vs 68.6 ± 16.9 (pre,
p < 0.05), 44.8 ± 17.8 vs 68.6 ± 21.3 (post, p <0.01);
Borg score in high vs low levels 5.0 ± 0.8 vs 3.0 ± 1.8
(pre, p <0.01), 5.0 ± 2.0 vs 3.0 ± 1.0 (post, p <0.01)).
However, the improvement ratio was not dependent
on the lesion level.
Table II. Pre-study and post-study lung function and patient-
reported outcome measures (PROM) results from the normocapnic
hyperpnoea (NH) and control groups
Parameters
Time
FVC (% predicted) Pre
FEV1 (% predicted) Post
IR (%)
Pre
MVV (% predicted) Post
IR (%)
Pre
Post
IR (%)
TLC (% predicted)
Pre
Post
IR (%)
DLCO (% predicted) Pre
Post
IR (%)
PHQ-9
Pre
CAT Post
IR (%)
Pre
SGRQ Post
IR (%)
Pre
Borg Post
IR (%)
Pre
Post
IR (%)
NH
Controls
Median (IQR) Median (IQR) p (group)
57.1 (30.2)
66.6 (30.1) a
7.8 (17.6)
56.3 (19.4)
65.6 (19.5) a
19.0 (20.8)
37.7 (25.9)
60.5 (37.5) a
54.7 (47.4)
72.3 (18.0)
74.6 (24.8)
3.5 (9.2)
76.2 (20.4)
74.1 (14.9)
–1.4 (8.2)
6.0 (9.0)
3.0 (8.0) a
–45.0 (25.1)
17.5 (5.5)
15.0 (5.0) a
–11.5 (5.3)
16.0 (27.5)
13.0 (24.5) a
–16.0 (7.4)
4.0 (1.5)
3.0 (1.0) a
–20.0 (15.0)
59.0 (15.0)
56.0 (14.7)
–1.7 (15.0)
56.1 (9.2) 0.515
0.016*
52.0 (10.9)
–3.3 (8.1)
62.2 (16.0) 0.101
0.000*
58.3 (17.0)
–5.9 (16.3)
73.0 (13.0)
72.6 (10.5)
–0.6 (4.0)
74.8 (30.7)
75.2 (17.0)
1.9 (14.9)
4.0 (12.0) 0.681
0.002*
4.5 (10.0)
0.0 (25.0)
14.5 (1.0) 0.393
0.000*
15.0 (1.0)
0.0 (0.0)
9.0 (6.0) 0.965
0.000*
9.0 (7.0)
0.0 (7.7)
3.0 (3.0) 0.372
0.000*
5.0 (2.0) a
26.7 (66.7)
0.758
0.055
0.699
0.918
0.022*
0.000*
*Significant difference between the NH and control groups.
a
Significant difference between pre-study and post-study.
IQR: interquartile range; NH: normocapnic hyperpnoea; FVC: forced vital
capacity; FEV1: forced expiratory volume in 1 s; MVV: maximal voluntary
ventilation; TLC: total lung capacity; DLCO: diffusing capacity of the lung
for carbon monoxide; PHQ-9: Patient Health Questionnaire-9; CAT: COPD
Assessment Test; SGRQ: St George’s Respiratory Questionnaire; IR: increase
ratio; p (group): p-value for comparing the NH and control groups.
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DISCUSSION
This study found that a 4-week NH training reduced
the incidence of respiratory symptoms, improved
pulmonary function (except for DLCO) and quality
of life, and reduced the level of depression in patients
with chronic SCI, regardless of their neurological
level of injury. These results indicate that it is not too
late to start RMT with NH, even more than 24 months
after injury.
In patients with recent SCI, no immediate or long-
term improvements in lung function were found,
even with the help of intermittent positive-pressure
breathing therapy (15). Patients might be able to adapt
to the situation and develop their own strategies for
coping with the limitations. However, the limitations
do not vanish and patients may subsequently develop
depression (8). The current study revealed that im-
provement in lung function may be associated with
a reduction in depression level, which coincides with
the findings in the Postma’s study, in which they found
that a decline in FVC may lead to negative changes in
social functioning over years (9). Better lung function
might have improved the patients’ well-being and qua-
lity of life, thus reduced their depression level. It may
be helpful to develop new strategies for psychosocial
recovery in patients with SCI, and this requires further
investigation.
SGRQ and CAT are used widely for the assessment
of patients with COPD. However, these 2 PROMs were
not validated in patients with SCI, and some activities
mentioned in these scales are not always relevant for
such patients. Although significant differences were
found between the NH and control groups in terms
of these PROMs, these results should be interpreted
with caution.
Previous studies have focused more on muscle
strength compared with muscle endurance. In a re-
trospective study by Raab et al., inspiratory or com-
bined inspiratory and expiratory muscle training was
performed in a group setting with respiratory function
measurements before and after the training period (16).
They found that the training improved respiratory
functions, but the relative improvements in combined
respiratory muscle training were comparable with
isolated inspiratory muscle training. As acknowledged
by Raab et al., the study did not have a control group
and the training groups were not randomized. In a
randomized controlled trial by Roth et al., patients
in the intervention group received expiratory muscle
training (17). Only the value of maximum expiratory
pressure was improved in the intervention group. Since
the training focused only on expiration, we suspected
that by also including inspiratory muscle training, im-
provement might also be observed in other lung func