4.2. The Effect of Pulmonary Rehabilitation
There was no modification to cytokine levels after the 8-week period of rehabilitation.
Rabinovich and associates [40] showed that the 8-wk protocol of high-intensity training had the expected effect
in control subjects. Compared with the untrained state, the trained vastus lateralis muscle maintained GSH
at significantly higher levels after a bout of exhaustive exercise. Thus, training appeared to increase the efficacy
of antioxidant buffering in control subjects as expected [41]. No such benefit was seen in individuals with
COPD. GSH concentrations measured after exhaustive exercise were unaltered by training. Worse, training increased
the GSSG levels measured after exhaustive exercise. The latter finding is contradictory to the findings in
the current study. Acute exercise increased GSSG levels in COPD subjects but not in healthy control, however,
after 8-week rehabilitation, GSSG levels were unaltered after exercise but instead there was trend toward reduction
in GSSG values but didn’t reach statistical significance, Figure 5.
Mercken reported that PR was associated with reduced oxidative stress after submaximal exercise in patients
A. I. El Gammal et al.
29
with COPD [28]. In the COPD group in our study, peak exercise samples were taken at exhaustion rather than at
the same duration of exercise before PR (isotime). The duration of endurance exercise was 74% longer after PR
(p = 0.0003). Measurements of oxidative stress at isotime may have demonstrated significant differences before
and after PR, as inflammatory response increases with the intensity and duration of exercise. The type of physical
activity and its intensity and duration seem to be highly relevant to differences in the cytokine response to
exercise [42].
4.3. Limitations of the Study
There are several limitations of the current worth discussing. A relatively small number of healthy subjects were
included in the study. Despite the small size, we note the large standard deviations for cytokine response and
consistency of our results. Our COPD patient sample is representative of the COPD regularly seen in clinical
practice.
Although the statistical model aims to adjust for the possible confounding factors, the existence of some uncontrolled
effects cannot be excluded. Our results could also be affected by other drawbacks. Of the COPD patients
in our study, almost all patients used inhaled corticosteroids and 12% used systemic corticosteroids. This
could contribute to the underestimation of the difference in systemic biomarkers between COPD patients and
control subjects. Nevertheless, the effect of inhaled corticosteroids on inflammatory biomarkers is still controversial.
Other chronic conditions, such as chronic heart failure or diabetes, also appear to be associated with a
similar systemic inflammatory process. Several studies have described that these disorders are more frequent in
COPD patients and, therefore, might also contribute to their pro-inflammatory state. In order to analyze only the
effect of COPD as an independent factor, we have carefully excluded these conditions from the present study.
5. Conclusion
In conclusion, these data support the now well-established view that systemic inflammation is higher in patients
with COPD and that systemic inflammatory mediators are associated with disease severity. Furthermore, exercise-
induced inflammatory response was higher but not exaggerated in COPD. Finally, our hypothesis that pulmonary
rehabilitation may modify pro-inflammatory mediators, as long-term training in healthy subjects does
[43], has not been demonstrated in this study.
Acknowledgements
This work was supported by the Irish Lung Foundation.
None of the authors have any personal or financial support or author involvement with organizations with financial
interest in the subject matter—or any actual or potential conflict of interest.