Introduction Chronic low grade systemic inflammation is well described in stable COPD and may affect exercise tolerance in this population (Broekhuizen et al, 2006). Some studies investigating the systemic inflammatory (SI) response to exercise in COPD have reported increased cytokine responses to exercise in COPD patients (Rabinovich et al, 2003) and all have used protocols where the individual patient and healthy comparator perform exercise at a percentage of their own maximal oxygen consumption or muscle strength. This inevitably leads to discrepancies in exercise duration and absolute intensity between COPD and healthy groups, meaning we are unable to determine the effect of COPD on the exercise-induced cytokine response. We hypothesised that COPD patients would have an enhanced systemic inflammatory response compared with healthy comparators completing an identical walking protocol.
Method 16 clinically stable COPD patients (5M: 11F) completed one treadmill endurance walking test at 85% VO2max until volitional exhaustion. Following this 16 age, sex-matched healthy participants completed identical walking protocols (speed, distance, duration) to that achieved by the 16 COPD patients. The concentration of systemic inflammatory markers (CRP, IL-6, TNF-α, IL-17) were analysed from venous blood taken at rest and post-walk. The exercise induced CRP and cytokine response was evaluated within groups using paired t tests or Wilcoxon sign tests. Comparison of the cytokine response data between groups was analysed using Wilcoxon sign tests.
Results Results are presented as median (25th, 75th percentile) or mean change (95% CI). Baseline concentrations of the systemic inflammatory markers were not significantly different between the COPD (FEV1 50 (38 to 87) %) and healthy participants (Abstract S30 table 1). IL-6 increased significantly post-walk in the COPD group (0.25 (95% CI 0.49 to 0.008) but not in the healthy participants. TNF-α, IL-17 and CRP were not significantly increased with exercise in either group. No significant differences were found between groups for the change (pre- to post-walk) in any inflammatory markers (CRP: p=0.07; IL-6: p=0.51; TNF-α: p=0.22; IL-17: p=0.44).
Conclusion Despite a significant increase in IL-6, the magnitude of the systemic inflammatory response to matched absolute workloads in COPD patients is not greater than in healthy comparators.