Does quadriceps contractile fatigue influence rehabilitation outcomes in COPD-chronic respiratory failure patients?

Background: In patients with moderate COPD, response to pulmonary rehabilitation including exercise training varies according to the presence of peripheral muscle fatigue (pMF) of quadriceps. This study investigates the role of pMF in predicting pulmonary rehabilitation outcomes in more severe COPD patients who have already developed chronic respiratory failure (COPD-CRF). Methods: A post hoc analysis of a prospective randomised controlled trial was performed at Istituti Clinici Scientifici Maugeri Lumezzane (Brescia, Italy), involving 30 COPD-CRF patients undergoing a pulmonary rehabilitation programme comprising 20 endurance training sessions. Pre-to-post assessment included a 6-min walk test (6MWT), Fatigue Severity Scale (FSS), Barthel dyspnoea index, and quality-of-life questionnaires. We assessed the contractile pMF of quadriceps via electrical nerve stimulation pre-to-post a cycling fatiguing task, using the change in potentiated quadriceps twitch for pMF. Results: At baseline, 12 (40%) patients developed pMF (pMF group), while 18 (60%) did not (no-pMF group). The pMF group had a lower baseline 6-min walk distance (6MWD) with greater FSS and lower quadriceps thickness. After pulmonary rehabilitation, no change in contractile pMF was found in the overall group, but pMF ameliorated only in the pMF group. The pMF group had a greater increase in 6MWD (71.67±53.64 m versus 35.28±36.01 m, p<0.05) and was more likely to exceed the minimal clinically important difference in 6MWD (OR 6.25, 95% CI 1.05-37.07; p=0.044). Other pulmonary rehabilitation outcomes improved similarly between groups. Conclusion: Baseline quadriceps pMF predicted greater improvement in the 6MWT in COPD-CRF patients, suggesting it may be a new target for predicting pulmonary rehabilitation outcomes and optimising training protocols.