Relationship between perceived and neuromuscular fatigue in COPD patients with chronic respiratory failure with...

To evaluate perceived fatigue (PF) and neuromuscular fatigue (NMF) in patients with COPD and chronic respiratory failure (CRF) on long-term oxygen therapy (CRF-COPD group), and the relationships between PF, NMF, patient's characteristics, comparing severe patients with COPD to patients without CRF (COPD group).

This cross-sectional study compared 19 CRF-COPD patients with 10 COPD patients attending a rehabilitation program. PF was determined by Fatigue Severity Scale (FSS), while dyspnea by the Barthel Dyspnea Index (BDI). We assessed quadriceps NMF via electrical nerve stimulation during and following a Maximal Voluntary Contraction (MVC) detecting changes after a Constant Workload Cycling Test (CWCT) at 80% of the peak power output at exhaustion.

CRF-COPD patients showed higher PF (+ 1.79 of FSS score, p = 0.0052) and dyspnea (+ 21.03 of BDI score, p = 0.0023) than COPD patients. After the fatiguing task and normalization for the total work, there was a similar decrease in the MVC (CRF-COPD -1.5 ± 2.4 vs COPD -1.1 ± 1.2% baseline kJ^-1, p = 0.5819), in the potentiated resting twitch force (CRF-COPD -2.8 ± 4.7 vs COPD -2.0 ± 3.3% baseline kJ^-1, p = 0.7481) and in the maximal voluntary activation (CRF-COPD -0.1 ± 3.9 vs COPD -0.9 ± 1.2 -2.0 ± 3.3% baseline kJ^-1, p = 0.4354). FSS and BDI were closely related (R = 0.5735, p = 0.0011), while no correlation between PF and NMF was found.

Patients with CRF-COPD develop higher levels of perceived fatigue and dyspnea than patients with COPD; while neuromuscular fatigue is similar, suggesting a mismatch between symptoms and neuromuscular dysfunction.