Acute effects of oxygen supplementation on quadriceps Neuromuscular Fatigue in COPD patients with Chronic Respiratory Failure.

Abstract

Patients with chronic obstructive pulmonary disease (COPD) and chronic respiratory failure (CRF) under Long Term Oxygen Therapy (LTOT) experience exaggerated quadriceps neuromuscular fatigue (NMF). In this context, the effect of oxygen therapy on NMF remains unclear. What is the impact of different FiO₂ levels on neuromuscular fatigue during intermittent isometric quadriceps exercise in a COPD-CRF population? Three intermittent isometric quadriceps tests (Ts), all at 80% of the time to exhaustion (TTE) at 30% of Maximal Voluntary Contraction (MVC), were randomly performed in each patient under three different FiO₂ (F): T-F21 at 21%, T-F30 at30%, T-F60 at 60%. TTE was previously evaluated by breathing FiO₂ at 21%. NMF was assessed through changes in MVC, twitch force quadriceps potentiated (Qtwpot), and voluntary activation (VA), following exercise (at peak, and at 30" and 10' after). EMG was continuously evaluated. We enrolled 20 patients (80.9% male, 71.80±5.81 years, FEV₁/FVC 39.56±9.32, RV 206.49±53.14%). MVC changes were -27.60±9.50%, -24.35±7.80%, and -22.00±7.13% in T-F21, T-F30, and T-F60, respectively (P = 0.0341), with differences between T-F21 and T-F30 (P = 0.032) and T-F21 and T-F60 (P = 0.032). ΔQtwpot showed changes of -31.10±14.30%, -31.25±16.70%, and -26.70±16.10% for T-F21, T-F30, and T-F60, respectively (P = 0.019), with differences between T-F21 and T-F60 (P = 0.027) and T-F30 and T-F60 (P = 0.014). VA decreased similarly across conditions (P=0.211). Acute oxygen administration reduces quadriceps NMF in COPD patients with CRF. These results highlight the role of oxygen availability in modulating NMF in this population. Future studies should investigate this effect during exercise training, as well as long-term consequences.