The influence of lung function and respiratory muscle strength on quadriceps muscle fatigability in COPD patients under long-term oxygen therapy

Background: This research investigates quadriceps muscle fatigability (MF) in Chronic Obstructive Pulmonary Disease (COPD) patients with chronic respiratory failure (CRF) at different levels of lung obstruction [severe obstruction (SO) = FEV1 <50% and > 30% versus very severe obstruction (VSO) = FEV1 ≤ 30%]. It explores the relationships between quadriceps MF and lung function, respiratory muscles, and oxygenation status. Methods: A post-hoc cross-over analysis in 45 COPD patients (20 SO and 25 VSO) undergoing long-term oxygen therapy was performed. Delta change in quadriceps maximum voluntary contraction (MVC) (absolute value and percentage) before and after a constant workload was calculated. Associations between quadriceps MF and lung function, respiratory muscles, and gas exchange were examined using Pearson's correlation and multivariate linear regression analysis. Results: SO patients experience a more substantial reduction in MVC compared to VSO (-15.15±9.13% vs -9.29 ± 8.90%, p=0.0357), despite comparable resting MVC. Dyspnea is more pronounced in VSO at the beginning and end of the exercise. Correlations were found between MF and Maximal Inspiratory Pressure (MIP) (r = -0.4412, p= 0.0056), Maximal Expiratory Pressure (MEP) (r= -0.3561. p=0.0282), and a tendency for FEV1% (r= -0.2931, p= 0.0507). The regression model (R2 = 0.4719) indicates that lower MIP and FEV1 and high total lung capacity are significant factors in reducing quadriceps muscle fatigability after a fatiguing task. Conclusion: COPD patients with more severe pulmonary obstruction and hyperinflation and lower respiratory muscle strength have lower quadriceps MF but higher dyspnoea both at rest and during exercise.