Differences of ventilatory muscle recruitment and work of breathing in COPD and ILD during exercise – a comprehensive evaluation

Abstract

IntroductionChronic obstructive pulmonary disease (COPD) and interstitial lung disease (ILD) are significant chronic respiratory disorders, impacting quality of life. Respiratory muscle roles and differences remains not entirely clear.ObjectivesTo evaluate the degree of recruitment of the respiratory muscles and the work of breathing (WOB) in COPD and ILD during exercise.MethodsWe compared the sensory-mechanical relationships in COPD, ILD, and healthy control (n= 20 each). They performed pulmonary function, non-invasive and invasive respiratory muscle strength, surface electromyography and work of breathing (WOB).ResultsCOPD and ILD didn't show lower static muscle strength compared to controls, but poor performance in the exercise test with increased transdiaphragmatic pressure (PDI). In ILD, there was a higher increase in oesophageal pressure (PEs) and a lower gastric pressure (PGa) on inspiration; in COPD, there was a significant increase in PGa on inspiration. In ILD, there is greater recruitment of accessory inspiratory muscles, whereas, in COPD, there is marked use of both inspiratory and expiratory muscles. The neuromechanical inefficiency (increased neural respiratory drive without the corresponding tidal volume) was found in both diseases. In COPD, there is a considerable increase in elastic work to overcome intrinsec PEEP (PEEPi) and expiratory WOB, whereas, in ILD, non-PEEPi elastic WOB is the highest part of total WOB.ConclusionsEarly and increased activity of the respiratory muscles and WOB components significantly contribute to dyspnoea, exercise intolerance, and neuromechanical inefficiency of ventilation in COPD and ILD. The mechanisms of Pdi generation were different between diseases.