Respiratory physiological reactions during expiratory muscle training in patients with stable severe chronic obstructive pulmonary disease (COPD)

Object: This study aimed to investigate the physiological responses of patients with severe Chronic Obstructive Pulmonary Disease (COPD) during incremental expiratory resistive loading (ERL). Method: Nine stable subjects with very severe COPD and hypercapnia were recruited. Baseline data were collected through spontaneous breathing for 10 min without resistive load. Subsequently, subjects breathed through a mouthpiece with varying levels of expiratory resistance using an expiratory threshold load trainer, set at moderate (10 cmH2O) and high intensity (20 cmH2O) for 15 min each. Physiological parameters, including diaphragmatic electromyography (EMGdi), respiratory muscle effort (esophageal pressure change [Pes] and gastric pressure change [Pgas]), expiratory muscle electromyography (EMGab), and airflow signals were monitored simultaneously. Result: EMGdi showed a significant increase during moderate ERL (10 cmH2O), but approached a plateau at high ERL (20 cmH2O). EMGab exhibited a progressive increase correlating with the escalating ERL. However, the increase in transdiaphragmatic pressure (Pdi =Pgas - Pes) was not significant with the rising expiratory load. Notably, the expiratory muscle effort, as indicated by Pgas, markedly increased during high ERL. Overall, while both breathing work and respiratory muscle effort increased, EMGdi did not exhibit a corresponding increase. Conclusion: Our findings suggest that appropriate levels of expiratory load can engage both inspiratory and expiratory muscles in COPD patients. Additionally, expiratory muscles appear to compensate for increased respiratory load, indicating a potential therapeutic avenue for enhancing respiratory muscle function in this population