Respiratory Muscle Dysfunction in Stable COPD: A Multimodal Assessment of Diaphragmatic and Cough-Related Impairment

BACKGROUND: Respiratory muscle dysfunction contributes to dyspnea, exacerbation risk, and impaired airway clearance in COPD, yet its multidimensional assessment remains limited in clinical practice. This study aimed to evaluate inspiratory and expiratory respiratory muscle function in stable COPD using a multimodal approach and to explore its associations with disease severity. METHODS: In this single-center cross-sectional study, 100 clinically stable COPD subjects underwent phrenic nerve conduction studies, assessment of postural changes in slow vital capacity (SVC), and cough peak flow (CPF) measurement. Diaphragmatic dysfunction was defined by abnormal phrenic nerve latency and/or amplitude, postural diaphragmatic impairment by a seated-to-supine SVC drop ≥ 25%, and cough inefficiency by CPF < 270 L/min. Associations with clinical characteristics, global initiative for chronic obstructive lung disease (GOLD) spirometric stages, GOLD ABE groups, nutritional status, and airway collapse were analyzed. RESULTS: Diaphragmatic dysfunction was present in 37% of subjects, a postural SVC drop ≥ 25% in 16%, and cough inefficiency in 69%. Diaphragmatic dysfunction was associated with higher symptom burden and GOLD group E, independently of air flow limitation severity. Postural SVC reduction was independently associated with severe air flow obstruction. Cough inefficiency was independently associated with older age, severe air flow limitation, and GOLD group E. Airway collapse was not independently associated with any respiratory muscle outcome. CONCLUSIONS: Respiratory muscle dysfunction is prevalent in COPD and affects distinct inspiratory, postural, and expiratory components. Phrenic nerve conduction studies, postural SVC assessment, and CPF provide complementary information beyond spirometry and symptom scores, supporting the value of a multimodal approach for improved phenotyping and risk stratification in COPD.