Ultrasound Evaluation of Diaphragmatic and Intercostal Muscle Function as an Indicator of COPD Severity: A Prospective Cross-Sectional Study.

Background: Chronic obstructive pulmonary disease (COPD) is frequently accompanied by respiratory muscle dysfunction, particularly involving the diaphragm and intercostal muscles. This may limit the feasibility of traditional pulmonary function testing. Purpose: To investigate the association between ultrasound-derived respiratory muscle parameters and COPD severity, and to evaluate the utility of respiratory muscle ultrasound for disease stratification. Patients and Methods: This single-center, prospective study was conducted at Zhejiang Hospital between January 2024 and June 2025, 78 COPD patients (35 mild-to-moderate, 43 severe) and 50 healthy volunteers were enrolled. Muscle thickness, thickening fraction, excursion, and shear-wave elasticity of the diaphragm and intercostal muscles were measured. Group comparisons and logistic regression analyses were performed. Repeatability was evaluated in the healthy cohort. Results: All 128 participants completed the study. Ultrasound measurements demonstrated excellent repeatability (ICC coefficients 0.851-0.969). Gender (male vs female, OR = 4.934, P = 0.014), DE (OR=0.393, P=0.008), ICMTF (OR=10.053, P=0.025), and ICM-SWV (OR=6.419, P<0.001) were predictive of screening-positive COPD, with an area under the curve (AUC) of 0.908. Within COPD severity stratification, end-inspiratory diaphragmatic thickness (OR=0.041, P=0.014), diaphragmatic thickening fraction (DTF; OR=0.188, P=0.027), and ICM-SWV (OR=5.662, P=0.024) were identified as independent predictors, with an AUC of 0.959. Conclusion: Respiratory muscle ultrasound offers reproducible and clinically informative parameters that support both COPD diagnosis and severity assessment, providing a potential complementary tool to pulmonary function testing in clinical practice.