Two-dimensional shear wave elastography: a new tool for evaluating respiratory muscle stiffness in chronic obstructive pulmonary disease patients

BACKGROUND: Impaired respiratory function caused by respiratory muscle dysfunction is one of the common consequences of chronic obstructive pulmonary disease (COPD). In this study, two-dimensional shear wave elastography (2D-SWE) was used to measure diaphragm stiffness (DS) and intercostal muscle stiffness (IMS) in patients with COPD; in addition, the value of 2D-SWE in evaluating respiratory function was determined. METHODS: In total, 219 consecutive patients with COPD and 20 healthy adults were included. 2D-SWE was used to measure the DS and IMS, and lung function was also measured. The correlation between respiratory muscle stiffness and lung function and the differences in respiratory muscle stiffness in COPD patients with different severities were analysed. RESULTS: 2D-SWE measurements of the DS and IMS presented with high repeatability and consistency, with ICCs of 0.756 and 0.876, respectively, and average differences between physicians of 0.10 ± 1.61 and 0.07 ± 1.65, respectively. In patients with COPD, the DS and IMS increased with disease severity (F(1) = 224.50, F(2) = 84.63, P < 0.001). In patients with COPD, the correlation with the forced expiratory volume in one second (FEV(1))/forced vital capacity (FVC), predicted FEV(1)% value, residual volume (RV), total lung capacity (TLC), RV/TLC, functional residual capacity (FRC) and inspiratory capacity (IC) of DS (r(1)=-0.81, r(2)=-0.63, r(3) = 0.65, r(4) = 0.54, r(5) = 0.60, r(6) = 0.72 and r(7)=-0.41, respectively; P < 0.001) was stronger than that of IMS (r(1)=-0.76, r(2)=-0.57, r(3) = 0.57, r(4) = 0.47, r(5) = 0.48, r(6) = 0.60 and r(7)=-0.33, respectively; P < 0.001). CONCLUSION: 2D-SWE has potential for use in evaluating DS and IMS. A specific correlation was observed between respiratory muscle stiffness and lung function. With the worsening of the severity of COPD and the progression of lung function impairment, the DS and IMS gradually increased.