SWE(mean) of Quadriceps, a Potential Index of Complication Evaluation to Patients with Chronic Obstructive Pulmonary Disease

PURPOSE: To develop a potential quadriceps’ index of complication evaluation for patients with chronic obstructive pulmonary disease (COPD) which is simple, convenient, and quantifiable. PATIENTS AND METHODS: We conducted a prospective study of 59 patients with COPD and 56 healthy controls recruited by the Chengdu First People’s Hospital. Grayscale ultrasound (US) of the rectus femoris was performed to measure thickness (RF(thick)) and cross-sectional area (RF(csa)). Shear wave elastography was used to determine the mean elasticity index (SWE(mean)) of the rectus femoris (SWE(RFmean)), vastus lateralis (SWE(VLmean)) and vastus medialis (SWE(VMmean)). Clinical features included dyspnea index score (modified British Medical Research Council (MMRC) score), COPD Assessment Test (CAT), the Five-Repetition Sit-to-Stand Test (5STS) and the Six-Minute Walk Test (6MWT). We compared the differences between US parameters and SWEmean in healthy controls and COPD patients. We also described the correlation between US parameters, SWE(mean) and clinical features of patients with COPD. RESULTS: The intra-observer repeatability for the performance of using SWE to measure quadriceps stiffness was excellent (intraclass correlation coefficient (ICC)>0.75, p < 0.001). There was a statistically significant difference in the SWE(mean) of the quadriceps (p < 0.001), but no significant difference in terms of RF(thic) and RF(csa) (p > 0.05) between healthy controls and COPD patients. The SWE(RFmean) was positively correlated with the 6MWT (r = 0.959, p < 0.001), and negatively related to the mMRC (r=−0.825, p < 0.001), CAT (r=−0.993, p < 0.001) and 5STS (r=−0.936, p < 0.001). However, the RF(thic), RF(csa), SWE(VLmean) and SWE(VMmean) were not correlated with clinical features (p > 0.05). CONCLUSION: As a supplement to US, SWE reflects changes of stiffness in the quadriceps of COPD patients, and can expanding the dimension of US for assessing the quadriceps. Furthermore, SWE(mean) was associated with clinical features, and represents a potential index with which to reflect the clinical features of COPD patients.