Ultrasound assessment of the rectus femoris in patients with chronic obstructive pulmonary disease predicts poor...

Reduced exercise tolerance is an important clinical feature of chronic obstructive pulmonary disease (COPD) and is associated with poor prognosis. The 6-min walk test (6MWT) is widely used to assess exercise capacity; however, it is not commonly administered in primary medical institutions because it requires a suitable site and professional training. Ultrasound has great potential for evaluating skeletal muscle dimensions in COPD. However, whether skeletal muscle ultrasound can predict impaired exercise tolerance is unclear.

The study included 154 stable patients with COPD, who were randomly divided into a development set and a validation set. The thickness (RF_thick) and cross-sectional area (RF_csa) of the rectus femoris were measured using ultrasound. Standardized RF_thick (STD- RF_thick) and Standardized RF_csa (STD-RFcsa) were obtained via standardization of RF_thick and RF_csa by patients' height.

Strong correlations were observed between the 6MWD and RF_thick (r = 0.84, p < 0.001) and between the 6MWD and RF_csa (r = 0.81, p < 0.001). In the development set, the optimal cut-off values for men and women for predicting poor exercise tolerance were < 3.098 cm/m and < 3.319 cm/m for STD-RF_thick and < 4.052 cm²/m and < 4.366 cm²/m for STD-RF_csa, respectively. In the validation set, the area under the curve (AUC) values for the prediction of a 6MWD < 350 by STD-RF_thick and STD-RF_csa were 0.881 and 0.903, respectively. Finally, the predictive efficacy of STD-RF_thick (AUC: 0.922), STD-RF_csa (AUC: 0.904), and the derived nomogram model (AUC: 0.98) for exercise tolerance was superior to that of the sit-to-stand test and traditional clinical features.

Rectus femoris ultrasound has potential clinical application to predict impaired exercise tolerance in patients with COPD.