Ultrasound measurement of rectus femoris cross-sectional area and the relationship with quadriceps strength in COPD

TLDR

Quadriceps weakness and loss of muscle mass predict mortality in chronic obstructive pulmonary disease. The study aimed to determine whether ultrasound could detect reduced quadriceps cross‑sectional area in COPD patients and whether this relates to strength and fat‑free mass. RF cross‑sectional area was measured by ultrasound, whole‑body fat‑free mass estimated by bioimpedance, and quadriceps strength assessed via maximum voluntary contraction and twitch tension after magnetic femoral nerve stimulation. COPD patients had a 25 % smaller RF CSA than healthy controls, which correlated strongly with maximal voluntary contraction (r = 0.78) and with dyspnea scores independent of fat‑free mass, indicating that ultrasound‑derived RF CSA is a valid, effort‑independent marker of quadriceps strength.

Abstract

<h3>Background:</h3> Quadriceps weakness and loss of muscle mass predict mortality in chronic obstructive pulmonary disease (COPD). It was hypothesised that a reduced quadriceps cross-sectional area could be detected by ultrasound in patients with COPD compared with healthy subjects, and that measurements relate to strength and fat-free mass (FFM). <h3>Methods:</h3> Rectus femoris muscle cross-sectional area (RF_CSA) was measured by ultrasound and whole-body FFM estimated using electrical bioimpedance. Quadriceps strength was measured by maximum voluntary contraction and twitch tension (TwQ) following magnetic femoral nerve stimulation. <h3>Results:</h3> 26 healthy volunteers of mean (SD) age 63 (9) years and 30 patients with COPD of mean (SD) age 67 (9) years and percentage predicted forced expiratory volume in 1 s (FEV₁) 48.0 (20.8)% with a similar FFM (46.9 (9.3) kg vs 46.1 (7.3) kg, p = 0.193) participated in the study. Mean RF_CSA was reduced in patients with COPD by 25% of the mean value in healthy subjects(−115 mm²; 95% CI −177 to −54, p = 0.001) and was related to MRC dyspnoea scale score, independent of FFM or sex. Maximum voluntary contraction strength was linearly related to RF_CSA in patients with COPD (r = 0.78, p&lt;0.001). TwQ force per unit of RF_CSA was similar in both healthy individuals and those with COPD (mean (SD) 17 (4) g/mm² vs 18 (3) g/mm², p = 0.657). Voluntary contraction strength per unit of RF_CSA was dependent on central quadriceps activation and peripheral oxygen saturation in COPD. <h3>Conclusion:</h3> Ultrasound measurement of RF_CSA is an effort-independent and radiation-free method of measuring quadriceps muscle cross-sectional area in patients with COPD that relates to strength.