Longitudinal change in ultrasound measurement of rectus femoris cross-sectional area in COPD

Background: Ultrasound measurement of rectus femoris cross sectional area (RFCSA) is a validated, reproducible surrogate marker of quadriceps muscle mass in COPD, and is correlated strongly with quadriceps strength. However longitudinal validity of RFCSA has not been determined. Method: RFCSA, quadriceps maximum voluntary contraction (QMVC), fat free mass index (FFMI) determined by bioelectrical impedance analysis, lower limb muscle physical performance (5 repetition sit to stand:5STS; 4 metre gait speed:4MGS) were measured in 42 patients with COPD at baseline (T0) and at 12 months follow-up (T1). Results: At T0, RFCSA was correlated strongly with QMVC and FFMI (r=0.76, 0.65; both p 0.20). Conclusion: Change in RFCSA is not a surrogate marker of change in lower limb muscle strength or performance in COPD.