Quadriceps weakness is recognised as an important complication of COPD but few data exist about loss of muscle bulk in early disease. We hypothesised that quadriceps wasting, measured by ultrasound rectus femoris cross-sectional (USRFCSA), would be observed in patients with mild COPD compared to healthy age-matched subjects and that this would correlate with daily physical activity levels.Methods
Rectus femoris cross-sectional area was measured using ultrasound (USRFCSA) and daily physical activity (step count and physical activity level—PAL) recorded using a multisensor biaxial armband accelerometer. Fat free mass index (FFMI) and the impedance ratio (Z200/Z5) were determined by bioelectrical impedance analysis. Quadriceps maximum voluntary contraction (QMVC) was used as a measure of strength.Results
150 patients with stable COPD, GOLD stage I (n=38), II (n=38), III (n=37) and IV (n=37), mean (SD) age 66 (9) years, 54% male and 40 age-matched healthy subjects participated in the study. USRFCSA was significantly reduced in stage I COPD patients compared to controls (530 mm2 vs 640 mm2; p=0.0002) (Abstract S94 figure 1); USRFCSA was also reduced in stages II (526 mm2), III (503 mm2) and IV (509 mm2) disease (p=0.0001). Daily physical activity was reduced in stage I patients (steps; p<0.0001, PAL; p=0.002) and stage II–IV COPD (steps and PAL; p<0.0001) compared to healthy subjects. Using multivariate linear regression, USRFCSA (p=0.0003), FFMI (p=0.0003) and the impedance ratio (p=0.001) were all independent predictors of quadriceps strength in COPD. In stage I patients, only USRFCSA was shown to be independently associated with daily physical activity (steps, p=0.03; PAL, p=0.003), while in stage II–IV disease, FEV1% predicted was retained as the only independent correlate with daily physical activity (steps and PAL, p<0.0001).Conclusions
Quadriceps wasting identified by USRFCSA exists in patients with early, as well as advanced, COPD when compared to healthy age-matched controls. Quadriceps bulk is associated with daily physical activity independent of airflow obstruction, in early but not advanced disease. Our data suggest that, rather than being an end-stage phenomenon, quadriceps wasting is present in a substantial minority of COPD patients and is related to physical inactivity in the absence of severe airflow limitation.