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

Abstract

Background: 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). Methods: 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. Results: 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 (FEV 1 ) 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(2115 mm 2 ; 95% CI 2177 to 254, 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,0.001). TwQ force per unit of RF CSA was similar in both healthy individuals and those with COPD (mean (SD) 17 (4) g/mm 2 vs 18 (3) g/mm 2 , p = 0.657). Voluntary contraction strength per unit of RF CSA was dependent on central quadriceps activation and peripheral oxygen saturation in COPD. Conclusion: 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.Even in non-cachectic patients with chronic obstructive pulmonary disease (COPD), quadriceps strength is typically reduced by up to 30% compared with healthy elderly subjects. 1 Quadriceps strength has been shown independently to predict increased healthcare utilisation and mortality in COPD. 2 3 In our cohort of patients with moderate to severe COPD, quadriceps strength together with age provided more powerful prognostic information than whole body fat-free mass (FFM) or forced expiratory volume in 1 s (FEV 1 ). 3 A related measure, mid-thigh cross-sectional area measured by computed tomography (CT), has also been shown to predict mortality. 4 Quadriceps strength may be assessed by maximum voluntary contraction force, but maximum effort cannot be guaranteed and formal testing equipment is cumbersome. 5 6 Effort-independent methods of assessing strength such as femoral nerve stimulation are expensive, not widely available and require specific expertise. 7 Bedside tests are attractive for their simplicity and accessibility but measurement of thigh circumference, for example, may not accurately reflect the muscle compartment. Ionising radiation exposure makes serial measurements with CT 4 or dual energy x ray absorptiometry scanning 8 9 undesirable in large populations. MRI avoids this concern, but accessibility and long scann...

Quadriceps wasting and physical inactivity in patients with COPD

“…The strong correlation of USRF CSA with both mid-thigh and rectus femoris CT measurements supports the use of the rectus femoris as a representation of quadriceps bulk and confirms our initial findings in a small cohort of COPD patients [17]. Furthermore, interobserver and inter-occasion agreement for USRF CSA measurement in this study were similar to that for other muscle ultrasound imaging [40].…”

“…Ultrasound rectus femoris cross-sectional area Measurement of quadriceps rectus femoris cross-sectional area was made by ultrasound using a technique previously described by SEYMOUR et al [17]. B-mode ultrasonography was used with an 8-MHz, 7-cm linear array transducer (PLF 805 ST; Toshiba Medical Systems, Crawley, UK).…”

“…Ultrasound rectus femoris cross-sectional area (USRF CSA ) is a radiation-free measure of muscle bulk that relates to quadriceps strength in COPD but is effort independent [17]. We hypothesised that quadriceps wasting measured by USRF CSA would be observed in mild, as well as advanced, COPD compared with healthy, age-matched subjects, and that this would correlate with daily physical activity levels.…”

Rectus Femoris Cross-Sectional Area and Muscle Layer Thickness: Comparative Markers of Muscle Wasting and Weakness

“…Two B-mode ultrasound measures have been reported that quantify wasting (2, 3): (1) combined thickness of the rectus femoris (RF) and vastus intermedius muscles ("muscle layer thickness," henceforth referred to as "thickness") (4, 5); and (2) RF cross-sectional area (RF CSA ), which correlates with lower-limb strength in other clinical circumstances (6). The degree to which either of these ultrasound measures reflect muscle weakness in the critically ill is unclear (7).…”

Ultrasound in obstructive lung diseases: the effect of airway obstruction on diaphragm kinetics. A short pictorial essay

“…Some authors [5,6] have proposed ultrasound assessment of lower limb muscles to quantify the improvements following resistance training. Scanning was performed at the mid-thigh region, and quadriceps mass was assessed by measuring rectus femoris cross-sectional area (RFcsa) and quadriceps muscle thickness (Qt).…”