Ultrasound measurement of rectus femoris cross-sectional area and the relationship with quadriceps strength in COPD
- J M Seymour1,
- K Ward1,
- P S Sidhu2,
- Z Puthucheary2,
- J Steier1,
- C J Jolley1,
- G Rafferty1,
- M I Polkey3,
- J Moxham1
- 1King’s College London School of Medicine, London, UK
- 2King’s College Hospital, London, UK
- 3Royal Brompton Hospital, London, UK
- Dr J Seymour, Department of Respiratory Medicine, King’s College Hospital, London SE5 9RJ, UK;
- Received 2 July 2008
- Accepted 31 December 2008
- Published Online First 21 January 2009
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 (RFCSA) 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 (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 RFCSA 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 RFCSA in patients with COPD (r = 0.78, p<0.001). TwQ force per unit of RFCSA 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 RFCSA was dependent on central quadriceps activation and peripheral oxygen saturation in COPD.
Conclusion: Ultrasound measurement of RFCSA is an effort-independent and radiation-free method of measuring quadriceps muscle cross-sectional area in patients with COPD that relates to strength.
Additional tables and figures are published online only at http://thorax.bmj.com/content/vol64/issue5
Funding: JMS was funded by a grant from the British Lung Foundation (PO4/8), and was the recipient of an educational grant from GlaxoSmithKline administered by the Royal Brompton Hospital, London. KW was funded by the Stroke Association and the Medical Research Council (UK). JSS was funded by a European Respiratory Society Research Fellowship. CJJ was funded by the Medical Research Council (UK).
Competing interests: None.
Ethics approval: King’s College Hospital local research ethics committee approved the study and informed consent was obtained.