title: 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(-115 mm(2); 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<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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Respiratory Medicine, King's College Hospital, London, UK. john.seymour@kcl.ac.uk
authors.forename: J M
authors.initials: JM
authors.lastname: Seymour
authors.forename: K
authors.initials: K
authors.lastname: Ward
authors.forename: P S
authors.initials: PS
authors.lastname: Sidhu
authors.forename: Z
authors.initials: Z
authors.lastname: Puthucheary
authors.forename: J
authors.initials: J
authors.lastname: Steier
authors.forename: C J
authors.initials: CJ
authors.lastname: Jolley
authors.forename: G
authors.initials: G
authors.lastname: Rafferty
authors.forename: M I
authors.initials: MI
authors.lastname: Polkey
authors.forename: J
authors.initials: J
authors.lastname: Moxham
mesh_terms: D000328:Adult; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology*; D018908:Muscle Weakness / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D029424:Pulmonary Disease, Chronic Obstructive / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D052097:Quadriceps Muscle / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D014463:Ultrasonography