title: Quadriceps strength predicts mortality in patients with moderate to severe chronic obstructive pulmonary disease.
abstract: BACKGROUND
  Prognosis in chronic obstructive pulmonary disease (COPD) is poorly predicted by indices of air flow obstruction, because other factors that reflect the systemic nature of the disease also influence prognosis.
  
  
  OBJECTIVE
  To test the hypothesis that a reduction in quadriceps maximal voluntary contraction force (QMVC) is a useful predictor of mortality in patients with COPD.
  
  
  METHODS
  A mortality questionnaire was sent to the primary care physician of 184 patients with COPD who had undergone quadriceps strength measurement over the past 5 years. QMVC was expressed as a percentage of the patient's body mass index. The end point measured was death or lung transplantation, and median (range) follow-up was 38 (1-54) months.
  
  
  RESULTS
  Data were obtained for 162 patients (108 men and 54 women) with a mean (SD) percentage of forced expiratory volume in 1 s (FEV1) predicted of 35.6 (16.2), giving a response rate of 88%. Transplant-free survival of the cohort was 93.5% at 1 year and 87.1% at 2 years. Cox regression models showed that the mortality risk increased with increasing age and with reducing QMVC. Only age (HR 1.72 (95% CI 1.14 to 2.6); p = 0.01) and QMVC (HR 0.91 (95% CI 0.83 to 0.99); p = 0.036) continued to be significant predictors of mortality when controlled for other variables in the multivariate analysis.
  
  
  CONCLUSIONS
  QMVC is simple and provides more powerful prognostic information on COPD than that provided by age, body mass index and forced expiratory volume in 1 s.
authors.affiliation: Respiratory Muscle Laboratory, Royal Brompton Hospital, Fulham Road, London SW3 6NP, UK. e.swallow@imperial.ac.uk
authors.forename: Elisabeth B
authors.initials: EB
authors.lastname: Swallow
authors.forename: Diana
authors.initials: D
authors.lastname: Reyes
authors.forename: Nicholas S
authors.initials: NS
authors.lastname: Hopkinson
authors.forename: William D-C
authors.initials: WD
authors.lastname: Man
authors.forename: Raphaël
authors.initials: R
authors.lastname: Porcher
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Cetti
authors.forename: Alastair J
authors.initials: AJ
authors.lastname: Moore
authors.forename: John
authors.initials: J
authors.lastname: Moxham
authors.forename: Michael I
authors.initials: MI
authors.lastname: Polkey
mesh_terms: D018572:Disease-Free Survival; D005260:Female; D005500:Follow-Up Studies; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology*; D011379:Prognosis; D029424:Pulmonary Disease, Chronic Obstructive / Q000401:mortality / Q000503:physiopathology*; D052097:Quadriceps Muscle / Q000502:physiology*