Quadriceps strength predicts mortality in patients with moderate to severe chronic obstructive pulmonary disease

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%. Transplantfree 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. Conclusion: 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.