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 airflow obstruction, because other factors which reflect the systemic nature of the disease also influence prognosis. This study was undertaken 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 COPD patients who had undergone quadriceps strength measurement over the last five years. QMVC was expressed as a % of the patients' body mass index. The endpoint measured was death or lung transplantation and median (range) follow up was 38 (1-54) months.

Results: Data was obtained for 162 patients (108 male, 54 female) with a mean 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, Hazard ratio 1.72 (95% CI 1.14- 2.60), p=0.01 and QMVC, HR 0.91 (0.83-0.99), p=0.036 continued to be statistically significant predictors of mortality when controlled for other variables in the multivariate analysis.

Conclusion: Quadriceps MVC is simple and provides more powerful prognostic information in COPD than that provided by age, Body Mass Index and FEV1.