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 (FEV 1 ) 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. C hronic obstructive pulmonary disease (COPD) is the fourth leading cause of death in the world, 1 but prognosis is only poorly predicted by indices of air flow obstruction. Given this limitation, a new severity classification, the Body Mass Index, Airflow Obstruction, Dyspnoea and Exercise Capacity (BODE) Index, 2 has been proposed that takes into account the multicomponent nature of COPD with considerable emphasis being placed on the body mass index (BMI) as an indicator of poor prognosis.3-6 However, many investigators consider that it is, more specifically, the loss of skeletal muscle mass which confers a poorer prognosis in patients with COPD. 7-10Muscle mass depletion is associated with reduced exercise performance, 11 12 increased dyspnoea 13 and worse health-related quality of life.14 Similarly, skeletal muscle weakness is a common finding in COPD and is associated with reduced exercise capacity. [15][16][17] As exercise capacity is thought to be an important factor in determining mortality in COPD, 18 it perhaps follows that muscle weakness should also predict mortality.In a recent paper by Marquis et al, 7 CT scanning was used to measure the mid-thigh cross-sectional area (MTCSA CT ) in patients with COPD. This radiological measure of quadriceps bulk was shown to predict mortality better than BMI, and this was particularly so in patients with more severe COPD (forced expiratory volume in 1 s, (FEV 1 ) ,50%). This measure is attractive as a single reproducible predictor of mortality from COPD, but some obvious drawbacks limi...

Extrapulmonary comorbidities in chronic obstructive pulmonary disease: state of the art

“…More than a quarter of GOLD stage I and II patients have skeletal muscle dysfunction, rising to 38% in GOLD stage IV. Quadriceps strength is related to fat-free mass index, Medical Research Council dyspnea score, BODE (BMI, airflow obstruction, dyspnea and exercise capacity) index and indeed mortality [74][75].…”

Systemic manifestations and comorbidities of COPD

“…In severe COPD, muscle wasting also has profound effects on morbidity, including an increased risk for hospital readmission after exacerbation as well as an increased need for mechanical ventilatory support. Furthermore, muscle wasting has been identified as a significant determinant of mortality in COPD, which is independent of lung function, smoking and BMI [74,75].…”

Quadriceps wasting and physical inactivity in patients with COPD

“…In particular, reduced quadriceps strength is associated with reduced exercise capacity [3], impaired quality of life [4], increased healthcare use [5] and mortality independent of airflow obstruction [6].…”