Late-breaking abstract: Impaired carbon monoxide diffusion capacity is the strongest predictor of exercise intolerance, even in moderate COPD

Background: Exercise intolerance is the hallmark of COPD and FEV 1 is the traditional method used to define the severity of COPD. However there is a dissociation between FEV 1 and exercise capacity in a large proportion of subjects with COPD. Therefore it is of interest to investigate if other lung function parameters are having an additive, predictive value of exercise capacity (EC) and if this differs according to the COPD stages. Methods: Spirometry, measurements of lung volumes and diffusing capacity for carbon monoxide (DLCO) were performed in 88 patients with COPD GOLD stages II-IV. EC was determined by symptom-limited incremental cycle ergometer test. Results: DLCO, FEV 1 and inspiratory capacity (IC) were found to be the best predictors of EC in a stepwise regression analysis and explain 72% of EC. These lung function parameters explained 71% of EC in GOLD II, 69% in GOLD III and 32% in GOLD IV. DLCO alone was the best predictor of exercise capacity in GOLD II and IV (Table). Predictive values of FEV 1 , IC and DLCO for exercise capacity in diffrent GOLD classes GOLD II GOLD III GOLD IV FEV 1 0.27* 0.53* 0.13* IC 0.42* 0.41* 0.17* DLCO 0.69* 0.51* 0.29* Numbers are presented as R 2 values from a simple regression model. *Indicates significant relation. Discussion: Additive information regarding COPD patients' exercise capacity is obtained by measuring diffusing capacity and inspiratory capacity. DLCO was the strongest predictor of exercise capacity in all subjects and the best individual predictor in patients with GOLD stage II. This suggests that clinically monitoring with measurements of diffusing capacity may be beneficial even in patients with moderate disease severity.