Relationship between symptoms and functional performance in COPD.

We studied the relationships among functional performance and three symptoms--dyspnea, fatigue, and sleep difficulty--in a sample of 100 people with chronic obstructive pulmonary disease (COPD). All participants had an FEV(1) 60% or less of the predicted level for age, sex, and height. Consistent with the Theory of Unpleasant Symptoms, dyspnea correlated with both fatigue and sleep difficulty. Dyspnea and fatigue both had moderate negative correlations with functional performance, while sleep difficulty had a small nonsignificant negative correlation with functional performance. After controlling for age and oxygen use, dyspnea was the only symptom to predict variance in functional performance significantly. Of the three symptoms studied, only dyspnea was related to both the other symptoms and to functional performance. Focusing on dyspnea may be the best way to improve both symptom experience and functional performance in people with COPD. (c) 2004 Wiley Periodicals, Inc.