Airflow limitation or static hyperinflation: which is more closely related to dyspnea with activities of daily living in patients with COPD?

BACKGROUND Dyspnea while performing the activities of daily living has been suggested to be a better measurement than peak dyspnea during exercise. Furthermore, the inspiratory capacity (IC) has been shown to be more closely related to exercise tolerance and dyspnea than the FEV1, because dynamic hyperinflation is the main cause of shortness of breath in patients with COPD. However, breathlessness during exercise is measured in most studies to evaluate this relationship. PURPOSE To evaluate the correlation between breathlessness during daily activities and airflow limitation or static hyperinflation in COPD. METHODS We examined 167 consecutive outpatients with stable COPD. The Baseline Dyspnea Index (BDI) was used to evaluate dyspnea with activities of daily living. The relationship between the BDI score and the clinical measurements of pulmonary function was then investigated. RESULTS The Spearman rank correlation coefficients (Rs) between the BDI score and the FEV1(L), FEV1(%pred) and FEV1/FVC were 0.60, 0.56 and 0.56, respectively. On the other hand, the BDI score also correlated with the IC, IC/predicted total lung capacity (TLC) and IC/TLC (Rs = 0.45, 0.46 and 0.47, respectively). Although all of the relationships studied were strongly correlated, the correlation coefficients were better between dyspnea and airflow limitation than between dyspnea and static hyperinflation. In stepwise multiple regression analyses, the BDI score was most significantly explained by the FEV1 (R2 = 26.2%) and the diffusion capacity for carbon monoxide (R2 = 14.4%) (Cumulative R2 = 40.6%). Static hyperinflation was not a significant factor for clinical dyspnea on the stepwise multiple regression analysis. CONCLUSION Both static hyperinflation and airflow limitation contributed greatly to dyspnea in COPD patients.