What is the difference between FEV1 change in percentage predicted value and change over baseline in the assessment of bronchodilator responsiveness in patients with COPD?

Background: Several criteria are clinically applied in the assessment of significant bronchodilator responsiveness in chronic obstructive pulmonary disease (COPD). The present study aimed to investigate the differences in various degree of severity of COPD among these criteria. Methods: After 400 micrograms of salbutamol administered via spacer by metered dose inhaler (MDI), forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) changes (including percentage change, absolute change and absolute change in percentage predicted value) were retrospectively analysed in 933 stable patients with mild-to-very-severe COPD. Significant bronchodilator responsiveness was assessed using American Thoracic Society and European Respiratory Society (ATS-ERS) criterion based on FEV1 or/and FVC (both >= 12% increase over baseline and >= 200 mL) and FEV1 percentage predicted criterion (>= 10% absolute increase in percentage predicted FEV1) in different grades of COPD. Results: Of the patients [age 66.8 years, baseline FEV1 974 mL (39.3% predicted) and FVC 2,242 mL], mean improvements were 126 mL in FEV1 and 265 mL in FVC; 21.4% and 45.3% met ATS-ERS criterion based on FEV1 and FVC, respectively; and 13.5% met FEV1 percentage predicted criterion. The responsive ratios of ATS-ERS criterion based on FEV1 to FEV1 percentage predicted criterion in grade I, II, III and IV of COPD were 0.95:1.26:2.53:6.00, respectively (P<0.01 in grade II and P<0.001 in grade III). As the degree of severity increased, the mean improvement of FEV1 was reduced; on the contrary, that of FVC was increased. Conclusions: Compared with FEV1 percentage predicted criterion, ATS-ERS criterion based on FEV1 as well as FVC, the later in particular, detected a larger percentage of patients with significant responsiveness. The increasing difference was relevant as a function of the severity of airflow obstruction.