Although the definition of a significant bronchodilator response is somewhat controversial, the American Thoracic Society (ATS) defines it, in both asthma and COPD, as having an increase in FEV1 post-bronchodilator of at least 12% from baseline and of at least 200 milliliters.
When there is a reversible component to one's COPD, therefore an asthma component, there will be a significant increase in post-bronchodilator FEV1 (12% or greater). When there is very little to no reversibility, therefore no asthma component, there will be less than a significant increase post bronchodilator (less than 12%).
Christopher B. Cooper, MD, Medscape Today. Assessment of Pulmonary Function in COPD: Response to Bronchodilator Therapy. Semin Respir Crit Care Med. 2005;26(2):246-252. © 2005 Thieme Medical Publishers.
Hakima Ouksel, Nicole Meslier, Anne Badatcheff-Coat et.al. International Journal of Thoracic Medicine. Influence of Predicted FEV1 on Bronchodilator Response in Asthmatic Patients. Vol. 70, No. 1, 2003.