Schuurmans MM, Botha P, Steyn D, Richter DC, Bolliger CT. Time to spirometric and exercise response in 4-week oral corticosteroid trial for stable COPD patients. Swiss Med Wkly. 2005 Sep 17;135(37-38):562–8. doi: 10.4414/smw.2005.11000. PMID: 16333767.