Exacerbations are known to worsen the long-term clinical course of COPD. Tanabe et al performed serial chest CTs on 60 people with COPD over 2 years; 26 had exacerbations and 34 did not (0.34 exacerbations per person-year). The two groups (exacerbation / no exacerbation) were similar in age, COPD severity, etc. However, those with exacerbations had significant radiographic progression of emphysema. AJRCCM 2011;183:1653-1659.