title: Impact of exacerbations on emphysema progression in chronic obstructive pulmonary disease.
abstract: BACKGROUND
  Low-attenuation areas assessed by computed tomography reflect the extent of pathological emphysema and correlate with airflow limitation and mortality in patients with chronic obstructive pulmonary disease. The cumulative size distribution of low-attenuation area clusters follows a power law characterized by an exponent, D. The values of D reflect the complexity of the terminal airspace geometry and sensitively detect alveolar structural changes. Exacerbations of chronic obstructive pulmonary disease have a negative impact on lung function and prognosis. However, the impact on emphysema progression remains unclear.
  
  
  OBJECTIVE
  We investigated the relationship between exacerbation and emphysema progression assessed by computed tomography in patients with chronic obstructive pulmonary disease.
  
  
  METHODS
  Exacerbations were prospectively recorded for 2 years. Annual changes in computed tomography parameters of emphysema were compared between patients with and without a history of exacerbations.
  
  
  RESULTS
  In patients with exacerbations, increases in the percentage of low-attenuation areas and decreases in D were greater than in patients without exacerbations. To interpret these results, we established a novel simulation model and found that not only enlargement of preexisting low-attenuation areas but also coalescence of adjoining low-attenuation areas due to alveolar wall destruction caused emphysema progression in patients with exacerbations.
  
  
  CONCLUSIONS
  This is the first longitudinal study to demonstrate that exacerbations are involved in emphysema progression in patients with chronic obstructive pulmonary disease. Emphysema progression should be evaluated as part of the outcomes of exacerbations in the management of chronic obstructive pulmonary disease.
authors.affiliation: Department of Respiratory Medicine, Graduate School of Medicine, Kyoto University, 53 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan.
authors.forename: Naoya
authors.initials: N
authors.lastname: Tanabe
authors.forename: Shigeo
authors.initials: S
authors.lastname: Muro
authors.forename: Toyohiro
authors.initials: T
authors.lastname: Hirai
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Oguma
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Terada
authors.forename: Satoshi
authors.initials: S
authors.lastname: Marumo
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kinose
authors.forename: Emiko
authors.initials: E
authors.lastname: Ogawa
authors.forename: Yuma
authors.initials: Y
authors.lastname: Hoshino
authors.forename: Michiaki
authors.initials: M
authors.lastname: Mishima
mesh_terms: D000368:Aged; D018450:Disease Progression; D005260:Female; D006801:Humans; D008168:Lung / Q000503:physiopathology; D008297:Male; D008962:Models, Theoretical; D011446:Prospective Studies; D029424:Pulmonary Disease, Chronic Obstructive / Q000000981:diagnostic imaging* / Q000503:physiopathology; D011656:Pulmonary Emphysema / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed