title: Role of small airways in asthma: investigation using high-resolution computed tomography.
abstract: BACKGROUND
  Small airways may have an important role in asthma but are more difficult to assess pathologically than central airways. Computed tomographic indices of lung density are assumed to reflect air trapping and may be a useful noninvasive measure of small airways disease, but their pathophysiological relevance remains undetermined.
  
  
  OBJECTIVE
  To evaluate lung density on high-resolution computed tomography and examine its correlations with clinical and physiologic variables in 29 patients with stable asthma.
  
  
  METHODS
  Both lungs were scanned at full-inspiratory and full-expiratory phases to quantify percentage of lung field occupied by low attenuation area (LAA%; < -960 Hounsfield units) and mean lung density. Asthma severity, pulmonary function, methacholine airway sensitivity and reactivity, and sputum eosinophil counts were evaluated.
  
  
  RESULTS
  The mean lung density increased and LAA% decreased in all patients at expiratory phase compared with inspiratory phase. The inspiratory density indices and expiratory mean lung density correlated only with FEV(1)/forced vital capacity (FVC). Expiratory LAA% correlated more strongly than other variables with FEV(1)/FVC and with indices of peripheral airflow obstruction. Expiratory/inspiratory ratios of LAA% and mean lung density correlated, the former more strongly, with disease severity, residual volume/total lung capacity, and airway sensitivity, as well as with indices of global (FEV(1) and FEV(1)/FVC) and peripheral airflow obstruction.
  
  
  CONCLUSIONS
  Expiratory/inspiratory high-resolution computed tomography is useful for assessing small airways disease in asthma. Small airways involvement is associated with airflow obstruction, airway hypersensitivity, and more severe disease.
  
  
  CONCLUSIONS
  Small airways are an important therapeutic target in asthma.
authors.affiliation: Department of Respiratory Medicine, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Ueda
authors.forename: Akio
authors.initials: A
authors.lastname: Niimi
authors.forename: Hisako
authors.initials: H
authors.lastname: Matsumoto
authors.forename: Masaya
authors.initials: M
authors.lastname: Takemura
authors.forename: Toyohiro
authors.initials: T
authors.lastname: Hirai
authors.forename: Masafumi
authors.initials: M
authors.lastname: Yamaguchi
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Matsuoka
authors.forename: Makiko
authors.initials: M
authors.lastname: Jinnai
authors.forename: Shigeo
authors.initials: S
authors.lastname: Muro
authors.forename: Kazuo
authors.initials: K
authors.lastname: Chin
authors.forename: Michiaki
authors.initials: M
authors.lastname: Mishima
mesh_terms: D000328:Adult; D000368:Aged; D001249:Asthma / Q000175:diagnosis* / Q000503:physiopathology* / Q000628:therapy; D001980:Bronchi / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012129:Respiratory Function Tests; D014057:Tomography, X-Ray Computed