title: Peripheral lung function in patients with stable and unstable asthma.
abstract: BACKGROUND
  Exacerbations of asthma are thought to be caused by airflow obstruction resulting from airway inflammation, bronchospasm, and mucus plugging. Histologic evidence suggests the small airways, including acinar air spaces, are involved; however, this has not been corroborated in vivo by measurements of peripheral small-airway function.
  
  
  OBJECTIVE
  We sought to determine whether asthma severity is linked to small-airway function, particularly in patients with acute severe asthma.
  
  
  METHODS
  Eighteen subjects admitted for an asthma exacerbation underwent lung function testing, including measures of acinar ventilation heterogeneity (S(acin)) and conductive ventilation heterogeneity (S(cond)) using the multiple-breath nitrogen washout. Treatment requirement was defined according to Global Initiative for Asthma scores. Data were compared with those obtained in 19 patients with stable asthma.
  
  
  RESULTS
  For the asthma exacerbation group, the median FEV1 was 59% of predicted value (95% CI, 45% to 75% of predicted value), the median S(cond) value was 185% of predicted value (95% CI, 119% to 245% of predicted value), and the median S(acin) value was 225% of predicted value (95% CI, 143% to 392% of predicted value). FEV1 (percent predicted) was correlated with S(acin) (percent predicted) values (Spearman rho = -0.67, P = .006) but not with S(cond) (percent predicted) values (P > .1). The Global Initiative for Asthma score was significantly related to S(acin) (percent predicted) (Spearman rho = 0.59, P = .016) but not to S(cond) (percent predicted) values (P > .1). The unstable group was characterized by considerably lower forced vital capacity (P < .001) and higher S(cond) (P = .001) values than the unstable group. In a subgroup of 11 unstable patients who could be reviewed after 4 weeks, FEV1, forced vital capacity, S(acin), and S(cond) values showed marked improvements.
  
  
  CONCLUSIONS
  Our findings suggest that unstable asthma is characterized by a combined abnormality in the acinar and conductive lung zones, both of which are partly reversible. Functional abnormality in the acinar lung zone in particular showed a direct correlation with airflow obstruction and treatment requirement in patients with acute severe asthma.
authors.affiliation: Department of Allergy, Immunology and Respiratory Medicine, The Alfred Hospital and Monash University, Melbourne, Australia. b.thompson@alfred.org.au
authors.forename: Bruce R
authors.initials: BR
authors.lastname: Thompson
authors.forename: Jo A
authors.initials: JA
authors.lastname: Douglass
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Ellis
authors.forename: Vanessa J
authors.initials: VJ
authors.lastname: Kelly
authors.forename: Robyn E
authors.initials: RE
authors.lastname: O'Hehir
authors.forename: Gregory G
authors.initials: GG
authors.lastname: King
authors.forename: Sylvia
authors.initials: S
authors.lastname: Verbanck
mesh_terms: D000208:Acute Disease; D000328:Adult; D001249:Asthma / Q000276:immunology / Q000503:physiopathology*; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008168:Lung / Q000276:immunology / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D012129:Respiratory Function Tests; D014797:Vital Capacity