title: Influence of distinct asthma phenotypes on lung function following weight loss in the obese.
abstract: OBJECTIVE
  There appears to be two distinct clinical phenotypes of obese patients with asthma-those with early-onset asthma and high serum IgE (TH2-high), and those with late-onset asthma and low serum IgE (TH2-low). The aim of the present study was to determine in the two phenotypes of obese asthma the effect of weight loss on small airway function.
  
  
  METHODS
  TH2-low (n = 8) and TH2-high (n = 5) obese asthmatics underwent methacholine challenge before and 12 months following bariatric surgery. Dose-response slopes as measures of sensitivity to airway closure and narrowing were measured as maximum % fall forced vital capacity (FVC) and forced expiratory volume in 1 s/FVC, respectively, divided by dose. Resting airway mechanics were measured by forced oscillation technique.
  
  
  RESULTS
  Weight loss reduced sensitivity to airway closure in TH 2-low but not TH2-high obese asthmatics (pre-post mean change ± 95% confidence interval: 1.8 ± 0.8 doubling doses vs -0.3 ± 1.7 doubling doses, P = 0.04). However, there was no effect of weight loss on the sensitivity to airway narrowing in either group (P = 0.8, TH2-low: 0.8 ± 1.0 doubling doses, TH2-high: -1.1 ± 2.5 doubling doses). In contrast, respiratory resistance (20 Hz) improved in TH2-high but not in TH2-low obese asthmatics (pre-post change median interquartile range: 1.5 (1.3-2.8) cmH₂O/L/s vs 0.6 (-1.8-0.8) cmH₂O/L/s, P = 0.03).
  
  
  CONCLUSIONS
  TH2-low obese asthmatics appear to be characterized by increased small airway responsiveness and abnormalities in resting airway function that may persist following weight loss. However, this was not the case for TH2-high obese asthmatics, highlighting the complex interplay between IgE status and asthma pathophysiology in obesity.
authors.affiliation: Department of Medicine, University of Vermont College of Medicine, Burlington, Vermont, USA.
authors.forename: David G
authors.initials: DG
authors.lastname: Chapman
authors.forename: Charles G
authors.initials: CG
authors.lastname: Irvin
authors.forename: David A
authors.initials: DA
authors.lastname: Kaminsky
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Forgione
authors.forename: Jason H T
authors.initials: JH
authors.lastname: Bates
authors.forename: Anne E
authors.initials: AE
authors.lastname: Dixon
mesh_terms: D000328:Adult; D017668:Age of Onset; D001249:Asthma / Q000276:immunology / Q000503:physiopathology; D050110:Bariatric Surgery / Q000379:methods*; D001985:Bronchial Provocation Tests / Q000379:methods; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D007073:Immunoglobulin E / Q000097:blood*; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000276:immunology / Q000503:physiopathology / Q000601:surgery; D010641:Phenotype; D012130:Respiratory Hypersensitivity / Q000276:immunology / Q000503:physiopathology; D012137:Respiratory System / Q000503:physiopathology; D015431:Weight Loss / Q000276:immunology
chemical_list: D007073:Immunoglobulin E
keywords: airway closure; airway hyperresponsiveness; asthma; obesity; weight loss