Influence of distinct asthma phenotypes on lung function following weight loss in the obese

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Journal Article
Respirology, 2014, 19 (8), pp. 1170 - 1177
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© 2014 Asian Pacific Society of Respirology. Background and 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 TH2-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 ofweight 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 followingweight loss.However, this was not the case for TH2-high obese asthmatics, highlighting the complex interplay between IgE status and asthma pathophysiology in obesity.
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