title: Airway impedance entropy and exacerbations in severe asthma.
abstract: Variability of peak flow measurements has been related to clinical outcomes in asthma. We hypothesised that the entropy, or information content, of airway impedance over short time scales may predict asthma exacerbation frequency. 66 patients with severe asthma and 30 healthy control subjects underwent impulse oscillometry at baseline and following bronchodilator administration. On each occasion, airway impedance parameters were measured at 0.2-s intervals for 150 s, yielding a time series that was then subjected to sample entropy (SampEn) analysis. Airway impedance and SampEn of impedance were increased in asthmatic patients compared with healthy controls. In a logistic regression model, SampEn of the resistance at 5 Hz minus the resistance at 20 Hz, a marker of the fluctuation of the heterogeneity of airway constriction over time, was the variable most strongly associated with the frequent exacerbation phenotype (OR 3.23 for every 0.1 increase in SampEn). Increased airway impedance and SampEn of impedance are associated with the frequent exacerbation phenotype. Prospective studies are required to assess their predictive value.
authors.affiliation: Dept of Infection, Immunity and Inflammation, University of Leicester, Leicester, UK. sg330@le.ac.uk
authors.forename: Sherif
authors.initials: S
authors.lastname: Gonem
authors.forename: Imraan
authors.initials: I
authors.lastname: Umar
authors.forename: Daniel
authors.initials: D
authors.lastname: Burke
authors.forename: Dhananjay
authors.initials: D
authors.lastname: Desai
authors.forename: Steven
authors.initials: S
authors.lastname: Corkill
authors.forename: John
authors.initials: J
authors.lastname: Owers-Bradley
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Brightling
authors.forename: Salman
authors.initials: S
authors.lastname: Siddiqui
mesh_terms: D001249:Asthma / Q000503:physiopathology*; D018450:Disease Progression; D017097:Electric Impedance; D019277:Entropy; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012720:Severity of Illness Index