title: Non-linear parameters of specific resistance loops to characterise obstructive airways diseases.
abstract: Specific resistance loops appear in different shapes influenced by different resistive properties of the airways, yet their descriptive ability is compressed to a single parameter - its slope. We aimed to develop new parameters reflecting the various shapes of the loop and to explore their potential in the characterisation of obstructive airways diseases.
  
  
  
  Our study included 134 subjects: Healthy controls (N = 22), Asthma with non-obstructive lung function (N = 22) and COPD of all disease stages (N = 90). Different shapes were described by geometrical and second-order transfer function parameters.
  
  
  
  Our parameters demonstrated no difference between asthma and healthy controls groups, but were significantly different (p < 0.0001) from the patients with COPD. Grouping mild COPD subjects by an open or not-open shape of the resistance loop revealed significant differences of loop parameters and classical lung function parameters. Multiple logistic regression indicated RV/TLC as the only predictor of loop opening with OR = 1.157, 95% CI (1.064-1.267), p-value = 0.0006 and R2= 0.35. Inducing airway narrowing in asthma gave equal shape measures as in COPD non-openers, but with a decreased slope (p < 0.0001).
  
  
  
  This study introduces new parameters calculated from the resistance loops which may correlate with different phenotypes of obstructive airways diseases.
authors.affiliation: Laboratory of Respiratory Diseases, University Hospital Leuven, Department of Clinical and Experimental Medicine, KU Leuven, Herestraat 49, 3000, Leuven, Belgium.
authors.forename: Marko
authors.initials: M
authors.lastname: Topalovic
authors.affiliation: Division Animal and Human Health Engineering, Department of Biosystems, Faculty of Bioscience Engineering, KU Leuven, Leuven, Belgium.
authors.forename: Vasileios
authors.initials: V
authors.lastname: Exadaktylos
authors.affiliation: Laboratory of Respiratory Diseases, University Hospital Leuven, Department of Clinical and Experimental Medicine, KU Leuven, Herestraat 49, 3000, Leuven, Belgium.|Department of Rehabilitation Sciences, Faculty of Kinesiology and Rehabilitation, KU Leuven, Leuven, Belgium.
authors.forename: Thierry
authors.initials: T
authors.lastname: Troosters
authors.affiliation: Laboratory of Respiratory Diseases, University Hospital Leuven, Department of Clinical and Experimental Medicine, KU Leuven, Herestraat 49, 3000, Leuven, Belgium.
authors.forename: Geert
authors.initials: G
authors.lastname: Celis
authors.affiliation: Division Animal and Human Health Engineering, Department of Biosystems, Faculty of Bioscience Engineering, KU Leuven, Leuven, Belgium.
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Aerts
authors.affiliation: Laboratory of Respiratory Diseases, University Hospital Leuven, Department of Clinical and Experimental Medicine, KU Leuven, Herestraat 49, 3000, Leuven, Belgium. Wim.Janssens@uzleuven.be.
authors.forename: Wim
authors.initials: W
authors.lastname: Janssens
mesh_terms: D000328:Adult; D000368:Aged; D000403:Airway Resistance; D001249:Asthma / Q000473:pathology* / Q000503:physiopathology*; D003198:Computer Simulation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D017711:Nonlinear Dynamics; D010991:Plethysmography / Q000379:methods; D029424:Pulmonary Disease, Chronic Obstructive / Q000473:pathology* / Q000503:physiopathology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: Airway resistance; Asthma; Body-plethysmography; Chronic obstructive pulmonary disease; Pulmonary function tests