Abstract
BackgroundSpecific 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.MethodsOur 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.ResultsOur 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).ConclusionThis study introduces new parameters calculated from the resistance loops which may correlate with different phenotypes of obstructive airways diseases.
Highlights
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
Baseline characteristics of the subjects are presented in the Table 1: i) Healthy group is defined as a group of asymptomatic subjects without smoking history with all lung function parameters falling in the normal reference range; ii) Asthma group: subjects with or without smoking history, a previous clinical diagnosis of asthma based on symptoms and therapy response, with a nonobstructive lung function and positive reaction on inhaled methacholine (FEV1 drop of at least 20% at maximal concentration of 8 mg/ml of methacholine) [18]; and iii) COPD group: subjects with at least 10 pack-years of smoking history and post-bronchodilator FEV1/FVC ratio below 0.7 [19]
Confirmation of the appropriate model selection was demonstrated with a high goodness of fit expressed as normalized root mean square error (NRMSE) of 90 (85–92)% for complete dataset
Summary
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. Spirometry requires forced maximal manoeuvres but cannot quantify increased resistance of the airways at tidal breathing, which may be characteristic and specific for the underlying disease. Whole-body plethysmography, allows the computation of airways resistance by measuring alveolar pressure changes and corresponding airway flows during tidal breathing in a closed body box [6]. Plethysmography records the small changes in box pressure by compression and decompression of thoracic gas which correspond to small volume changes, known as shift volume.
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