Non-linear parameters of specific resistance loops to characterise obstructive airways diseases

Background 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. Methods 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. Results 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 R 2 = 0.35. Inducing airway narrowing in asthma gave equal shape measures as in COPD non-openers, but with a decreased slope ( p < 0.0001). Conclusion This study introduces new parameters calculated from the resistance loops which may correlate with different phenotypes of obstructive airways diseases.