Improved characterization of obstructive airways diseases by parameterization of specific resistance loops

Abstract

Specific resistance loops appear in different shapes influenced by different resistive properties of the airways, yet theirs descriptive ability is compressed to a single parameter (slope). We aimed to develop different parameters reflecting the opening of the loop and explore mechanism behind it in obstructive airways diseases.

Study included 134 subjects with completely performed pulmonary function tests, divided into groups: 1/ Healthy controls (N=22), 2/ Asthma, with non-obstructive lung function (N=22), 3/ COPD, including all disease stages (N=90). Opening of the expiratory part of the loop was described with geometrical parameters: 1/ area under the loop, 2/ roundness, 3/ asynchrony.

No significant difference was found comparing developed parameters in asthma and healthy groups. However, significant difference was observed comparing these two groups with COPD. Grouping mild COPD subjects by open-not open shape revealed significant difference between geometrical parameters, but also lung function: FEV₁, RV and RV/TLC. Multiple logistic regression indicated RV/TLC ratio as only predictor of loop opening with OR =0.84, 95%CI of (0.73 – 0.94), p value =0.0006 and R² =0.35. Methacholine induced airway narrowing in asthma showed equal shape descriptors as COPD non-openers, but not slope. In contrast, all shape descriptors were significantly different comparing to COPD openers, yet slope was identical. RV/TLC was the main lung function determinant that differentiated obstructive asthma and COPD openers.

This study introduces new parameters describing differences in the shape of specific resistance loops affected by different resistive mechanisms in obstructive airways diseases.