In silico study on the impact of heterogeneous narrowing of small airways on spirometry results

Abstract

Introduction: It is postulated that chronic respiratory diseases are associated with heterogeneous narrowing of airways and that early changes in small airways are weakly reflected in spirometric indices. Aim: To assess the impact of different levels of small airways narrowing heterogeneity on the spirometric curve and indices. Methods: The spirometric curves were reproduced in silico (Polak, A.G. et al. Ann. Biomed. Eng. 2003; 31:891-907) for four cases of narrowed bronchioles with the same (threefold) mean constriction level: homogenous, and mild, moderate and severe heterogeneous ones. In each case 30 results were obtained. Then the hypothesis that the samples came from the same distribution was tested against: they were from different distributions (Kolmogorov-Smirnov), they did not have equal medians (Wilcoxon), and they had larger dispersions for larger heterogeneity (Ansari-Bradley). Results: All spirometric curves generated in the heterogeneous cases were very similar to the curve representing homogeneous narrowing. Mean FEV 1 , FEV 1 %VC, FEF 25-75% and PEF were similarly reduced by 12.5, 12.5, 40.3 and 3.5 % from the baseline. No statistically significant differences were observed between these groups in terms of distributions and medians. Dispersions were significantly higher for all the indices, comparing severe to mild heterogeneity. Conclusion: Spirometric curves and indices are insensitive to the heterogeneity level of small airways narrowing, the effect disenabling differentiation between homogenous and inhomogeneous changes occurring in the lung periphery. Acknowledgments: This work was supported by the grant no. 2016/21/B/ST7/02233 from the National Science Centre, Poland.