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Original Research ARTICLE Provisionally accepted The full-text will be published soon. Notify me

Front. Physiol. | doi: 10.3389/fphys.2019.01390

Low frequency forced oscillation lung function test can distinguish dynamic tissue nonlinearity in COPD patients

Maria Ghita1,  Dana Copot1*, Mihaela Ghita1, Eric Derom2 and  Clara Ionescu1
  • 1Ghent University, Belgium
  • 2Ghent University Hospital, Belgium

This paper introduces the use of low frequencies forced oscillation technique (FOT)
in the presence of breathing signal. The hypothesis tested is to evaluate the sensitivity of FOT
to various degrees of obstruction in COPD patients. The use of FOT to evaluate respiratory impedance has been broadly recognized and its complementary use next to standardized
method as spirometry and body plethysmography has been well documented. Typical use of
FOT uses frequencies between 4-32 Hz and above. However, interesting information at frequencies below 4 Hz is related to viscoelastic properties of parenchyma. Structural changes
in COPD affect viscoelastic properties and we propose to investigate the use of FOT at low
frequencies with a fourth generation fan-based FOT device. The generator nonlinearity introduced by the device is separated from the linear approximation of the impedance before
evaluating the results on patients. Three groups of COPD obstruction, GOLD II, III and IV
are evaluated. We found significant differences in mechanical parameters (tissue damping,
tissue elasticity, histeresivity) and increased degrees of nonlinear dynamic contributions in
the impedance data with increasing degree of obstruction (p 0:01). The results obtained
suggest that our propsoed index for nonlinearity evaluation correlates better with degrees of
heterogeneity linked to COPD GOLD stages, than the currently used histeresivity index. The
protocol and method may prove useful to improve current diagnosis percentages for various
COPD phenotypes.

Keywords: Forced oscillation technique, respiratory impedance, COPD, Viscoelastic properties, Small airways, remodelling

Received: 01 Feb 2019; Accepted: 25 Oct 2019.

Copyright: © 2019 Ghita, Copot, Ghita, Derom and Ionescu. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Dana Copot, Ghent University, Ghent, 9000, East Flanders, Belgium, dana.copot@ugent.be