Elsevier

Journal of Biomechanics

Volume 49, Issue 14, 3 October 2016, Pages 3543-3548
Journal of Biomechanics

Short communication
The role of anisotropic expansion for pulmonary acinar aerosol deposition

https://doi.org/10.1016/j.jbiomech.2016.08.025Get rights and content

Abstract

Lung deformations at the local pulmonary acinar scale are intrinsically anisotropic. Despite progress in imaging modalities, the true heterogeneous nature of acinar expansion during breathing remains controversial, where our understanding of inhaled aerosol deposition still widely emanates from studies under self-similar, isotropic wall motions. Building on recent 3D models of multi-generation acinar networks, we explore in numerical simulations how different hypothesized scenarios of anisotropic expansion influence deposition outcomes of inhaled aerosols in the acinar depths. While the broader range of particles acknowledged to reach the acinar region (dp=0.0055.0μm) are largely unaffected by the details of anisotropic expansion under tidal breathing, our results suggest nevertheless that anisotropy modulates the deposition sites and fractions for a narrow band of sub-micron particles (dp~0.50.75μm), where the fate of aerosols is greatly intertwined with local convective flows. Our findings underscore how intrinsic aerosol motion (i.e. diffusion, sedimentation) undermines the role of anisotropic wall expansion that is often attributed in determining aerosol mixing and acinar deposition.

Section snippets

Background

The past two decades have witnessed important efforts to resolve respiratory flows in the acinar depths, motivated in part by the prospect of predicting the fate of inhaled aerosols for therapeutic delivery (Sznitman, 2013, Tsuda et al., 2013). Parallel to the emergence of true-scale experimental acinar platforms (Fishler et al., 2013, Fishler et al., 2015), numerical simulations have served as a backbone to help advance our understanding of acinar aerosol transport given their appeal and

Methods

Drawing on recent models of multi-generational acinar networks (Hofemeier and Sznitman, 2015, Sznitman et al., 2009, Tian et al., 2015), our airway trees feature an asymmetric bifurcating structure reaching up to 6 generations with a total of 277 polyhedral alveolar units (Fig. 2) that capture the space-filling acinar morphology (Fung, 1988). Despite their simplicity and limitations (e.g. see discussion in Hofemeier and Sznitman, 2015), these domains constitute a versatile computational

Results and discussion

Modulations in the acinar expansion kinematics are anticipated to give rise to changes in airflow characteristics across the acinar network. While the underlying parabolic-like velocity profiles in the ducts and recirculation zones in alveoli remain common features across breathing motions, Fig. 2 exemplifies differences in flow magnitudes along the acinar tree. Here, 1D velocity profiles are presented at peak inspiration (t/τ~0.25) across the acinar ducts and alveoli (l/W, see domain in Fig. 2

Conflict of interest statement

None declared.

Acknowledgments

The authors would like to thank Dr. R. Fishler for constructive discussions. This work was supported in part by the Israel Science Foundation (Grant no. 990/12) and the European Research Council (ERC) under the European Union׳s Horizon 2020 research and innovation programme (Grant agreement no. 677772).

References (50)

  • A. Tsuda et al.

    Gas and aerosol mixing in the acinus

    Respir. Physiol. Neurobiol.

    (2008)
  • A. Tsuda et al.

    Why chaotic mixing of particles is inevitable in the deep lung

    J. Theor. Biol.

    (2011)
  • C. Darquenne et al.

    Two- and three-dimensional simulations of aerosol transport and deposition in alveolar zone of human lung

    J. Appl. Physiol.

    (1996)
  • R.R. Delvadia et al.

    In vitro tests for aerosol deposition. IVSimulating variations in human breath profiles for realistic DPI testing

    J. Aerosol Med. Pulm. Drug Deliv.

    (2015)
  • E. Denny et al.

    Relationships between alveolar size and fibre distribution in a mammalian lung alveolar duct model

    J. Biomech. Eng.

    (1997)
  • R. Fishler et al.

    Particle dynamics and deposition in true-scale pulmonary acinar models

    Sci. Rep.

    (2015)
  • Y.C. Fung

    A model of the lung structure and its validation

    J. Appl. Physiol.

    (1988)
  • J. Gil et al.

    Alveolar volume-surface area relation in air- and saline-filled lungs fixed by vascular perfusion

    J. Appl. Physiol.

    (1979)
  • Greaves, I.A., Hildebrandt, J., Hoppin, F.G., 2011. Micromechanics of the Lung. Compr. Physiol. Supplement 12: Handbook...
  • A.J. Hajari et al.

    Morphometric changes in the human pulmonary acinus during inflation

    J. Appl. Physiol.

    (2012)
  • F.S. Henry et al.

    Kinematically irreversible acinar flowa departure from classical dispersive aerosol transport theories

    J. Appl. Physiol.

    (2002)
  • J. Heyder et al.

    Convective mixing in human respiratory tractestimates with aerosol boli

    J. Appl. Physiol.

    (1988)
  • W.C. Hinds

    Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles, 2nd edition

    (1999)
  • P. Hofemeier et al.

    Role of alveolar topology on acinar flows and convective mixing

    J. Biomech. Eng.

    (2014)
  • P. Hofemeier et al.

    Revisiting pulmonary acinar particle transportconvection, sedimentation, diffusion, and their interplay

    J. Appl. Physiol.

    (2015)
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