Steady streaming: A key mixing mechanism in low-Reynolds-number acinar flows

Kumar, Haribalan; Tawhai, Merryn H.; Hoffman, Eric A.; Lin, Ching‐Long

doi:10.1063/1.3567066

Cited by 37 publications

(42 citation statements)

References 42 publications

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“…This finding led to the concept of chaotic mixing (i.e., flow-induced mixing), which may occur in the acinus [4,11]. Recently, numerous experimental [12][13][14][15][16] and numerical studies [17][18][19][20][21][22] of acinar flows have appeared in the literature, and many of these have confirmed the presence of recirculating alveolar flow. The occurrence of chaotic, or convective, mixing in the acinus is particularly interesting because no flow-induced mixing was assumed to occur in the classical descriptions of acinar flows [23].…”

Section: Introductionmentioning

confidence: 90%

The Simultaneous Role of an Alveolus as Flow Mixer and Flow Feeder for the Deposition of Inhaled Submicron Particles

Henry¹,

Haber

Haberthür

et al. 2012

Journal of Biomechanical Engineering

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In an effort to understand the fate of inhaled submicron particles in the small sacs, or alveoli, comprising the gas-exchange region of the lung, we calculated the flow in threedimensional (3D) rhythmically expanding models of alveolated ducts. Since convection toward the alveolar walls is a precursor to particle deposition, it was the goal of this paper to investigate the streamline maps' dependence upon alveoli location along the acinar tree. On the alveolar midplane, the recirculating flow pattern exhibited closed streamlines with a stagnation saddle point. Off the midplane we found no closed streamlines but nested, funnel-like, spiral, structures (reminiscent of Russian nesting dolls) that were directed towards the expanding walls in inspiration, and away from the contracting walls in expiration. These nested, funnel-like, structures were surrounded by air that flowed into the cavity from the central channel over inspiration and flowed from the cavity to the central channel over expiration. We also found that fluid particle tracks exhibited similar nested funnel-like spiral structures. We conclude that these unique alveolar flow structures may be of importance in enhancing deposition. In addition, due to inertia, the nested, funnel-like, structures change shape and position slightly during a breathing cycle, resulting in flow mixing. Also, each inspiration feeds a fresh supply of particleladen air from the central channel to the region surrounding the mixing region. Thus, this combination of flow mixer and flow feeder makes each individual alveolus an effective mixing unit, which is likely to play an important role in determining the overall efficiency of convective mixing in the acinus.

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Section: Introductionmentioning

confidence: 90%

The Simultaneous Role of an Alveolus as Flow Mixer and Flow Feeder for the Deposition of Inhaled Submicron Particles

Henry¹,

Haber

Haberthür

et al. 2012

Journal of Biomechanical Engineering

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“…The unique capability to nondestructively image and segment individual whole acini in the ultra-HRES datasets opens up an opportunity to study the 3D morphometry in such a way as to provide the geometries needed in, for example, computational fluid dynamics (15)(16)(17)(18)(19), allowing for improved understanding of gas exchange and particle delivery to the lung periphery. The imaging and image analysis methods described here provide for branch morphometry at the acinar level that has not been available previously.…”

Section: Discussionmentioning

confidence: 99%

Assessment of morphometry of pulmonary acini in mouse lungs by nondestructive imaging using multiscale microcomputed tomography

Vasilescu

Gao

Saha

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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110

111

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Establishing the 3D architecture and morphometry of the intact pulmonary acinus is an essential step toward a more complete understanding of the relationship of lung structure and function. We combined a special fixation method with a unique volumetric nondestructive imaging technique and image processing tools to separate individual acini in the mouse lung. Interior scans of the parenchyma at a resolution of 2 µm enabled the reconstruction and quantitative study of whole acini by image analysis and stereologic methods, yielding data characterizing the 3D morphometry of the pulmonary acinus. The 3D reconstructions compared well with the architecture of silicon rubber casts of mouse acini. The image-based segmentation of individual acini allowed the computation of acinar volume and surface area, as well as estimation of the number of alveoli per acinus using stereologic methods. The acinar morphometry of male C57BL/6 mice age 12 wk and 91 wk was compared. Significant increases in all parameters as a function of age suggest a continuous change of the lung morphometry, with an increase in alveoli beyond what has been previously viewed as the maturation phase of the animals. Our image analysis methods open up opportunities for defining and quantitatively assessing the acinar structure in healthy and diseased lungs. The methods applied here to mice can be adjusted for the study of similarly prepared human lungs.

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“…For all scenarios, the alveolar topology is connected to a cylindrical duct or a dodecagonal prism for the polyhedral alveolus (see Ref. [50]). Note that the multi-alveolated geometries are populated with four rows of alveoli where each row is composed of four (spherical model) to six alveoli (other models).…”

Section: Generic Aiveoiar Topoiogiesmentioning

confidence: 99%

Role of Alveolar Topology on Acinar Flows and Convective Mixing

Hofemeier

Sznitman

2014

Journal of Biomechanical Engineering

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Due to experimental challenges, computational simulations are often sought to quantify inhaled aerosol transport in the pulmonary acinus. Commonly, these are performed using generic alveolar topologies, including spheres, toroids, and polyhedra, to mimic the complex acinar morphology. Yet, local acinar flows and ensuing particle transport are anticipated to be influenced by the specific morphological structures. We have assessed a range of acinar models under self-similar breathing conditions with respect to alveolar flow patterns, convective flow mixing, and deposition of fine particles (1.3 μm diameter). By tracking passive tracers over cumulative breathing cycles, we find that irreversible flow mixing correlates with the location and strength of the recirculating vortex inside the cavity. Such effects are strongest in proximal acinar generations where the ratio of alveolar to ductal flow rates is low and interalveolar disparities are most apparent. Our results for multi-alveolated acinar ducts highlight that fine 1 μm inhaled particles subject to alveolar flows are sensitive to the alveolar topology, underlining interalveolar disparities in particle deposition patterns. Despite the simplicity of the acinar models investigated, our findings suggest that alveolar topologies influence more significantly local flow patterns and deposition sites of fine particles for upper generations emphasizing the importance of the selected acinar model. In distal acinar generations, however, the alveolar geometry primarily needs to mimic the space-filling alveolar arrangement dictated by lung morphology.

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Steady streaming: A key mixing mechanism in low-Reynolds-number acinar flows

Cited by 37 publications

References 42 publications

The Simultaneous Role of an Alveolus as Flow Mixer and Flow Feeder for the Deposition of Inhaled Submicron Particles

The Simultaneous Role of an Alveolus as Flow Mixer and Flow Feeder for the Deposition of Inhaled Submicron Particles

Assessment of morphometry of pulmonary acini in mouse lungs by nondestructive imaging using multiscale microcomputed tomography

Role of Alveolar Topology on Acinar Flows and Convective Mixing

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