Flow and Particle Dispersion in Lung Acini: Effect of Geometric and Dynamic Parameters During Synchronous Ventilation

Abstract

The human lung comprises about 300 million alveoli which are located on bronchioles between the 17th to 24th generations of the acinar tree, with a progressively higher population density in the deeper branches (lower acini). The alveolar size and aspect ratio change with generation number. Due to successive bifurcation, the flow velocity magnitude also decreases as the bronchiole diameter decreases from the upper to lower acini. As a result, fluid dynamic parameters such as Reynolds (Re) and Womersley (α) numbers progressively decrease with increasing generation number. In order to characterize alveolar flow patterns and inhaled particle transport during synchronous ventilation, we have conducted measurements for a range of dimensionless parameters physiologically relevant to the upper acini. Acinar airflow patterns were measured using a simplified in vitro alveolar model consisting of a single transparent elastic truncated sphere (representing the alveolus) mounted over a circular hole on the side of a rigid circular tube (representing the bronchiole). The model alveolus was capable of expanding and contracting in-phase with the oscillatory flow through the bronchiole thereby simulating synchronous ventilation. Realistic breathing conditions were achieved by exercising the model over a range of progressively varying geometric and dynamic parameters to simulate the environment within several generations of the acinar tree. Particle image velocimetry was used to measure the resulting flow patterns. Next, we used the measured flow fields to calculate particle trajectories to obtain particle transport and deposition statistics for massless and finite-size particles under the influence of flow advection and gravity. Our study shows that the geometric parameters (β and ΔV/V) primarily affect the velocity magnitudes, whereas the dynamic parameters (Re and α) distort the flow symmetry while also altering the velocity magnitudes. Consequently, the dynamic parameters have a greater influence on the particle trajectories and deposition statistics compared to the geometric parameters. The results from this study can benefit pulmonary research into the risk assessment of toxicological inhaled aerosols, and the pharmaceutical industry by providing better insight into the flow patterns and particle transport of inhalable therapeutics in the acini.

Investigation on Microparticle Transport and Deposition Mechanics in Rhythmically Expanding Alveolar Chip

“…Several experimental studies using enlarged alveolar models have been proposed to study the alveolar flow and particle transport in the alveolar region [ 21 , 22 , 23 , 24 , 25 , 26 ]. Ma et al [ 24 ] and Berg et al [ 25 ] used the scaled-up model to track the particles in the ducts.…”

“…Ma et al [ 24 ] and Berg et al [ 25 ] used the scaled-up model to track the particles in the ducts. Chhabra and Prasad [ 26 , 27 , 28 ] in their studies focused on the deposition regions of the particles. These researchers have made great contributions to display the fates of particles in the alveoli.…”

“…For the real particles, the gravity also has large impacts on the particle transport besides the drag force and diffusion, because larger particles can also deposit in the alveoli due to gravitational sedimentation [ 34 , 35 ]. According to the previous studies [ 1 , 26 , 36 , 37 ], the directions of the alveolar openings vary across the whole lungs. On the other hand, according to Lv et al [ 38 ] and Dong et al [ 39 ], compared with multi-generation alveolar chip, the alveolar chip with single alveolus has the advantage in closely matching the flow parameters with the real ones.…”

Microparticle Transport and Sedimentation in a Rhythmically Expanding Alveolar Chip

“…Several experiments have been carried out to study particle transport and sedimentation in the alveoli, including scaled-up models and microfluidic chips [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ]. Chhabra et al [ 26 ] and Oakes et al [ 17 ] developed scaled-up alveolar models and adopted the particle imaging velocimetry (PIV) system to investigate particle transport and deposition in the alveoli. Rong et al [ 18 , 25 ] studied the effect of functional residual capacity on the deposition of particles in the human alveolar region by setting up a scale-up model with multiple alveoli.…”

A Microfluidic Model of Biomimetically Breathing Pulmonary Acinar Airways

“…. As a result, state-of-the-art investigations of respiratory flow phenomena in the acinus remain dominated by studies focusing on generic anatomically-inspired geometries of the acinar environment On the experimental side, various setups featuring an airway with one or several alveoli have been developed over the years [21][22][23][24] . Yet, there exists no experimental models of bifurcating alveolated airways that are capable of mimicking physiological respiration by expanding and contracting in a breathing-like fashion.…”