Flow and Particle Dispersion in a Pulmonary Alveolus—Part II: Effect of Gravity on Particle Transport

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
Sudhaker Chhabra ◽  
Ajay K. Prasad
Keyword(s):  
Gas Exchange ◽  
Particle Transport ◽  
In Vitro Model ◽  
Particle Dispersion ◽  
Gravitational Settling ◽  
Image Velocimetry ◽  
Large Particles ◽  
Vitro Model ◽  
Complex Trajectories

The acinar region of the human lung comprises about 300×106 alveoli, which are responsible for gas exchange between the lung and the blood. As discussed in Part I (Chhabra and Prasad, “Flow and Particle Dispersion in a Pulmonary Alveolus—Part I: Velocity Measurements and Convective Particle Transport,” ASME J. Biomech. Eng., 132, p. 051009), the deposition of aerosols in the acinar region can either be detrimental to gas exchange (as in the case of harmful particulate matter) or beneficial (as in the case of inhalable pharmaceuticals). We measured the flow field inside an in-vitro model of a single alveolus mounted on a bronchiole and calculated the transport and deposition of massless particles in Part I. This paper focuses on the transport and deposition of finite-sized particles ranging from 0.25 μm to 4 μm under the combined influence of flow-induced advection (computed from velocity maps obtained by particle image velocimetry) and gravitational settling. Particles were introduced during the first inhalation cycle and their trajectories and deposition statistics were calculated for subsequent cycles for three different particle sizes (0.25 μm, 1 μm, and 4 μm) and three alveolar orientations. The key outcome of the study is that particles ≤0.25 μm follow the fluid streamlines quite closely, whereas midsize particles (dp=1 μm) deviate to some extent from streamlines and exhibit complex trajectories. The motion of large particles ≥4 μm is dominated by gravitational settling and shows little effect of fluid advection. Additionally, small and midsize particles deposit at about two-thirds height in the alveolus irrespective of the gravitational orientation whereas the deposition of large particles is governed primarily by the orientation of the gravity vector.

Fluid and Particle Transport in an In-Vitro Model of an Expanding/Contracting Human Alveolus

2007 ◽  
Author(s):  
Sudhaker Chhabra ◽  
Ajay K. Prasad
Keyword(s):  
Particulate Matter ◽  
Respiratory Tract ◽  
Fluid Mechanics ◽  
Respiratory System ◽  
Particle Transport ◽  
In Vitro Model ◽  
Adverse Health Effects ◽  
Fields Of Study ◽  
Vitro Model

Inhaled particulate matter from the environment can produce adverse health effects on the human respiratory system. Conversely, inhalable therapeutics can be delivered to the respiratory tract to treat local and systemic ailments. Both of these fields of study require the accurate prediction of particle transport and deposition in the lung, particularly in the acinar region. A necessary first step to predict particle trajectories is to characterize the airflow in which the particles are suspended. Only particles smaller than 5 μm reach the acinar region [1], hence it can be assumed that such particles will closely follow the fluid streamlines. The current work focuses on the fluid mechanics of the acinar region of the lung to infer particle transport and deposition.

Flow and Particle Dispersion in a Pulmonary Alveolus—Part I: Velocity Measurements and Convective Particle Transport

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
Sudhaker Chhabra ◽  
Ajay K. Prasad
Keyword(s):  
Particle Transport ◽  
Vector Fields ◽  
Wall Motion ◽  
Flow Patterns ◽  
Particle Dispersion ◽  
Alveolar Wall ◽  
Spherical Cap ◽  
Image Velocimetry ◽  
Transport And Mixing

The alveoli are the smallest units of the lung that participate in gas exchange. Although gas transport is governed primarily by diffusion due to the small length scales associated with the acinar region (∼500 μm), the transport and deposition of inhaled aerosol particles are influenced by convective airflow patterns. Therefore, understanding alveolar fluid flow and mixing is a necessary first step toward predicting aerosol transport and deposition in the human acinar region. In this study, flow patterns and particle transport have been measured using a simplified in-vitro alveolar model consisting of a single alveolus located on a bronchiole. The model comprises a transparent elastic 5/6 spherical cap (representing the alveolus) mounted over a circular hole on the side of a rigid circular tube (representing the bronchiole). The alveolus is capable of expanding and contracting in phase with the oscillatory flow through the tube. Realistic breathing conditions were achieved by exercising the model at physiologically relevant Reynolds and Womersley numbers. Particle image velocimetry was used to measure the resulting flow patterns in the alveolus. Data were acquired for five cases obtained as combinations of the alveolar-wall motion (nondeforming/oscillating) and the bronchiole flow (none/steady/oscillating). Detailed vector maps at discrete points within a given cycle revealed flow patterns, and transport and mixing of bronchiole fluid into the alveolar cavity. The time-dependent velocity vector fields were integrated over multiple cycles to estimate particle transport into the alveolar cavity and deposition on the alveolar wall. The key outcome of the study is that alveolar-wall motion enhances mixing between the bronchiole and the alveolar fluid. Particle transport and deposition into the alveolar cavity are maximized when the alveolar wall oscillates in tandem with the bronchiole fluid, which is the operating case in the human lung.

An in vitro model for investigation of vitamin A effects on wound healing

2021 ◽  
pp. 1-6
Author(s):  
Hoda Keshmiri Neghab ◽  
Mohammad Hasan Soheilifar ◽  
Gholamreza Esmaeeli Djavid
Keyword(s):  
Wound Healing ◽  
Endothelial Cell ◽  
Vitamin A ◽  
In Vitro Model ◽  
Cellular Proliferation ◽  
Endothelial Cell Migration ◽  
Normal Fibroblast ◽  
Anti Inflammatory ◽  
Vitro Model

Abstract. Wound healing consists of a series of highly orderly overlapping processes characterized by hemostasis, inflammation, proliferation, and remodeling. Prolongation or interruption in each phase can lead to delayed wound healing or a non-healing chronic wound. Vitamin A is a crucial nutrient that is most beneficial for the health of the skin. The present study was undertaken to determine the effect of vitamin A on regeneration, angiogenesis, and inflammation characteristics in an in vitro model system during wound healing. For this purpose, mouse skin normal fibroblast (L929), human umbilical vein endothelial cell (HUVEC), and monocyte/macrophage-like cell line (RAW 264.7) were considered to evaluate proliferation, angiogenesis, and anti-inflammatory responses, respectively. Vitamin A (0.1–5 μM) increased cellular proliferation of L929 and HUVEC (p < 0.05). Similarly, it stimulated angiogenesis by promoting endothelial cell migration up to approximately 4 fold and interestingly tube formation up to 8.5 fold (p < 0.01). Furthermore, vitamin A treatment was shown to decrease the level of nitric oxide production in a dose-dependent effect (p < 0.05), exhibiting the anti-inflammatory property of vitamin A in accelerating wound healing. These results may reveal the therapeutic potential of vitamin A in diabetic wound healing by stimulating regeneration, angiogenesis, and anti-inflammation responses.

A new in vitro model for pre-transplantation diagnosis of frozen/thawed human ovarian tissue

2011 ◽  
Vol 71 (05) ◽  
Author(s):  
M Salama ◽  
K Winkler ◽  
KF Murach ◽  
S Hofer ◽  
L Wildt ◽  
...  
Keyword(s):  
In Vitro Model ◽  
Ovarian Tissue ◽  
Human Ovarian Tissue ◽  
Vitro Model
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