scholarly journals Axial Mass Transport by Reciprocating Flow in Branching Tube Network. Gas Exchange Mechanism in Conducting Airways of Human Lung.

2002 ◽  
Vol 68 (667) ◽  
pp. 831-838 ◽  
Author(s):  
Sadanari MOCHIZUKI ◽  
Akira MURATA ◽  
Yuki TOGASHI
Keyword(s):  
Gas Exchange ◽  
Mass Transport ◽  
Human Lung ◽  
Exchange Mechanism ◽  
Axial Mass ◽  
Conducting Airways ◽  
Reciprocating Flow

Fluid Flow and Particle Dispersion in Acini During Asynchronous Ventilation

2008 ◽  
Author(s):  
Sudhaker Chhabra ◽  
Ajay K. Prasad
Keyword(s):  
Carbon Dioxide ◽  
Fluid Flow ◽  
Gas Exchange ◽  
Surface Area ◽  
Opposite Direction ◽  
Respiratory System ◽  
Human Lung ◽  
Alveolar Epithelium ◽  
Particle Dispersion ◽  
Conducting Airways

The human lung comprises 24 generations of dichotomously branching tubes known as bronchi [1]. Functionally, these generations can be categorized as: (1) conducting airways which are non-alveolated and comprise the first 16 generations, and (2) the acini which consist of flexible, alveolated airways and are responsible for gas exchange. The alveoli are the most important units of the human respiratory system and provide large surface area (about 70–80 m2) for efficient gas exchange; oxygen diffuses into the blood through the alveolar epithelium, whereas carbon dioxide diffuses in the opposite direction from the blood to the lung.

VISUALIZATION EXPERIMENT OF MASS TRANSPORT IN PULMONARY VENTILATION INSIDE BRONCHIAL TUBE MODEL

2001 ◽  
Vol 01 (02) ◽  
pp. 181-192 ◽  
Author(s):  
S. MOCHIZUKI ◽  
Y. TOGASHI ◽  
A. MURATA ◽  
W. J. YANG
Keyword(s):  
Gas Exchange ◽  
Human Lung ◽  
Pulmonary Ventilation ◽  
Bronchial Tube ◽  
Working Fluid ◽  
High Frequency Ventilation ◽  
Release Mechanism ◽  
Tube Model ◽  
Human Respiration ◽  
Reciprocating Flow

Flow visualization in reciprocating flow inside branching tubes was performed to investigate the mechanism of axial gas exchange in the human lung system. A bronchial tube model is employed which is geometrically similar to the average human lung system. Water is used as the working fluid. The ranges of Reynolds and Womersley numbers in the present study correspond to those of normal human respiration and HFV (high frequency ventilation), respectively. It is revealed that the axial gas exchange phenomenon occurring in the human lung system is governed by a "trap-and-release" mechanism caused by the formation-and-destruction of the separation regions, which are formed on the wall of the parent tube and or daughter tubes, depending on the direction of the reciprocating flow.

Effect of Geometric and Dynamic Parameters on Fluid Flow and Particle Dispersion in Human Lung Acini

2009 ◽  
Author(s):  
Sudhaker Chhabra ◽  
Ajay K. Prasad
Keyword(s):  
Carbon Dioxide ◽  
Fluid Flow ◽  
Gas Exchange ◽  
Surface Area ◽  
Respiratory System ◽  
Human Lung ◽  
Alveolar Epithelium ◽  
Particle Dispersion ◽  
Dynamic Parameters ◽  
Conducting Airways

Breathing, defined as the exchange of gases between the respiratory system and the environment, is an essential process for life. The human respiratory system can be divided into three parts: (i) nose, mouth, and nasopharynx, (ii) trachea, and (iii) lungs. The human lung can be further subdivided into conducting airways which are non-alveolated and comprise the upper part of lung, and the acini which consist of flexible, alveolated airways and are responsible for gas exchange [1]. The alveoli collectively provide a large surface area (∼70 m2) for efficient gas exchange [1]; oxygen diffuses into the blood through the alveolar epithelium, whereas carbon dioxide diffuses in the opposite direction from the blood to the lung.

scholarly journals Evidence for minimal oxygen heterogeneity in the healthy human pulmonary acinus

2011 ◽  
Vol 110 (2) ◽  
pp. 528-537 ◽  
Author(s):  
Annalisa J. Swan ◽  
Merryn H. Tawhai
Keyword(s):  
Gas Exchange ◽  
Small Degree ◽  
Quantitative Prediction ◽  
Significant Heterogeneity ◽  
Healthy Human ◽  
Indirect Measurements ◽  
Alveolar Air ◽  
Pulmonary Acinus ◽  
Hemoglobin Binding ◽  
Conducting Airways

It has been suggested that the human pulmonary acinus operates at submaximal efficiency at rest due to substantial spatial heterogeneity in the oxygen partial pressure (Po2) in alveolar air within the acinus. Indirect measurements of alveolar air Po2 could theoretically mask significant heterogeneity if intra-acinar perfusion is well matched to Po2. To investigate the extent of intra-acinar heterogeneity, we developed a computational model with anatomically based structure and biophysically based equations for gas exchange. This model yields a quantitative prediction of the intra-acinar O2 distribution that cannot be measured directly. Temporal and spatial variations in Po2 in the intra-acinar air and blood are predicted with the model. The model, representative of a single average acinus, has an asymmetric multibranching respiratory airways geometry coupled to a symmetric branching conducting airways geometry. Advective and diffusive O2 transport through the airways and gas exchange into the capillary blood are incorporated. The gas exchange component of the model includes diffusion across the alveolar air-blood membrane and O2-hemoglobin binding. Contrary to previous modeling studies, simulations show that the acinus functions extremely effectively at rest, with only a small degree of intra-acinar Po2 heterogeneity. All regions of the model acinus, including the peripheral generations, maintain a Po2 >100 mmHg. Heterogeneity increases slightly when the acinus is stressed by exercise. However, even during exercise the acinus retains a reasonably homogeneous gas phase.

Axial mass transport in liquid–liquid Taylor–Couette–Poiseuille flow

2000 ◽  
Vol 55 (21) ◽  
pp. 5079-5087 ◽  
Author(s):  
Xiaoyan Zhu ◽  
Richard John Campero ◽  
R.Dennis Vigil
Keyword(s):  
Mass Transport ◽  
Poiseuille Flow ◽  
Axial Mass ◽  
Taylor Couette

Carbon dioxide added late in inspiration reduces ventilation-perfusion heterogeneity without causing respiratory acidosis

2004 ◽  
Vol 96 (5) ◽  
pp. 1894-1898 ◽  
Author(s):  
Thomas V. Brogan ◽  
H. Thomas Robertson ◽  
Wayne J. E. Lamm ◽  
Jennifer E. Souders ◽  
Erik R. Swenson
Keyword(s):  
Carbon Dioxide ◽  
Gas Exchange ◽  
Respiratory Acidosis ◽  
Respiratory Cycle ◽  
Inert Gas ◽  
Arterial Oxygenation ◽  
Arterial Ph ◽  
Mixed Breed ◽  
Conducting Airways ◽  
Area Difference

We have shown previously that inspired CO2 (3-5%) improves ventilation-perfusion (V̇a/Q̇) matching but with the consequence of mild arterial hypercapnia and respiratory acidosis. We hypothesized that adding CO2 only late in inspiration to limit its effects to the conducting airways would enhance V̇a/Q̇ matching and improve oxygenation without arterial hypercapnia. CO2 was added in the latter half of inspiration in a volume aimed to reach a concentration of 5% in the conducting airways throughout the respiratory cycle. Ten mixed-breed dogs were anesthetized and, in a randomized order, ventilated with room air, 5% CO2 throughout inspiration, and CO2 added only to the latter half of inspiration. The multiple inert-gas elimination technique was used to assess V̇a/Q̇ heterogeneity. Late-inspired CO2 produced only very small changes in arterial pH (7.38 vs. 7.40) and arterial CO2 (40.6 vs. 39.4 Torr). Compared with baseline, late-inspired CO2 significantly improved arterial oxygenation (97.5 vs. 94.2 Torr), decreased the alveolar-arterial Po2 difference (10.4 vs. 15.7 Torr) and decreased the multiple inert-gas elimination technique-derived arterial-alveolar inert gas area difference, a global measurement of V̇a/Q̇ heterogeneity (0.36 vs. 0.22). These changes were equal to those with 5% CO2 throughout inspiration (arterial Po2, 102.5 Torr; alveolar-arterial Po2 difference, 10.1 Torr; and arterial-alveolar inert gas area difference, 0.21). In conclusion, we have established that the majority of the improvement in gas exchange efficiency with inspired CO2 can be achieved by limiting its application to the conducting airways and does not require systemic acidosis.

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