Airflow In Human Airways Research Articles

A Numerical Simulation of Inspiratory Airflow in Human Airways during Exercise at Sea Level and at High Altitude

At high altitudes, the air pressure is much lower than it is at sea level and contains fewer oxygen molecules and less oxygen is taken in at each breath. This requires deeper and rapid breathing to get the same amount of oxygen into the blood stream compared to breathing in air at sea level. Exercises increase the oxygen demand and make breathing more difficult at high altitude. In this study, a numerical simulation of inspiratory airflow in a three-dimensional bifurcating human airways model (third to sixth generation) during exercise at sea level and at high altitude was performed. The computational fluid dynamics (CFD) solver FLUENT was used to solve the governing equations for unsteady airflow in the model. Flow velocity, pressure, and wall shear stress were obtained from the simulations with the two breathing conditions. The result of this study quantitatively showed that performing exercise with a given work rate at high altitude increased inspiratory airflow velocity, pressure, and wall shear stress more than that at sea level in the airway model. The ranges of the airflow fields were also higher at high altitude than sea level. The simulation results showed that there were no significant differences in flowing pattern for the two breathing conditions.

Investigation on the Effect of Stenosis in Respiratory Airflow in Human Airway by Particle Image Velocimetry

Using the Particle Image Velocimetry experimental method, the airflow from both left and right bronchus of human trachea was observed and analyzed. In this study, the accurate models using the actual geometry of the human trachea were created and scaled to 1.3 compared to the original size in order to visualize the flow at both branches. Models consist of healthy and stenosis models where most of the major shape and geometry were preserved to evaluate the effect from the stenosis to the inlet and along the branches. Three different flow rates at the main trachea inlet were used in order to represent three different activities of human breathing. A flow passage includes the main trachea and both left and right bronchus. As for the results, it show that stenosis did affect the normal breathing condition and disturb the flow distribution along the branches.

Comparison of turbulent models in the case of a constricted tube

The validation of a proper solution is an indispensable phase of every numerical simulation. Nowadays, many turbulent models are available, whose application leads to slightly different solution of flow behaviour depending on the boundary conditions of a specific problem. It is essential to select the proper turbulence model appropriate for the given situation. The aim of this study is to select the most suitable two-equation eddy-viscosity model, which can be further used during calculations of airflow in human airways. For this purpose, geometry of a constricted tube with well-documented experimental measurements was chosen. The flow in the constricted tube was calculated using Spallart-Almaras, k-omega, k-epsilon and SST model approach using commercial software. The outcome of the comparison is a choice of the suitable model which is capable of simulating the transition of the boundary layer from laminar to turbulent flow. This transition typically arises in the upper part of the respiratory system, where the airways are constricted, specifically in the area, where the oral cavity continues through the glottis to trachea. The simulations were performed in a commercial solver Star-CCM+.

A quasi‐3D wire approach to model pulmonary airflow in human airways

The models used for modeling the airflow in the human airways are either 0-dimensional compartmental or full 3-dimensional (3D) computational fluid dynamics (CFD) models. In the former, airways are treated as compartments, and the computations are performed with several assumptions, thereby generating a low-fidelity solution. The CFD method displays extremely high fidelity since the solution is obtained by solving the conservation equations in a physiologically consistent geometry. However, CFD models (1) require millions of degrees of freedom to accurately describe the geometry and to reduce the discretization errors, (2) have convergence problems, and (3) require several days to simulate a few breathing cycles. In this paper, we present a novel, fast-running, and robust quasi-3D wire model for modeling the airflow in the human lung airway. The wire mesh is obtained by contracting the high-fidelity lung airway surface mesh to a system of connected wires, with well-defined radii. The conservation equations are then solved in each wire. These wire meshes have around O(1000) degrees of freedom and hence are 3000 to 25000 times faster than their CFD counterparts. The 3D spatial nature is also preserved since these wires are contracted out of the actual lung STL surface. The pressure readings between the 2 approaches showed minor difference (maximum error=15%). In general, this formulation is fast and robust, allows geometric changes, and delivers high-fidelity solutions. Hence, this approach has great potential for more complicated problems including modeling of constricted/diseased lung sections and for calibrating the lung flow resistances through parameter inversion.

Comparative analysis of realistic CT-scan and simplified human airway models in airflow simulation

Efforts to model the human upper respiratory system have undergone many phases. Geometrical proximity to the realistic shape has been the subject of many research projects. In this study, three different geometries of the trachea and main bronchus were modelled, which were reconstructed from computed tomography (CT) scan images. The geometrical variations were named realistic, simplified and oversimplified. Realistic refers to the lifelike image taken from digital imaging and communications in medicine format CT scan images, simplified refers to the reconstructed image based on natural images without realistic details pertaining to the rough surfaces, and oversimplified describes the straight wall geometry of the airway. The characteristics of steady state flows with different flow rates were investigated, simulating three varied physical activities and passing through each model. The results agree with previous studies where simplified models are sufficient for providing comparable results for airflow in human airways. This work further suggests that, under most exercise conditions, the idealised oversimplified model is not favourable for simulating either airflow regimes or airflow with particle depositions. However, in terms of immediate analysis for the prediction of abnormalities of various dimensions of human airways, the oversimplified techniques may be used.

Investigation on the respiratory airflow in human airway by PIV

The creation of the accurate transparent flow passage is essential to analyze the flow inward a geometrically complex flow passage like human airway by PIV. We established the procedure to create a transparent box containing a model of the human airway for PIV measurements. A flow passage includes the whole human upper airway, nasal cavities, larynx, trachea, and 2 generations of bronchi. The phase averaged mean and RMS velocity distributions in sagittal and coronal planes are obtained for 7 phases in a respiratory period by tomographic PIV. Some physiologic conjectures are obtained. The main stream went through the backside of larynx and trachea in inspiration and the frontal side in expiration.

An experimental investigation on airflow in human airway

An experimental investigation on airflow in human airway