FSI Analysis of the Coughing Mechanism in a Human Trachea

Abstract

The main physiological function of coughing is to remove from the airways the mucus and foreign particles that enter the lungs with respirable air. However, in patients with endotracheal tubes, further surgery has to be performed to improve cough effectiveness. Thus, it is necessary to analyze how this process is carried out in healthy tracheas to suggest ways to improve its efficacy in operated patients. A finite element model of a human trachea is developed and used to analyze the deformability of the tracheal walls under coughing. The geometry of the trachea is obtained from CT of a 70-year-old male patient. A fluid structure interaction approach is used to analyze the deformation of the wall when the fluid (in this case, air) flows inside the trachea. A structured hexahedral-based grid for the tracheal walls and an unstructured tetrahedral-based mesh with coincident nodes for the fluid are used to perform the simulations with the finite element-based commercial software code (ADINA R&D Inc.). Tracheal wall is modeled as an anisotropic fiber reinforced hyperelastic solid material in which the different orientation of the fibers is introduced. The implantation of an endotracheal prosthesis is simulated. Boundary conditions for breathing and coughing are applied at the inlet and at the outlet surfaces of the fluid mesh. The collapsibility of a human trachea under breathing and coughing is shown in terms of flow patterns and wall stresses. The ability of the model to reproduce the normal breathing and coughing is proved by comparing the deformed shape of the trachea with experimental results. Moreover the implantation of an endotracheal prosthesis would be related with a decrease of coughing efficiency, as clinically seen.

Control mechanism for the upper airway collapse in patients with obstructive sleep apnea syndrome: a finite element study

“…By now, it is accustomed to assign an idealized flux in the inlet and a velocity or pressure in the outlet, since it is easy to measure the velocity and pressure variation in the inlet while they are difficult to obtain inside the deeper part of the upper airway. Most of the previous studies assume the airflow velocity or pressure as a regular periodic triangle waveform or sinusoidal waveform whose peak value depends on the tidal volume [19][20][21][22][23]. Yet there exists a shortage for this type of load condition which makes the total flux during the whole breath simulation to be a constant.…”

“…Up to now, similar works with the FSI method [19][20][21][22][23] have usually focused on the local structure's influence on airflow inside the upper airway. In contrast to these studies, the whole upper airway as well as the surrounding tissues was considered in the FSI simulation presented in this paper.…”

“…The restriction of these studies lies in that the influence of deformation of the airway wall is not taken into account [12][13][14][15][16][17][18]. Although some studies have paid attention to the interaction effect between airflow and soft tissue deformation, the geometrical model was usually oversimplified due to anatomical complexity and the huge cost of the coupled algorithm [19][20][21][22][23].…”

CFD Transient Simulation of a Breathing Cycle in an Oral-Nasal Extrathoracic Model

“…Furthermore, the trachea and the main bronchus bifurcation, were included, as previously done (Johnstone et al 2004;Malvè et al 2010). The geometry used is shown in detail in Fig.…”

“…The developed model was obtained as a result of smooth transition combining geometries previously tested and validated in the literature: the idealised oropharynx model, Johnstone et al (2004) with an oral volume of 53000 mm 3 , the normal nasal male anatomy without sinuses model of Weinhold and Mlynski (2004), with 35000 mm 3 volume, and the CT male trachea of Malvè et al (2010), with 23000 mm 3 .…”