Tech Briefs

Fluid-structure Interaction Analysis of the Human Coughing Mechanism

In biomedical engineering, ADINA is extensively used for mechanical analyses of various human physiological processes to provide better understanding for the improvement of surgical procedures and other treatment options.

We highlight a biomechanical study of the coughing mechanism in the human trachea. ADINA FSI is used to analyze and compare the deformation and collapsibility of the human tracheal wall under normal breathing and coughing conditions. This study is motivated by the need for further surgery to improve cough effectiveness in patients with endotracheal tube implants (see Ref.). A better understanding of the coughing process can help the surgeon to position the implant for maximum efficiency.

The fact that ADINA can be used to simulate closely the normal breathing and coughing processes is demonstrated by comparing the actual deformed shape of the tracheal cross-section with the numerical results.

In the model, the tissues in the trachea wall are modeled as isotropic and anisotropic hyperelastic materials using the Holzapfel material model. Air flow in the trachea is modeled as a Newtonian fluid under laminar and turbulent flow conditions respectively for normal breathing and coughing processes. The interaction between the air flow and the tracheal wall is modeled using the Arbitrary Lagrangian-Eulerian (ALE) formulation.

Figure 1 shows the deformed shape of a tracheal wall and the cross-section of the tracheal tube during normal breathing. The figure shows the flow rate during breathing, and an animation of the cartilage tissue (part of the tracheal wall) deformation. At the far right, the numerical results and corresponding photographs of the deformed shape of the tracheal cross-section are shown. The shape of the cross-section predicted by ADINA compares well with the actual shape.

Figure 1 Breathing

The coughing process is addressed in Figure 2. As coughing is a much quicker process than breathing, the graph in this figure presents the flow rate in the tracheal tube in a shorter period of 1.3 seconds compared to the 4 seconds of Figure 1. The animation of the tracheal wall shows a much larger deformation than in normal breathing. This larger deformation is clearly seen in the shape of the cross-section of each band plot and its corresponding photograph.

Figure 2 Coughing

ADINA FSI was used to simulate accurately the deformation of the tracheal wall, both in normal breathing and in the much quicker coughing process. The results give insight into the difficulty of coughing for patients with the endotracheal implant, due to the increase of the tracheal wall stiffness and the consequent loss of tracheal tube muscle contraction capability.

This study demonstrates an effective use of ADINA FSI in biomedical research. A list of publications featuring many applications of ADINA FSI in biomechanics and other fields may be found at ADINA FSI publications.

Reference

• M. Malvé, A. Pérez Del Palomar, J.L. López-Villalobos, A. Ginel, and M. Doblaré, "FSI Analysis of the Coughing Mechanism in a Human Trachea", Annals of Biomedical Engineering, Vol. 38, No. 4, pp. 1556-1565, 2010

Keywords:
Trachea, biomechanics, endotracheal implant, fluid-structure interaction, FSI, coughing, fiber reinforced material, large deformation, Holzapfel, ALE, turbulence

Courtesy of M. Malvé, A. Perez Del Palomar, M. Doblaré (Universidad de Zaragoza, Spain; CIBER-BBN, Spain and Instituto de Salud Carlos III, Spain); J.L. López-Villalobos, A. Ginel (Hospital Virgen del Rocío, Seville, Spain)