Investigation on forced vibration characteristics of Nitinol tracheal stent

BACKGROUND

Tracheal stents can be placed in a narrow position in the human trachea to ensure smooth breathing. And the stent will deform during service by the influence of the physiological environment or random excitations, such as coughing.

METHODS

This paper divides the vibration into periodic and random vibrations according to the different pressures. And a coupling vibration model was established by analyzing the contact relationship between the stent and the trachea tissue. And this study discusses the influence of tracheal diameter, respiratory pressure, and frequency on the stent vibration characteristics through Ansys simulation. In addition, the nonlinear equations were solved by the Matlab numerical analysis method, which could help analyze the influence of cough intensity on the stability of the tracheal stent system.

RESULTS

The results showed that when tracheal stenosis occurred in the trachea's more significant grade, the trachea stent was more likely to fall off when treated with a tracheal stent. With the increase in respiratory frequency and pressure, the deformation of the tracheal stent is more considerable. Moreover, the frequency of normal cough hardly affects the stability of the stent system, while the excitation force and damping coefficient value greatly influence the system. When the excitation force of the cough exceeds the critical importance of 20 N, the tracheal stent is prone to fall off. This study comprehensively obtained the forced vibration characteristics of the stent under service conditions, which could make up for the shortage of the vibration theory of the stent.

CONCLUSION

The results can provide a theoretical basis for predicting the possibility of stent loss in clinical treatment.

Biomechanical analysis of tracheal stent during cough reflex

Tracheal stenting is a common method which is widely used to cure different tracheal disorders including airways stenosis, chronic coughs, and accidents. In this study, we aimed to analyze the reaction of the trachea wall to exhale in three phases of light, moderate, and vigorous activities at air flows of 15 L/min (light), 26 L/min (medium), and 30 L/min (vigorous). Fluid structure interaction (FSI) was used for the numerical analysis using computed tomography (CT) images. The flow was assumed incompressible and turbulent. The stent is silicone with a Young’s modulus equal to 1 MPa, Poisson’s ratio 0.28, and density of 2330 kg/m3. The stent length was 60 mm and fix support boundary condition was applied for all inputs and outputs. Numerical simulation was performed using ANSYS software. The induced stresses, strains, wall deformation, flow pressure, and the flow velocity were obtained. The results showed that the stent prevented the local deformation of the wall of trachea and it reduced the induced strain in the position. But the stenting could lead to stress concentration. Finally, the stent prevented the damage to the trachea muscles during coughs in row.