Yingxi Liu

Fluid–structure interaction modeling of upper airways before and after nasal surgery for obstructive sleep apnea

Nasal obstruction frequently has been associated with obstructive sleep apnea (OSA). Although correction of an obstructed nasal airway is considered an important component in OSA treatment, the effect of nasal surgery on OSA remains controversial. Variation in airway anatomy between before and after nasal surgery may cause significant differences in airflow patterns within the upper airway. In this paper, anatomically accurate models of the interaction between upper airway and soft palate were developed from prenasal and post-nasal surgery multidetector computed tomography data of a patient with OSA and nasal obstruction. Computational modeling for inspiration and expiration was performed by using fluid-structure interaction method. The airflow characteristics such as velocity, turbulence intensity and pressure drop, and displacement distribution of soft palate are selected for comparison. Airway resistances significantly decrease after the nasal surgery, especially in the velopharynx region because of an enlarged pharyngeal cavity and a reduced upstream resistance. Meanwhile, the decreased aerodynamic force would result in a smaller displacement of soft palates, which would lead to slight impact of the soft palate motion on the airflow characteristics. The present results suggest that airflow distribution in the whole upper airway and soft palate motions have improved following nasal surgery.

ESTIMATION OF THERMAL CONDUCTIVITY OF POROUS MATERIAL WITH FEM AND FRACTAL GEOMETRY

The relationship between thermal conductivity of porous material and fractal dimension is numerically simulated by using the finite element method. The solid matrix and pore space are generated randomly according to material porosity. Material parameters and element properties are changed by using ANSYS parameter design language. The effective thermal conductivity is derived according to thermal flux through some sections computed by FEM and Fourier heat transform law. The investigation shows that the effective thermal conductivity decreases with increasing porosity. The effective thermal conductivity will decrease exponentially with increasing fractal dimension of porosity space and increase exponentially with increasing fractal dimension of solid matrix.

Evaluation of the Upper Airway in Children with Obstructive Sleep Apnea Undergoing Adenoidectomy Using Computational Fluid Dynamics

Adenoidectomy is a common surgical procedure performed on children with Obstructive Sleep Apnea (OSA). Owing to lack of objective data, the studies on evaluation postoperative outcomes have been limited. The present study takes computational fluid dynamics (CFD) approach to assessing postoperative effect in children with OSA undergoing adenoidectomy by comparison of the flow field characteristics between postoperative with preoperative upper airway. The computational fluid dynamics models were constructed using raw data from preoperative and postoperative computed tomogram images of three children with OSA. Considering three- dimensional transient turbulent flow in the airway, flow field was solved for a cycle of normal breathing. The simulation results are validated by the clinical measurements and results in literature. It is shown that the airflow patterns in postoperative nasopharyngeal airway are significantly different from preoperative subjects. The resistance in nasopharyngeal passage can be an objective parameter to evaluate the treatment effects.

A Biomechanical Model of the Inner Ear: Numerical Simulation of the Caloric Test

Whether two vertical semicircular canals can receive thermal stimuli remains controversial. This study examined the caloric response in the three semicircular canals to the clinical hot caloric test using the finite element method. The results of the developed model showed the horizontal canal (HC) cupula maximally deflected to the utricle side by approximately 3 μm during the hot supine test. The anterior canal cupula began to receive the caloric stimuli about 20 s after the HC cupula, and it maximally deflected to the canal side by 0.55 μm. The posterior canal cupula did not receive caloric stimuli until approximately 40 s after the HC cupula, and it maximally deflected to the canal side by 0.34 μm. Although the endolymph flow and the cupular deformation change with respect to the head position during the test, the supine test ensures the maximal caloric response in the HC, but no substantial improvement for the responses of the two vertical canals was observed. In conclusion, while the usual supine test is the optimum test for evaluating the functions of the inner ear, more irrigation time is needed in order to effectively clinically examine the vertical canals.

Numerical Analysis of the Relationship between Nasal Structure and Its Function

The functions of the nasal cavity are closely related to its structure. In this study the three-dimensional finite element models were established based on the clinical data of twenty-four volunteers to study the influence of nasal structure on nasal functions of heating the inhaled airflow. Numerical simulations mainly concerning the airflow distribution and the airflow temperature are performed. The character of airflow heating process in these models is gained from the simulation results of these nasal cavities. The parameters describing the geometry of nasal cavity, such as the surface area of nasal airway and the volume of nasal cavity, are considered to be related to the nasal function of heating the inhaled airflow. The approximate function describing the relationship between the geometric parameters of the nasal airway and the nasal functions is gotten. This study can provide a numerical platform for studying some clinical problems and will contribute to the further research on the relationship between nasal structure and nasal functions.

Applications of Acoustic Rhinometry in the Modeling of Living Human Nasal Cavity Based on CT Scan

Acoustic rhinometry can quantify upper airway condition of air draft by drawing a graph plotting the distance from the nostril vs. the cross-sectional area. Some decrease on the graph corresponds to the typical anatomic structures of human nasal cavity. The 3-dimensional, computing fluid dynamic model of the same person was developed based on computed tomography scans. The veracity of the CFD model were valued by contrasting the relevant areas of stenosis site between the model and the AR graph. The aim in this study is to make clear how to use an AR to help improve and enrich the CFD model with the information of graph acquired from the measurement. The combination of AR and CT can be used to establish a living human nasal cavity model with higher significant information content.© 2005 ASME

Numerical simulation of the role of the utriculo-endolymphatic valve in the rotation-sensing capabilities of semicircular canals

The utriculo-endolymphatic valve (UEV) has an uncertain function, but its opening and closure have been predicted to maintain a constant endolymphatic pressure within the semicircular canals (SCCs) and the utricle of the inner ear. Here, the study׳s aim was to examine the role of the UEV in regulating the capabilities of the 3 SCCs in sensing angular acceleration by using the finite element method. The results of the developed model showed endolymphatic flow and cupula displacement patterns in good agreement with previous experiments. Moreover, the open valve was predicted to permit endolymph exchange between the 2 parts of the membranous labyrinth during head rotation and, in comparison to the closed valve, to result in a reinforced endolymph flow in the utricle and an enhanced or weakened cupula deflection. Further, the model predicted an increase in the size of the orifice would result in greater endolymph exchange and thereby to a greater impact on cupula deflection. The model findings suggest the UEV plays a crucial role in the preservation of inner ear sensory function.

Numerical study of the effects of bronchial structural abnormalities on respiratory flow distribution

BackgroundThe anatomical configurations of respiratory tract would be directly associated with their ventilatory function. It is necessary to fully understand the association between airway configurations and their functions as well as the interactions between different airway segments. In this study, we developed a respiratory airway model to investigate the effects of bronchial structural abnormalities on flow distribution in the bronchi and upper airway.MethodsDerived from computed tomography (CT) scanner data, three-dimensional (3D) finite element (FE) models of healthy human respiratory tracts were developed with anatomically realistic configurations, including the nasal cavity, oral cavity, pharynx, larynx, trachea, and partial bronchi. Abnormal bronchial configurations were built to correspond to four common bronchial diseases. Through numerical simulation, airway configurations of normal and abnormal bronchi were obtained, and flow patterns were compared between normal and abnormal respiratory tracts, as well as the effects of lower airway changes on flow distribution in the upper airway.ResultsThe simulation results showed that during inspiration, abnormal bronchial structures can cause flow redistribution in each generation of bronchi and have significant effects on flow distribution in the daughter bronchi of abnormal segments, but no effect on flow distribution of the upper airway. During expiration, abnormal bronchus structures had a remarkable influence on flow distribution in the trachea, while there was no significant difference in flow distribution when airflow passed from the vocal cords and entered the laryngeal cavity.ConclusionsTherefore, abnormal bronchial structures can affect the downstream flow distribution and cause flow redistribution throughout the entire bronchial branches. During expiration, the configurations of the trachea and glottis can diminish the effects of abnormal bronchial structures on flow distribution.

Prediction of death rate of breast cancer induced from average microelement absorption with neural network

Breast cancer is one of the leading causes of deaths from cancer for the female population in both developed and developing countries. The average microelement absorption can affect death rate of breast cancer. Artificial neural networks have been successfully applied to problems in the prediction of death rate of breast cancer induced from average microelement absorption. To predict the death rate of breast cancer induced from average microelement absorption using artificial neural network is feasible and a well trained artificial neural network by Levenberg-Marquardt algorithm reveals an extremely fast convergence and a high degree of accuracy. The investigation demonstrates that the proposed training and forecasting procedure is almost 100 times faster than that of classical BP algorithm and poses higher forecasting precision. With the growth of the database, more and more cases will be collected and used as training set.

Three-Dimensional Numerical Simulation of Airflow and Vibration Analysis for Upper Airway of Humans

Obstructive sleep apnea syndrome (OSAS) may cause apneas or hypopneas, both physically and emotionally harmful to their sufferers. It has been realized that the periodic intermittent cessations of breathing or reductions in airflow resulted from OSAS is closely related to the developed pathological change in upper airways of the patients. In this paper, the authors present numerical simulations of airflows and fluid-solid interaction analysis for human upper airways. The objective of the research is to investigate airfield characteristics of the human upper airway by means of computational fluid dynamics (CFD) and the finite element (FE) method. The authors reconstruct three-dimensional models of the upper airway from the nostril to the epiglottis based on CT scanning images collected from two clinic volunteers. Based on the reconstruction three-dimensional CFD models that precisely preserve original configuration of upper airways are created. The CFD analysis is carried out by the FE method with boundary conditions of pressure at the nostril and of velocity at the top of vocal cord. The non-slip boundary conditions are used on the interior walls of the upper airway. With the CFD results the pressure and velocity distributions in the airflow field are quantitatively determined. For fluid-solid interaction analyses, the upper airway in the vicinity of the pharyngeal cavity is meshed using the reconstructed model. The fluid-solid interactive computations are performed for the healthy person and the OSAS patient. The results show that the hypertrophy of the soft palate remarkably escalates both the pressure and the deformation levels of the upper airway and hinders the airflow in the cavity channels.