Research And Clinical Application Of Biomechanical Model Based On Chinese Upper Respiratory Tract

Sleep-disordered breathing, which is closely related to narrow upper airway, has been a prominent and important clinical and public health issues concerning high prevalence and serious perniciousness. The most potentially dangerous sleep-disordered breathing is obstructive sleep apnea/hypopnea syndrome (OSAHS). It is necessary to perform quantitative analysis on the airway structure-function interaction in order to understand thoroughly these upper respiratory tract diseases associated with structural abnormalities. In this paper, biomechanical model of upper respiratory system, which focus on the pathogenesis and individual care planning problems of OSAHS, are researched based on the computational fluid dynamics (CFD) and fluid structure interaction (FSI) methods to conquer the difficulties of individual differences and structure complexity of the upper respiratory tract. The numerical simulation model is reconstructed on the basis of the feasibility of analytical methods and computational results by comparing with the clinical and experimental data. The simulation results provide a platform of numerical and quantitative analysis for the interrelation between airway structure and function. The main contents are as follows:1. Based on the multidetector computed tomogram (MDCT) images of volunteers without any respiratory diseases, accurate anatomical models of the upper airway are developed. After comparing the numerical results of four different turbulence models with the experimental data of recent documents, a rational and reliable calculating method is determined for predictions of the flow field distribution of upper airway. The characteristics of flow structures within the normal upper respiratory tract based on sixteen healthy volunteers are summarized as solid groundwork for subsequent biomechanical characteristics investigation on abnormal upper airway.2. Upper airway models of adults and children are reconstructed aiming at simulating typical surgery schedules. The particular quantitative analysis of velocity, pressure, and airway resistance in preoperative and postoperative upper airway models are performed. The comparison of simulation results and the clinical measurements by polysomnograph (PSG) and acoustic rhinometry (AR) indicates that the ventilation condition evaluated by computational simulation is consistent with the results of clinical measurements. The biomechanical quantitative parameter of the upper respiratory tract, which is not accessible by routine clinical measurements, can provide quantitative reference basis for preferred surgical option and treatment evaluation.3. The airflow characteristics of the upper respiratory tract and movement of the soft palates in the pre-and post-nasal surgery models in three patients with nasal airway obstruction and OSAHS, provide quantitative basis for the investigation of the exact role of the nasal airway in the pathogenesis of OSAHS and the effect of nasal surgery alone on OSAHS. Numerical simulation results show that two models of mild OSAHS patients demonstrated significant ventilation improved phenomenon after the correction of nasal structure and expansion of nasal volume. Although the nasal obstruction relief after the nasal surgery for the patient with severe OSAHS, the airflow characteristics, such as velocity and pressure, the displacements of soft palates, especially the negative pressure of velopharynx are higher than those in preoperative model. The assessment of respiratory function according to available indicators by numerical simulation is consistent with that of the PSG results. Because of the individual differences in human upper airway and the complex adaptive relationship between the airway structure and air environment, distinct effects of the relief of nasal airway obstruction on airway ventilation for different upper respiratory tract, the surgical program should be established according to individual and comprehensive consideration of the consistency and complex relativity between the upper part and the lower part of the upper respiratory tract.4. The investigation on the effect of abnormal airway structure on the airflow characteristics can provide quantitative basis for comprehensive understanding of the pathogenesis of OSAHS and the inherent relationship between OSAHS with respiratory diseases. As a result of velopharyngeal stenosis, the airflow velocity and pressure drop in respiratory tract of OSAHS patients are much higher than that in normal model. For the structural abnormalities of the bronchial, in addition to the airflow characteristics of the the trachea and bronchi change significantly, the pressure drop of the upper airway increases mainly in the expiratory phase. Besides, the influences of different breathing modes (nasal breathing and combined oral-nasal breathing) on the flow characteristics are investigated to reveal the reason of increased risk of upper airway collapse and obstruction brought by mouth breathing. A dramatical increase of oral airflow leads to the redistribution of airway resistance, the significantly reduced nasal resistance and also the increased airway resistance in the airway below the oral cavity.