Biomechanical Models of Human Upper and Tracheal Airway Functionality

The respiratory tract, in other words, the airway, is the primary airflow path for several physiological activities such as coughing, breathing, and sneezing. Diseases can impact airway functionality through various means including cancer of the head and neck, Neurological disorders such as Parkinson\u27s disease, and sleep disorders and all of which are considered in this study. In this dissertation, numerical modeling techniques were used to simulate three distinct airway diseases: a weak cough leading to aspiration, upper airway patency in obstructive sleep apnea, and tongue cancer in swallow disorders. The work described in this dissertation, therefore, divided into three biomechanical models, of which fluid and particulate dynamics model of cough is the first. Cough is an airway protective mechanism, which results from a coordinated series of respiratory, laryngeal, and pharyngeal muscle activity. Patients with diminished upper airway protection often exhibit cough impairment resulting in aspiration pneumonia. Computational Fluid Dynamics (CFD) technique was used to simulate airflow and penetrant behavior in the airway geometry reconstructed from Computed Tomography (CT) images acquired from participants. The second study describes Obstructive Sleep Apnea (OSA) and the effects of dilator muscular activation on the human retro-lingual airway in OSA. Computations were performed for the inspiration stage of the breathing cycle, utilizing a fluid-structure interaction (FSI) method to couple structural deformation with airflow dynamics. The spatiotemporal deformation of the structures surrounding the airway wall was predicted and found to be in general agreement with observed changes in luminal opening and the distribution of airflow from upright to supine posture. The third study describes the effects of cancer of the tongue base on tongue motion during swallow. A three-dimensional biomechanical model was developed and used to calculate the spatiotemporal deformation of the tongue under a sequence of movements which simulate the oral stage of swallow

Effect of the velopharynx on intraluminal pressures in reconstructed pharynges derived from individuals with and without sleep apnea

The most collapsible part of the upper airway in the majority of individuals is the velopharynx which is the segment positioned behind the soft palate. As such it is an important morphological region for consideration in elucidating the pathogenesis of obstructive sleep apnea (OSA). This study compared steady flow properties during inspiration in the pharynges of nine male subjects with OSA and nine body-mass index (BMI)- and age-matched control male subjects without OSA. The k–ωωSST turbulence model was used to simulate the flow field in subject-specific pharyngeal geometric models reconstructed from anatomical optical coherence tomography (aOCT) data. While analysis of the geometry of reconstructed pharynges revealed narrowing at velopharyngeal level in subjects with OSA, it was not possible to clearly distinguish them from subjects without OSA on the basis of pharyngeal size and shape alone. By contrast, flow simulations demonstrated that pressure fields within the narrowed airway segments were sensitive to small differences in geometry and could lead to significantly different intraluminal pressure characteristics between subjects. The ratio between velopharyngeal and total pharyngeal pressure drops emerged as a relevant flow-based criterion by which subjects with OSA could be differentiated from those without

Validation of Novel Obstructive Sleep Apnea Treatment with Silicone Gel Experimental Models

Predictive modeling to increase treatment success rates for surgical procedures is becoming more common in the scientific community. For obstructive sleep apnea (OSA), modeling has been predominately performed using computers as opposed to experimental models. Computer simulation saves time by eliminating the need to fabricate complex experimental models but comes at the expense of insight gained through physical observations made in real time. Experimental models for studying OSA are needed to validate computational work, provide perspective on anatomical scale and demonstrate complex deformations in real time. This work addresses prior hurdles in experimental model fabrication with a novel process using 3D printed dissolvable molds for casting encapsulated silicone gel. The resulting models exhibited lifelike characteristics such as velopharynx collapse during inspiration, negative effort dependence and snoring. Each of these behaviors are characteristics of OSA which have not been observed in any prior experimental models. Computer aided design (CAD) data for the models came from segmentations of CT scans of 2 patients with OSA. These segmentations were used in prior research which sought to determine whether a force applied to the back of a patient’s tongue could clear an obstruction and if so, how much force would be needed. Computational results from the original study predict 95 to 125 grams would be sufficient compared to the experimental results of this work which indicate 50 to 80 grams is sufficient. This work provides a physical model upon which experimental devices for treating OSA may be tested. Notably, this approach demonstrates the potential for an implantable device with an adjustable constant force output to successfully treat OSA

미니스크류를 이용한 급속구개확장술이 폐쇄성 수면무호흡증이 있는 성인 환자의 상기도 호흡에 미치는 영향: 유체구조연계 분석법

학위논문 (박사)-- 서울대학교 대학원 치의학대학원 치의학과, 2017. 8. 백승학.The purpose of this study was to investigate the effects of miniscrew-assisted rapid palatal expansion (MARPE) on changes in airflow in the upper airway (UA) of an adult patient with obstructive sleep apnea syndrome (OSAS). Three-dimensional (3D) UA models of a young adult male patient with OSAS [age of 18 years and 7 months, body mass index (BMI), 25.0 kg/m2apnea and hypopnea index (AHI), 49.5 events/hourrespiratory disturbance index (RDI), 52.2 events/hourlowest O2 saturation rate (LSR), 85%] were fabricated using cone-beam computed tomography images taken before (T0) and after MARPE treatment (T1). The signs [age of 19 years and 1 month, BMI, 24.9 kg/m2AHI, 2.2 events/hourRDI, 20.2 events/hourLSR, 95%] and symptoms at the T1 stage significantly improved. A total of sixteen cross-sectional planes were set with the inter-plane distance of 10 mm along the upper airway: 7 planes for the nasal cavity and 9 planes for the pharynx. Using 3D computational fluid dynamics (3D-CFD) and fluid-structure interaction (FSI) analysis, changes in the cross-sectional area (CSA), velocity and pressure of airflow, displacements of nodes, and total resistance were investigated at maximum inspiration (MI), rest, and maximum expiration (ME). Compared to the T0 stage, the T1 stage exhibited significant increase in CSA at the most of parts of the nasal cavity and at the upper part of pharynx. Velocity of airflow was decreased primarily in the anterior part of the nasal cavity at MI and ME, and in the upper and middle parts of the pharynx at MI. However, the amounts of decrease were greater in the nasal cavity than the pharynx. Pressure of airflow was decreased mainly in the anterior parts of the nasal cavity and consistently in the whole pharynx. In terms of node displacement, the amount of displacement was insignificant at both T0 and T1 stages. In aspects of total resistance, there was significant decrease in the absolute values at MI (-55.1%), rest (-35.9%) and ME (-33.9 %) during T0-T1. Since MARPE improved airflow and reduced resistance in the UA, it might be an effective treatment modality for adult OSAS patients who have moderate to severe narrow basal arch and crowding and refuse to the oral appliance or MMA surgery.1. INTRODUCTION 1 2. REVIEW OF LITERATURE 3 3. MATERIALS AND METHODS 8 4. RESULTS 11 5. DISCUSSION 14 6. CONCLUSION 17Docto

Effect of Orthognathic Surgery on the Upper Airway System

Sleep apnea is a disease which has not been getting an adequate amount of attention in the research community for a long time. However, the strain on the cardiovascular system and other serious problems, such as daytime sleepiness and even neurocognitive dysfunction, that it causes may be severe in advanced cases of the illness, as such it can significantly affect the heart especially and lead to cardiac arrest. Thus, it has been receiving a lot of attention recently. Tampere University Hospital has a goal of creating a comprehensive upper airway airflow model for surgery outcome prediction. That requires knowledge of available models and analysis of static magnetic resonance images, among other things. This document deals with these two main issues. This thesis has two major parts, one of them being a literature review of sleep apnea and models used in airflow modelling in the upper airways. Modelling of airflow generally includes acquisition of a static upper airway system model (in the case of upper airway modelling) and then adding a dynamic component to it. The second part of this thesis deals with acquisition of the static model, which involves segmentation of MRI image sets from 3 patients (pre- and post-operative sequences). It also answers the question, whether the effect of orhtognathic surgery on the upper airway system can be seen from volumetric analysis of the segmented images and the segmented images themselves. The main methods of adding a dynamic component to the static model turned out to be computational fluid mechanics and finite element modelling, including their sub-methods, such as direct numerical simulation of large eddy simulation. As with the second part of the thesis, the volumetric segmentation data is rather inconclusive and should not be related solely for evaluation of the effect of orthognathic surgery on the upper airway system. It can be said, nonetheless, that the volume of the upper airway itself is rather easily obtainable and reliable. The images themselves, however, provide very visual information about that, and shifting of certain muscles and muscle groups and other structures can be seen

Numerical modelling of fluid-structure interactions for fluid-induced instability in the upper airway

This study is concerned with fluid-structure interactions (FSI) involved in the human upper airway, in particular, those associated with snoring and obstructive sleep apnoea/hypopnoea syndrome (OSAHS). Further examining this area of interest, the goal of the current research is to contribute further understanding and enhance development of computational modelling, for retroglossal obstruction and palatal snoring. To that end, the investigation was divided into three major parts. Firstly, extending previous laminar, 2-D reduced Navier-Stokes model, an idealised 3-D computational model was constructed for studying retroglossal obstruction. A full Navier-Stokes solver in an Arbitrary Lagrangian-Eulerian (ALE) framework was coupled to a linear thin shell, where both laminar and turbulent flow was investigated. Numerical results showed increase flow-induced tongue replica deflection under turbulent conditions and demonstrated cross-flow pressures that may encourage side wall collapse. In the second part of the thesis, palatal snoring was further examined and its potential to detect retroglossal obstruction was proposed. In order to investigate this, flow-induced instability of a cantilever plate in an obstructed channel was modeled and a relationship between critical velocity and obstruction depth was established. Correlating the critical velocity with typical breathing flow curve, a time difference between palatal snoring episodes or onset of palatal snoring, may represent a key variable for non-invasive measurement of retroglossal obstruction severity. Further enhancement of the 2-D computational model by including contact was proposed using an immersed boundary method (IBM). This may represent a more complete model of palatal snoring by modelling pre- and post-contact response of unstable cantilever plate, which showed potential to capture more complicated palatal snoring signals. Finally, the third part of this thesis examined flow-induced instability of a soft palate in a 3-D realistic upper airway. To model this, a full 3-D Navier-Stokes solver under an ALE framework was coupled to a non-linear soft palate model. Appropriate soft palate properties were applied giving palatal snoring frequency within range of clinically measured values. Palatal flutter was observed at high flow rates, demonstrating irreversible transfer of flow energy to soft palate. This computational model may perhaps be exploited for future investigation of more accurate palatal snoring, necessary for developing non-invasive snoring signals for measurement or diagnosis of retroglossal obstruction