Evaluation of human obstructive sleep apnea using computational fluid dynamics.

Obstructive sleep apnea (OSA) severity might be correlated to the flow characteristics of the upper airways. We aimed to investigate the severity of OSA based on 3D models constructed from CT scans coupled with computational fluid dynamics (CFD) simulations. The CT scans of seven adult patients diagnosed with OSA were used to reconstruct the 3D models of the upper airways and CFD modeling and analyses were performed. Results from the fluid simulations were compared with the apnea-hypopnea index. Here we show a correlation between a CFD-based parameter, the adjusted pressure coefficient (Cp*), and the respective apnea-hypopnea index (Pearson's r = 0.91, p = 0.004), which suggests that the anatomical-based model coupled with CFD could provide functional and localized information for different regions of the upper airways

Transient Numerical Simulation of Airflow Characteristics in the Mouth-Throat 3D Model

Air pollution is a public health problem that has a serious effect on human health, as it leads to increased morbidity and mortality. Each year, more than 3 million people die from air pollution, while many more have higher risks of stroke, heart attack, and lung diseases as a result of the pollution. The available epidemiological studies indicate that exposure to particulate matter in the air can have a toxic effect on the cardiovascular system, and increase the death risk from cardiovascular diseases such as ischemic heart disease and heart failure. In this study, we have reconstructed the upper respiratory tract model from the CT images in order to analyze airflow patterns during the inhalation part of the breathing cycle and to track NO2 particles inhaled through the mouth or nose. The numerical analysis has been performed using the computational fluid dynamics (CFD) method and the discrete particle method (DPM). The continuous phase flow was solved using the k-ω Shear Stress Transport model with low Reynolds number corrections

Computational fluid dynamics in the upper airway: comparison between different models and experimental data for a simplified geometry with major obstruction

The present study aims at comparing different computational models used for simulating the fluid-structure interaction within an in-vitro setup resembling simplified major obstruction of pharyngeal airway. Due to the nature of the problem, i.e. air flow passing over a deformable latex surface, a fully coupled fluid-structure interaction algorithm is used. A comparison is made between two finite element models for the solid domain, one using shell and the other using volume elements. The material properties of these models follow a hyperelastic behavior. For the fluid part, laminar and various turbulence models such as standard k-epsilon, Shear Stress Transport, SSG Reynolds Stress and BSL Reynolds Stress are compared. We evaluate the efficiency of the models and how close to the experimental data are their results. The predictions of the structural model containing volume elements showed better consistency with the experimental data. In addition, the results obtained with the standard k-epsilon turbulence model were the least deviated among all turbulence models

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

CFD simulation of the airflow through the human respiratory tract

This study compares the effect of extra-thoracic airways (ETA) on the flow field through the lower airways by carrying out simulations of the airflow through the human respiratory tract. Three geometries, consisting of the ETA, CT-derived lower airway, and a combination of the two were utilized in simulations that were performed for transient breathing in addition to constant inspiration/expiration. Physiologically-appropriate regional ventilation for two different flow rates was induced at the distal boundaries by imposing appropriate lobar specific flow rates. Two breathing rates were considered, i.e., 7.5 and 15 breaths per minute with a tidal volume of 0.5 liter. For comparison, the flow rates for constant inspiration/expiration were selected to be identical to the peak flow rates during the transient breathing. Significant differences indicate that simulations that utilize constant inspiration or expiration may not be appropriate for gaining insight into the flow patterns through the human airways

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