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

Numerical modeling of a sneeze, a cough and a continuum speech inside a hospital lift

The global COVID-19 and its variants put us on notice of the importance of studying the spread of respiratory diseases. The most common means of propagation was the emission of droplets due to different respiration activities. This study modeled by computational fluid dynamics (CFD) techniques a high risk scenario like a hospital elevator. The cabin was provided with an extraction fan and a rack for air renewal. Inside, a sneeze, a cough and a continuum speech were simulated. Inside the lift, two occupants were introduced to observe the risk of propagation of emitted droplets and the impact in diseases spreading risk. The fan effectivity over the droplets ejection was analyzed, as well as environmental condition of a clinical setting. For this purpose the amount of droplets inside were counted during whole time of simulations. The effect of the fan was concluded as able to eject the 60% of small droplets, but also a high performance in spreading particles inside. Among the three cases, the riskiest scenario was the continuum speech due to the saturation of droplets in airborne.This work was supported by Ekonomiaren Garapen eta Lehiakortasun Saila, Eusko Jaurlaritza [ELKARTEK 20/71 & ELKARTEK 20/78]

Flow characterization inside airways with unsteady breathing patterns

Flow through human airways is characterized by unsteady flows, with flow separations at airway bifurcations. The oscillatory nature of airflow, unequal durations of inhalation time (IT), and exhalation time (ET) can facilitate gas exchange in higher generations of the human airway. Normal respiratory rate (RR) in adults ranges between 10-15 breaths per minute (bpm). RR varies in exercise conditions, mechanical ventilation strategies such as high-frequency oscillatory ventilation (HFOV), metabolic activities and pathological state to facilitate alveolar gas exchange. Previous studies characterized flows at steady inhalation and exhalation through airways. The individual effects of varying inhalation duration and breathing flow rate on flow through airways remains unknown. Our study focuses on various unsteady breathing patterns inside idealized airway models. The goal of this study is to characterize the effects of unsteady internal airflow through idealized airway geometries. Various scenarios of unsteady breathing patterns were simulated in ANSYS software (ANSYS, Inc., Canonsburg, PA, USA) to characterize the fluid dynamics involved in such an unsteady airflow mechanism. The first study includes unsteady breathing patterns such as normal, moderate, and high-frequency ventilation were investigated with variation in inhalation time (IT) to breathing time (BT) ratio. The second study includes abnormal breathing patterns such as tachypnea (~ 1.5x increase in RR), bradypnea (~ 1.5x decrease in RR), hyperpnea (deep breathing with abnormally large peak flow rate), and hypopnea (shallow breathing with abnormally low peak flow rate); and final study includes single nostril inhalation as in yoga pranayama breathing techniques. Simulations were performed for each breathing pattern as in internal airflow studies. Our results showed that secondary flow was an effective transport mechanism for flow inside idealized human airways. Airway local geometry plays a key role in flow distribution in higher generations. Discrepancy in the oscillatory flow relation Re/Wo^2 = 2L/D (L = stroke length; D = trachea diameter) was observed for IT/BT does not equal 50%, as L changed with IT/BT. We developed a modified dimensionless stroke length term including IT/BT. While viscous forces and convective acceleration were dominant for lower Wo, unsteady acceleration was dominant for higher Wo. Time to peak jet length during inhalation increased with an increase in breathing time. Single nostril and double nostril inhalation showed equal ventilation at higher generations in an idealized airway geometry

Functional respiratory imaging : opening the black box

In respiratory medicine, several quantitative measurement tools exist that assist the clinicians in their diagnosis. The main issue with these traditional techniques is that they lack sensitivity to detect changes and that the variation between different measurements is very high. The result is that the development of respiratory drugs is the most expensive of all drug development. This limits innovation, resulting in an unmet need for sensitive quantifiable outcome parameters in pharmacological development and clinical respiratory practice. In this thesis, functional respiratory imaging (FRI) is proposed as a tool to tackle these issues. FRI is a workflow where patient specific medical images are combined with computational fluid dynamics in order to give patient specific local information of anatomy and functionality in the respiratory system. A robust high throughput automation system is designed in order get a workflow that is of a high quality, consistent and fast. This makes it possible to apply this technology on large datasets as typically seen in clinical trials. FRI is performed on 486 unique geometries of patients with various pathologies such as asthma, chronic obstructive lung disease, sleep apnea and cystic fibrosis. This thesis shows that FRI can have an added value in multiple research domains. The high sensitivity and specificity of FRI make it very well suited as a tool to make decisions early in the development process of a device or drug. Furthermore, FRI also seems to be an interesting technology to gain better insight in rare diseases and can possibly be useful in personalized medicine

Lung Alveolar and Tissue Analysis Under Mechanical Ventilation

Mechanical ventilation has been a major therapy used by physicians in support of surgery as well as for treating patients with reduced lung function. Despite its many positive outcomes and ability to maintain life, in many cases, it has also led to increased injury of the lungs, further exacerbating the diseased state. Numerous studies have investigated the effects of long term ventilation with respect to lungs, however, the connection between the global deformation of the whole organ and the strains reaching the alveolar walls remains unclear. The walls of lung alveoli also called the alveolar septum are characterized as a multilayer heterogeneous biological tissue. In cases where damage to this parenchymal structure insist, alveolar overdistension occurs. Therefore, damage is most profound at the alveolar level and the deformation as a result of such mechanical forces must be investigated thoroughly. This study investigates a three-dimensional lung alveolar model from generations 22 (alveolar ducts) through 24 (alveoli sacs) in order to estimate the strain/stress levels under mechanical ventilation conditions. Additionally, a multilayer alveolar tissue model was generated to investigate localized damage at the alveolar wall. Using ANSYS, a commercial finite element software package, a fluid-structure interaction analysis (FSI) was performed on both models. Various cases were simulated that included a normal healthy lung, normal lung with structural changes to model disease and normal lung with mechanical property changes to model aging. In the alveolar tissue analysis, strains obtained from the aged lung alveolar analysis were applied as a boundary condition and used to obtain the mechanical forces exerted as a result. This work seeks to give both a qualitative and quantitative description of the stress/strain fields exerted at the alveolar region of the lungs. Regions of stress/strain concentration will be identified in order to gain perspective on where excess damage may occur. Such damage can lead to overdistension and possible collapse of a single alveolus. Furthermore, such regions of intensified stress/strain are translated to the cellular level and offset a signaling cascade. Hence, this work will provide distributions of mechanical forces across alveolar and tissue models as well as significant quantifications of damaging stresses and strains

Numerical Simulation of Particle Deposition in the Human Lungs

We model, simulate and calculate breathing and particle depositions in the human lungs. We review the theory and discretization of fluid mechanics, the anatomy, physiology and measuring methods of lungs. A new model is introduced and investigated with a sensitivity analysis using the singular value decomposition. Particle depositions are simulated in patient-specific and schematized human lungs and compared to the particle deposition in a multiplicative model of subsequent bifurcations

Imaging and Treatment of Bronchiectasis:Chest computed tomography to diagnose bronchiectasis and to optimise inhalation treatment

This thesis covers image analysis of bronchiectasis and treatment with inhalation antibiotics