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Newborns admitted to the neonatal intensive care unit can suffer from various respiratory diseases due to prematurity or abnormality. Tracheomalacia (TM) is an airway condition characterized by airway collapse during breathing. Newborns diagnosed with TM may require respiratory support for breathing and there is no reliable method to quantify the breathing effort. The standard diagnosis for TM is bronchoscopy. However, bronchoscopy cannot precisely evaluate the severity of the disease and measure the effect of airway motion on airflow. This study aims to quantify airflow measurements such as work of breathing, airway resistance, and pressure in the central airway (trachea and main bronchi). Magnetic resonance imaging (MRI) was used to obtain the airway anatomy and motion during the breathing cycle. The acquired MR images were reconstructed based on respiration to obtain four MR images that show four main breathing phases (end expiration, peak inspiration, end inspiration, and peak expiration). Airway surfaces were segmented from MR images to create virtual airway models. Surface registration between the airway surfaces at each phase of breathing was used to obtain the physiologic motion during the breathing cycle. However, MRI cannot quantify airflow measurements alone. Computational fluid dynamics (CFD) is a well-known technique to model the airflow in airway models derived from MRI. Virtual airway models, airflow rates and airway motion were obtained for each subject and used as inputs for the CFD simulation. The main bronchi's airflow rates were obtained using the lung tidal volumes and the free induction decay waveform. Using these techniques, three studies were performed to investigate the effect of TM on neonatal respiration. The first study investigates the effect of airway motion on breathing by comparing airflow measurements in dynamic airways with static airways in four subjects with TM and without TM. Results indicated that CFD simulations should be performed using dynamic airway models and when dynamic imaging is not available, static imaging should be acquired at the correct phase of breathing. The second study calculates the increase in tracheal resistive work of breathing per day due to airway motion using 14 neonatal subjects (8 TM, 6 non-TM). For each subject, 2 CFD simulations were performed. The first simulation used an airway model with dynamic airway motion and the second simulation used a static airway which represented the biggest airway of each subject. The study showed that neonates with TM have a nearly five times increase in breathing effort due to airway motion compared to the static airway. The third study investigates the effect of the glottis on airflow in 21 neonatal subjects (11 TM, 10 non-TM). The glottis motion during the breathing cycle was measured and the total pressure loss along the airway was calculated using individual CFD simulations. The study showed that neonates with TM self-generate positive end expiratory pressure (auto-PEEP) by narrowing their glottises during breathing. The studies presented in this dissertation provide clinically relevant information that can enhance patient care and health based on MRI and CFD, both of which rely on basic Physics principles. |
