Purpose or Case Report: Large airway obstruction, subglottic stenosis, tracheal narrowing, and tracheomalacia are common morbidities associated with prematurity secondary to prolonged intubation. Laryngotracheoplasty is often required to alleviate subglottic stenosis and allow a patient to be decannulated from their tracheostomy. Patients will often have continued airway and voice issues despite being able to live without a tracheostomy. The clinical conundrum in treating this patient is whether vocal folds can be surgically moved closer together to improve vocalization without compromising the airway further and increasing resistance. Here we demonstrate how this clinical conundrum can be informed by CT-derived CFD modeling in a 15-year-old male former 31-week preterm infant with dysphonia and subglottic airway narrowing at the cervical trachea and narrow vocal cords.
Methods & Materials: Prospective consent was obtained to enroll the subject in a study for modeling airway flow from dynamic CT images. Respiratory airflow and pressure measured in a CPAP mask were combined with synchronous dynamic CT imaging of the airway over one tidal breathing cycle. Segmentation of the dynamic CT was performed with ITK-SNAP to create a 3D surface mesh of the airway from dynamic CT at 200 ms intervals. The mesh then underwent registration and interpolation to a higher temporal resolution to capture the physiologic motion of the airway. CFD simulation was performed within the 3D moving boundaries using the air flow and pressure inputs obtained simultaneously with the dynamic CT to calculate pressure drops, resistance and velocity over the entire respiratory cycle.
Results: The results indicated resistance was greatest at the A-frame narrowing in the subglottic trachea during inspiration (Peak Resistance = 1 Pas/kg) and the vocal fold resistance was reasonable (Peak Resistance = 0.2 Pas/kg) during inspiration. During the expiratory phase the resistance from the vocal folds and subglottic A-frame narrowing were elevated and both peaked at about 0.5 Pas/kg.
Conclusions: Surgically bringing the vocal folds together to alleviate the patient’s dysphonia would probably worsen the patient’s breathing and would be ill-advised. Since the patient’s symptoms were only dysphonia and noisy breathing, no further procedures were recommended. Patient specific CFD modeling of airway resistance provides additional objective information for decision making.