Fluid dynamic assessment of positive end-expiratory pressure in a tracheostomy tube connector during respiration.

High-flow oxygen therapy using a tracheostomy tube is a promising clinical approach to reduce the work of breathing in tracheostomized patients. Positive end-expiratory pressure (PEEP) is usually applied during oxygen inflow to improve oxygenation by preventing end-expiratory lung collapse. However, much is still unknown about the geometrical effects of PEEP, especially regarding tracheostomy tube connectors (or adapters). Quantifying the degree of end-expiratory pressure (EEP) that takes patient-specific spirometry into account would be useful in this regard, but no such framework has been established yet. Thus, a platform to assess PEEP under respiration was developed, wherein three-dimensional simulation of airflow in a tracheostomy tube connector is coupled with a lumped lung model. The numerical model successfully reflected the magnitude of EEP measured experimentally using a lung phantom. Numerical simulations were further performed to quantify the effects of geometrical parameters on PEEP, such as inlet angles and rate of stenosis in the connector. Although sharp inlet angles increased the magnitude of EEP, they cannot be expected to achieve clinically reasonable PEEP. On the other hand, geometrical constriction in the connector can potentially result in PEEP as obtained with conventional nasal cannulae.

Airway performance in infants with congenital tracheal stenosis associated with unilateral pulmonary agenesis: effect of tracheal shape on energy flux.

Congenital tracheal stenosis (CTS) with unilateral pulmonary agenesis (UPA) is characterized by the absence of one or both lungs in the hemithorax and is often associated with airway distortion. Some UPA patients have high mortality and morbidity even postoperatively, and it remains unclear whether surgery increases the energy flux needed to drive airflow. Here, we used pre- and postoperative patient-specific airway models to numerically investigate tracheal flow in patients with CTS, especially flow associated with right UPA (CTS-RUPA). Airflow was simulated with the large-eddy model, and energy flux was investigated to quantify airway performance and the contribution of surgical intervention. Although energy flux decreased postoperatively, clinical respiratory status did not improve. Standard surgical intervention for CTS, which expands the minimal cross-sectional area, decreased energy flux, i.e., improved airway performance. The simulation also included artificial airways with a straightened bend or reduced tracheal lumen roughness. The numerical results clearly showed interindividual differences in the percent reduction of energy flux caused by straightening the tracheal bend versus correcting tracheal lumen roughness. Although this study was limited to small sample size, these numerical results indicated that energy flux alone is insufficient to evaluate breathing performance in patients with CTS-RUPA but it can be used to estimate airway performance.