Respiratory airflow simulations and experiments investigating superimposed high-frequency jet ventilation

Abstract

Introduction: In mechanical ventilation, a machine takes over breathing for a patient. Superimposed high-frequency jet ventilation (SHFJV) is a mechanical ventilation technique that uses high-frequency jet ventilation (HFJV) and low-frequency jet ventilation (LFJV) simultaneously. While SHFJV has clinical fields of application, the exact mechanisms of action are still mostly unknown. The aim of this thesis is to investigate the impact of SHFJV on the lungs using fluid dynamics simulations and experiments. Methods: An idealized lung model suitable for respiratory airflow studies was created. This model was used for computational fluid dynamics (CFD) simulations. After mesh independence studies, multiple CFD simulations mimicking different phases of SHFJV were performed employing three different turbulence models. Furthermore, micro particle image velocimetry (μPIV) experiments imitating airflow through lower airway bifurcations and alveoli were conducted to compare simulated and experimental results. Results and Discussion: Simulation outcome analyses examining velocity-, turbulence-, and pressure distributions yielded reasonable results for all employed turbulence models. Experimentally determined velocity vector fields showed good agreement with the simulations in some respects, but also discrepancies. While the model could be implemented and verified well, more work and adjustments are necessary to truly validate simulation results. Conclusion and Outlook: Comparison of the three turbulence models shows only minor differences in the flow field during SHFJV. Fluid flow is mostly laminar. However, areas of turbulence in the upper airways are still present. μPIV can be used to study SHFJV, but multiple methodological challenges arise. The idealized lung model can be verified and roughly validated, although not perfectly, as experimental results and simulated results show differences. Possible mechanical SHFJV effects can be mostly attributed to HFJV, while LFJV is more involved in gas exchange mechanisms. Further research is needed to confirm the reliability of the utilized methodology and the implied conclusions.