Effects of Pulsatile Bi-level Ventilation on flow characteristics in an alveolated duct: A comparative study

This study investigates the fluid flow behavior in a single alveolated duct, comparing Bi-level Ventilation (BLV) and Pulsatile Bi-level Ventilation (PBLV) techniques. While clinical studies have shown that PBLV enhances gas exchange, there has been a lack of detailed exploration of the flow fields within the alveolus for these ventilation methods. Using Computational Fluid Dynamics (CFD) including Fluid-structure Interaction (FSI) and boundary conditions measured in experiments, this work examines the differences in alveolar flow characteristics between PBLV and BLV. This study reveals that PBLV induces more dynamic and transient vortex behavior, with the vortex core moving centrally within the alveolus at each pulsation of the high-frequency jet, contributing to enhanced recirculating flows and chaotic patterns. In contrast, BLV produces a less mobilized vortex core that quickly settles. In addition, a more prominent three-dimensional spiral flow is observed in PBLV, which might lead to better air mixing compared to BLV. These observations provide insight into the main differences in flow features during BLV and PBLV. However, further quantitative analysis that includes gas exchange models is required to directly examine the improvements at the alveolar level. This research lays the groundwork for understanding the aerodynamic factors that might contribute to PBLV's enhanced performance, offering a new perspective on ventilation strategies.