Time resolved 3D flow measurements in idealized and realistic upper airway models under high frequency ventilation

When the inhalation and exhalation phase alternate rapidly, respiratory flows are fundamentally different from steady conditions. This is particularly relevant for high frequency ventilation (HFV), a technique of mechanical ventilatory support routinely employed to treat acute lung injury and respiratory distress syndrome, which uses higher-than-normal airflow oscillation frequencies coupled with low tidal volumes. Here, we experimentally investigate the three-dimensional structure of respiratory flows for Reynolds and Womersley numbers relevant to HFV. We first focus on an idealized airway model which mimics the self-similar branching of the human bronchial tree. Volumetric velocity fields are acquired via Magnetic Resonance Velocimetry (MRV) and Tomographic Particle Image Velocimetry (Tomo-PIV). These are compared with measurements obtained, under identical regimes, in a 3D morphometrically-faithful airway model to assess the impact of true bronchial anatomy on airflow features. In both idealized and realistic cases, the simultaneous presence of inspiratory and expiratory air motions highlights the importance of transport mechanisms specific to HFV.