Numerical simulations of high-frequency ventilation in the presence of airway and lung tissue heterogeneities

<bold>Introduction:</bold> Whilst high-frequency ventilation (HFV) is widely used, it is mostly recommended in homogeneous lungs. Our aim was to evaluate the efficiency of pressure and volume transfer from the airway opening to a heterogeneous alveolar compartment in a simulation model of HFV. <bold>Methods:</bold> We created a numerical simulation based on <italic>in-vivo</italic> data from a porcine model with measurements at the airway opening (<italic>p</italic>_ao) and at the lung periphery using alveolar capsules (<italic>p</italic>_alv). Simulations assume a 5-Hz oscillation frequency in a model consisting of an endotracheal tube in series with a parallel impedance network of branches including an airway, a chest wall and a lung tissue compartment of variable inhomogeneity (set as a factor of 5 between extreme branches). Each branch comprises an airway resistance (<italic>R</italic>_aw), inertance and constant-phase tissue impedance (<italic>Z</italic>_ti). <bold>Results:</bold> The simulations yield <italic>p</italic>_alv/<italic>p</italic>_ao in good agreement with in vivo results and show that increasing net <italic>R</italic>_aw from 2 to 10 cmH₂O⋅s/l reduces palv/pao from 0.155 to 0.098, respectively. With heterogeneity in <italic>R</italic>_aw, these <italic>R</italic>_aw changes increase the relative difference in regional <italic>p</italic>_alv/<italic>p</italic>_ao (112% to 328% at 2 to 10 cmH₂O⋅s/l of net <italic>R</italic>_aw, respectively) and in regional tidal volume (VT_r) (111% to 328%). With heterogeneity in <italic>R</italic>_aw, a 2.5-fold increase in <italic>Z</italic>_ti reduces the relative difference in <italic>p</italic>_alv/<italic>p</italic>_ao between extreme branches from 206% to 75%, and reduces VT_r from 205% to 74%. <bold>Conclusion:</bold> Our simulation validated by <italic>in-vivo</italic> data allows predictions of net and regional alveolar pressure and volume distribution, contributing to the understanding of HFV in the presence of ventilation heterogeneities. <bold>Funding:</bold> OTKA-NKFIH K138032 and FK134274