A model of neonatal tidal liquid ventilation mechanics

Tidal liquid ventilation (TLV) with perfluorocarbons (PFC) has been propose d to treat surfactant-deficient lungs of preterm neonates, since it may pre vent pulmonary instability by abating saccular surface tension. With a prev ious model describing gas exchange, we showed that ventilator settings are crucial for CO2 scavenging during neonatal TLV. The present work is focused on some mechanical aspects of neonatal TLV that were hardly studied, i.e. the distribution of mechanical loads in the lungs, which is expected to dif fer substantially from gas ventilation. A new computational model is presen ted, describing pulmonary PFC hydrodynamics, where viscous losses, kinetic energy changes and lung compliance are accounted for. The model was impleme nted in a software package (LVMech) aimed at calculating pressures (and app roximately estimate shear stresses) within the bronchial tree at different ventilator regimes. Simulations were run taking the previous model's outcom es into account. Results show that the pressure decrease due to high saccul ar compliance may compensate for the increased pressure drops due to PFC vi scosity, and keep airway pressure low. Saccules are exposed to pressures re markably different from those at the airway opening; during expiration nega tive pressures, which may cause airway collapse, are moderate and appear in the upper airways only. Delivering the fluid with a slightly smoothed squa re flow wave is convenient with respect to a sine wave. The use of LVMech a llows to familiarize with LV treatment management taking the lungs' mechani cal load into account, consistently with a proper respiratory support. (C) 2001 IPEM. Published by Elsevier Science Ltd. All rights reserved.