A Morphometric Model of Airway Mechanics and Gas Transfer during Neonatal Tidal Liquid Ventilation

INTRODUCTION The great development and diffusion of Liquid Assisted Ventilation (LAV) techniques (perfluorocarbon (PFC) lavage, Tidal Liquid Ventilation (TLV), and Partial Liquid Ventilation (PLV)) [1] is mainly due to the benefits they provide to patients with respect to other methods of ventilatory support. Such benefits derive from eliminating the liquid-gas interface in the alveoli. In fact, the instillation of liquid PFCs into the lungs increases pulmonary compliance and improves alveolar recruitment; in addition, it provides lavage of the debris that may be present in the airways, and may support surfactant secretion. TLV and PLV were demonstrated to be extremely useful in the case of very premature lambs, whose saccules (the precursors of alveoli) have a tendency to remain collapsed due to scarce or absent surfactant production secondary to lung immaturity. Up to now, the ranges for TLV ventilatory settings (breathing frequency f, tidal volume TV, inspiratory to expiratory time ratio I:E) that yield adequate CO2 removal have been suggested by means of animal studies. However, the effects of the variations of such settings on blood arterialization and lung mechanics have not been studied quantitatively. This work is about the development of a lumped-parameter mathematical model of airway mechanics during a volume-controlled neonatal TLV treatment. The mechanics model has been coupled with a model of O2 and CO2 transport in PFC, from the trachea to pulmonary capillary blood and vice versa. The overall model allows the treatment effectiveness to be simulated at any variation of the ventilatory settings, so as to shed light upon possible ventilation strategies that allow for an optimal management of blood arterialization and lung mechanical load.