Liquid ventilator

A liquid ventilator is similar to a medical ventilator except that it should be able to ensure reliable total liquid ventilation with a breatheable liquid (a perfluorocarbon) · . Liquid ventilators are prototypes that may have been used for animal experimentations but experts recommend continued development of a liquid ventilator toward clinical applications.

In total liquid ventilation (TLV), the lungs are completely filled with a perfluorocarbon (PFC) liquid while the liquid ventilator renews the tidal volume of PFC. The liquid ventilator operates in mandatory mode: it must force the PFC in and out of the lungs with a pumping system.

The pumping system is either a peristaltic pump (in the simplest liquid ventilators) or two piston pumps (in the most advanced liquid ventilators).

Because of the PFC viscosity, the head loss in the airways requires a low negative driving pressure during the expiration phase that can collapse the airways. This is the choked flow phenomenon in TLV · which compromises the minute ventilation and consequently the gas exchanges. To address this limitation, liquid ventilator integrates a control of the pumping system.

The introduction of computers in liquid ventilators to control the pumping system provides different control modes, monitoring and valuable data for decision making · .

The liquid ventilator is always volume-controlled because the specified tidal volume of PFC must be accurately delivered and retrieved. It is also pressure-limited because it must stop the expiratory or inspiratory phase when a too low, or a too large, driving pressure is detected.

However, during the expiratory phase, the expiratory flow can be commanded by an open-loop controller or a closed-loop controller:

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