Of these two only HFJV would be feasible for transport as HFOV requires the use of a long, rigid tube to introduce gas flow through the endotracheal tube. Small tidal volumes are generated by gas being propelled through a small injector canula that opens into the lumen of the endotracheal tube or the trachea. The inspiratory and expiratory times are determined by a solenoid or pneumatic valve that interrupts gas flow to the jet. Peak inspiratory pressure, inspiratory time and rate are set on the jet ventilator by the operator. The patient is also connected to a conventional ventilator through which PEEP and FiO2 are controlled.
Inspiration is active and expiration is passive with the jet ventilator.
A continuous bias gas flow must also be provided which permits adjustment of the mean airway pressure. The amount of displacement of the membrane or piston determines the size of the tidal volume. When the piston or membrane of HFOV is on the backstroke an active expiratory phase is created due to the fall in airway pressure. Because of this active phase ventilation and oxygenation can, to a certain extent, be controlled independently of each other. Decreasing the Hz increases the tidal volume.