Page 16 (Model J)
Note that all jet pressures actually sum in the exhalation block, for example, to ventilate a
patient with a PEEP pressure of 5 mbar and a PIP pressure of 30 mbar, the mean jet will be
set to generate a continuous circuit pressure of 5 mbar and the forward jet will be set to
generate a circuit pressure varying between zero (exp phase) and 25 mbar (insp. phase).
Since the jet pressures will sum, this will result in the desired patient pressure.
2.2.4 HFO ventilation
In pure HFO mode the mean jet pressure regulator is used purely to set the mean pressure.
The forward and reverse jet pressure regulators are used to generate steady positive and
negative delta P components that will be superimposed on the mean pressure. These
components are switched quickly using the high-speed solenoid valves to generate the HFO
pressures.
For example to ventilate a patient with a mean pressure of 10 mbar and a delta P pressure
of 60 mbar, the mean jet will be set to generate a continuous pressure of 10 mbar, the
forward jet will be set to generate a continuous pressure of 30 mbar and the reverse jet will
be generating a continuous pressure of –30 mbar. The HFO rate is determined by the rate of
switching between the forward and reverse pressures on the high-speed valves. Again,
because the jet pressures sum, the resulting patient pressures will be switching between –
20 mbar and +40 mbar.
Mean HFO pressures up to 35mbar are required but the mean jet can only generate
pressures up to about 20 mbars. To obtain higher mean pressures than 20mbars in HFO it is
necessary to apply a higher pressure on the forward pressure regulator and a lower
pressure on the reverse pressure regulator. Using this method, the desired mean must be
less than half the desired delta p pressure plus 20 mbars.
See “Pneumatic Unit Schematic” on page 222.
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