EXPIRATORY PHASE
At the beginning of the Expiratory phase the electrical signal to the
PEEP solenoid is turned off, which closes it. The pneumatic signal to
the
PEEP/Exhalation valve is removed and the valve closes. The gas
in the peep valve now flows only between the
load(L) and
exhaust(EXH). If PEEP is set at
0
cmH20 there is no gas flow from the
PEEP regulator into the PEEP venturi assembly. The gas from the
expiratory drive line flows back into the
PEEP/exh. valve and bleeds
out of the PEEP venturi assembly.
The expiratory drive line pressure
falls to
0
cmH2O and the exhalation valve opens allowing the patient
to exhale.
If the PEEP were set above zero, then at the end of inspiration, the gas
from the PEEP regulator would flow into the PEEP venturi assembly,
and through the
PEEP/Exhalation valve to maintain the expiratory
drive line pressure. The expiratory drive line pressure depends on the
PEEP setting. The expiratory drive line pressure will close the
exhalation valve enough to maintain the PEEP pressure in the
breathing circuit. The PEEP pressure in the circuit is read on the
manometer or baseline pressure display during expiration. In normal
operation the PEEP pressure is always set below peak inspiratory
pressure. In the expiratory phase the spontaneous valve is open and a
spontaneous flow (depending on the settings), flows through the
circuit.
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