A-5
Check valve (CV4) ensures the unidirectional gas flow. When the patient inspires
spontaneously, gas goes from the ambient air, through check valve (CV3) of the inspiratory
safety module, patient hose, and into the patient’s respiratory tract. At this point, CV4 is
closed. When the patient expires spontaneously, gas flows out of the patient’s respiratory
tract, through the patient hose, expiration valve, CV4, expiratory flow sensor, and into the
ambient air. CV4 opens. At this point, CV4 is open while CV3 is closed. It can be seen from
this process that the co-effort made by CV3 and CV4 ensures the unidirectional gas flow
during the patient’s spontaneous breathing and prevents repeated breathing.
Expiratory heater (EXH HTR) is a heating device which heats the expiration valve, check
valve, and expiratory flow sensor to prevent the expired gas from condensation which
compromises the measurement accuracy.
Expiratory flow sensor (Q3) is a flow sensor based on the principle of differential pressure.
Diaphragm-type sensor is characterized by high sensitivity and low requirement for electric
circuit. After long term of use, however, the diaphragm will be distorted. Therefore,
periodical user calibration is necessary to ensure measurement accuracy. When the gas
passes through the expiratory flow sensor, differential pressure is produced on both sides of
the diaphragm. Flow information is acquired based on the differential pressure after
collected and processed by differential pressure sensor (PQ3).
Expiratory pressure sensor (PE) measures the expiratory pressure. SOL2 is a zeroing
three-way valve. Small flow is formed at the rear end of R2 and flows into the expiratory
circuit continuously, for the purpose of flushing the pressure sampling line so as to prevent
water from condensing in the sampling line, which compromises pressure measurement
accuracy.
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