Principles of Operation
2-18
the A/D converter, and finally processed by the MCU. After that, the systolic pressure, diastolic
pressure and mean pressure can be obtained. For neonates, pediatric and adults, it is
necessary to select the cuffs of a proper size to avoid possible measurement errors. In the
NIBP measurement, there is a protection circuit used to protect patient from over-high
pressure.
The NIBP measurement modes include:
1) Adult/pediatric/neonate mode: To be selected according to the build, weight and age of the
patient;
2) Manual/Auto/Continuous mode: The manual measurement is also called single
measurement; in this mode, only one measurement is done after being started. In the auto
measurement mode, the auto measurement be done according to the preset procedure. In the
continuous measurement mode, quick continuous measurement will be done within 5 minutes
after being started; it detects the changes in blood pressure effectively.
2.4.2 SpO
2
The SpO
2
value is obtained through the pulse waves of the finger tips based on specific
algorithm and clinical data. The SpO
2
probe is the measurement transducer. It has two inbuilt
LEDs and an inbuilt light receiver. The two LEDs include one red-light diode and one infrared
diode, which emit light in turns. When the capillaries in the finger tip are iteratively congested
with blood pumped by the heart, the light emitted by the LEDs, after absorbed by the
capillaries and tissue, casts on the light receiver, which can sense, in the form of electric signal,
the light strength changing with the pulsated blood. The DC/AC ratio of the two photoelectric
signals corresponds to the content of the oxygen in the blood. Therefore, the correct pulse
oxygen saturation can be obtained with specific algorithm. Moreover, the pulse rate can be
obtained according to the pulse waveform.
The circuit of the SpO
2
module is involved in four parts: SpO
2
probe, signal processing unit,
LED-driven sequencing control part and the MCU.
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