GE TruTrak+ 3900, Руководство пользователя

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3900/3900P User’s Manual
1-4
Principles of operation
The 3900/3900P pulse oximeter uses a two-wavelength pulsatile system—red and
infrared light—to distinguish between oxygenated (O
2
Hb) and reduced (HHb)
hemoglobin, each of which absorbs different amounts of light emitted from the
oximeter sensor. The system then calculates the relative percentage of these two
constituents and displays SpO
2
.
Absorption
Time
Figure 1-2. Comparative light absorption
Arterial blood pulsation at the test site modulates transmission of the oximeter
sensor’s light. Since other fluids and tissues present generally don’t pulsate, they
don’t modulate the light passing through that location. The attenuation of light
energy due to arterial blood flow is detected and isolated by using the pulsatile
portion of the incoming signal. PI
r
pulsatile value is a measure of the relative size
of this portion of the signal.
Extinction (10x)
Wavelength (nm)
Figure 1-3. Extinction versus wavelength graph
The sensor’s photodetector converts the light, which is partially absorbed and
modulated as it passes through the tissue sample, into an electronic signal. Since
O
2
Hb and HHb allow different amounts of light to reach the photodetector at the
selected wavelengths, the electronic signal varies according to the light source that
Variable absorption
(due to arterial pulse)
Arterial blood absorption
Venous blood absorption
Other tissue absorption
(Red)
660 nm
(Infrared)
940 nm