Principles Of Operation; Figure 1-2. Comparative Light Absorption; Figure 1-3. Extinction Versus Wavelength Graph - GE TruTrak+ 3900 User Manual

3900/3900P User's Manual

Principles of operation

The 3900/3900P pulse oximeter uses a two-wavelength pulsatile system—red and
infrared light—to distinguish between oxygenated (O
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
Absorption

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
of this portion of the signal.
Extinction (10 x )

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
selected wavelengths, the electronic signal varies according to the light source that
1-4
(Red)
660 nm
Hb and HHb allow different amounts of light to reach the photodetector at the
2
.
2
Time
pulsatile value is a measure of the relative size
r
(Infrared)
940 nm
Wavelength (nm)
Hb) and reduced (HHb)
2
Variable absorption
(due to arterial pulse)
Arterial blood absorption
Venous blood absorption
Other tissue absorption