OXITEST PLUS 7 OPERATING MANUAL
2.2
Detailed Description
Pulse oximeters commonly utilized in hospitals are based on the principle of the absorption of light
by blood, at two separate wavelengths, 660 nm and 940 nm. Specifically, the relationship between
the absorption of light for Oxygenated Haemoglobin (HbO
2
) and reduced Haemoglobin (Hb)
allows the calculation of HbO
2
, and subsequently oxygen saturation.
A typical pulse oximeter probe incorporates one 660 nm light emitting diode (LED) and one 940
nm LED on the transmitting side of the sensor, and one broad spectrum photosensitive element on
the receiving side of the sensor. The pulse oximeter activates the LEDs in a particular sequence
which allows the received signals to be correctly interpreted. The light passes through a portion of
the body of the patient, commonly the finger, ear, toe, scalp, etc., and falls on the photosensitive
element, which translates the attenuated light signals into electrical signals.
Using various means, the pulse oximeters interpret the
ratio
of the attenuated signals at the two
wavelengths as a percentage of oxygen saturation. A more detailed description of the process, and
the scientific principles of pulse oximetry can be found in the article “Knowing Your Pulse
Oximetry Monitors”, S. Ackerman and P. Weith, Medical Electronics, February, 1995, pp 82-86.
A block diagram of the
Oxitest Plus 7
is provided in
Figure 1
. The
Oxitest Plus 7
incorporates a
probe, resembling a finger, which is placed between the transmitting and receiving elements of the
oximeter. The
Oxitest Plus 7
probe intercepts the light signals produced by the pulse oximeter
and generates pulses of light that are controlled in level, and which simulate the light levels which
would normally be received by the pulse oximeter’s photosensitive element, at predetermined
oxygen saturation levels.
Overview/Chapter 2
#
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