Hardware Overview Theory of Operation
1 - 6 0070-10-0604-01 Duo™ Service Manual
1.2.5 SpO
2
Overview
Pulse oximetry (SpO
2
) measurement is used to determine the oxygen saturation level of the
patient's blood. The SpO
2
numeric display indicates the amount of hemoglobin that has
bonded with oxygen molecules to form oxyhemoglobin. By analyzing the pulse in the
fingertip using specified algorithm and consulting the clinical data table, we can obtain the
SpO
2
value. The SpO
2
sensor consists of two LEDs (one red and one infrared) and a
photodetector. The two LEDs are alternately lighted at a precise frequency. When the
capillary vessels of the fingertip are filled, a certain amount of light from the LEDs is
absorbed by blood in the capillaries. The remaining red and infrared light is then picked up
by the photodetector. The photodetector detects the varying light intensity due to pulsations
and transmits the changing light intensity in the form of changing electronic signals. The
amount of light absorption is then compared to the known fixed LED output by the SpO
2
board. The pulse rate is counted and the SpO
2
value is determined by using an algorithm
contained in the software on the SpO
2
board.
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