15 Theory of Operation
15.1 Pulse Oximeter Theory
BabySat measures functional Oxygen Saturation of arterial Hemoglobin
(SpO2) and Pulse Rate. Pulse oximetry measurements are based on two
physiological principles:
The dierences in optical absorbance properties between
oxyhemoglobin (HbO2, oxygenated blood) and
deoxyhemoglobin (Hb, non-oxygenated blood), and
The volume (and therefore light absorption) of arterial
blood changes due to heart pulsation as it is distributed
in tissue throughout the body.
A Pulse Oximeter determines the saturation of arterially
Perfused tissue by sequential illumination with the red and
infrared wavelengths of light via light emitting diodes
(LED's). Refer to the figure below. The time-varying signal
passing through the tissue is measured from a photodiode
detector many times per second, and the dierences
between the maximum and minimum absorbance due to
pulsation are used to determine the saturation, and the
pulsation time period is used to calculate the Pulse Rate.
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