Nellcor OXIMAX N-560, Operator'S Manual

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Principles of Operation
N-560 Operator’s Manual 91
P r i n c i p l e s o f O p e r a t i o n
Oximetry Overview
The N - 560 uses pulse oximetry to measure functional oxygen saturation
in the blood. Pulse oximetry works by applying a sensor to a pulsating
arteriolar vascular bed, such as a finger or toe. The sensor contains a dual
light source and a photo detector.
Bone, tissue, pigmentation, and venous vessels normally absorb a
constant amount of light over time. The arteriolar bed normally pulsates
and absorbs variable amounts of light during the pulsations. The ratio of
light absorbed is translated into a measurement of functional oxygen
saturation (SpO
2
).
Because a measurement of SpO
2
is dependent upon light from the sensor,
excessive ambient light can interfere with this measurement.
Specific information about ambient conditions, sensor application, and
patient conditions is contained throughout this manual.
Pulse oximetry is based on two principles: that oxyhemoglobin and
deoxyhemoglobin differ in their absorption of red and infrared light
(spectrophotometry), and that the volume of arterial blood in tissue (and
hence, light absorption by that blood) changes during the pulse
(plethysmography). A pulse oximeter determines SpO
2
by passing red
and infrared light into an arteriolar bed and measuring changes in light
absorption during the pulsatile cycle. Red and infrared low
- voltage
light - emitting diodes (LED) in the oximetry sensor serve as light sources;
a photo diode serves as the photo detector.
Because oxyhemoglobin and deoxyhemoglobin differ in light absorption,
the amount of red and infrared light absorbed by blood is related to
hemoglobin oxygen saturation. To identify the oxygen saturation of
arterial hemoglobin, the N-560 uses the pulsatile nature of arterial flow.
During systole, a new pulse of arterial blood enters the vascular bed, and
blood volume and light absorption increase. During diastole, blood
volume and light absorption reach their lowest point. The N-560 bases its